Making HIIT a Hit Part I/II: The Quest for the Optimal Interval to Rest Ratio for Your Type & Goals - Warming up: Selected Studies + Individual Take Home Messages to Set the Scene

This series will not readdress the "HIIT and/or LISS debate", but simply try to do what the title says: Help you to determine the "ideal" form of HIIT for your type & goals.

After posting yet another article about the benefits of high intensity interval training (HIIT) training on Wednesday, I thought it may be a good idea to take a look at the pertinent literature to get a better grasp of what exactly high intensity interval training actually is... "What it is? What do you mean?" While almost everyone appears to recommend you do at least some amount of high intensity interval training, these days, the definition of both the "high intensity" and the "intervals" which are more than just eponymous of this type of training are usually pretty wooly. The two questions this article is supposed to answer are therefore: How long should the intervals and rest periods be and at which intensity should they be performed.

Attention, this article turned into a two part series: I must warn you, this "quest" turned out to be hell lot of work and way more than I had expected. So I will have to split it up into a two-part series. With today's first part discussing exemplary "success stories" and the subsequent follow up on next Sunday providing a more comprehensive overview and general conclusions one may draw based on the picture that emerges.

Part I: Success stories - learning from the "best"

I decided that it may be a good idea to initially compile some examples of which you could say that they are examples of a successfully implementation of high intensity interval training. In that, I will put an emphasis on "old" studies that have not yet been discussed on the SuppVersity. This means, if you want more examples before next week's 2nd installment with a more general overview, you can simply click through the archive of articles that are marked with the keyword HIIT - either as HTML or RSS (I recommend the latter if you do not intend to read all of them anyway; opens in all good browsers without a reader).

Untrained participants and non-athletes

• 5min on, 2min off HIIT to increase fitness (VO2max) alternated with 40 min steady state cardio for 4 + 5 weeks (Hickson. 1981) -- Hard to believe but it's more than 30(!) years ago that Hickson, Hagberg and Ehsani were able to show that a combination of high intensity interval training with 6x5min cycling at 90-100% of the VO2max and 2-min at 30%-50% active rest between intervals on day one and 40 min of steady state "cardio" on a treadmill on day 2 (6 workouts per week) yielded profound increases in VO2max:
  

  

  Figure 1: Adaptation to combined HIIT + steady state protocol in "occasionally active" but not "regularly" trained men (n=8) and women (n=1) in the Hickson study (Hickson. 1982).

  For our purpose, the most significant finding of this study may however be that the t_1/2, i.e. the amount of time it takes for 50% of the adaptations to take place is only 10 days (on this intense protocol).
  
  Take home message: If VO2Max and overall conditioning is your goal you should up the intensity every three weeks, to make sure you continue to make progress. If you go by VO2max, this would be an increase in the speed you run or bike - not (!) the duration of the intervals and / or their number.

• 2 series of 5s sprint cycling (8-13x) with 55s of active rest increase force production and rids subjects of "useless" type IIb fibers (Linossier. 1993) -- The 10 students (8 men, 2 women; age 22y; VO2max = 51.2ml/kg/min, everything below 55 is still considered ) in the Linossier study performed 4 HIIT only workouts consisting of 5s all-out sprints on a cycle ergometer interspersed by 55s of active rest cycling at a heart rate of 130-140bpm per week. The number of sprints in each of the two sessions on a single training day (15 min of rest between) were increased from 8 to 13 sprints over the 7-week study period. The main results were improvements in both peak performances +25%  and in the 30-s total work +16%.
  
  

  

  Figure 2: Unexpected shift in muscle fiber type distribution (Linossier. 1993)

  What's also relevant, though not directly performance related is the 19% increase in phosphofructokinase and a 20% increase in lactate dehydrogenase, both are glycolytic enzymes and are indicative of improvements in the glycolytic pathway, which goes to show you that you don't have to be afraid of the fiber type changes hampering either your ability to handle glucose or your strength - I mean +29% in maximal force production in the sprint tests are everything else but "weak".
  
  Take home message: Shorter sprints appear to be a valid means to hammer and improve the glycolytic pathway and get rid of the useless type IIb fibers, of which not endurance athletes, but bodybuilders have the lowest amount and sedentary controls the most (cf. figure 1 in the overview of the Intermittent Thoughts on Building Muscle). To actually build muscle the 1% increase in muscle weight the scientists observed, is yet not sufficient enough.

• 7 sessions of 10x4 min cycling at 90% with 2 min rest ramp up skeletal muscle fat metabolism in young women (Talanian. 2006) -- The 8 healthy recreationally active women (22 yr old, 65.0 kg body wt) who had previously engaged in 2-3 just-for-fun sessions of various activities from weight lifting, soccer and cycling to swimming, or walking, participated in no more than 7 HIIT sessions within 2 weeks (1 day on, 1 day off) which consisted of 10x 4min sprints at 90% of their individual VO2max with two minutes of rest in between.
  
  

  

  Figure 3. Changes in substrate utilization during standardized 60 min LISS test at 60% of the VO2Max (Talanian. 2006)

  Contrary to the previously discussed studies, the scientists were in this case less interested in the performance than in the metabolic benefits, which were - as the data in figure 1 show - surprisingly significant given the short duration of the study. The increases in fat oxidation and decreases in the respiratory ratio (the ratio of glucose to fatty acid oxidation) during a standardized 60min light intensity (60% VO2max) test that was performed at the beginning and end of the study, were a consequence of increases in citrate synthase and beta-hydroxyacyl-CoA dehydrogenase (beta -HAD) activity.
  
  Take home message: In view of the important contribution of beta-HAD to the beta oxidation of (esp. medium-chain) fatty acids, the fact that an upregulation of this enzyme has been observed in response to the long duration intervals, but neither light intensitsy exercise (even w/ 2h per day, 5-6 times per week; cf. Phillipps. 1996), nor during a similar 2-week sprint training protocol (30s all-out on cycle ergometer, 4 min rest; cf. Burgomaster. 2005) points towards "long" duration intervals when mitochondrial adaptations that favor fatty oxidation and thus subsequent increases in fat loss with light activity are concerned. 

Highly trained participants and pro-athletes
 

• 3 sessions of 10 intervals at 96% VO2Max with 60-180s rest increase running economy and relative fatty oxidation during subsequent steady state exercise test (Zavorsky. 1998) -- Twelve highly trained endurance athletes volunteered for this study, four of them qualified for the 1996 Canadian Olympic Trials, and one subject was a Canadian record holder in triathlon. On three different occasions the subject ran 10 x 400-m sprints with active recovery periods of 60, 120, 180s (randomly assigned). 10 min before and afterwards standardized running economy tests were performed.
  
  

  

  Figure 4: Respiratory exchange ratio in RE test before and after the sprinting protocol (Zavorsky. 1998)

  During these running economy tests, which consisted of 2 x 5 min running on a treadmill at 12km/h or 16km/h (5 min total rest in between), the subjects exhibited, much contrary to the research hypothesis, by the way, an increase in the running economy (RE, a measure of how efficiently a person uses oxygen while running at a given pace) and - probably of greater interest for most of you an increase in fatty acid oxidation, as evidenced by the reduced respiratory exchange ratio (RER, figure 4). The latter was particularly pronounced in the "low intensity" RE test at 12km/h.
  
