Resting 3 vs. 1 Min. Between Sets Pays Off: Greater Size + Strength Gains - Probably Mediated by 15% Higher Volume

Resting long enough to maximize your training volume could be the key to success, i.e. strength and size gains.

If you have been following the various affords to ascribe differences in strength and, even more so, size-increases to a specific training variable, you will remember that the only promising parameters that appear to be supported by more than the literal "outlier study" are training load and volume.

Of these, the former is pretty much uncontested. The latter, however, is still questioned by a camp of inconvincible skep- tics, who simply ignore the fact that there's ample evidence that "[h]igher-volume, multiple-set protocols have consistent- ly proven superior over single set protocols with respect to increased muscle hypertrophy" (Schoenfeld. 2010).

It would be interesting to see if rest periods should also be periodized!

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What still isn't clear, though, is the role of other training parameters, such as the time you take to recover between multiple sets and exercises aka the "rest intervals". As Schoenfeld et al. point out in the introduction to their most recent study, "several studies have investigated the effects of varying rest interval length on muscular adaptations," (Schoenfeld. 2015) albeit with contradictory results: While Ahtiainen et al (2005) were unable to find a significant inter-group size or strength difference in well-trained subjects (6.6 +/- 2.8 years of continuous strength training) who rested 2 minutes compared to those who rested only 5 minute in response to their 21-week training intervention, Buresh et al (2005) reported more recently that significantly greater size increases of the arms and a trend for greater muscle hypertrophy in the legs in young, albeit untrained subjects who rested for 2.5 minutes instead of just one.

Figure 1: Previous studies found "conflicting" evidence. While Ahtiainen et al. found no effects of 2 vs. 5 minutes in trained, Buresh et al. found effects of 2 vs. 1 minutes rest in untrained subjects. With different subjects, different workouts and most importantly different rest times that were compared it is yet not exactly right to say that the studies contradict each other.

Now, obviously, the ostensible "contradiction" I alluded to in the previous paragraph does eventually not exist. With trained vs. untrained subjects, different workout protocols and most importantly different rest intervals (1 vs. 2 minutes and 2 vs. 5 minutes) the studies by Ahtiainen and Buresh cannot really contradict each other. The same must be said of an even more recent study by Villanueva et al. (2014) the surprising findings of which, i.e. "longer rest periods compromise the gains of older trainees", I've discussed last year, already.

What about the lack of different increases in strength endurance? I have to admit that I do not discuss this finding of the study in detail. While one would expect that shorter rest intervals would produce greater strength endurance adaptations, the researchers observed the opposite, an - albeit non-significantly larger increase in strength endurance in the 3-minute-rest group that correlated with the increase in 1RM strength. Further studies will have to show what the underlying mechanism of this counter-intuitive observation is and whether it may be muscle specific, i.e. occur only in the upper, but not in the lower body.

Eventually, however, this does not change that there is, as Schoenfeld et al. write that "a need for more research to provide greater clarity on the topic" (Schoenfeld. 2015). A "clarity" Schoenfeld et al. sought to find with a study that "used current rest interval recommendations for hypertrophy and strength of 1 versus 3 minutes, respectively, and employed validated measures to directly assess site-specific changes in muscle thickness" (ibid). In that, the researchers speculated that ...

"[c]onsistent with generally accepted guidelines on the topic (Willardson. 2006), we hypothesized that short rest intervals would produce greater increases in muscle growth and local muscle endurance while long rest intervals would result in superior strength increases" (Schoenfeld. 2015).

As you will know if you didn't miss the headline of this SuppVersity article, this hypothesis was only partly validated. The data in Figure 2 confirms that the subjects, "experienced lifters (defined as consistently lifting weights for a minimum of 6 months and a back squat / body weight ratio ≥ 1.0)" (Schoenfeld. 2015), gained significantly more strength, when they rested 3 versus just 1 minute between the 3 sets of their three weekly workouts (Figure 2 does also tell you that the strength endurance increases were identical in both groups).

Figure 2: Changes in markers of strength and strength endurance; * denotes significant pre- vs. post difference, # denotes significant inter-group difference (here in favor of long(er) rest periods | Schoenfeld. 2015).

What was Schoenfeld et al. did not find, however, were increased size gains in the short-rest period group whose 24 workouts that were performed on non-consecutive days over the course of the 8-week study period, were otherwise identical with those of the long-rest period group and comprised a total of 7 exercises for all major body parts, namely...

