A popular theory among fitness professionals is that taking short rest periods between sets maximizes muscular growth. The theory is primarily based on the hormone hypothesis, whereby limiting inter-set rest promotes greater elevations in post-exercise growth hormone, IFG-1 and testosteron...
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December 21, 2016
A popular theory among fitness professionals is that taking short rest periods between sets maximizes muscular growth. The theory is primarily based on the hormone hypothesis, whereby limiting inter-set rest promotes greater elevations in post-exercise growth hormone, IFG-1 and testosterone, and thus enhances the anabolic response to resistance training. One little problem: Emerging evidence indicates that acute increases in anabolic hormones have little if any effect on muscular adaptations, as detailed in my comprehensive review of the topic
In an effort to directly test the theory, our group published a study last year titled, Longer inter-set rest periods enhance muscle strength and hypertrophy in resistance-trained men. In brief, the study not only refuted the claim of a hypertrophic benefit to short rest periods, but in fact showed that resting 3 minutes between sets actually produced superior growth compared to resting 1 minute. Importantly, the study was carried out using a moderate rep range (8-12 reps/set) with all sets performed to muscular failure. The question therefore arises whether results would be applicable when training with lighter weights. No study had ever investigated the topic.
In collaboration with colleagues in Japan, we sought to investigate the effects of low-load resistance training with different rest intervals on muscular adaptations. The study titled, Acute and Long-term Responses to Different Rest Intervals in Low-load Resistance Training, was just published in the International Journal of Sports Medicine.
Here’s the lowdown.
What We Did
Subjects were 21 young collegiate athletes who had not performed resistance training for at least 2 years prior to the study. The subjects were randomly divided into two groups: A short rest group (SHORT) that rested 30 seconds between sets and a long rest group (LONG) that rested 2.5 minutes between groups. The load was set at 40% of the subjects’ 1RM in the back squat and bench press using a tempo of 1-0-2 (1 second on the concentric, 2 seconds on the eccentric). Four sets were performed for each exercise, with all sets taken to muscular failure. Training was carried out twice a week for 8 weeks.
What We Tested
Measures of muscle hypertrophy and strength were assessed pre- and post-study. Muscle cross sectional area (CSA) of the triceps and thigh was measured by MRI. A 1RM bench press and squat was employed to measure changes in maximal strength.
What We Found
With respect to hypertrophy, the SHORT group increased muscle CSA by 9.8% while LONG showed an increase of 10.6%. Thigh CSA increased by 5.7% in SHORT versus 8.3% in LONG. No statistically significant differences were noted between any measure of muscle growth.
From a strength standpoint, 1RM in the bench press increased by 9.9% in SHORT and 6.5% in LONG while increases in the squat were virtually identical between groups (5.2% versus 5.4) As with the hypertrophy results, no statistically significant between-group differences were observed in the strength measures.
How Can You Apply These Findings
There are a number of interesting takeaways from the study. First and foremost, this is yet another study showing that training with light weights can promote marked gains in muscle mass in a relatively short time period. There is now a large body of supporting research on the topic using varied methodologies across a variety of populations. The evidence is too compelling for even the most ardent critic to dismiss.
Intriguingly, we found that rest interval length had no statistically significant effects on muscular adaptations. On the surface, these results conflict with our previous research showing that 3 minutes rest produced superior increases in strength and hypertrophy compared to resting 1 minute when training in a moderate rep range (~10RM). Our findings here seem to indicate that rest interval length isn’t an important consideration when training with lighter loads.
A closer look at the data, however, suggests a more nuanced take-home message.
It’s important to realize that the term “statistical significance” refers to the probability of an event happening by chance. Our study had a fairly small sample size, which reduces the ability to detect significance. Hence, we have to look beyond whether results were “significant” and consider other statistical measures. To that end, while hypertrophy of the arms was fairly equal between conditions, gains in thigh muscle CSA clearly favored resting longer between sets. A statistic called the effect size, which is a gauge of the meaningfulness of the results, bears out these differences were indeed consequential. The effect size for the LONG group was 0.93 (considered a large effect) while that of the SHORT group was just 0.58 (considered a moderate effect). The chart above illustrates the absolute differences between thigh growth and rest intervals.
When attempting to reconcile the differences between upper and lower body hypertrophy, it may well come down to total training volume. Short rest blunted increases in training volume in both upper and lower training, but the disparity was much more pronounced in the squat than in the bench. This is logical as the leg/glute muscles have much greater muscle mass than those of the upper trunk/arms, and thus the associated fatigue during high-rep training is greater in multi-joint lower body training, particularly a demanding exercise like the squat. Given the known dose-response relationship between hypertrophy and volume (as clearly displayed in our recent meta-analysis on the topic), the substantial decrease in number of reps performed with short rest periods could conceivably explain the lesser muscle growth seen in the thighs.
In addition to the long-term effects, we also measured hormonal elevations from each condition post-exercise. Both SHORT and LONG showed significant acute spikes in growth hormone and IGF-1, but the increases were similar between groups. Since hormonal increases are related to levels of metabolic stress, it can be inferred that metabolic stress was similar between conditions as well. Although short rest periods have generally been shown to enhance metabolic stress, these findings are specific to moderate rep training. Training with very high reps elicits large increases in lactic acid regardless of how long you rest between sets. Thus, rest interval length seemingly has less relevance in promoting metabolite buildup. Whether metabolic stress influenced results in this study is undetermined as we didn’t seek to assess mechanisms of adaptations. That’s an intriguing topic for future research.
The Bottom Line
* Training with light weights can pack on some serious muscle.
* Short rest between sets has a detrimental effect on lower body hypertrophy when squatting while there does not seem to be much if any negative impact on growth from the bench press when training with light weights. Thus, shorter rest periods for light-load upper body work are a viable option to cut down on training time without sacrificing gains.
* Since single joint exercise does not elicit comparable fatigue to multi-joint movements, it is conceivable that short rest would be similarly viable for single-joint lower body exercises such as the leg extension. This remains speculative, however, as the topic wasn’t directly investigated in our study.