  As far as the differential effects of the rest intervals is concerned, significant effects were observed for the rates of perceived exertion (60s: 17.7; 120s: 16.1; 180s: 14.4), but not for the performance related measurements velocity, and the time it took the athletes to run the 400m sprints (actually the latter should be self-evident with identical velocities).
  
  Take home message: Doing ten short sprints (if you are not an athlete, shorter ones will suffice) before you go jogging (or do any other type of steady state cardio) won't hamper your running economy. And since the study at hand suggests that the relative increase in fatty acid oxidation is specifically pronounced in the lower intensities (this is supposedly even more the case if you jog at 10km/h), the combination of sprints + steady state cardio appears to be an ideal "cardio" only day, when you are trying to lose body fat.

• 8x all-out (100% VO2max) 2.5min intervals with 4 min of active rest increase VO2Max, peak aerobic power and 5k time trial performance regardless rest between sessions (Gross. 2007) -- With the unique twist with respect to the training frequency this study is somewhat unique. While other studies report similar benefits in highly trained collegiate cyclists (13 men, 4 women; VO2Max at baseline 62ml/kg/min) or other endurance athletes, this is one of the few that investigates whether it makes a difference if the athletes implement the 3-days per week HIIT regimen as a block or interspersed by one day of rest into their regimen.
  
  

  

  Percent change in TT5k velocitym TT5k power output VO2peak, and peak aerobic power output in cyclists trainin on consecutive vs. non-consecutive days (Gross. 2007)

  Interestingly enough, neither the performance outcome on the pre- and post tests, i.e. increases in VO2Max (+5.7%), peak aerobic power (+7.2%), 5k time trial performance (+6.9%), nor the actual performance during each of the workouts the subjects performed in the course of the 3-week study period suffered from doing the HIIT sessions back to back. These results refute previous speculations that doing HIIT as a block would trigger greater metabolic adaptations, specifically in athletes (e.g. Padilla. 2000). Even more, though the changes were not statistically significant, the data in figure 5 shows that - with one for endurance athletes important exception, namely the VO2Max - training on non-consecutive days produced marginally better results.
  
  Take home message: While it appears as if it would not make a difference whether you perform your HIIT workouts blocked or within your training week. The non-significant differences in figure 5 could suggest that endurance athletes intending to improve their already high VO2Max even further would be better off with the blocked training. Everybody else has the choice and I would pick the interspersed variety, whenever my schedule allows me to do this - my personal experience told me that this works better for me... apropos, take another look at figure 5 you see the narrow bars indicating the standard deviations? This goes to tell you that it is very likely that not just the personal preferences, but also the actual outcome will vary from trainee to trainee, which supports the notion that you will have to experiment to find what works best for you.

That's it for the "success stories"! Don't forget to come back next Sunday for part II and in case you have not done so already, just browse the previous SuppVersity posts on this matter, either as HTML version, post by post, or from the RSS overview (works in every modern browser, yet not in Google spyware ;-). I know you are smart enough to draw your own conclusions. And what's more, this may yield some cognitive input for the comment area of this article, where you can post questions. I will try to tackle those I can answer in the next installment.

References:

• Burgomaster KA, Hughes SC, Heigenhauser GJF, Bradwell SN, Gibala MJ. Six sessions of sprint interval training increase muscle oxidative potential and cycle endurance capacity in humans. J Appl Physiol. 2005; 98: 1985–1990.  
• Gross M, Swensen T, King D. Nonconsecutive- versus consecutive-day high-intensity interval training in cyclists. Med Sci Sports Exerc. 2007 Sep;39(9):1666-71.
• Hickson RC, Hagberg JM, Ehsani AA, et al. Time course of the adaptive responses of aerobic power and heart rate to training. Med Sci Sports Exerc 1981; 13: 17-20.
• Linossier MT, Denis C, Dormois D, Geyssant A, Lacour JR. Ergometric and metabolic adaptation to a 5-s sprint training programme. Eur J Appl Physiol Occup Physiol. 1993;67(5):408-14. 
• Padilla S, Mujika I, Orbañanos J, Angulo F. Exercise intensity during competition time trials in professional road cycling. Med Sci Sports Exerc. 2000 Apr;32(4):850-6.
• Phillips SM, Green HJ, Tarnopolsky MA, Heigenhauser GJ, Grant SM. Progressive effect of endurance training on metabolic adaptations in working skeletal muscle. Am J Physiol Endocrinol Metab. 1996: 270: E265– E272, 1996
• Talanian JL, Galloway SD, Heigenhauser GJ, Bonen A, Spriet LL. Two weeks of high-intensity aerobic interval training increases the capacity for fat oxidation during exercise in women. J Appl Physiol. 2007 Apr;102(4):1439-47. 
• Zavorsky GS, Montgomery DL, Pearsall DJ. Effect of intense interval workouts on running economy using three recovery durations. Eur J Appl Physiol. 1998; 77: 224-30.

4x4 Minutes of HIIT Per Week That's All It Takes For Already Well-Conditioned Individuals to Stimulate Mitochondrial Growth ➯ 15% Increase in VO2Max, Peak & Mean Power

HIIT is a builder, not a burner - it builds the powerplants you need to burn.

For you as loyal SuppVersity readers, the fact that HIIT is the #1 growth promoter for your mitochondria is no news. That 4x4 minutes of HIIT per week are yet already enough to promote significant increases in the mitochondrial counterpart of mTOR, PGC-1α - the master regulator of mitochondrial biogenesis (Wu. 1999) - will probably still comes as a surprise. This is all the more true in view of the fact that these observations have been made in young, healthy, recreationally active adult men - not fat rodents, frail heart disease patients or sedentary type II diabetics.

You can learn more about HIIT at the SuppVersity

Never Train To Burn Calories!

Tabata = 14.2kcal /min ≠ Fat Loss

30s Intervals + 2:1 Work/Rec.

Making HIIT a Hit Part I/II

Making HIIT a Hit Part II/II

Triple Your Energy Exp.

The corresponding study, which was conducted by researchers from the Queen’s University, the Kingston General Hospital and the University of British Columbia Okanagan, involved four weeks of "tabata style" high intensity interval training. The 4x4 training sessions consisted of 8x20s intervals separated by 10 s of rest. The equipment of choice was a Monark Ergomedic 874 E stationary bicycle ergometer with the resistance being set to 170% of the individual subject's peak aerobic power at 100 rpm.

Figure 1: Changes in performance parameters and protein + enzyme expression (Ma. 2013)

When you take a look at the changes, I want you to keep in mind that 19%, 14% and 13% increase in VO2Peak, peak aerobic performance and mean power during the Wingate test were the result of exactly 43min* of active exercise distributed across a 4-week timespan (*excluding the rest periods)... now that you've digested that, ask yourself: Is my training regimen anywhere near as effective? I mean, what was the result you got from the last 43 minutes you've been sweating in the gym?

