What’s the best weight load and rest interval for developing muscle size and strength? The answer depends on a lot of things, and is likely a little different for everyone, but a study published in theJournal of Strength and Conditioning Research offers some tips for beginners or anyone looking to change up a stale routine.

Scientists recruited 6 males in the mid-20s and had them perform 4 different weight training sessions on different days, all equalized for volume (sets x reps x load). Strength sessions involved 8 sets of 3 reps at 85% of 1RM. The muscle size routines were 3 sets of 10 reps at 70% of 1RM. One day, subjects were allowed a minute of rest between sets. On other days, they were allowed 90 seconds.

The biggest increases in testosterone came from the muscle size session using a short rest interval. The lowest was the strength session with short rest interval. So if you’re looking to boost your natural production of testosterone in the weight room, keep the rest interval about a minute in length. Recovery is going to take up to 48 hours either way.