Performing contractions for about 30 seconds between work sets may enhance hypertrophy.

“The other name for this is the people in the gym does typically seem to be guys in the gym flexing their muscles in between sets. And indeed the research supports the fact that contractions have about 30 seconds in between the actual work sets, they're not going to favor better performance on the work sets, if anything they're going to compromise them. But those hard contractions in between sets for a variety of reasons related to local muscle metabolism as well as what we talked about before which are stress, tension, and damage, they seem to improve stress, tension, and damage and the nerve to muscle contraction in ways that facilitate hypertrophy.”