While you are pondering this question, let's briefly take a look at the way Jasmin K. Ma, Trisha D. Scribbans, Brittany A. Edgett, J. Colin Boyd, Craig A. Simpson, Jonathan P. Little, and Brendon J. Gurd evaluate the results of their latest study and the differences to previous low-volume HIIT interventions:

Suggested: "Cardio or Weights? What Do Lean People Do to Lose 20% Abdominal Fat in 10 Weeks?" | more

"While other low volume HIT protocols have reported non-significant (Burgomaster. 2005, 2006) or small (below 10%) increases in aerobic capacity (Burgomaster. 2008; Hazell. 2010) the current protocol induced rela- tively large increases in both VO2peak (+19%) and an- aerobic performance (+12% - 14%). These findings con- firm the results of Tabata et al.(1996) who reported ele- vated VO2peak at both 3 and 6 wks of training, and demonstrate that increases in VO2peak occur following 2 wks of training. Interestingly, while VO2peak is traditionally believed to be determined by cardiac output, a recent report demonstrated increased VO2peak without an accompanying increase in maximal cardiac output following treadmill sprint interval training (MacPherson. 2011)."

In other words: You don't necessarily have to do "cardio" training to improve what people usually call your "cardiovascular fitness", when they actually mean your overall conditioning. In the end, that's similar to sports cars. If you build a sports car or formula one racer, the best engine is useless, when the gear can't transfer its power to the wheels. For humans that's not much different. It is thus only logical to accept Ma et al.'s hypothesis that the "elevated aerobic capacity following low volume HIT may be result from peripheral [and not central cardiovascular] adaptations." (Ma. 2013)

Bottom line + important reminder:  Despite the fact that the increase in citrate synthase (CitSyn; cf. Figure 1) didn't reach statistical significance, the overall increase in mitochondrial protein (COX I and IV) will still allow for an increase in fatty acid oxidation during exercise. If you still believe that HIIT sessions were mainly used to lose body fat you are totally off track. The total calorie expenditure is way too low to have any effect on your body fat levels.

The thing HIIT is good for is what you see in the study at hand. It's a mitochondrial builder that will ramp up PGC-1α, increases the mitochondrial firepower of your cells and promote the oxidative capacity of their power houses. How you use this increased "firepower", i.e. to run faster or longer or to burn a couple of additional calories while you are doing steady state cardio, play basketball or perform any other kind of aerobic activity to promote the baseline fat loss effects of your diet, is up to you, though.

References: 

• Burgomaster, K.A., Hughes, S.C., Heigenhauser, G.J.F., Bradwell, S.N. and Gibala, M.J. (2005) Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans. Journal of Applied Physiology, 98, 1985-1990.  
• Burgomaster, K.A., Heigenhauser, G.J.F. and Gibala, M.J. (2006) Effect of short-term sprint interval training on human skeletal muscle carbohydrate metabolism during
  exercise and time-trial performance. Journal of Applied Physiology, 100, 2041-2047. 
• Burgomaster, K.A., Howarth,K.R., Phillips, S.M., Rakobowchuk, M., MacDonald, M.J., McGee, S.L. and Gibala, M.J. (2008) Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans. The Journal of Physiology,
  586, 151-160. 
• Hazell, T.J., MacPherson, R.E.K., Gravelle, B.M.R. and Lemon, P.W.R. (2010) 10 or 30-s sprint interval training bouts enhance both aerobic and anaerobic performance. European Journal of Applied Physiology, 110, 153-160.  
• Ma, J. K., Scribbans, T. D., Edgett, B. A., Boyd, J. C., Simpson, C. A., Little, J. P., & Gurd, B. J. (2013). Extremely low-volume, high-intensity interval training improves exercise capacity and increases mitochondrial protein content in human skeletal muscle. Open Journal of Molecular and Integrative Physiology, 3, 202.
• MacPherson, R.E.K., Hazell, T.J., Olver, T.D., Paterson, D.H. and Lemon, P.W.R. (2011) Run sprint interval training improves aerobic performance but not maximal cardiac output. Medicine & Science in Sports & Exercise, 43, 115-122.
• Wu, Z., Puigserver, P., Andersson, U., Zhang, C., Adelmant, G., Mootha, V., ... & Spiegelman, B. M. (1999). Mechanisms controlling mitochondrial biogenesis and respiration through the thermogenic coactivator PGC-1. Cell, 98(1), 115-124.

3.2g of Beta Alanine Reduce Rate of Perceived Exertion, Increase Time to Exhaustion and Ventilatory Threshold. Vegetarians, Older People and Diabetics May Benefit Most.

Image 1: If you are into running, ladies, beta alanine is for you ;-)

Those of you who make sure that they are getting their highly educative daily dose of the SuppVersity *rofl* will be aware that today's blogpost is, once again, dealing with beta alanine. Contrary to yesterday's post, which dealt with its pharmacokinetics, we are today going to have another look at what kind of real world performance outcomes the average (female!) physical culturist can expect from taking at least 3.2g of the beta amino acid per day - a dosage that has been shown in previous studies to increase intra-muscular carnosine levels by 27–39% in fast- and slow-twitch muscle fibers, respectively (Baguet. 2009). And though I do not want to spoil things, I can already tell you that the results make it quite clear why beta alanine is not the next creatine.

Somehow ergogenic, yet not really antioxidant

For the study that was conducted at the Applied Physiology Laboratory at the University of North Carolina, study that was conducted by A.E. Smith recruited 24 "recreationally active" women, of which the authors state that they "engag[ed] in 3–7 days per week of aerobic, resistance or recreational activities, but were not highly trained competitive athletes". With a mean age of 21.8 years, a height of 165cm and a body weight of 61.5kg the subjects are thusly representative of the average young woman who goes to the gym to either get or keep in shape. I am specifically emphasizing this, because - at least in the early days - beta alanine was heavily marketed as "the creatine for women" who fear the water retention people still claim was an inevitable side effect of creatine supplementation.

Image 2: If you retain water, this is not due to creatine monohydrate. Either you are taking to much (creatine loading is a thing of the past) or you have bought a product with shitloads of carbs in it - in that case, chances are its not only water you are gaining ;-)

Does creatine supplementation inevitably lead to water retention and weight gain? Just because this myth is still perpetuated, especially among female figure competitors, I thought it may be worth addressing this again: Pure creatine monohydrate without the sugar and the other bullshit you will find in many creatine supplements does not necessarily lead to increases in either total body or water weight. A study by Rawson et al. showed only recently that the consumption of 0.03g/kg creatine for six weeks did not result in statistically significant changes in body weight or water in men or women, despite significantly increased plasma creatine concentration and enhanced resistance to fatigue during repeated bouts of high-intensity contractions (Rawson. 2011).

The women were advised to simply stick to their usual routine and to refrain from taking any supplements and medications except from their 2x800mg beta alanine tablets. The latter were to be taken 3x a day... so according to Cocker, they should have consumed 2x0.8g x3/day = 4.8g/day and not, as the scientists state "3.2 g daily". Now, according to Smith et al. this was the "required dosage" all participants met. I can however not say, whether this means that the third dose was optional... and this is not the only oddity in this study, where it is well worth to look beyond the assessments and conclusions of the authors.

