How does rest period duration affect gains in strength?
The effect of rest period duration on gains in muscular strength and size has been reviewed previously (see De Salles, 2009). However, at the time that review was written, there were only three studies that had previously reported on the difference in strength and size gains between long-term resistance training programs with short or long duration inter-set rest periods (i.e. Robinson, 1995; Pincivero, 1997; and Pincivero, 2004). De Salles et al. concluded that longer rest intervals (i.e. 2 – 3 minutes) led to significantly greater increases in strength compared with shorter rest intervals (i.e. 30 – 90 seconds). They also concluded that the longer rest intervals allowed for greater relative loading to be used and also greater training volumes.
Robinson (1995) – The researchers compared the effects of a 5-week, high-volume resistance-training program with three different rest interval durations on increases in power and maximum strength. They recruited 33 resistance-trained young male subjects and allocated them into 3 training groups who performed the same training program except that a long-rest group used a rest period of 3 minutes, a moderate-rest group used a rest period of 1.5 minutes and a short-rest group used a rest period of 30 seconds. Before and after the 5-week intervention, the researchers measured vertical jump height and 1RM squat. They found that the vertical jump height did not improve in any of the groups. However, they found that the 1RM squat did improve and improved by significantly more in the long-rest group (7%) than the short rest group (2%). This study suggests that longer rest periods are better for gains in strength.
Pincivero (1997) – The researchers compared the effects of a 4-week, isokinetic resistance-training program with two different rest interval durations on increases in power and maximum strength. The researchers recruited 15, college-aged individuals and allocated them to either a short rest group (40 seconds) or a long rest group (160 seconds). The training intervention involved unilateral lower body isokinetic resistance training, 3 days per week for 4 weeks. Before and after the training intervention, the researchers measured quadriceps and hamstring isokinetic strength at 60 and 180 degrees/second as well as lower body power using the single leg hop for distance. The researchers reported significantly greater improvements for isokinetic hamstring total work and average power at 180 degrees/second for the long-rest group compared to the short-rest group. However, there was no difference in the single leg hop for distance.
Pincivero (2004) The researchers compared the effects of different rest intervals on lower body strength and fatigue following a 6-week period of high-intensity resistance-training. They recruited 15 healthy males and allocated them to one of three groups, a short-rest group (40 seconds), a long-rest group (160 seconds), and a control group. The training groups performed isokinetic knee extension exercises at 180 degrees/s, 2 days per week for 6 weeks. Before and after the intervention, the researchers measured isokinetic knee extension torque, work and power at 180 degrees/s. They also measured fatigue as the reduction in isokinetic work and power over 30 maximal concentric contractions. The researchers reported an increase in isokinetic knee extension torque in the long-rest group but not in the short-rest or control groups.
Ahtiainen (2005) – The researchers explored the effects of rest period duration on the hormonal and neuromuscular adaptations following a 6-month period of resistance-training. The researchers recruited 13 recreationally resistance-trained male subjects. The study was divided into two separate 3-month training periods in a crossover design. In one 3-month period, the subjects performed a training protocol using a short rest (2 minutes) and in the other they used a long rest (5 minutes). Before and after the interventions, the researchers measured hormonal concentrations as well as maximal isometric leg extension torque, unilateral leg press 1RM, and muscle cross-sectional area of the quadriceps femoris using magnetic resonance imaging (MRI) scans. The training protocol involved leg presses and squats with 10RM sets and were matched for volume (i.e. load x sets x reps) but were different in respect of the relative load used and the rest period durations. The researchers observed significant increases in maximal isometric force (7%) and unilateral leg press 1RM (16%) over the 6-month strength-training period. However, both 3-month training periods resulted in similar gains in strength.
Willardson (2008) – The researchers compared the effect of rest period on squat strength gains and volume of work performed. The researchers recruited 15 resistance-trained male subjects and allocated them to either a 2-minute or a 4-minute rest interval group. The groups performed the same training program and the only difference being the rest interval and the number of reps that the subjects were able to perform. The training program comprised 2 squat workouts per week as part of a periodized program, with one workout being heavy and the other light. The researchers reported that both groups displayed significant gains in squat strength but there were no significant differences between groups. The researchers also reported that the 4-minute group displayed significantly higher volumes for the heavy workouts but not the light workouts.
