Journal Title (Medline/Pubmed accepted abbreviation): J Strength Cond Res
Page numbers: 3343-3351
doi (if applicable):
Summary of Background and Research Design
Background: Creatine is converted to phosphocreatine in the body, which plays a vital role in cellular energy production and muscle function. Creatine monohydrate supplementation coupled with resistance training has been demonstrated to improve multiple performance-related variables, and it is believed that this is largely a result of increased intramuscular phosphocreatine stores. Although creatine has been widely studied, there are limited data on the effects of creatine supplementation in the absence of a concurrent resistance training regimen. Furthermore, recent studies indicate that creatine uptake is more efficient when taken as a conjugate with polyethylene glycol (PEG).
Hypothesis/purpose of study:To examine the effects 5 g/day polyethylene glycosylated creatine (PEG-creatine) supplementation for 28 days on 1-repetition maximum bench press (1RMBP) and leg extension (1RMLE), mean power (MP), and peak power (PP) on Wingate anaerobic tests, and body weight (BW) in untrained subjects.
Subjects:22 untrained men (mean age, 22.1 ± 2.1 years; BW, 80.3 ± 8.4 kg; height, 181.6 ± 6.5 cm)
Experimental design: Randomized, double-blind, placebo-controlled, parallel study
Treatments and protocol: Subjects were randomly assigned to the creatine or placebo groups and were given creatine (5 g/d) and PEG or maltodextrin powder (5 g/d), respectively. Baseline 1RMBP and 1RMLE were obtained, as well as MP and PP on a cycle ergometer before supplementation. Subjects repeated the tests after 7 days and 28 days of supplementation.
Summary of research findings:
- There was a significant time × group interaction (P = .0167) for 1RMBP, such that the 1RMBP was significantly increased on day 28 compared with day 7 and day 0 in the creatine group only.
- There were no statistically significant changes in 1RMLE, MP, PP, or BW for the creatine or placebo group, although there were several parameters that trended toward improvement.
- 1RMLE, MP, and PP increased from day 0 to day 28 in the placebo group.
- 1RMLE and PP increased from day 0 to day 28 in the creatine group.
Interpretation of findings/Key practice applications:
The authors suggest that this study supports the use of PEG-creatine supplementation to improve upper body strength, but not lower body strength or anaerobic capacity, in untrained men. There was, however, some improvement in PP and 1RMLE with creatine, and non-significant improvement in all areas (except the significant increase in 1RMBP)with placebo. These results differ from those of previous reports, which generally reflect more pronounced effects on both upper and lower body strength. The differing results here may reflect the lower dose used (5 g/d vs the traditional loading dose of 20 g/d) or the pegylated formulation versus creatine monohydrate.
Little detail was provided regarding the source of the creatine-PEG supplement used in this study or its exact composition. In addition, there was no treatment arm for the more conventional creatine monohydrate form, which could have served as a useful comparison point. Finally, a follow-up study in a resistance-training population with creatine-PEG vs creatine monohydrate would be interesting as well.