At the beginning and the end of the 28-day supplementation period, the women had to perform a graded oxygen consumption test (VO2max) to evaluate VO2max, time to exhaustion, ventilatory threshold and establish peak velocity (PV), as well as a "non-damaging treadmill run (oxidative stress run) for 40 min at 70% PV [peak velocity]". Before, immediately after and in the 2-6h post running window total antioxidant capacity (TAC), superoxide dismutase (SOD), 8-isoprostane (8ISO) and reduced glutathione (GSH) were measured. In addition to that, heart rate and ratings of perceived exertion were recorded during the 40 min run. The two main metrics of the study were thusly the potential anti-oxidant effects (TAC, SOD, 8ISO, GSH) and the anticipated immediate ergogenic effects (VO2Max, time to exhaustion, heart rate and perceived exertion) of beta alanine supplementation.

Figure 1: Effect of 28 days of beta alanine supplementation on maximal oxygen consumption (VO2max), time to exhaustion during a graded exercise test (VO2TTE) and ventilatory threshold (VT) and qualitative practical significance (data and caption adapted from Smith. 2011)

If you now have a look at the my graphical rehash of the scientists own evaluation of the effect beta alanine supplementation had on VO2Max, the time to exhaustion (VO2TTE) and the ventilatory threshold (VT), you will have to concede that mean improvements of 0.28%, 6.6% and 3.7%, respectively, as well as the large discrepancies among the subjects (from beneficial over negligible to harmful) do not actually speak for beta alanine.

Figure 2: Effect of beta alanine supplementation on oxidative stress markers measured as total
antioxidant capacity (TAC) and glutathione (GSH) and the qualitative practical significance
for women (data and caption adapted from Smith. 2011)

Things get even more confusing when we take a look at the antioxidant effects of beta alanine. Not only were the levels of superoxide dismutase (SOD) and 8-isoprostane (8ISO) not different between groups, and the effect of beta alanine on the total antioxidant capacity (TOC) of the subjects negligible, the scientists' summary of the effects does even suggest that, after an initial amelioration of the negative effect of treadmill running on GSH, there was some sort of a "likely harmful" rebound 6h after the 40 min exercise bout. Before you do now flush your beta alanine stores down the toilette, I suggest you first take a look at the actual (absolute) effects beta alanine supplementation had on the exercise induced changes in GSH levels:

Figure 3: Absolute GSH levels (in µM) immediately before (pre), post, 2h and 4h after treadmill running in the placebo and beta alanine supplemented women before (pre) and after (post) the 28-day supplementation period (compiled based on data from Smith. 2011)

As you can see in figure 3, there was an (unexplained) increase in GSH in the course of the 28-day supplementation period in both groups. With 2%, the latter was statistically non-significantly greater in the beta alanine group, and the "likely harmful" effect of beta alanine supplementation 6h after the end of the treadmill-run is simply the result of a smaller increase in GSH, when you compare the pre- to post-supplementation levels at the 6h mark - and I guess, you would agree that a +27% increase in GSH is not exactly something that deserves to be called "likely harmful", wouldn't you?

All-clear: Beta alanine is not ergolytic ;-)

Now that we have gotten that straight, let's get to the last (and most) significant benefit the women in the beta alanine group had from taking the supplement: a statistically significant reduction in the rate of perceived exertion during treadmill running (cf. figure 4).

Figure 4: Rates of perceived exertion during 40 min treadmill running before (pre) and after (post) 28 days of supplementation with beta alanine or placebo; small graph: relative difference post supplementation in women receiving BA vs. placebo (data calculated based on Smith. 2011)

It goes without saying that being 18% less fatigued is something that could well be worth spending the roughly 7$ for a 28-day supply on (calculation based on a dose of 3.2g per day taken over 28 days and assuming you buy your beta alanine in bulk at one of the major suppliers). This, by the way, could be particularly true if you belong to one of the following groups, who have been found to have low intra-muscular carnosine levels, to begin with:

Image 3: Older people are only one of the three groups who are "at risk" of low carnosine levels and are thusly most likely to benefit from beta alanine supplementation.

1. vegetarians - a 2011 study by Evaraert et al. found that "Vegetarians have a lower carnosine content of 26% in gastrocnemius compared to omnivores" (Everaert. 2011); and according to another recent study, the soleus carnosine content of vegetarians was "non-significantly" reduced by -9% after 5 weeks of sprint training, while the same protocol elicited increases of +11% in omnivores (Baguet. 2011)
2. older people - Evaraert et al. found a linear decline (ca. -10% in 20 years) in carnosine levels with age (correlation r=-0.26; Everaert. 2011); and Stout et al. report a highly significant +29% increase in physical working capacity at the fatigue threshold in twenty-six men (n = 9) and women (n = 17) (age ± SD = 72.8 ± 11.1 yrs) who  had been supplementing with 800 mg three times per day for 90 days (Stout. 2008)
3. type-2 diabetics - according to Gualano et al. type-2 diabetics have "significantly lower carnosine content (−45%) in gastrocnemius muscle", a relative deficiency of which the scientists argue that it "may be partially associated with defective mechanisms against oxidative, glycative and carbonyl stress in muscle." (Gualano. 2011)

After all, it does yet not really matter whether you are a type-2 diabetic, a vegetarian or simply getting older, compared to many (if not most) of the other overpriced ergogenics that are advertised all over the web, beta alanine is certainly not only one of the cheapest, but also one of the most promising candidates for the 3rd place on your list of staples, where (whey) protein and creatine should nevertheless still occupy position 1 and 2, respectively. And the fact that it did not prove to be a potent antioxidant in this study need not really be a disadvantage, after all, we still do not know whether the exercise-induced oxidative "damage" is not what actually triggers the highly desirable adaptive responses (cf. previous posts on "hormesis"), we are all looking for, when we are hitting the gym.

Beta Alanine Fails to HIIT Back: No Increased Training Effect in Response to Nine 4x4 Min HIIT Workouts W/ BA Preload, But Evidence in Favor of Chronic Supplementation

Contemporary scientific evidence suggest that you have to pick the right type of (short intense) exercise if you don't want your beta alanine supplement to end up as another "false starter" in your closet.

In the past couple of weeks beta alanine (BA) has gotten some bad press, here at the SuppVersity. While some conspiracy theorists may already have smelled a personal vendetta of a sodium bicarbonate advocate like myself against its 'high tech competitor', the actual reason for the negative, or at least not necessarily exciting news is the exercise specificity of beta alanine (BA) supplementation.

The most recent BA study from the  University of Bern and the Swiss Federal Institute of Sport in Switzerland and the Karolinska University Hospital in Sweden is yet another rather disappointing BA study to support my previous assertion that the benefits for the average gymrat are largely overblown.

What did the researchers do

As Gross et al. point out, the aim of their two-part intervention study was to alter the physiological systems discussed above in ways that could improve severe exercise performance. In that, their hypotheses were that

1. 

