Rest is an important factor determining the volume and intensity of an exercise program. Short rest intervals between sets prevent recovery but increase the stress of exercise. Long rest intervals reduce metabolic stress but allow greater recovery and increased force output during subsequent sets. Researchers from Kennesaw State University in Georgia compared the effects of 1-minute and 2.5-minute rest intervals between sets on hormone levels, strength and muscle size during a 10-week study.
One-minute rest intervals triggered greater increases in testosterone and cortisol levels only during the first week of the study. Rest intervals had no effect on growth hormone, strength or muscle size with the exception of arm size, which was 50 percent greater in the 2.5-minute rest group. Rest intervals have variable effects on hormone levels that are not necessarily related to changes in strength and muscle size.
Source: Journal Strength Conditioning Research, in press; published online December 2008