Many moons ago our ancestors of the old intuitive-lifting era claimed that stretching between sets helped you grow more muscle.
Previous research has suggested that passive interset stretching might positively influence neuromuscular, metabolic, and hormonal responses to training, largely resulting from the increased total time under mechanical tension.
While the research is far from clear, It is thought that this mechanism may have possible benefits to the hypertrophic effect of training.
In the literature, static stretching has taken a beating recently for the many benefits it has failed to produce. However, new research has come to light, that cautiously suggests there may be something to the rumours of additional hypertrophy benefits.
Researchers examined the effects of stretching between sets (interset stretching) on hypertrophy and strength gains in untrained men.
They put two groups on the same eight-week full-body training program, consisting of 4 sets of 8-12 reps to failure twice per week on nonconsecutive days.
One group rested between sets, the other gently stretched the main muscle group worked for 30 seconds between sets.
Results showed that there was little difference between many of the resulting measurement areas. The interset stretching group, however, did experience larger increases in vastus lateralis thickness. With all measurements combined, the interset stretching group had significantly greater thickness increases overall.
Although, the mechanism of effect is still not yet clear.
This study does lend some support to the suggestion that light stretching between sets may be beneficial for muscle growth. Provided of course, you’re not stretching too aggressively into discomfort or pain.
Interset Stretching vs. Traditional Strength Training: Effects on Muscle Strength and Size in Untrained Individuals. Evangelista, et al. 2019