December 5, 2016
Dating back to my early years as a personal trainer in the mid-90’s, I began to become intrigued by the concept of “loading zones” whereby different rep ranges purportedly could bring about differential effects on muscular adaptations. Prevailing wisdom at the time was that heavy loads (1-5 RM) promote maximal strength gains, moderate loads (6-12 RM) elicit maximal increases in muscle mass, and light loads (15+ RM) produce the greatest improvements in local muscular endurance. This concept, discussed extensively in exercise science texts, was termed the “strength-endurance continuum” (see the image below) although direct research on the topic was limited.
The topic of rep ranges was so intriguing to me that I ultimately made it a focus of my doctoral work. Several years ago I published the data collected in accordance with my dissertation study. In brief, the study looked at muscular adaptations in a “bodybuilding-type” routine versus a “powerlifting-type” routine in resistance-trained men when the routines were equated for volume load. Consistent with the “strength-endurance continuum” concept, the study found that the powerlifting-type routine produced the greatest strength increases. Contrary to prevailing wisdom, however, both routines produced similar increases in hypertrophy of the biceps brachii. You can read my write-up of the routine in this blog post.
Importantly, the findings of that study are specific to the respective routines being equated for volume load. While this provides interesting insights on the topic, it is impractical to carry out long-term training with very heavy loads at the volumes used in that study (in fact, the majority of subjects in the powerlifting-type group displayed clear signs of overtraining by study’s end). So the question arises as to whether results would differ if an equal number of sets were performed between heavy and moderate loads?
Recently I carried out a study that investigated this very topic. The study was just published in the Journal of Sports Science and Medicine.
Here’s the lowdown.
What We Did
Nineteen college-aged men were recruited to participate in the study. All subjects had at least one year of resistance training experience lifting at least three times per week. Subjects were randomized to either a group that trained in a heavy loading range of 2-4 repetitions per set (HEAVY) or a group that trained in a moderate loading range of 8-12 repetitions per set (MODERATE). All other aspects of the subjects’ program were kept constant between groups. The training protocol consisted of seven exercises that worked all the major muscles of the body each session, with three sets performed per exercise. Training was carried out on three non-consecutive days per week for eight weeks. Subjects were instructed to maintain their normal daily nutritional intake and no differences in either calories or macronutrient consumption was found between groups over the course of the study.
What We Measured
We tested hypertrophy of the elbow flexors, elbow extensors, and quads using b-mode ultrasound. Maximal strength was assessed in the squat and bench press via 1 repetition maximum (RM) testing. Upper body local muscular endurance was determined by assessing the subject’s initial 1RM in the bench press for as many repetitions as possible to muscular failure.
What We Found
The infographic to the left (courtesy of Thomas Coughlin) illustrates the results of the study. In general, overall muscle growth was greater for MODERATE compared to HEAVY. Increases in thickness of the elbow flexors (i.e. biceps brachii and brachialis) modestly favored the use of moderate reps (~5% vs ~3% for MODERATE vs HEAVY, respectively) while gains in the quads substantially favored the moderate rep group (10% vs 4% for MODERATE vs HEAVY, respectively). Interestingly, growth of the triceps was similar between groups.
On the other hand, strength gains were decidedly greater when training with heavy loads. This was seen for improvements in both the 1RM squat (29% versus 16%) and bench press (14% vs 10%), which favored HEAVY compared to MODERATE. Muscle endurance increases were similar between rep ranges.
What are the Practical Implications
The study provides evidence that training with heavy loads helps to maximize muscle strength and training with moderate loads promotes greater increases in muscle mass. Importantly, these findings are specific to routines where the number of sets are equated. At face value, this is consistent with the “strength-endurance continuum” and supports what gym bro’s have been preaching for years in regards to rep ranges.
However, when the results are taken into account with my previous study on the topic that equated volume load, an interesting hypothesis emerges. Since strength gains were greater with heavy loads in both studies, it can be concluded that low-rep training is best for maximizing strength regardless of volume load. On the other hand, since the previous study showed no differences in hypertrophy between conditions when volume load was equated, it can be inferred that volume load is a greater driver of muscle growth irrespective of the rep range. In other words, strength is maximized even with lower training volumes provided heavy loads are used, but higher volumes are needed to maximize gains in size whether you train with moderate or heavy weights.
The study had several limitations including a relatively small sample size, the use of a single-site measurement for muscle growth on each of the respective muscles, and possible confounding from the “novelty factor” (i.e. virtually all the subjects trained with moderate loads, so it is possible that the novel stimulus for those in the heavy load group might have impacted results). These issues must be taken into account when attempting to draw evidence-based conclusions. Most importantly, one study is never the be-all-end-all when it comes to answering questions on an applied science topic. Rather, each study should be considered a piece in a puzzle that lends support to a given theory. The practical implications of programming loading zones will become increasingly clear as we continue to build on this line of research. For now, though, the evidence suggests to train heavy if your goal is maximal strength, and to focus on accumulating volume for maximal gains in muscle mass.
July 25, 2016
The question as to how much strength training volume is needed to maximize muscular gains has been an ongoing source of debate, both in scientific circles as well as the realm of social media. Some claim that a very low volume approach is all that’s required while others subscribe to the belief that marathon training sessions are an absolute necessity.
Who’s right? Well…
Back in 2010, my colleague James Krieger carried out a meta-analysis to provide evidence-based clarity on the topic. In case you’re not aware, a meta-analysis pools data from all relevant studies on a given subject to provide greater statistical power and thus enhance the ability to draw practical inferences from the literature. In short, the analysis showed that performance of multiple sets was associated with a 40% greater hypertrophy-related effect size (a statistical measure of the meaningfulness of results) compared to single-set training.
While this paper provided good evidence in support of higher training volumes, there were some issues with the analysis. For one, James only looked at sets per muscle per workout; a potentially more important marker in determining the hypertrophic response is the weekly volume per muscle group. Moreover, only 8 studies qualified for inclusion in James’ analysis at the time, and only 3 of these studies used direct site-specific measures of muscle growth (i.e. MRI, ultrasound, etc).
