In this recent work, researchers from Brazil compared the muscle building effects of resistance training that incorporated constant rest intervals or decreasing rest intervals between sets. The training period was 8 weeks and the subjects were trained men who were using a creatine monohydrate supplement. At the end of the 8-week study they reported that, independent of rest interval length, creatine and resistance training increased muscular strength, peak torque, and muscle size. Of note, those who had constant rest intervals completed more work volume than those with decreasing rest intervals---suggesting that creatine supplementation may have boosted adaptations for those in the latter group. Unfortunately, however, the researchers did not include a placebo group in this study, thus limiting the interpretation of the data.
Souza-Junior TP, Willardson JM, Bloomer R, Leite RD, Fleck SJ, Oliveira PR, Simão R. Strength and hypertrophy responses to constant and decreasing rest intervals in trained men using creatine supplementation. J Int Soc Sports Nutr. 2011 Oct 27;8(1):17.