Buresh (2009) The researchers wanted to compare the effects of short (1 minute) and long (2.5 minutes) rest periods on strength and muscular cross-sectional area during a 10-week training period. They recruited 12 untrained male subjects who performed a training routine of 3 sets using a load that led to failure on the third set of each exercise, including the squat and bench press exercises. The researchers found that both groups increased strength but they found that there were no significant differences between the two groups in respect of the strength increases.
De Salles (2010) – The researchers compared the effect of rest period on gains in upper and lower body strength over a 16-week resistance-training program. They recruited 36 recreationally-trained male subjects and allocated them to either a short-rest (1 minute), a medium-rest (3 minutes), or a long-rest (5 minutes) group, who all performed the same basic program. Before and after the intervention, the researchers measured 1RM bench press and leg press. The researchers reported significant increases in bench press 1RM in the medium- and long-rest groups after the 16-week intervention. They also reported that the increase in the long-rest group was significantly greater than the increase in the short-rest group. The researchers reported significant increases in leg press 1RM in all groups after the 16-week intervention. They also reported that the increases in the long-rest and medium-rest groups were significantly greater than the increase in the short-rest group.
Gentil (2010) – The researchers investigated the effects of different between-set rest interval durations on muscle strength. The researchers recruited 34 untrained, college-aged men and allocated them to 2 groups. The subjects trained 2 times per week for 12 weeks, using the same exercises and the same workload for 2 sets of 8 – 12 repetitions to muscular failure. However, one group used short rests (work-to-rest ratio of 1:3) while the other used long rests (work-to-rest ratio of 1:6). Assuming a 1-second concentric, a 1-second pause and a 1-second eccentric, as well as an average of 10 of repetitions per set, this translates to approximately 1.5 minutes of rest for the short-rest period group and 3 minutes for the long-rest group. Before and after the intervention, the researchers measured leg press and bench press 1RM. They found that the increase in bench press 1RM was 14.4 ± 8.1% for the short-rest group and 10.5 ± 6.4% for the long-rest group. They found that the increase in leg press 1RM was 17.5 ± 9.2% for the short-rest group and 17.8 ± 12.3% for the long rest group. However, the differences between groups were not significant.
In the studies that did not match work volumes between the groups training with different rest periods, which included Robinson (1995), Pincivero (1997), Pincivero (2004), Willardson (2008) and De Salles (2010), all but two (i.e. Willardson, 2008; and Buresh, 2009) found that the longer rest periods led to greater gains in strength. Of these two, one study compared only relatively long rest periods (2 minutes vs. 4 minutes).
It is possible that the greater strength gains observed in the longer-rest groups occurred as a result of the greater volume of work that the subjects were able to perform. This suggestion is supported by the observation that in the two studies that compared matched volumes of work (Ahtiainen, 2005 and Gentil, 2010), there were no differences observed between the groups in strength gains. On balance, it seems that strength gains are maximized by longer (>3 minutes) rest periods and this may be a function of the greater volume of work performed when using longer rest periods.
How does rest period duration affect gains in hypertrophy?
The effect of rest period duration on gains in muscular strength and size has been reviewed previously (see De Salles, 2009). However, at the time that review was written, there were no studies that had studied the long-term effects of rest period duration on muscular size gains! Consequently, conclusions drawn for muscular hypertrophy in that review were based on acute studies of hormones and metabolites. Since then, two studies have been performed, as follows:
Ahtiainen (2005) – The researchers explored the effects of rest period duration on the hormonal and neuromuscular adaptations following a 6-month period of resistance-training. The researchers recruited 13 recreationally resistance-trained male subjects. The study was divided into two separate 3-month training periods in a crossover design. In one 3-month period, the subjects performed a training protocol using a short rest (2 minutes) and in the other they used a long rest (5 minutes). Before and after the interventions, the researchers measured hormonal concentrations as well as maximal isometric leg extension torque, unilateral leg press 1RM, and muscle cross-sectional area of the quadriceps femoris using magnetic resonance imaging (MRI) scans. The training protocol involved leg presses and squats with 10RM sets and were matched for volume (i.e. load x sets x reps) but were different in respect of the relative load used and the rest period durations. The researchers observed significant increases in quadriceps muscle cross-sectional area (4%) over the 6-month strength-training period. However, both 3-month training periods resulted in similar gains in muscle mass but no statistically significant changes were observed in hormone concentrations.