• three leg exercises, i.e. barbell back squats, plate-loaded leg presses, and plate-loaded leg extensions), 
• two exercises for the anterior torso muscles, i.e. flat barbell presses and seated barbell military presses, and 
• two exercises for the posterior torso muscles, i.e. wide-grip plate-loaded lateral pulldowns, and plate-loaded seated cable rows

This is a highly significant result even for you who is - according to an older SuppVersity Poll - probably training according to a split regimen, albeit most likely with very similar exercises. What may be different from the some, but obviously *smile* not your workout though, is that the supervision by members of the research team ensured that the subjects stuck to the prescribed cadence of 1 second for the concentric and "approximately 2 seconds" (ibid.) for the eccentric part of every the exercise. This as well as the imperative progression to higher weights, whence the prescribed number of 8-12 reps per set could be performed is unfortunately overlooked by many recreational trainees - with disappointing consequences in the form of inferior or even no size and strength gains, by the way... but I am digressing, let's rather take a look at the already mentioned, unexpectedly superior strength size gains in the long(er) rest interval group (Figure 3).

Figure 3: Changes in muscle thickness and corresponding effect sizes; * denotes significant pre- vs. post-changes, # denotes significant inter-group differences; overall it is obvious that there's a long(er) rest advantage (Schoenfeld. 2015).

As the single "#" in Figure 3 tells you, the inter-group differences and thus the advantage of the long(er) rest intervals was statistically significant only for the quads, though. If we also take into account the lack of statistically significant effects on the sleeve sizes (biceps and triceps) in the short rest interval group, as well as the obvious differences in effect sizes (Figure 3, right), there's yet little doubt that the hypothesis that shorter rest intervals yield greater size increases must be considered falsified - at least under the given experimental conditions (trained subjects, three full-body workouts per week, standard hypertrophy set and rep-ranges, etc.).

So what's the verdict, then? At first sight it would appear as if the study at hand would totally refute the idea that shorter rest intervals, or I should clarify, rest intervals that are as short as 60s (*) should have a place in your training regimen altogether (*Schoenfeld, et al. rightly point out that Ahtiainen's result suggest that even 120s could have been enough time to rest - it is thus important to give precise recommendations for rest intervals, not something as arbitrary "short" vs. "long"). We should not forget, though, that even a thoroughly conducted study like the one at hand has its limits and definite conclusions should not be drawn hastily based on a single study result - even if it is, as in this case, corroborated by the results of Buresh et al (2009).

Figure 4: The total training volume in the long(er) rest period group (3 vs. 1 minutes of rest) was on average 15% higher. Due to the relatively high inter-individual differences and the relatively low number of participants (N=21) a statistically significant correlation between the weight lifted per week (total volume in kg as in the figure) and the surprisingly superior gains in the 3-min-rest group could not be established (based on Schoenfeld. 2015).

With that being said, a secondary outcome of the study provides a reasonable explanation for why both, the strength and the size gains benefited from long(er) rest intervals: The total training volume I've plotted in Figure 4. As Schoenfeld et al. point out, the latter has previously been suspected to mediate the effects of inter-set rest on strength and hypertrophy on total training volume and strength (Henselmans. 2014). A correlation between the visible differences in training load (see Figure 4) and the magnitude of training adaptations, however, could not be found in the study at hand. As the authors highlight, the reason for this lack of statistical significant correlations may yet be a simple lack of statistical power, so that one "cannot rule out the possibility that the greater training load achieved by the longer rest period group was responsible for the greater training adaptations" (Schoenfeld. 2015 | Buresh et al. found such an effect for the upper, yet not for the lower body).

Personally, I tend to believe that, with a higher number of subjects, a correlation between the total training volume that was on average 15% higher in the 3 vs. 1 minute rest group could have been established. This, in turn, would support the notion that long(er) rest periods - maybe, as Schoenfeld et al. suggest based on the data from Ahtiainen's study, at least 120s - are necessary to maximize the total training volume and thus the overall = strength and hypertrophy response to workouts. Whether that is true for all types of workouts (e.g. split- vs. full-body), all subject groups (e.g. people who are used to short rest periods vs. those who are not) as well as special athletic requirements (e.g. power vs. strength & hypertrophy) will have to be determined in future studies, however | Comment on Facebook!