   If we look at the results of previous studies, it appears that the question, whether BA ↪ promotes or ↪ blunts the ergogenic effects of baking soda does also depend on the type of exercise.

   ... HIIT, by improving VO2max and VO2 kinetics, would enhance aerobic energy contribution during severe cycling exercise
2. ... beta-alanine supplementation, by increasing intramuscular carnosine, would improve buffering capacity and reduce pH disturbance, or otherwise dampen muscle fatigue during severe cycling exercise; and 
3. ... prior supplementation with beta-alanine would allow for greater training load and better recovery during HIIT,which would enhance benefits of training on physiological determinants of severe exercise performance. 

As a seasoned SuppVersity veteran you know about the profound training effect of high intensity (if you don't educate yourself). You will also know / have expected that the 38-day preload in the course of which the participants consumed either

• * supplements were provided as 400-mg gel capsules and taken with the 3 main meals and before bed
  4 x 800mg/day "purified beta alanine"* (BA), or
• 4 x 800mg/day maltedextrin (PLA),

would increase the intramuscular carnitine stores of the participants in the BA group. What you don't know, however, is whether the eight endurance, team, or combat sport athletes in the active study arm would also display lower serum pH levels, experience less fatigue, and record greater improvements in VO2max than the remaining nine subjects in the placebo arm of the study.

Let's take a look at the results

I guess, it doesn't make sense to keep you on the tenderhooks any longer, so let's see what happened  during and after the obligatory nine 4 x 4 minute interval HIIT sessions on a cycle ergometer (10 min warm-up; heart rate 90-95% of max; 3min light cycling between intervals).

Simply taking your beta alanine supplements with food increases the absorption of BA more effectively than fancy "time-release" caps or tablets | read more

Chronic vs. cyclic BA supplementation: It is an interesting side-finding of he study at hand that 9 HIIT sessions and a 7-day rest-period can reduce the carnosine overload in the vastus lateralis and vastus internus (the teardrop muscle) by statistically significant 6.5% and 12.2%, respectively. This would mean that a chronic high intensity overload can very well induce significant reductions in carnosine levels within less than a month. A workout fanatic who wants to keep his muscles supersaturated with carnosine on all 365 days of the year should thus not follow my previous suggestion to do 6-weeks on, 4-weeks off cycles. In view of the results of the study at hand, I will yet leave it to you to decide whether you feel this is actually worth the effort / money.

The sessions were performed as follows: Sessions 1-3, 1 day rest, sessions 4-7, one day rest, sessions 8-9; and all participants had been following their habitual training and nutrition regimen during the 38-day "preload".

Figure 1: Changes in VO2max, peak power output, max. blood lactate, and power at second ventilatory threshold in from baseline (pre) to post-supplementation (before HIIT) and from baseline (pre) to the end of the study (after HIIT +7-days)

If you read the text in Figure 1, you will be aware that the changes the scientists observed in response to the exercise regimen look impressive, but lack statistical significance. In the end, the results are thus way less exciting than the relative performance increases in the 10 ± 5% range would suggest.

It is difficult to say if the overall effect size is the reason that there were no significant inter-group differences. Since there were not differences at all (not even borderline or non-significant ones), it is however unlikely that a longer study duration and correspondingly more pronounced increases in VO2Max, peak power and co, as well as the likewise identical post workout glycogen synthesis and muscle fiber cross-sectional area would have yielded a significant advantage on part of the BA supplemented trainees. The fact that the increases in skeletal muscle buffering capacity reached significance only in the placebo group, would even support the exact opposite hypothesis, i.e. more pronounced long-term adaptive effects without beta alanine supplementation.

The 2012 meta-analysis by Hobson et al. demonstrated two things (a) BA produces predictable performance increases only in the 60-120s range and (b) the overall effect size is much smaller than what most people are (mis-)lead to believe, when they read the advertisements... ah "write-ups" on the Internet.

What do we make of these results? In view of the overall rather disappointing results, I am not sure if you feel that the 1.3% increase in aerobic activity and -5% decrease in O2 deficit is convincing enough to subscribe to idea that beta alanine powered carnosine loading is a viable strategy to improve the adaptive response to long(er)-duration interval training (here "longer" is 4-min).

In my humble opinion this is not the case. Not necessarily because I feel that BA is a supplemental non-starter, but rather in view of its exercise- / duration-specificity, of which Hobson et al. wrote in their 2012 meta-analysis that it restricts the usefulness of beta alanine to sports where the overall duration of high intensity muscular contractions is longer than 60s, but shorter than 240s. This is a pretty narrow margin and even within this "performance zone" the mean effect size of 2.85% does not come remotely close to what you'd expect to see when you read the boastful promises in the "write-ups" of the supplement industry.

References:

• Hobson RM, Saunders B, Ball G, Harris RC, Sale C. Effects of β-alanine supplementation on exercise performance: a meta-analysis. Amino Acids. 2012 Jul;43(1):25-37.
• Gross M, Boesch C, Bolliger CS, Norman B, Gustafsson T, Hoppeler H, Vogt M. Effects of beta-alanine supplementation and interval training on physiological determinants of severe exercise performance. Eur J Appl Physiol. 2013 Nov 9. [Epub ahead of print]

Additional(!) HIIT Training Beneficial for Professional Judo Athletes: +15% Increases in Peak and Mean Power & Less Body Fat after 8-Week Training Camp.

Image 1: The Korean National Team - this are the kind of study subjects you want to look for if you are searching for studies that may help you, a fit physical culturist to improve your performance (img Yahoo)

Those of you who have been following the SuppVersity posts for quite some time now, know that I have continuously been ranting against classic endurance training. Not so much, because I think that this is not a sport you can enjoy (I know from personal experience that the "joy" can easily become addictive, though), but because many people perform what they think would be "healthy cardiovascular exercise" with the false expectation that running a marathon will improve their health and physique - more often, than not, the opposite is the case. And negative effects on both your physique (unless you consider being called a skeleton flattering) and longterm health become almost inevitable, when your daily 30 minutes of jogging or your 1h brief walk with your dog progressively increases to a frantic 10k run.

To each his own high intensity training

Image 2: Add 100-150lbs to a weight-west and test how "low" the intensity of a 4km/h walk on a treadmill is for the morbidly obese subjects in the studies that perpetuate the myth of the fat-burning effects "low intensity" exercise (img rosstraining.com).

And while the medical orthodoxy keeps putting out review after review emphasizing how beneficial classic endurance exercise is for the obese prediabetic, they do not give a damn that the 4km/h walk on a treadmill that makes the 250pound sedentary housewife sweat, pant and lose weight, will not have any impact on the girl with the unsexy love-handles who finally wants to get the body of the Shape cover models she is admiring. I mean, think about it: It's all about intensity! If the girl with the love-handles grabbed one of those military backpacks and loaded it with 5x30lbs plates, hopped on the treadmill and started walking at 4km/h, what would you call that? I would call it High Intensity Training (HIT). Now, the girl would probably fall off the treadmill every 30s because the load was way to heavy. What would you call it if she jumped back on after catching her breath? I would call it High Intensity Interval Training (HIIT). 

