Strength and hypertrophy responses to constant and decreasing rest intervals in trained men using creatine supplementation

Journal Title (Medline/Pubmed accepted abbreviation): J Int Soc Sports Nutr
Year: 2011
Volume: 8
Number: 1
Page Numbers: 17 (open access)

Summary of background and research design:

Background:Creatine monohydrate (CR) supplementation during resistance training has been shown to increase muscle fiber hypertrophy and cross-sectional area. However, the mechanism of CR action is unclear and may include an enhanced capacity to restore cellular ATP concentrations, especially between exercise sets. Rest intervals between exercise sets are a key variable in muscle performance during resistance training, and CR supplementation may allow increased training volume for a given amount of time without a decrease in performance.  

Hypothesis/Purpose: The purpose of this study was to compare the effects of a constant rest interval versus decreasing rest intervals in resistance training on strength and muscle hypertrophy responses during CR supplementation.

Subjects: Twenty-two recreationally trained (resistance exercise 4/wk for ≥ 1 y) men (mean age, ~22 y; height, ~179.5 cm; weight, ~77 kg) participated in the study.

Experimental design: Randomized, double-blind 

Treatments and protocol:
Each man received CR supplementation (loading dose of 20 g CR + 20 g maltodextrin/day for 7 days, then 5 g CR + 5 g maltodextrin after every training session) and was randomized to an 8-week resistance-training program that had either a constant rest interval (CI; 2 min) between sets or a decreasing rest interval (DI; 2 min for 2 wk, then a 15-sec decrease each subsequent wk). The training program consisted of a warm up (2 sets of 20 reps at 50% maximal 1-rep [1-RM], determined previously) and 4 sets of 8 to 10 RM for each resistance exercise (4 to 6/day, predetermined by day) 6 days per week. All parameters were tested before and after the training regimen. Strength was assessed by bench press 1-RM followed by at least a 10-second rest before the free weight back squat 1-RM. Muscle cross-sectional area of the right thigh and upper arm was determined 72 hours after the strength testing, and was immediately followed by isokinetic peak torque assessment (knee extensors and flexors).

Summary of research findings:
  • Total training volume (load × rep) for bench press and back squat were greater in the CI group compared with the DI group (22.9% and 14.6%, respectively; P < .05 for both).
  • There were no significant differences between the groups in maximal bench press or back squat strength, muscle cross-sectional area, or isokinetic peak torque.
    • All parameters increased significantly from baseline in each group.
    • The effect sizes were similar for strength and isokinetic peak torque.
    • The effect size for muscle cross-sectional area was larger in the DI group compared with the CI group.

Interpretation of findings/Key practice applications:

CR supplementation together with resistance training increased muscular strength, cross-sectional area, and isokinetic peak torque, regardless of rest interval between exercise sets. Given the decrease in training volume in the DI vs. CI group, the creatine supplementation could not attenuate the performance decrement associated with DI training. One limitation of the study design, though, was that that was no control group without creatine supplementation that was exposed to both training methodologies. Such a design would have helped in evaluating if the DI-induced training volume decrement would be lessened with versus without creatine supplementation.

It was interesting, however, that the DI training resulted in a similar increase in strength and a somewhat greater increase in muscle cross sectional area effect sizes versus CI, despite the fact that training volume was lower in the DI group. This suggests that DI training might be more efficient than CI training for muscular hypertrophy and strength. More research is needed in this area.


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