Since publication of James’ meta-analysis, a number of additional studies have been published in the peer-reviewed literature. Given this info and in an attempt to resolve previous issues, James and I decided it was appropriate to carry out a follow-up meta-analysis that encompassed all the evidence to date. We recruited our colleague Dan Ogborn to collaborate on the project, and centered our focus on the effects of weekly sets per muscle group on changes in muscle mass. I’m happy to report the paper was recently published in the Journal of Sport Sciences.
Here’s the lowdown:
What We Did
A literature search was conducted to locate all studies that directly compared measures of hypertrophy between higher versus lower resistance training volumes with all other variables equated between conditions. Only human studies with healthy subjects that had a minimum duration of six weeks were considered for inclusion.
What We Found
A total of 15 studies were identified that met inclusion criteria. We ran multiple comparisons to assess the topic from different perspectives. First we evaluated the effects of volume within each study and found that higher volumes were associated with a 3.9% greater average increase compared to lower volumes; the findings were statistically significant (i.e. high probability that they weren’t due to chance alone). As shown in the accompanying forest plot, only 1 of the 15 studies showed a favorable effect for lower volume training, emphasizing the high probability that greater volumes produce greater increases in muscle growth.
We next looked at the effects of volume on a two-level categorical basis, splitting the data into performing less than 9 sets versus 9 sets or more. In this model, the lower volume condition was associated with a gain of 5.8% while the higher volume condition produced a gain of 8.2%. Although the results did not reach statistical significance in this model, the probability of an effect was nevertheless very high (p = 0.076).
Finally, we employed a three-level categorical analysis whereby volume was stratified into less than 5 weekly sets per muscle, 5 to 9 weekly sets per muscle, and 10+ sets per muscle. Here we found a graded dose response whereby gains in muscle progressively increased across each category from 5.4% to 6.6% to 9.8%, respectively. As with the two-level model, results did not quite reach significance, but a high level of confidence can be inferred that results were not due to chance alone (p = 0.074).
What are the Practical Implications
There are several important take-aways from our meta-analysis. First off, a low volume approach can build appreciable muscle. Performing less than 5 weekly sets per muscle produced an average hypertrophic gain of 5.4%. Not too shabby. So if you are time-pressed and not concerned about achieving the upper limits of your muscular potential, it should be heartening to know that you can build an impressive physique without spending a lot of time in the gym.
That said, there is a clear dose-response relationship between volume and hypertrophy. In the three way categorical model, performing 10+ sets produced almost twice the gains as performing less than 5 weekly sets per muscle (9.8% vs 5.4%). Performing 10+ weekly sets per muscle was also associated with a markedly greater increase in muscle mass compared to 5-9 sets (9.8% vs 6.6%). Thus, a higher volume approach is clearly necessary if you want to maximize muscular gains.
So how many sets should you perform to maximize hypertrophy? That remains to be determined. While 10+ weekly sets per muscle was established as a minimum threshold, we were not able to determine an upper threshold where optimal muscle growth is achieved. The effects of volume on hypertrophy undoubtedly follows an inverted-U curve, whereby results progressively increase up to a certain point, then level off, and then ultimately decrease at exceedingly high volumes due to the negative consequences of overtraining. Moreover, the adaptive response to volume will be specific to the individual, with some lifters able to benefit from higher volumes more so than others. Thus, experimentation is needed to tweak the number of sets you perform based on how you respond.
It may well be that periodized approach is best here. Given that repeatedly training with high volumes can lead to an overtrained state, cycling from lower to higher volume blocks that culminate in a brief period of functional overreaching would hypothetically allow for sustained muscular gains over time while staving off the potential for overtraining. It’s a strategy that I’ve employed with good success when working with clients.
Interestingly, a previous study indicated that higher volumes were beneficial for the lower but not upper body musculature. A follow-up study by the same research group similarly found that satellite cell activation was dependent on volume only in the lower body musculature. However, our pooled analysis did not support these findings. Rather, volume was equally important irrespective of body region, with higher volumes translating into greater increases in size.
A limitation of the analysis is that the findings are largely specific to the muscles of the upper arms and frontal thighs; there simply isn’t enough evidence to generalize results to other body regions (i.e. muscles of the back, shoulders, chest, calves, etc). What’s more, the vast majority of studies were carried out in untrained subjects; only two studies used resistance-trained individuals. It has been speculated that increasingly higher volumes are necessary as one gains lifting experience, but more research is needed to support such a conclusion. My lab currently has a large scale study in development to investigate the topic in well-trained men that should help to fill in the gaps in the current literature. Stay tuned…
April 6, 2016
If you follow my work you’ll undoubtedly know that our lab has carried out a number of studies seeking to determine the effects of training in different repetition ranges on muscle strength and growth. The overall findings from these studies showed similar increases in hypertrophy between both heavy and moderate rep ranges, as well as moderate and high rep ranges.
However, the choice of rep ranges is not necessarily an either-or proposition; you can in fact combine strategies to potentially achieve greater hypertrophic benefits. Daily undulating periodization (DUP) routines are specifically designed for this purpose. However, no study to date had compared a varied rep approach to traditional constant-rep training using site-specific measures of muscle growth.
Our study, just published in the International Journal of Sports Medicine, set out to investigate if muscular adaptations would differ between DUP-style routine and a traditional hypertrophy-style protocol. Here’s the scoop.
What We Did
Nineteen young men with over four years average resistance-training experience were randomly assigned to 1 of 2 experimental groups that trained 3 days per week: a constant-rep protocol (CONSTANT) that trained using a standard bodybuilding rep range of 8-12 RM per set, or a DUP-style varied-rep protocol (VARIED) that trained with 2-4 RM per set on Day 1, 8-12 RM per set on Day 2, and 20-30 RM on Day 3. All subjects performed a total-body routine consisting of the following seven exercises per session: flat barbell press, barbell military press, wide grip lat pulldown, seated cable row, barbell back squat, machine leg press, and machine knee extension. We tested subjects for changes in hypertrophy of the arm flexors, elbow flexors and quads, as well as maximal strength in the squat and bench press, and upper body muscle endurance. Training was carried out over an 8-week period, with testing done pre- and post-study.
