The Effects of Creatine Supplementation Combined with Resistance Training on Regional Measures of Muscle Hypertrophy: A Systematic Review with Meta-Analysis

Abstract

The purpose of this paper was to carry out a systematic review with a meta-analysis of randomized controlled trials that examined the combined effects of resistance training (RT) and creatine supplementation on regional changes in muscle mass, with direct imaging measures of hypertrophy. Moreover, we performed regression analyses to determine the potential influence of covariates. We included trials that had a duration of at least 6 weeks and examined the combined effects of creatine supplementation and RT on site-specific direct measures of hypertrophy (magnetic resonance imaging (MRI), computed tomography (CT), or ultrasound) in healthy adults. A total of 44 outcomes were analyzed across 10 studies that met the inclusion criteria. A univariate analysis of all the standardized outcomes showed a pooled mean estimate of 0.11 (95% Credible Interval (CrI): -0.02 to 0.25), providing evidence for a very small effect favoring creatine supplementation when combined with RT compared to RT and a placebo. Multivariate analyses found similar small benefits for the combination of creatine supplementation and RT on changes in the upper and lower body muscle thickness (0.10-0.16 cm). Analyses of the moderating effects indicated a small superior benefit for creatine supplementation in younger compared to older adults (0.17 (95%CrI: -0.09 to 0.45)). In conclusion, the results suggest that creatine supplementation combined with RT promotes a small increase in the direct measures of skeletal muscle hypertrophy in both the upper and lower body.

Keywords: lean mass; muscle cross-sectional area; muscle thickness; nutritional supplements; strength training.

Figure 1

PRISMA flow chart of the search process.

Figure 2

Bayesian forest plot of controlled standardized mean difference effect sizes across all outcomes [33,34,35,36,37,38,39,40,41,42].

Figure 3

Funnel plot of all standardized effect sizes. Data are colored according to the individual studies. Blue region illustrates the pooled mean estimate and 95% credible interval.

Figure 4

Multivariate controlled mean difference posterior estimates for elbow flexors and extensors. Points represent multivariate mean difference posterior estimates. Positive values favor creatine supplementation and negative values favor control. Red dot illustrates median values for the marginal mean difference posterior estimates. Black curve represents the 95% highest posterior density region.

Figure 5

Multivariate controlled mean difference posterior estimates for knee flexors and extensors. Points represent multivariate mean difference posterior estimates. Positive values favor creatine supplementation and negative values favor control. Red dot illustrates median values for the marginal mean difference posterior estimates. Black curve represents the 95% highest posterior density region.

Figure 6

Distributions of controlled mean difference effect sizes according to age of participants and duration of study. Distributions represent posterior estimates of pooled mean difference effect size. Results illustrate distributions obtained from two separate meta-regression models, the first with a group variable for age, and the second with a group variable for duration.