References:

• Ahtiainen, Juha P., et al. "Short vs. long rest period between the sets in hypertrophic resistance training: influence on muscle strength, size, and hormonal adaptations in trained men." The Journal of Strength & Conditioning Research 19.3 (2005): 572-582.
• Buresh, Robert, Kris Berg, and Jeffrey French. "The effect of resistive exercise rest interval on hormonal response, strength, and hypertrophy with training." The Journal of Strength & Conditioning Research 23.1 (2009): 62-71.
• Henselmans, Menno, and Brad J. Schoenfeld. "The Effect of Inter-Set Rest Intervals on Resistance Exercise-Induced Muscle Hypertrophy." Sports Medicine 44.12 (2014): 1635-1643.
• Schoenfeld, Brad J. "The mechanisms of muscle hypertrophy and their application to resistance training." The Journal of Strength & Conditioning Research 24.10 (2010): 2857-2872.
• Schoenfeld, et al. "Longer inter-set rest periods enhance muscle strength and hypertrophy in resistance trained men." Journal of Strength and Conditioning Research (2015): Publish Ahead of Print.
• Villanueva, Matthew G., Christianne Joy Lane, and E. Todd Schroeder. "Short rest interval lengths between sets optimally enhance body composition and performance with 8 weeks of strength resistance training in older men." European journal of applied physiology (2014): 1-14.
• Willardson, Jeffrey M. "A brief review: factors affecting the length of the rest interval between resistance exercise sets." The Journal of Strength & Conditioning Research 20.4 (2006): 978-984.

Longer Rest Periods Compromise Adaptational Response in Resistance Training Older Men in 12 Week Study

Best-agers listen up: If you want to make progress, socialize after your workouts and stick to rest periods in the 60-90s range.

Best-agers, listen up! If you are the kind of person who likes to chat for four minutes between his / her sets you are not just wasting time. You are also making your workouts less effective. While there is little evidence that there are major differences between rest times of 60s and 90s, a recent study from the Division of Biokinesiology and Physical Therapy at the Clinical Exercise Research Center of the University of Southern California is not the first study to suggest that resting longer than maximally 120s is going to compromise the changes in body composition, muscular performance, and functional performance that occur in response to resistance training.

I have to admit, with a mean age of 70.3 years, the 22 male volunteers of said study don't qualify as the "classic" gymrat. On the other hand, you will probably have heard the argument that aging muscle cannot sustain the same extent of high intensity hammering that's highly productive in younger folks against.

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Against that background, it's actually all the more surprising that the 11 men in the 60s rest period groups of this recent 4 weeks resistance training study saw significantly greater increase in lean muscle mass, bench press & leg press 1RM max, performance on the pull-down and several parameters of functional performance (not shown in Figure 1).

Figure 1: Changes in body composition and strength after 8 and 12 weeks; expressed relative to the values that were measured after the 4-week pre-training phase that was identical for both groups (Villanueva. 2014)

Except from the rest times, the periodized strength training regimen was 100% identical for both groups. This means that all 22 study subjects performed the same progressive total body resistance training program which was preluded by a 4-week familiarization protocol that was 100% identical for both groups:

• Training frequency: 3 days/week for the 4-week training cycle
• Sets / reps: 2 to 4 sets with 15 to 8 repetitions (set number increased, rep number decreased over time)
• Exercise number: Four to six exercises per workout

Only after the subjects had completed the first four weeks of training they were paired based on the similarity of their flat bench machine chest press 1-RM and randomly placed into one of the two groups: The SS = short (60s) and the SL = long (240s) rest group. As the scientists say they chose

"this strength outcome measure, because previous work from our lab has indicated there is relatively less variability among study participants with chest press 1-RM val ues, versus leg press 1-RM values, and, therefore, it would allow us to more easily randomize and create two treatment groups that are similar in (upper body maximum) strength.

In the following 8-week 'actual' study period the subjects were subjected to a progressive total-body resistance training program emphasizing development of upper and lower body strength.

• Training frequency: 3 days/week for 8 weeks by both groups (SS and SL)
• Sets / reps: sets ranged from 2 to 3, repetitions from 6 to 4
• Exercise number: 4–6 exercises

During this active study period, the only difference in program design between the two strength RT groups in was the rest interval length utilized between sets: 60 s (SS group) versus 4 min (SL group).

"Throughout the entire resistance training program, all sets were performed maximally for the assigned number of repetitions and with proper lifting technique, and loads were adjusted in accordance with recovery and performance, across the repeated sets progression.