What We Found
Both groups significantly increased markers of muscle strength, muscle thickness, and local muscular endurance. No statistically significant differences were found between conditions in any of the outcomes studied. Sounds like it really doesn’t matter which option you choose, right?
Well, not so fast…
It’s important to understand that the term “statistically significant” simply refers to the probability of results being due to chance at a predetermined level of 5%. This binary method of determining probability has been widely criticized by those in the know about statistics, who proclaim that practical conclusions cannot be drawn merely on the basis of whether a p-value passes a specific threshold. Rather, probability exists on a continuum, and in this regard the p-values (a measure of probability) in our study favored the VARIED condition in several outcome measures. Moreover, magnitude-based statistics (i.e. effect sizes) indicated a benefit to the VARIED condition for upper body hypertrophy, strength, and muscular endurance; no effect size differences were noted for lower body outcomes.
What are the Practical Implications
The study showed a potential benefit – albeit small – to varying repetitions across a spectrum of ranges for increasing upper body muscle strength and hypertrophy. Whether the differences between the varied versus constant rep approach seen in our study would amount to practically meaningful improvements is specific to the individual. For the average gym-goer it probably wouldn’t be of much consequence; alternatively, to a bodybuilder or competitive athlete it very well may. It’s not clear why these findings did not translate into similar differences in lower body muscular adaptions, but based on our findings either approach would seem to be an equally viable choice for leg training.
It’s important to note that this was a relatively short-term study, lasting a total of 8 weeks. When factoring in missed sessions, this means subjects in VARIED trained in each loading zone for a total of only 7-8 sessions over the course of the study period. If the differences in upper body outcomes favoring VARIED would persist over time – highly speculative but certainly possible – the magnitude of results could widen and thus be potentially meaningful for a wide array of fitness enthusiasts.
Another important point is that volume load was consistently lower across all conditions (pushing exercises, pulling exercises, leg exercises, and total volume of all exercises) in VARIED as compared to CONSTANT. This indicates that training in a varied fashion provides comparable or better results with less volume load than training at a constant 8-12 RM repetition range. It also suggests that if volume load were equated between conditions, there might have been even better results for the varied approach.
In sum, our study shows that both varied and constant loading schemes are viable strategies to increase strength and hypertrophy in resistance-trained men. The data suggest a potential modest benefit to varying loading ranges over time, at least for maximizing upper body muscular adaptations. Importantly, findings clearly indicate that contrary to what many believe, training in the “hypertrophy zone” (6-12 RM) is not superior for building muscle. When considering the practical implications of the findings, remember that exercise prescription is always a function of the needs/abilities/goals of the individual.
February 14, 2016
Proper manipulation of program variables is essential for maximizing the hypertrophic response to resistance training. Variations in volume, loading and rest intervals all have been shown to impact muscular adaptations.
One variable that hasn’t received as much attention is lifting tempo – i.e. how fast you perform a repetition. When you’re using very heavy loads this is moot; although you’ll necessarily need to try to move the weight quickly, the actual concentric speed will be fairly slow. To illustrate this point, a study by Mookerjee and Ratamess found that the first concentric repetition of a 5RM bench press took 1.2 seconds to complete while the fourth and fifth repetitions took 2.5 and 3.3 seconds, respectively. These findings occurred despite subjects being instructed to perform the reps explosively.
When the loads are lightened, however, you have a lot more control over lifting cadence. A wide range of volitional tempos are possible depending on the magnitude of load. Recommendations on the topic are highly disparate depending on who you listen to. Some fitness pros advocate explosive lifts while others recommend slowing tempo down to where a single repetition takes 45 seconds to complete as seen in this video
In an effort to synthesize the evidence and gain clarity on the issue, I collaborated on a meta-analysis with uber-pros James Krieger and Dan Ogborn. The study titled, Effect of repetition duration during resistance training on muscle hypertrophy: a systematic review and meta-analysis was recently published in the journal, Sports Medicine. In case you’re not aware, a meta-analysis pools data from all studies on a given topic and then statistically quantifies the results to provide a gauge of how meaningful the differences are between conditions.
Here’s the scoop.
What We Did
An extensive search of the literature was carried out for randomized controlled trials that directly compared the effects of different training tempos on muscle hypertrophy in healthy individuals. Studies had to last a minimum of 6 weeks and both groups had to perform reps to the point of momentary concentric muscle failure. A total of 8 studies comprising 204 total subjects ultimately met inclusion criteria – a surprisingly low number for such an important topic.
What We Found
There was no difference in hypertrophy between lifting durations of 2 to 6 seconds when using dynamic constant external resistance (typical free weights and machines). A single study using isokinetic dynamometry showed that durations of a half-second up to 8 seconds produced similar hypertrophy, although the generalizability of this study to traditional training methods is somewhat questionable.
There does seem to be a threshold as to how slow you can go, as evidence suggests that “superslow” lifting (i.e. durations above 10 seconds) is suboptimal for hypertrophy. The research on this topic is limited thereby making it difficult to draw firm conclusions, but a recent study found that a traditional speed group increased muscle cross sectional area by 39% compared to only 11% in a group performing reps at a tempo of 10 seconds up, 4 seconds down. These results held true despite an almost five-fold greater time-under-tension for the superslow group. A follow-up study by the same lab showed satellite cell content and myonuclear domain – important components in the ability to increase muscle mass over time – were substantially greater with traditional compared to superslow training. These findings are consistent with research showing that muscle activation is reduced up to 36% when training at very slow speeds (5 seconds concentric and eccentric). And since maximal hypertrophy is predicated on recruiting the full spectrum of muscle fibers and keeping them stimulated for a sufficient period of time, it is logical to speculate that training in a superslow fashion is inferior if your goal is to optimize muscular gains.