Assuming that you got the message, it should stand out of question that you as a reasonably fit physical culturist can adopt short (max. 50min) bouts of low intensity endurance training as a means of regeneration, but if you are looking to improve your physique or exercise performance (outside of long-distance running) you are way better of if you follow the example of the 29 judoists from the Yongin University in Korea who participated in an 8-week study at the Korea National Sport University in Seoul (Lee. 2011).

Figure 1: Subject characteristics (left) and training program (right) of the 29 judoist participating in study (Lee. 2011)

If you take a look at the subject characteristics in figure 1 (left), you may note that this is the kind of study you and I must rely on, when we are designing our training routines if we want to improve our cardiovascular fitness level and shed the last unaesthetic pounds of body fat - and, if the results from this study translate into your training practice, the addition of an early morning HIIT sprinting session on Monday, Tuesday, Thursday and Friday (exact protocol cf. figure 1, right) could provide exactly that: a drop in body-fat and an increase in anaerobic performance. This is particularly noteworthy, because the subjects performed the interval training as part of an already arduous 8-week training camp with concurrent strength and judo training (I wonder if any of the participants was afraid to lose muscle ;-)

Figure 2: Effects of standard and standard + additional HIIT training on VO2Max, peak and mean power (left), as well as body composition in 29 judoists during an 8-week training camp (Lee. 2011)

With their already low body fat percentage of ~13% and a caloric intake of 3.500kcal/day (remember none of the athletes wanted to lose weight), the slight (and statistically non-significant), yet nonetheless evident body-recompositioning effect is certainly not to be scoffed at, if you look at the profound performance increases in the anaerobic peak and mean power test (cf. figure 2).

That the VO2Max, i.e. the aerobic performance did not benefit above the normal protocol is yet an oddity of the study, (cf. "HIIT Even For Infarction Patients") of which the scientists assume that it could be related to the fact that the normal training protocol alone would have been enough to max out on the already high aerobic capacity of the athletes. Which, and thusly we have again come full circle, leads me back to my initial recommendation to fine-tune your training protocol to your needs, which (I would hope) are completely different from the ones of the average sedentary, obese, pre-diabetic resident of the Western hemisphere. And in case you want to learn more about how to do that, I suggest you come back tomorrow, for the next installment of the Intermittent Thoughts with tipps on programming success that will work regardless of whether you will or won't use an intermittent fasting protocol ;-)

HIIT is the Hit! Interval, not Steady State Aerobics is the Way to Go - Even for Patients with Myocardial Infarctions!

Image 1: Right in the starting block is where heart health begins... and on the finish line of a marathon race probably is where heart health ends (if not much earlier)

I think it is unnecessary to pose this question again, but in case you missed the innumerable blogposts, where I asked you whether you would rather like to look like an ultra-endurance runner or like a sprinter - here you go: Whose physique would you rather want to have? The sinewy physique of Haile Gebrsellasie or the muscled physique of Usain Bolt and co? I assume in most cases this question is unnecessary... but what if you are sick, obese or even have a heart failure? Obviously you cannot train like a sprinter, then... can you? Yes, you can - at least within your personal physiological limitations! In view of the results of a recent study from the KG Jebsen Center of Exercise Medicine at the Norwegian University in Trondheim, Norway, aerobic interval training would even be the healthier choice (Moholdt. 2011)!

For their study Trine Moholdt and her colleagues recruited 107 patients who had been hospitalized for myocardial infarction 2-12 weeks before the study and randomly assigned them to usual care rehabilitation or an aerobic interval training performed. In the course of the 12 week study period the exercise protocol was performed thrice a week. Two sessions were supervised, the other one had to be performed at home.

• usual care rehabilitation program - the standard program comprised 60 minutes of aerobic exercises performed to music; the sessions were lead by a physiotherapists, and after a 10-minute warm-up, the patients did aerobic exercises like walking, jogging, lunges and squats for 35 minutes, which were followed by a 5-minute cool-down with stretching and relaxation exercises.
• aerobic interval training - the total session time of the interval training was 38 minutes; it consisted of an 8-minute warm-up, followed by 4x4-minute intervals at 85–95% of the maximum heart rate (monitored by heart rate monitor), with active rest of 3 minutes of walking at 70% of maximum heart in between the intervals; the exercise session was terminated with a 5-minutes cool-down.

In view of the still commonly held believe that interval training could easily become (over-)exerting, quite a few medical practitioners, would probably shake their heads over the "irresponsibility of [their] Norwegian collegues - how dare those idiots put ailing cardiac patients on such an tortorous exercise regimen" ... I think I won't have to continue, you know the whole litany... and if you, just like me cannot stand that anymore, and your own (your father's, mother's, grandpa's or grandma's) doctor is one of those, take the following data, print it and use it to shut him up.

Figure 1: Improvements in VO2Max, peak heart rate, respiratory exchange rate at peak heart rate and heart rate recovery in cardiac patients after 12 weeks on the usual care rehabiliation program or an intense aerobic interval training (data calculated based on Moholdt. 2011)

Obviously, the poor cardiac patients did not only survive the "torture", their hearts even thrived on it. The increase in peak oxygen uptake (VO2Max), the standard measure of aerobic performance, was 2.7x higher in the interval group than in the patients who did the usual 60-minutes reha-sessions (cf. figure 1). For the other parameters the differences were not statistically significant after analysis for initial randomization:

Flow-mediated vasodilatation, both non-normalised and normalised to shear stimulus, increased significantly after exercise training in both groups [...] Quality of life increased significantly after exercise training (between-group differences, not significant)

If we look at the blood parameters, however, we do yet see some interesting differences, even your medical practitioner could not argue away:

Figure 2: Changes in high density lipoprotein and adiponectin in cardiac patients after 12 weeks on the usual care rehabiliation program or an intense aerobic interval training (data calculated based on Moholdt. 2011)

While the changes in triglycerides, CRP, ferritin, haemoglobin, and glucose were - within their respective standard-deviations - identical in both groups, there was a marginal but statistically significant greater improvement in high density lipoprotein (HDL) levels (a statistician would say there was an improvement in the interval group, while there was none / no statistically significant one in the reha-group) in the interval group. While this would indicate a lower risk of future (recurrent) heart disease, the accompanying  increase in adiponectin would suggest that the interval training group either had already or were about to lose more body fat than their endurance trained peers.

Unfortunately, the body composition of the patients was not tracked in the study, so this leaves us with the "surprising" benefits of intense interval training for the hearts of patients with prior myocardial infarction as the main result of a study some medical practitioners would probably not even have dared conducting.

Medium Intensity Interval Training (MIIT) Increases Fitness of Overweight Sedentary Women Slower, But Eventually Just As Effectively as HIIT. Neither Cuts Fat / Body Weight

It does not always have to be "all out", but 70% is probably the minimum for intervals - esp. for the non-obese.

If you know all SuppVersity articles by heart, the name Astorino may ring a bell. I mentioned a previous study by Todd A. Astorino in my 2012 article "Are You Still Burning Calories or Already Losing Fat? Study Shows: 5x15 Min HIIT Reduce Body Fat & Improve Fitness Twice as Effectively as 5x40min of Classic Cardio" (read more). In their most recent study, the researchers from the Department of Kinesiology at the California State University took another look at HIIT exercise for the average female US citizen, to be precise. And the observation they made is actually quite astonishing.