At least in untrained subjects shorter rest periods (60s vs. 150s) may have more beneficial effects on body composition, i.e. they elicit greater lean mass gains and higher losses of body fat (Buresh. 2009)

What about studies in younger subjects? The results are not consistent, but generally speaking there appears to be slight advantage in terms of strength gains with rest periods in the 90s-150s range as they were observed by Robert Buresh et al. (2009) in healthy, recently untrained males. In previously strength-trained men the benefits appear to vanish, when the total exercise volume is not controlled for, though (Willardson. 2008). Moreover, the previously cited study by Buresh et al.  (2009) indicates that shorter rest periods will elicit more favorable changes in body composition (see Figure on the left). We must be careful, though - short is not generally better.  A review by de Salles et al. (2009) indicates that rest periods below 60s can impair the strength gains and while respective data is lacking, it is likely that this will also have negative effects on the amount of lean mass you will gain on otherwise identical training regimen.

Furthermore, it is important to note that study participants were never expected to perform sets to absolute muscular failure; given an appropriate loading progression, with alterations in set/repetition schemes throughout and across microcycles (i.e., a series of 3 training sessions), the repetition maximum assignments allowed for successful completion of the assigned number of repetitions at the load(s) prescribed, across multiple sets, and with minimal need for assistance/'spotting'" (Villanueva. 2014.)

Now this certainly sounds as if the protocol was realistic. But there is one major difference that puts a question mark behind the results of the study: usually regimen with long and short rest times differ significantly in the number of sets and the number of reps. Thus it is possible that future studies using different protocols for both groups would yield different results.

Figure 2: More helps more... at least in elderly study subjects increasing the intake of whey protein after a workout from 20g to 40g will yield significant benefits (Yang. 2012).

Bottom line: The study at hand certainly supports previous evidence that older men and women don't necessarily have to train with the "handbreak firmly fixed". The relatively large increase in strength and functional performance, however, stand in stark contrast to the pathetic increase in lean mass. And the standardized set and rep ranges make it impossible for the 240s rest group to benefit from the ability to train at higher volumes.

Another thing that is wirth mentioning is that the subjects consumed >1.0 gram protein/kilogram body weight/day - without the addition of fast absorbing high BCAA protein sources, however, elderly men (and women) are always having a hard time to build practically relevant amounts of lean muscle.

Against that background, I would love to see this study being repeated with 30-40g of whey protein being consumed in the vicinity of the workout; and in case you want to do your own N=1 experiment using this or any other workout protocol described in the study at hand, I would suggest you make sure to add some extra-protein, as well. Previous studies do after all indicate that "more" as in 40g vs. just 15-20g helps more in men and women in their 60s or older | Comment on Facebook!

References:

• Buresh, Robert, Kris Berg, and Jeffrey French. "The effect of resistive exercise rest interval on hormonal response, strength, and hypertrophy with training." The Journal of Strength & Conditioning Research 23.1 (2009): 62-71.
• de Salles, Belmiro Freitas, et al. "Rest interval between sets in strength training." Sports Medicine 39.9 (2009): 765-777.
• Villanueva, Matthew G., Christianne Joy Lane, and E. Todd Schroeder. "Short rest interval lengths between sets optimally enhance body composition and performance with 8 weeks of strength resistance training in older men." European journal of applied physiology (2014): 1-14.
• Willardson, Jeffrey M., and Lee N. Burkett. "The effect of different rest intervals between sets on volume components and strength gains." The Journal of Strength & Conditioning Research 22.1 (2008): 146-152.
• Yang, Yifan, et al. "Resistance exercise enhances myofibrillar protein synthesis with graded intakes of whey protein in older men." British Journal of Nutrition 108.10 (2012): 1780-1788.

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." 

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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:

• 

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  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 ;-)

---

(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]

Training for Size & Strength - Does the Rest Matter? Study Finds 7-9% Greater Increase in Muscle Size With Decreasing Rest Periods.

Image 1: If you want to build Arnold-esque arms you better not sit around too long in-between your sets.

"Short rest periods to burn fat, medium rest periods to build muscle and long rest periods to build strength" - it's actually pretty likely that one of your trainers, gym buddies or fatherly mentors told you something along those lines in the past. In view of the results of a soon to be published international study by Brazilian researchers from the State University of Campinas and the Federal University of Rio de Janeiro and their American colleagues from the Eastern Illinois University, the University of Memphis and the Colorado College (Souza-Junior. 2011), this is probably the next item on list of widely accepted bodybuilding myths that have a spark of truth to them... at least for recreational strength trainees who use some creatine monohydrate to promote their strength and mass gains.

