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Differences in Maximal Strength and Hypertrophy when Comparing Constant and Decreasing Rest Interval

By Paul Henning, PHD


A group of exercise scientist from Brazil conducted a very interesting study to compare the differences of using constant rest intervals and decreasing rest intervals between sets and exercises on strength and hypertrophy during a resistance training program [1]. Rest period length between sets and exercises is an important acute resistance training program variable and is one way to increase the difficulty to complete a set with the prescribed number of repetitions [2]. Typically, when using short rest intervals, we see a decrease in the number of repetitions per set with each succeeding set using the same resistance; thus indicating fatigue [3, 4]. This decrease in the number of reps decreases total training volume and could compromise maximal strength increases during a training program. A benefit that is inherent to short rest intervals is an increase in the anabolic hormonal response (growth hormone, IGF-1) which could result in increased muscle hypertrophy. The authors of this study compared a program using constant rest intervals (2 minutes) between sets and exercises and a program using decreasing rest intervals (2 minutes decreasing to 30 seconds) as the 8 weeks of training progressed. They hypothesized that the increased hormonal response with the short rest intervals will counteract any decrease in the volume of training due to decreasing rest period length which will result in similar hypertrophy and strength increases in both groups [1].


The authors form Brazil recruited twenty young men recreationally trained in strength training were randomly assigned to two groups of 10 each. These men performed a strength training program for at least a year with minimum frequency of 3 times per week prior to the study. The constant rest interval (CI) and decreasing rest interval (DI) groups performed exactly the same exercises, reps per set, and sets during the 8-week monitored training program. Both groups trained 6 days per week using a split routine. The only difference between groups was as the weeks progressed, rest period intervals were gradually decreased with the DI training [1].


Results from this study showed that the CI group had much more training volume over the course of 8 weeks than the DI group. Both groups demonstrated significant increases in bench press and squat 1RM, muscle cross-sectional area (CSA) and knee extensor and flexor peak torque pre to posttraining. Interestingly, there were no significant differences between the CI or DI groups in 1-RM, peak torque or muscle CSA. In conclusion, this is the first study to the author’s knowledge demonstrating that similar strength and muscle CSA increases are achieved with either constant or decreasing rest periods between sets and exercises over short training periods. This appears to be true for both upper and lower body exercises and muscle groups. Therefore, we can achieve similar adaptations in strength and muscle hypertrophy with a weight training program utilizing decreasing rest periods between sets and exercises as we do with a weight training program utilizing constant rest periods. This can be of benefit since we may be able to decrease our total time and training volume in the gym while still reaping the same benefits in strength and muscle size!


References:

1. de Souza, T.P., Jr., et al., Comparison between constant and decreasing rest intervals: influence on maximal strength and hypertrophy. J Strength Cond Res, 2010. 24(7): p. 1843-50.

2. Fleck, S.a.K., WJ, ed. Designing Resistance Training Programs. 2004, Human Kinetics: Champaign, IL. 164.

3. de Salles, B.F., et al., Rest interval between sets in strength training. Sports Med, 2009. 39(9): p. 765-77.

4. Miranda, H., et al., Effect of two different rest period lengths on the number of repetitions performed during resistance training. J Strength Cond Res, 2007. 21(4): p. 1032-6.

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