Buresh (2009) – The researchers wanted to compare the effects of short (1 minute) and long (2.5 minutes) rest periods on strength and muscular cross-sectional area during a 10-week training period. They recruited 12 untrained male subjects who performed a training routine of 3 sets using a load that led to failure on the third set of each exercise, including the squat and bench press exercises. The researchers found that arm cross-sectional area increased more with long rest periods (12.3 ±7.2%) than with short rest periods (5.1 ± 2.9%) but they did not notice any significant differences in respect of leg muscle cross-sectional area.
These studies found conflicting results. Ahtiainen (2005) found no differences in muscular hypertrophy when short (2 minutes) vs. long (4 minutes) rest periods were used in a volume-matched program of resistance-training. On the other hand, Buresh (2009) found that hypertrophy was greater when using long (2.5 minutes) versus short (1 minute) rest periods when volume was dictated by muscular failure and therefore lower in the short-rest group.
The differences between these studies may again arise because of the failure of the short-rest period in the latter study to achieve sufficient training volume. Slightly longer rest periods than 1 minute (e.g. 90 – 120 seconds) may therefore be preferable in order to maintain optimal workloads while maintaining some metabolic stress, which is thought to be beneficial for hypertrophy based on acute studies (Schoenfeld, 2013). However, the exact duration of rest period that leads to the optimal recovery of strength between sets is outside the scope of this review and deserves separate consideration in its own article. Moreover, persisting working with short rest periods may lead to beneficial adaptations which permit higher volumes while using short rests, as the next sections will demonstrate.
Therefore, it remains difficult to assess whether rest period has any significant effect on hypertrophy irrespective of volume based on the current long-term studies. It seems appropriate to recommend that individuals seeking hypertrophy do not prejudice training volume too much by reducing rest periods to the point where it is difficult to perform as much work as they would otherwise be able to with longer rest periods.
How does reducing rest periods alter gains in strength?
A rather interesting couple of studies have been initiated since the review by De Salles et al. in 2009, which involve the use of reducing rest periods over the sequence of resistance-training sets, as follows:
De Souza (2010) – The researchers compared the effect on strength and hypertrophy of 8 weeks of resistance-training using either (1) constant rest intervals, or (2) decreasing rest intervals. They recruited 20 young, recreationally-trained subjects and allocated them to one or other of the training groups, who performed resistance-training including the bench press and squat exercises. In the first 2 weeks of training, the subjects performed 3 sets of 10 – 12RM with 2-minute rests. In the following 6 weeks of training, the subjects performed 4 sets of 8 – 10RM and while the constant-rest group rested 2-minutes between sets, the decreasing-rest group rested with progressively shorter rests (2 minutes decreasing to 30 seconds) over the 6 weeks of training. Before and after the intervention, the researchers measured 1RM bench press and squat, as well as isokinetic peak knee extension and flexion torque and muscular cross-sectional area. The researchers found that total training volume of the bench press and squat were significantly lower for the decreasing-rest group compared to the constant-rest group (bench press 9.4% lower, and squat 13.9% lower). However, they found that there were no significant differences in the strength gains between constant-rest period and decreasing-rest period groups (bench press 28 vs. 37%, squat 34 vs. 34%) or in respect of isokinetic peak torque.
Souza-Junior (2011) – The researchers compared the effect on strength and hypertrophy of 8 weeks of resistance-training and creatine supplementation using either (1) constant rest intervals, or (2) decreasing rest intervals. They recruited 22 young, recreationally-trained males and allocated them to one or other of the training groups, who performed resistance-training including the bench press and squat exercises. In the first 2 weeks of training, the subjects all performed exercises with 2-minute rests. In the following 6 weeks of training, while the constant-rest group rested 2-minutes between sets, the decreasing-rest group rested with progressively shorter rests (2 minutes decreasing to 30 seconds) over the 6 weeks of training. Before and after the intervention, the researchers measured 1RM bench press and squat, as well as isokinetic peak knee extension and flexion torque and muscular cross-sectional area. The researchers found that total training volume of the bench press and squat were significantly lower for the decreasing-rest group compared to the constant-rest group. The researchers found that both groups displayed significant increases in back squat and bench press 1RM and knee extensor and flexor isokinetic peak torque but there were no significant differences between groups for any variable.
