Shorten up those rest intervals to get leaner.

If you have ever seen Phil Heath train while he is dieting for Mr. Olympia, he is not one for much talking; in fact he rests very little between sets.  While dieting for Mr. Olympia, Phil takes very short rest periods between sets, but can this be any coincidence to his flawless conditioning.  In addition to diet, it also seems that rest period duration can also be a determining factor for fat loss.  Many bodybuilders rest less than 1 minute between sets to enhance muscle mass and reduce bodyfat as opposed to strength athletes that traditionally rest greater than 3 minutes or more.

Researchers examined short and long duration rest periods during 8 weeks of periodized strength resistance training.  22 male volunteers were assigned to one of two resistance-training groups, the groups were separated into either short rest periods with 60-seconds rest intervals or longer 4-min rests intervals between sets. The subjects all trained 3 days per week. Before and after the intervention, the researchers measured lean and fat mass changes using dual-energy X-ray absorptiometry (DEXA) scans, changes in upper and lower body strength, muscular power by reference to Margaria stair-climbing power. At the end of the eight weeks, all participants experienced increases in lean body mass, upper and lower body strength, and dynamic power, as well as decreases in percentage body fat. The group that performed the short rest periods with 60 seconds or less, had significantly greater increases in lean body mass, flat machine bench press 1-RM, bilateral leg press 1-RM, narrow/neutral grip lat pull-down, and stair-climbing power compared to the group that rested 4 minutes between sets.  This study suggests 8 weeks of periodized high-intensity resistance training with shortened rest intervals (< 60 seconds) induces significantly greater enhancements in body composition, muscular performance, and functional performance, compared to the same resistance training prescription with extended rest intervals.

In short, if you’re trying to get leaner, consider using short rest intervals between sets.
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References:

Villanueva MG, Lane CJ, Schroeder ET. Short rest interval lengths between sets optimally enhance body composition and performance with 8 weeks of strength resistance training in older men. Eur J Appl Physiol. 2015 Feb;115(2):295-308.

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Robbie Durand has been in the sports supplement and  bodybuilding industry for 15 years. He has contributed to many national magazines and web sites. He has an M.A. in exercise physiology from Southeastern University and a B.A. in Dietetics from Louisiana State University.