MIIT vs. HIIT: Can both be equally effective?

In this group of healthy sedentary (<1h/week of regular physical activity) women (n=30; age 18-40; BMI >35kg/m²) it did effectively not make a difference, whether the participants trained at a high or medium intensities.

As you can see in figure 1, over time, both workouts yielded the exact same increases in VO2Max (marker of cardiovascular fitness)., What is however significantly different is the slope and the general look of the VO2max graph.

Figure 1: Study design and results of the 12-week intervention; training was performed 3 days/week on a cycle
ergometer and consisted of 6–10 bouts of 1 min duration at the given intensities; the asterisk after the week # indicates that the intensity values were adapted to the increase in W-Max over the past weeks (Astorino. 2013)

While the latter is clearly logarithmic for the high intensity interval training arm (HIIT; intensities see figure 1, left), the MIIT (LO in figure 1) VO2Max development is much more linear and does not display the same ceiling effect you see in the HI group. It would thus be reasonable to argue that...

MIIT hits HIIT, but...

... it is VERY likely that this is a "overweight woman phenomenon". After all, the heart rate was essentially the same regardless of whether the ladies worked out at an average intensity of 176W (MIIT) or 202W.

Figure 2: Heart rate and workload develoment over the 12-week study period (Astorino. 2013)

At first that may seem odd, but to push your heart rate through the 200 mark, you actually need a pretty decent fitness level. If you have been sitting around your whole life, you will be up to 190bpm when you simply take the stairs instead of the elevator; and while this is no health benefit it makes the same walk in the park that's just a nasty way of locomotion for the average athletic person an intense workout for the morbidly obese.

And what do we know about "intense workout"? Right, those are the true "cardio workouts" adaptation does not happen in the comfort zone and it does not entail weight loss (!) - I don't know how often I have to repeat that, but weight loss happens in the kitchen. You can only steer and promote what and how much you lose by working out... but that's the topic of another article.

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"Men are different women, too..." We all know that, but can we still train together or will women have to do cardio first, while men would be better off starting out lifting weights? (learn more)

Bottom line: If you, family or friends are starting out to work out - keep things at a pace that's intense for YOU - not for whomever you are trying to emulate or you are training with. If there is one beauty of doing cardio in the gym instead of outside, it is that you can train right next to a friend at your personal intensity level.

So don't put a spoke into your own wheels by trying not too look bad in front of a friend. Stick to your own tempo and use yourself as a reference to judge your progress - and if the latter looks like the orange graph in figure 2 (right) you know you are on track, no matter what the absolute wattage (or RPMs) say.

References:

• Astorino TA, Schubert MM, Palumbo E, Stirling D, McMillan DW, Cooper C, Godinez J, Martinez D, Gallant R. Magnitude and time course of changes in maximal oxygen uptake in response to distinct regimens of chronic interval training in sedentary women. Eur J Appl Physiol. 2013 Sep;113(9):2361-9.

HIIT Economy: 30s Intervals + 2:1 Work-To-Recovery Ratio Allow For Maximal Peak Oxygen Uptake at Minimal Power Output During HIIT Exercises in Advanced Trainees

We all know and follow the fundamental rules of the marketplace, but when we are in the gym we tend to forget about profit maximization and the minimal investment, maximal returns principle.

It is quite funny that our gyms are among the few places in our economy-driven society where people tend to forget about the fundamental rules of the marketplace. The way many of weekend-warriors and fitness junkies train is in fact the exact opposite of the all-governing principle of profiteering. In their desperate and in many cases misinformed efforts to maximize their muscle gains, fat loss or overall fitness, many of them fail to realize that the "optimal" training strategy is not the one that leads to suboptimal results at a maximal level of exhaustion. Think about the 2h cardio sessions in the non-existent fat burning zone, for example, or the two hour resistance training workout with 10 different exercises per body part.

Even if you don't belong to this group of miserably misguided souls, I believe there is this innate masochistic side in all of us that makes us believe that the degree of post-workout exhaustion is an adequate measure of the efficacy of a given workout. It does not matter if we are talking about classic cardio training, weight lifting or the high intensity interval training - all of them could benefit from goal-specific modifications, such as those that researchers from the Lillehammer University College in Norway have recently tested in a small scale intervention trial involving 13 well-trained male cyclists (Rønnestad. 2013).

Note: Your Tmax is the time to exhaustion during continuously cycling to exhaustion at the minimal power output (MAP) that elicits peak oxygen uptake (VO2max).

The goal Rønnestad and Hansen had had in mind, when they came up with the study design  was to investigate the effect of interval durations of 30s, 50% of Tmax [Tmax = ], and 80% of Tmax on the corresponding time-periods the athletes would exercise at ≥90% of their peak oxygen uptake. The three workouts that were performed on three different occasions had a work-to-rest ratio 2:1 and the intensity during the active recovery periods was 50% of the minimal power output (MAP) that elicits peak oxygen uptake (VO2max).

The latter, i.e. the time spent at a minimal power output that elicits peak oxygen uptake, was obviously also the criteria to define the "optimal" HIIT workout. After all, it can be expected that the "cardiovascular" (=fitness) benefits and the corresponding increases in the max. VO2 will be most pronounced, when you work out close to your individual VO2max without subjecting yourself to a potentially detrimental strain.

Figure 1: Maximal rate of perceived exertion, lactate levels and rtime at >90% heart rate in % of the total exercise time (left); VO2 levels at different timepoints expressed as percentage of time to exhaustion (Rønnestad. 2013)

As the scientists point out, their observation that their interval protocol using 30 s work periods induced a longer time ≥90% of VO2peak, longer time ≥90% of HR peak, and longer work durations at MAP intensity than the interval protocols using work periods of 50% of Tmax and 80% of Tmax

"diverge somewhat from the findings of Millet et al. (2003) [who] compared, amongst others, intermittent runs at MAP with a work duration of 30 s and 50% of Tmax with a 1:1 work:recovery ratio and a recovery intensity of 50% of MAP [and] found that work intervals lasting 50% of Tmax resulted in greater time ≥ 90% of VO2peak than work intervals of 30 s (~ 8 min vs. ~ 2.5 min, respectively)." (Rønnestad. 2013)

According to the authors this difference is probably a direct consequence of the extended active rest periods in the Millet trial. While the study at hand used rest periods of 15s (50% of the time spent ad MAP intensity), the participants in Millet's study rested for 30s. Enough time for the heart rate to recover and the "workout economy to decline".

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Suggested read: "Eight HIIT Sessions on the Rowing Ergometer Cut Body Fat, Increase Adiponectin, VO2Max & Performance in National Level Rowers - Workmatched Classic "Cardio" Does Nothing" | read more

Bottom line: "Cardio" as in "cardiovascular exercise" is supposed to be a form of training that is challenging enough to elicit beneficial adaptation processes that will results in increased exercise performance and/or VO2max. For most advanced trainees, a conventional "cardiovascular training" at say 70-80% of the individual VO2max is not going to deliver the stimulus that would be necessary to elicit significant adaptation processes.