What are the Practical Implications
Current research indicates that a wide range of lifting durations can be used to maximize hypertrophy. Given the limited number of studies and their diverse methodology, however, the topic is far from settled. Based on the evidence it would seem prudent to take no more than about 3 seconds on the concentric portion of the movement. Beyond this cadence, you’d need to reduce the load to a point where it could negatively impact the ability to fully stimulate the highest threshold motor units. Eccentric actions should be performed so that the load is controlled against the forces of gravity; simply letting the weight drop fails to provide sufficient muscular tension for the majority of the action (and it also increases the risk of joint-related injury). As with concentric actions, there does not seem to be any advantage to slowing the movement down to more than about 3 seconds and it is possible that doing so might actually be detrimental to growth. I’d add that the reps should be carried out with sufficient control so that a mind-muscle connection can be established with the target musculature – the current body of evidence suggests that such a strategy is beneficial for maximizing muscle activation, which may in turn lead to greater gains.
I’ll note that the above recommendations are rather liberal, giving the benefit of doubt to somewhat slower tempos. My general feeling is that the concentric portion of a rep should be around 1-2 seconds – the most important thing here is to control of the weight by using an internal focus to visualize the target muscle as you lift. Although results of our meta-analysis showed no “statistically significant” differences in tempos up to 3 secs concentric, data from Tanimoto et al show a substantially greater effect size (a measure of the “meaningfulness” of results) for muscle growth favoring traditional (1 sec on concentric and eccentric – effect size 1.08) vs slower (3 secs concentric and eccentric – effect size 0.74) lifting cadences. It therefore would seem a slightly faster tempo is warranted, at least on multi-joint exercises
Could combining different repetition durations potentially enhance the hypertrophic response to training? It’s impossible to say as no study to date has investigated this possibility. As such, the best advice therefore is to experiment for yourself and see if this may spur additional growth. Remember: the best research often comes from what is learned in the trenches!
February 5, 2016
Current resistance training guidelines recommend long rest intervals (i.e. 3 minutes) to maximize muscle strength. Alternatively, short rest intervals of around 1 minute are generally recommended for maximizing muscle growth. This is based on the premise that higher metabolic stress associated with limiting rest between sets will promote a greater muscle-building stimulus. Some have specifically pointed to acute post-exercise increases in anabolic hormones as a primary driving factor in the process.
Back in 2014, I co-authored a review paper on the topic with my colleague Menno Henselmans that was published in the journal Sports Medicine. After a thorough scrutiny of the literature, we determined that there was little basis for the claim that shorter rest intervals was beneficial to hypertrophy. As I discussed in this blog post, It would appear from current evidence that you can self-select a rest period that allows you to exert the needed effort into your next set without compromising muscular gains. That said, our recommendations were limited by a dearth of controlled studies on the topic. Moreover, no study had investigated the generally accepted guidelines of taking 3 minutes rest for strength gains and 1 minute for hypertrophy in resistance-trained individuals.
I recently collaborated on a just-published study that investigated the effect of rest intervals on strength and hypertrophy. Here’s the scoop:
What We Did
A cohort of 21 young men were randomly assigned to either a group that performed a lifting routine with 1- or 3-minute rest intervals. All other resistance training variables were held constant. Subjects performed a typical bodybuilding-style routine that comprised 7 different exercises working the major muscle groups of both upper and lower body. Three sets of 8-12RM were performed per exercise. Training was carried out 3 days a week for 8 weeks.
We tested subjects immediately before and after the study period. Tests for muscle strength included 1RM for the bench press and back squat. Muscle-specific growth was assessed by b-mode ultrasound for the elbow flexors, triceps brachii, and quadriceps femoris.
What We Found
Maximal strength was significantly greater for both 1RM squat and bench press for the group taking longer rest. No big surprise here. Somewhat unexpectedly, however, muscle thickness tended to be greater when taking longer rest intervals as well. Although we can’t be sure of the underlying mechanisms, we speculated that results may be attributed a reduction in total volume load (i.e. reps /x/ load) over the course of the study. There is a well-established dose-response relationship between volume and hypertrophy, whereby higher volumes correlate with greater muscle growth. Thus, very short rest periods may compromise growth by reducing the amount of weight you can use on subsequent sets. This would indicate that if there are synergistic benefits to heightened metabolic stress, they are overshadowed by the associated decreased volume.
What are the Practical Implications
The obvious take-home here would seem to be that resting 1 minute between sets compromises gains in muscle size. But if 1 minute is in fact too short a rest period, how long should you then rest when maximal hypertrophy is the goal? Well, based on previous work in well-trained individuals, it would seem that 2 minutes provides sufficient recovery so as not to undermine growth.
That said, it’s important to take these results in proper context. Realize that we looked only at effects of the two respective conditions (i.e. 1- versus 3-minutes rest) on muscular adaptations. But rest interval length does not have to be a binary either-or choice. There is no reason you can’t combine different rest periods to potentially maximize hypertrophy.
A viable strategy is to take longer rest intervals on your large-muscle compound exercises such as squats, presses and rows. These movements generate very high levels of metabolic disturbance, particularly when performed with moderate rep ranges (i.e. 8-15 reps). Thus, longer recovery periods are needed to fully regenerate energy levels for your next set so that volume load is maintained across sessions.
On the other hand, single joint movements are not as metabolically taxing and thus you’re able to recover more quickly from set to set. Exercises like biceps curls, triceps pressdowns, and leg extensions therefore could conceivably benefit from shorter rest periods. In this way, you can heighten metabolic stress and its potential hypertrophic benefits without negatively impacting volume load. In this scenario, it’s best to keep the short-rest sets at the end of your workout to ensure they don’t interfere with recovery of compound exercise performance.
A final word: Research is still emerging on this topic. Each study is simply a piece in a puzzle. As more studies are carried out we’ll hopefully develop a better understanding of how programming can be tweaked to maximize the growth-related response. Stay tuned.
October 20, 2014
I recently collaborated with my colleague Menno Henselmans on a review paper that sought to provide clarity on the effects of rest intervals on muscle hypertrophy. Based on the current literature, we concluded that evidence was lacking to support the contention that rest interval length has an impact on growth. Problem is, there have been very few studies carried out to investigate the topic. Thus, it’s difficult to say with any degree of confidence as to whether there are or aren’t any benefits to varying how long you should rest between sets. For more on specifics of the review paper check out my blog post where it is discussed in detail.