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For their study, the results of which are going to be published in the next issue of the Journal of the International Society of Sports Nutrition, Tacito P. Souza-Junior and his colleagues recruited 22 "recreationally trained" men with a minimum of one year resistance training experience at a frequency of 4 sessions a week, who were randomly assigned to one out of two exercise protocols, which differed only in the time the subjects were allowed to rest in-between sets (cf. figure 1).

Figure 1: Identical training protocol for all subjects participating in the study (compiled based on information from Souza-Junior. 2011)

The only difference between the groups was that half of the subjects trained with a constant rest time of 2 minutes between sets over the whole 8 weeks (CI group), while the remaining subjects had to decrease their rest times from week to week (DI group) according to the scheme illustrated in figure 2. The training sessions were supervised and the subjects were " verbally encouraged to perform all sets to voluntary exhaustion". Considering the overall workload and the training frequency, this were probably pretty hard weeks for the 22 trainees.

Figure 2: The rest times decreased according to a standardized protocol by 15 sec each week.

In addition all subjects, who btw. did not follow a standardized diet, consumed the proven creatine + maltodextrin mix (7 day loading phase with 20g/day creatine + 20g maltodextrin followed by a maintenance dose of 5g creatine + 5g maltodextrin taken immediately post workout) that has been used in numerous studies before.

Figure 3: 1RM performance (in kg) for bench press and barbell squat before and after the 8-week training period in subjects with constant and decreasing rest periods (data adapted from Souza-Junior. 2011).

Now, if the initially stated "wisdom" held true, then the 11 subjects with constant rest periods should either have gained more muscle (if you consider 2 minutes a "medium" rest period) or built more strength (if you would say that 2 minutes belong to the realm of "long" rest periods) - yet figures 3 and 4 seem to indicate that neither of that was the case.

Figure 4: Muscle CSA (in cm²) of arm and tigh muscles before and after the 8-week training period (data adapted from Souza-Junior. 2011).

If we have do yet a closer look at the effect sizes, there is yet a notable advantage of the DI protocol in terms of the measured increases in muscle CSA with +14% and +19% in arm and tigh CSA in the constant rest interval group (CI) and +21% and +28% in the decreasing rest interval (DI) group.

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There is a spark of truth to every myth To give you an idea of how significant - and I am talking about "posing significance" not statistical significance here - this is, I have calculated the respective increases in arm- and tigh-circumference, which would differ by 0.4cm and 0.7cm, respectively. Not really outstanding, but nevertheless an important finding of which the researchers say that it lends support to the notion that

decreasing [rest] interval[s] seems to be more efficient than constant interval to produces [sic!] hypertrophic responses.

It has yet to be stated that the 11 subjects in the decreasing rest interval group paid dearly for this increase in muscular hypertrophy, as their "exercise performance" as measured by the total workload per session decreased profoundly from week 1 to week 8: -35% total volume for barbell squats and -30% for bench presses.

The subjects who used constant rest periods, on the other hand, increased their total volume by +20% for squats and by +30% for bench presses. That being said, all powerlifters out there better stick to their constantly (long) rest periods if they do not want to compromise their game.

No Influence of Rest Between Sets on Creatine Kinase and Lactate Levels

Probably, you would assume that the reduction of rest in between sets from 3 minutes to 60 seconds would have an effect if not on creatine kinase, then at least on lactate levels. A recent study published in The Journal of Strength and Conditioning Research refutes this common-sense assumption (Machado. 2010):

Each session consisted of 4 sets of 10 repetitions with 10 repetition maximum loads for the chest press, pullover, biceps curl, triceps extension, leg extension, and prone leg curl. The sessions differed only in the length of the rest interval between sets and exercises, specifically: 60, 90, 120, 180 seconds. Serum CK and LDH were significantly (p < 0.05) elevated 24-72 hours after each session, with no significant differences between rest intervals (p = 0.94 and p = 0.99, respectively). The mechanical stress imposed by the 4 resistance exercise sessions invoked similar damage to the muscle fibers independent of the rest interval between sets.

Since the exact relation between markers of muscle damage, hypertrophy and strength gains have yet to be established, it is as of yet impossible to derive concrete training advice from these findings. In other words, this does not mean that resting times do not make a difference in view of the eventual training results. Shorter rest periods, for example have been associated with increased growth hormone response and an overall more pronounced anabolic stimulus.