For the advanced trainee looking to increase his cardiovascular capacity, high intensity interval training should thus be the training method of choice and as the study at hand confirms, the most economic form of HIIT is one that maximizes the time spent in the magic >90% of your HR peak training zone, at minimal intensities.

References:

• Millet, GP, Candau, R, Fattori, P, Bignet, F, and Varray, A. VO2 responses to different intermittent runs at velocity associated with VO2max. Can J Appl Physiol 28: 410-423, 2003.  
• Rønnestad BR, Hansen J. Optimizing interval training at power output associated with peak oxygen uptake in well-trained cyclists. J Strength Cond Res. 2013 Aug 12. [Epub ahead of print] 

Sex, HIIT & Perceived Readiness: Any News on the Optimal Rest Times for Self-Paced HIIT Regimen in Men & Women?

Surrender bro, women are tougher than we'll ever be... and let's not talk about the other tactics by the means of which they trick us into doing whatever they want without us even noticing :-o

In the world of search engines for scientific papers on training and exercise science the acronym "HIIT" is currently what the word "sex" has always been on Google & co. Against that background it is actually surprising that no one else but me has taken notice of a paper on the "Sex specific  responses  to  self-paced,  high-intensity  interval  training  with  variable  recovery periods". The corresponding research was conducted by C. Matthew Laurent et al. from the School of Human Movement, Sport and Leisure Studies at the Bowling Green State University in Ohio and the paper is about to be published in an upcoming issue of the Journal of Strength and Conditioning Research (Laurent. 2013)

Men are different, women too

The results of previous experiments suggest that women are tougher than men, when it comes to steady state high intensity exercise at a self-selected pace. In their most recent study that involved 16 subjects (8 men and 8 women) between 19 and 30 years of age who had been participating in at least one session of interval training per week within the past months, Laurent et al. set out to test whether this would apply to HIIT sessions with fixed rest periods, but also variable, self-selected intensities. To this end, they had their subjects perform three bouts of HIIT.

"Each session consisted of 6, 4-minute intervals interspersed with either 1, 2, or 4 minutes of recovery. The recovery duration was counterbalanced and subjects  were  informed  of  the  specific  work-to-rest ratio  prior  to  performing  each  session.   Each  trial began  with  a  5-minute  warm-up  that  consisted  of  walking  4.8  km/h at  5%  incline." 

Suggested read: "8x Increase in PGC1-Alpha Cycling in Glycogen Depleted State" (read more)

The subjects were told to set the treadmill to the highest possible speed they felt they could maintain for 4 minutes knowing they were to perform 6 intervals.

The treadmill remained elevated at 5% incline for the duration of the whole session. Prior to each interval, subjects estimated their level of readiness using a perceived readiness scale.

Throughout and at the end of each interval, VO2(ml/kg/min), heart rate (bpm), and rate of perceived exertion (RPE) were measured, recorded and statistically processed.

At the conclusion of the fourth minute, the treadmill was slowed to 4.8 km/h for an active recovery.

"These procedures were followed identically for each of the 6 intervals and across all 3 trials. At the conclusion of the final interval of each session, subjects were disconnected from the metabolic system and sat quietly in a chair in the laboratory for approximately 15-20 minutes whereupon they provided a session RPE (SRPE) using the OMNI scale. "

All subjects were given at least 72 hours but no more than 10 days of rest between HIIT sessions, at the end of which the scientists had made the following observations:

• 

  Triple your energy expenditure by doing shorter shuttle runs (learn more)

  Men ran at significantly higher relative velocities (i.e., %VO2peak) during the  1-minute  recovery  trial  with  the  effect size suggesting a large difference.
• The same velocity and effect size advantage for the strong sex was evident during the trial with 2 min rest times, as well, but in this case the difference was no longer significant.
• Even during the 4-minute recovery trial, men ran at higher velocities but the values were not significantly different and the effect size was considerably low.

Interestingly the women still had the higher %VO2 peak values during all conditions - in other words, relative to their physical constitution, they were performing at a higher intensity than the men irrespective of the fact the latter were running faster. Interestingly the difference was only significant during the 4-min rest condition (if you look at the data in figure 1 you will realize they had to pay for that dearly).

"Apropos active rest - what's the best?"
If you take a closer look at the data in figure 1, you will realize that the 4-min-condition with a work-to-rest ratio of 4:2 (in other words, the 2min rest-condition) appears to have a slight advantage over the other conditions. While the VO2 max may be ~1% higher in the short rest condition (VO2 data not shown), this is not worth the increased exertion both men and women experienced when they ran their 4-min intervals with only 1min of active rest in-between.

Figure 1: Lactate levels, perceived readiness before the HIIT bout, rate of perceived exertion right after and 15min the self-paced HIIT bout with 1, 2 and 4min active rest between sets in male and female subjects; all data expressed relative to the mean value for the respective parameter, data calculated for men and women separately (Laurent. 2013)

As far as the 4:4 condition is concerned it is certainly remarkable that the female participants appear to totally exhaust themselves during that condition. It is difficult to determine, whether this is a result of "getting out of the groove" due to the long rest period (if you are jogging you may know that once you stop for more than a minute it's very difficult to get into the groove again), or whether that may be a result of the fact that they were pushing themselves harder when they knew there would be a long recovery period. Personally I tend to believe that it's the latter effect. Otherwise, the male participants of the study at hand should have experienced a similar negative effect of resting too long. Now, whether that's a sign of toughness or rather one of hubris is a question I'd rather not answer ;-)

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(Re)read the SuppVersity HIIT Series and learn about the optimal interval:rest ratios for your personal training goals (click here)

Bottom line: Whether you can truly argue, that 4:2 is the optimal ratio is at least in my humble opinion still open - regardless of your sex by the way. So, if you are not sure what to do, try a couple of different interval:rest ratios and see how you feel. Meanwhile, I'd suggest you remember that the word "training" comes from "to train" and refers to the "sustained practice [...] in an art, profession, occupation, or procedure, with a view to proficiency in it" (Oxford English Dictionary). Proficiency in this context means that you achieve performance increases and those are not a necessary (and in most cases not even a likely) consequence of feeling like you have been run over by a train.

Once you've figured out what works best for you, stick to it! I don't care if it's 2:1 or 30s:1min, as long as it works for you and you don't have to drag yourself to the track or the gym, whenever your HIIT sessions are due, that's your personal optimum. You should still keep in mind that this optimum may change with your current performance / weight loss / hypertrophy goals and the corresponding amount of energy you consume. Previous research, for example, suggests that long(er) intervals (in the 4min range) could have a slight edge over very short ultra-intense ones, especially when your primary goal is to shed body fat (learn more in the HIIT Special Part I & Part II)

References: 

• Laurent CM, Vervaecke LS, Kutz MR, Green JM. Sex specific responses to self-paced, high-intensity interval training with variable recovery periods. J Strength Cond Res. 2013 Jul 8. [Epub ahead of print]