Fast forward to today: A new study has just been published titled, Short rest interval lengths between sets optimally enhance body composition and performance with 8 weeks of strength resistance training in older men that sheds further light on how the duration of rest intervals may affect muscular adaptations. If you just read the abstract, you might think the answer is clear.
Not so fast…
Here’s my take:
22 older men (mean 68 yrs) were recruited for participation. Subjects were healthy but were not involved in resistance training. All subjects underwent a 4-week “break in” phase where they performed a “hypertrophy-type” total body routine consisting of 2-4 sets of 8-15 reps per set. The subjects were then tested for various measures including strength and body composition, and then pair-matched based on 1RM bench press to perform an 8-week strength-type program with short rest (1 minute) or long rest (4 minutes) between sets. The strength-type routine consisted of 2-3 sets of 4-6 reps carried out 3 days a week. The exercises included leg press, flat bench machine chest press, lat pulldown, seated row, dumbbell step-ups, dumbbell Romanian deadlifts, knee extension, and knee flexion. Reps were performed with the intent to move the loads as fast possible while maintaining proper form. All sessions were supervised by trained personnel.
Results were determined over the final 8-week strength phase of the program. Significantly greater increases in fat free mass (FFM), 1RM bench press, and 1RM leg press were noted for the short-rest group compared to those who took long rest periods. The researchers investigated a wide array of additional outcomes including power measures, which also generally favored the short rest group as well.
Based on these results, it would appear that limiting rest between sets is beneficial to enhancing strength and hypertrophy. The increase in FFM for the short-rest group was 1 kg vs just a 0.3 kg increase for the long-rest group. The effect size — a measure of the meaningfulness of the results — was 0.37 indicating a fairly small effect. That said, a difference of 0.7 kg (equating to ~1.5 pounds) could certainly be meaningful for those seeking to maximize hypertrophy — particularly over a fairly short period (8 weeks). The effect sizes for strength were fairly large (0.65 and 0.76 for the 1RM bench and squat, respectively). Combined, these findings indicate that muscular adaptations are enhanced by taking short rest periods between sets.
But…a closer scrutiny of the study’s methodology gives reason for caution when drawing conclusions.
First and foremost, the researchers used DXA to measure body composition. The authors reported results for FFM, which as stated were higher for the short rest group. However, FFM encompasses all tissues in the body other than fat mass. This includes bone, connective tissue, and importantly water. You can probably rule out any differences associated with bone and connective tissue, which almost certainly would be minimal over an 8 week resistance training in terms of contribution to body mass. However, variances in water weight could easily have accounted for a large portion of the the reported 0.7 kg difference in FFM. It’s curious why the researchers did not choose to quantify the subject’s segmental muscle mass. There are equations that can be employed with DXA to obtain these values, which would have given a better sense as to true increases in muscle. Unfortunately, the reported data do not allow for a true understanding of changes in the lean component of body composition between groups.
Second, the subjects did not train to failure in either condition. The researchers stated that this was done to reduce neuromuscular fatigue and thus ensure that the subjects could tolerate the program over its duration. While I have no problem with that reasoning, it does raise a major issue: Since those in the short rest interval group had to lift again after only 60 seconds, they would have been taxed to a greater extent on each successive set. The long-rest group on the other hand would have sufficient time to recover prior to the next set, and thus would not have been substantially taxed at point during the workout. Now it is a bit difficult to determine how much the subjects were actually challenged on each set based on the study write up. Ideally the researchers should have quantified the level of effort exerted (perhaps by RPE or similar scale) to provide context. Without this info, I’m left wondering if the design was biased to produce a greater effect with shorter rest periods.
Finally and importantly, the study was carried out on elderly, untrained subjects. These individuals would no doubt have been sarcopenic, and their response to an exercise stimulus therefore would not necessarily mimic that of young, fit individuals. Thus, generalizability of results is limited to the population studied.
In conclusion, this is an interesting study that adds to the body of literature. However, caution must be exercised when attempting to draw conclusions as to the effects of rest interval length on muscular adaptations. The limitations of the study preclude extrapolation of results to those seeking maximal muscle mass.
The good news is that I am currently collaborating on a study on the topic that directly measures hypertrophy in well-trained subjects. Target completion for data collection is early next year. I will update when results are available.
August 13, 2014
There is compelling evidence that the onset of fatigue during resistance training results in an increase in motor unit activation, whereby the strength-oriented type II fibers are progressively recruited to sustain muscular contractions. Some have taken this to mean that any load, regardless of how light, will ultimately lead to full fiber recruitment provided that training is carried out to muscle failure (i.e. the point where you are unable to complete an additional rep with proper form).
Recently, my lab sought to test this hypothesis. Here is an overview of the study and its practical implications. The study, titled, Muscle activation during low- versus high-load resistance training in well-trained men, was just published ahead-of-print in the European Journal of Applied Physiology.
The purpose of the study was to compare muscle activation in the leg press at 30% and 75% 1RM when sets are carried out to muscular failure. Ten college-aged men were recruited for participation. Subjects were all experienced in resistance training, including regular performance of lower body exercise.
A within-subject design was employed where each participant performed both 30% and 75% 1RM conditions. Testing was carried out over two sessions. Subjects were initially tested to determine their 1RM in the leg press. They then returned to the lab at least 48-hours later for muscle activation testing of the quads (rectus femoris, vastus lateralis, and vastus medialis) and the hamstrings (biceps femoris) during heavy- vs. light-load training. The order of performance was counterbalanced whereby Subject 1 performed the high-load condition first, Subject 2 performed the low-load condition first, etc. In this way, we ensured that order of performance did not confound results. Fifteen minutes rest was provided between trials to ensure that previous fatigue was not a factor. We verbally encouraged subjects to perform each set to the point where they could physically no longer continue training with proper form.
Both mean and peak muscle activation was markedly and significantly greater during the heavy- compared to light-load condition (by 57% and 29%, respectively). Importantly, not a single subject displayed equal or greater activation during low-load training. These findings strongly suggest that training at 30% 1RM in a compound lower-body exercise is insufficient to recruit the entire motor unit pool for the target musculature.