Both of these studies found that despite lower training volume being performed by the shortening rest periods, the decreasing-rest period groups and the constant-rest period groups both achieved similar strength gains. It is difficult to interpret these results but they indicate that reducing rest periods steadily over a period of time may in some way mitigate the adverse effects on strength that short rest periods otherwise seem to have in most of the rest of the literature (i.e. Robinson, 1995; Pincivero, 1997; Pincivero, 2004; Willardson, 2008; and De Salles, 2010; but not Willardson, 2008; or Buresh, 2009). Exactly why this is the case is very unclear but may relate to progressive adaptations relating to metabolic stress.
How does reducing rest periods alter gains in hypertrophy?
A rather interesting couple of studies have been initiated since the review by De Salles et al. in 2009, which involve the use of reducing rest periods over the sequence of resistance-training sets.
De Souza (2010) – The researchers compared the effect on strength and hypertrophy of 8 weeks of resistance-training using either (1) constant rest intervals, or (2) decreasing rest intervals. They recruited 20 young, recreationally-trained subjects and allocated them to one or other of the training groups, who performed resistance-training including the bench press and squat exercises. In the first 2 weeks of training, the subjects performed 3 sets of 10 – 12RM with 2-minute rests. In the following 6 weeks of training, the subjects performed 4 sets of 8 – 10RM and while the constant-rest group rested 2-minutes between sets, the decreasing-rest group rested with progressively shorter rests (2 minutes decreasing to 30 seconds) over the 6 weeks of training. Before and after the intervention, the researchers measured 1RM bench press and squat, as well as isokinetic peak knee extension and flexion torque and muscular cross-sectional area.. The researchers found that total training volume of the bench press and squat were significantly lower for the decreasing-rest group compared to the constant-rest group (bench press 9.4% lower, and squat 13.9% lower). However, they found that there were no significant differences in the arm or thigh cross-sectional area increases (arm 13.8 vs. 14.5%, thigh 16.6 vs. 16.3%) between the two training groups.
Souza-Junior (2011) – The researchers compared the effect on strength and hypertrophy of 8 weeks of resistance-training and creatine supplementation using either (1) constant rest intervals, or (2) decreasing rest intervals. They recruited 22 young, recreationally-trained males and allocated them to one or other of the training groups, who performed resistance-training including the bench press and squat exercises. In the first 2 weeks of training, the subjects all performed exercises with 2-minute rests. In the following 6 weeks of training, while the constant-rest group rested 2-minutes between sets, the decreasing-rest group rested with progressively shorter rests (2 minutes decreasing to 30 seconds) over the 6 weeks of training. Before and after the intervention, the researchers measured 1RM bench press and squat, as well as isokinetic peak knee extension and flexion torque and arm and thigh muscular cross-sectional area. The researchers found that total training volume of the bench press and squat were significantly lower for the decreasing-rest group compared to the constant-rest group. The researchers found that both groups displayed significant increases in arm and thigh muscular cross-sectional area but there were no significant differences between groups for either variable.
These two studies found identical results, which were that the rest periods had no effect on muscular hypertrophy. However, the period of time was quite short for measuring hypertrophy differences (6-weeks for the different protocols). Similarly, Ahtiainen (2005) found no differences in muscular hypertrophy when short (2 minutes) vs. long (4 minutes) rest periods were used but this study differed in that a volume-matched program was used. On the other hand, Buresh (2009) found that hypertrophy was greater when using long (2.5 minutes) versus short (1 minute) rest periods when volume was dictated by muscular failure and therefore lower in the short-rest group. Exactly why Buresh (2009) found different results to these two studies is unclear but again may relate to the progressive adaptations achieved by steadily decreasing rest periods rather than maintaining short rest periods from the outset.
What are the practical implications?
For strength
While the research is slightly limited and a little conflicting, it seems that when using constant rest periods, longer rest periods (probably >3 minutes) are better for strength gains.
For hypertrophy
While the research is extremely limited and very conflicting, it seems when using constant rest periods, care should be taken not to reduce volume at the expense of using short rest periods, as this may lead to sub-optimal hypertrophy gains. Rest periods of 90 – 120 seconds may be superior to those of <60 seconds for this reason.
While the research is extremely limited albeit not conflicting, it seems that it is possible to use progressively decreasing rest periods (from 2 minutes down to 30 seconds) and achieve similar hypertrophy gains to constant rest periods of 2 minutes even when using lower volumes.