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The length of a rest period between sets is believed to be important for muscle hypertrophy. In the past, it was touted that short rest periods were associated with greater spikes in hormones such as growth hormone and testosterone. Subsequent research has brought the importance of temporary shifts in hormones into question. Nevertheless, short rest periods increase metabolic stress in the muscle, and this has been suggested to be one possible mechanism of blood flow restriction to produce muscle hypertrophy. On the flip side, short rest periods are known to accelerate fatigue and limit the number of reps a lifter can perform. A recent study published in the Journal of Experimental Physiology reports the results of a study comparing long and short rest periods.
Researchers from the University of Birmingham compared the effect of rest period length in 16 male lifters. Subjects performed four sets of leg press and four sets of leg extensions followed by a whey protein drink. Rest periods between sets were one minute or five minutes. Muscle biopsies were taken to measure activity of anabolic pathways, and infusion of radiolabeled phenylalanine was given to measure rates of protein synthesis.
It was found that the rate of muscle protein synthesis from zero to four hours after training was much greater (i.e., double) in the five-minute interset rest group. Muscle protein synthesis rates for both groups remained elevated at 24–28 hours post exercise with no difference between groups at this time period.
Post-exercise some anabolic pathways were reduced with one minute of rest compared with five minutes. In addition, the activity of some pathways known to blunt anabolic pathways was greater for one minute compared with the five-minute rest. Serum testosterone was greater at 20–40 minutes post-exercise in the one-minute rest group compared with the five-minute group.
Using rest periods of one minute between sets blunts short-term muscle protein synthesis compared with five-minute rest periods. It’s possible, however, that this effect is acute and will not affect long-term gains.
The data looking at the ideal rest period are mixed, likely due to adaptation that occurs using either long or short rest periods. For long-term training goals, do not get into a rigid mindset that rest periods have to be long or short. Both strategies offer advantages and disadvantages. If strength or total volume is important, use longer rest periods to ensure that fatigue does not interfere with the target volume. If you have been using longer rest periods and need to change things up, cut the rest in half and give it a go. – FLEX