It has been well-established that training to muscle failure causes an increase in motor unit recruitment. This outcome was in fact confirmed in our study, as EMG amplitude increased in both the high- and low-load conditions over the course of each set. However, the magnitude of these increases were substantially lower during light- versus heavy-loading. The take home message here (in conjunction with a recent study on the topic using single-joint lower body exercise) indicates that a minimum threshold exists to achieve activation of the full spectrum of fibers and that 30% 1RM is below this threshold. Thus, it can be inferred that some of the highest threshold motor units — those associated with the type IIx fibers — were not recruited during the low-load condition.
From an applied standpoint, it might seem that these findings show training at very low-loads is useless. After all, why would you train with a load that does not generate complete fiber recruitment, right?
Not so fast.
Understand that there are two aspects to maximizing muscle development: recruiting a fiber and then keeping it stimulated for a sufficient period of time (i.e. time under load). While the loading strategy used in the light-weight condition here (i.e. 30% 1RM) did not bring about full muscle activation, it did maintain tension in the lower-threshold motor units for an extended time period. This could be particularly important in optimizing development of the type I fibers that are highly fatigue-resistant. This lends credence to the hypothesis that training throughout the full spectrum of rep ranges is the best strategy for maximal muscle hypertrophy. I have a longitudinal training study currently in review that seems to support this hypothesis. More on that in the near future.
An interesting secondary finding of the study was that the hamstrings displayed only minimal activation during the leg press — much less than that seen in the quads. This refutes the claims by some fitness pros that single-joint exercise is unnecessary provided you perform compound lower body exercises. Our results clearly indicate that movements such as the leg curl, stiff-leg deadlift, and good morning are important components of a well-rounded resistance training program to ensure proper symmetry between the quads and hamstrings.
A limitation of the study is that we only assessed a single set at each condition. Thus, it is not clear whether accumulated fatigue from performing multiple light-load sets would ultimately bring about complete recruitment. This requires further study. But even if this turns out to be the case — which is far from a certainty — it would mean that you’d need to perform a lot of additional volume just to achieve similar levels of activation; at the very least, an inefficient training strategy.
I am in the process of finishing a follow-up bench press study looking at 80% vs. 50% 1RM in an attempt to determine the approximate minimum threshold necessary for complete muscle activation. This will provide important info to those who are unable to lift heavier weights due to medical conditions or other issues. Realize, though, that muscle activation (and hypertrophy for that matter) do not necessarily translate into optimal strength gains. My recent study showed that even moderate load training (~10 RM) is inferior to very heavy lifting (~3 RM) if absolute strength is the goal. I discussed that study in-depth in this blog post
On a side note, I’ll be discussing the ramifications of this study and others currently in progress at my upcoming seminar in Montreal next month. Hope to see you there!
Cook SB, Murphy BG, Labarbera KE. Neuromuscular function after a bout of low-load blood flow-restricted exercise. Med Sci Sports Exerc. 2013 Jan;45(1):67-74.
Schoenfeld BJ, Contreras B, Willardson JM, Fontana F, Tiryaki-Sonmez G. Muscle activation during low- versus high-load resistance training in well-trained men. Eur J Appl Physiol. 2014 Aug 12. [Epub ahead of print]
Schoenfeld BJ, Ratamess NA, Peterson MD, Contreras B, Tiryaki-Sonmez G, Alvar BA. Effects of different volume-equated resistance training loading strategies on muscular adaptations in well-trained men. J Strength Cond Res. 2014 Apr 7. [Epub ahead of print]
July 23, 2014
Recently, I collaborated with my friend and colleague, Menno Henselmans, to review the literature on the effects of rest interval length on muscle growth. I’m pleased to report that this review has just been published in the prestigious journal, Sports Medicine. If you’re into the science of hypertrophy, I encourage you to read the paper as we delve into all the relevant research on the topic. In the meantime, here is an overview of the take-aways with practical implications.
General resistance training guidelines recommend that rest intervals should remain relatively short to maximize hypertrophy. In a previous review, The Mechanisms of Muscle Hypertrophy and Their Application to Resistance Training I echoed these sentiments, suggesting that rest periods of 60-90 seconds would seemingly provide an optimal balance between mechanical tension and metabolic stress (primary mechanisms in the hypertrophic response) to enhance anabolism. It should be noted, however, that these recommendations were based primarily on a logical extrapolation of mechanistic data; there simply have not been a sufficient number of studies that have investigated the topic in a well-controlled fashion.
In what is the most comprehensive study on the topic to date Ahtiainen et al. found no differences in muscle cross sectional area between 2 versus 5 minute rest periods in a sample of well-trained men. The study had several strengths including a randomized crossover design (which substantially increases statistical power), the inclusion of experienced trainees, and the use of the gold-standard imaging modality, MRI, to measure muscle growth. The one issue here is that the 2-minute rest period employed by the researchers is longer than what is generally advised for hypertrophy-type training. The impact on metabolic stress diminishes with longer rest periods, and this conceivably could have had negatively affected anabolic signaling in this study.
The other study of note that attempted to investigate the effects of rest interval length on hypertrophy was carried out by Buresh et al, whereby 12 untrained individuals performed their workout with either 1 or 2.5 minutes rest between sets. This study actually showed superior results for hypertrophy in the arms and a trend for greater growth in the legs in the subjects using longer intra-set rest intervals. While these results may seem compelling, it should be noted that muscle cross sectional area was determined by anthropometric means (i.e. surface measurements) which can be quite unreliable and thus compromise accuracy. Further confounding matters is the small number of subjects (only 6 in each group) and the fact that subjects were inexperienced with resistive exercise. Thus, while the findings here are interesting they must be interpreted with caution.
So what practical applications can we derive from the literature? Based on current research, it seems highly doubtful that rest interval length has a substantial effect on muscle growth. Bottom line: It would appear that you can self-select a rest period that allows you to exert the needed effort into your next set without compromising hypertrophic results.
That said, the paucity of controlled studies on the topic make it difficult to draw concrete conclusions. Certainly we know that shortening the duration of rest between sets increases metabolic stress, which is known to stimulate muscle remodeling. We also know that well-trained individuals such as bodybuilders are able to sustain a high percentage of their repetition maximum with rest periods as short as a minute. Could the combination of these factors may provide an additional hypertrophic stimulus — albeit a small effect — over time in well-trained subjects? Could other factors such as increased hypoxia and cell swelling also contribute to such a response?
These are questions that require further research. I’m currently in the process of carrying out a study that will provide relevant answers. I hope to begin data collection before the year is out. Stay tuned.
Henselmans M, Schoenfeld BJ. The Effect of Inter-Set Rest Intervals on Resistance Exercise-Induced Muscle Hypertrophy. Sports Med. 2014 Jul 22. [Epub ahead of print]
April 11, 2014
I’m stoked to announce that my dissertation study, Effects of different volume-equated resistance training loading strategies on muscular adaptations in well-trained men, was just published ahead-of-print in the Journal of Strength and Conditioning Research. I had actually devised the protocol during my master’s degree course in research methods back in 2008. The study I ultimately carried out had some different wrinkles than the one originally proposed, but overall the essence remained the same. Most importantly, it investigated a topic that’s been debated for many years: What are the differences in muscular adaptations (strength and hypertrophy) between bodybuilding- vs powerlifting-type training programs? Here is an overview of the study and a discussion on its practical implications.
20 well-trained subjects (minimum of 1 year resistance training experience working out at least 3 days/week) were recruited to participate in the study. Subjects were randomly assigned to one of two groups: A hypertrophy group (HT) that performed a bodybuilding style routine or a strength group (ST) that performed a powerlifting-style routine. The HT protocol was a split routine where each muscle was worked once per week with 3 exercises per session, performing 3 sets of 10 reps and resting for 90 seconds. The ST protocol was a total body routine where each muscle was worked 3 times per week with 1 exercise per session, performing 7 sets of 3 reps. The volume load (sets x reps x load) was equated so each group essentially lifted about the same amount of total weight per week. Training was carried out over 8 weeks. All sets were performed to the point of momentary concentric muscular failure.
Strength was measured by 1RM in the squat and bench press. Muscle thickness of the biceps was measured with ultrasound. Testing was carried out pre- and post-study, and results were then compared between groups to assess differences in strength and hypertrophy.
3 of the subjects dropped out of the study before completion leaving 17 subjects for analysis (9 in the HT group, 8 in the ST group). Both groups significantly increased biceps muscle thickness by ~13% with no differences seen between groups. Both groups also significantly increased 1RM strength, but the ST group had greater increases in the bench press and showed a trend for greater increases in the squat.
On the surface, the study showed that muscle hypertrophy is similar between powerlifting and bodybuilding type routines provided that volume is equated between protocols. Moreover, the study showed that maximal strength is slightly greater in a powerlifting protocol. This could lead to the conclusion that if your goal is hypertrophy then it doesn’t matter what rep range you use (at least in the heavy to moderately-heavy range) as long as you perform equal volumes, but that maximizing strength requires lifting very heavy weights. From a mechanistic standpoint with respect to muscle hypertrophy, the study suggests that either 1) the increased mechanical tension in the ST group was offset by the greater metabolic stress in the HT group on a volume-equated basis or, 2) there is a threshold for mechanical tension and once the threshold is reached, it doesn’t matter as long as the stimulus is maintained for similar timeframes. With respect to strength, this would suggest that neural factors related to training are still relevant in well-trained individuals, and that using very heavy weights does indeed have a greater transfer to maximal lifts compared to moderate intensity loads.
But the devil is often in the details and that is the case here.
First, it is important to point out that total training time in the ST group was 70 minutes while that of the HT group was 17 minutes. So from a time-efficiency standpoint, the bodybuilding-type training produced similar hypertrophy (as well as nearly similar strength increases) in about a quarter of the time as the powerlifting routine. Moreover, exit interviews revealed that those in the ST group were fried by the end of the study. Almost all of them complained of sore joints and general fatigue, and the two dropouts from this group were because of joint-related injury (and these routines were highly supervised with respect to form, so we took every precaution for safety). On the other hand, the HT group all felt they could have worked substantially harder and done more volume.
This brings up an important take-away message: While mechanistically it appears that it does not matter whether heavy or moderately-heavy weights are used for hypertrophy, from an application standpoint it simply isn’t practical to train constantly with the volumes used in this study on multiple body parts. The grinding on the joints and the taxation of the neural system that is involved with repeated performance of very heavy loads ultimately has a negative impact on the lifter; I am certain that if we had continued this program for any longer, most of those in the ST group would have been overtrained and seen performance decrements. If nothing else, these finding reinforce the importance of periodizing programs so that cycles of deloading are interspersed with very heavy loading protocols.
Additionally, realize that only three major muscle groups were worked in the study: the pecs (upper body pushing); the back (upper body pulling) and the thighs. Thus, the HT group could have easily done a couple of extra sets for each muscle group without overtaxing their resources. Although impossible to say for sure, it certainly is plausible that additional work would have enhanced the hypertrophic response in the bodybuilding-style training group. Moreover, the HT group could have performed exercises for other muscle groups, including some targeted work with single joint movements. Working specific muscles (and aspects of muscles) such as the middle and posterior delts, the hamstrings and the calves alone would definitely have benefited overall muscle hypertrophy.
So bottom line: The study indicates that the best approach to building muscle is to perform a combination of heavy and moderately heavy loads. The “hypertrophy range” is applicable from the standpoint that it allows the performance of a greater amount of volume without overtaxing the body’s resources. Adding in loads in the 1-5 RM range can enhance strength (which ultimately allows the use of heavier loads during moderate rep lifting) as well as providing a potent hypertrophic stimulus.
It should be noted that.I made a conscious decision to investigate the two types of routines as lifters usually perform them. Thus, the HT routine was a split routine since the vast majority of bodybuilders train in this fashion, while the ST routine was a total body routine since this is the way most powerlifters train. While staying true to the usual performance gives insight into how muscular adaptations generally play out in everyday practice, they also obscure the ability to attribute results entirely to the set/rep scheme. I will be carrying out a follow up study that seeks to address this issue in the near future. Stay tuned!