Resistance training combined with creatine supplementation: a three-level meta-analysis of multidimensional outcomes...

This study aimed to determine (1) the effects of resistance training combined with creatine supplementation on muscle strength (upper- and lower-body strength) and body composition (lean mass, fat mass, body-fat percentage, and body mass), and (2) whether these effects were moderated by participant characteristics (age, gender, and training experience) and intervention protocols (intervention duration, weekly frequency, dosing strategy, daily dose, and supplementation protocol).

We conducted a systematic search of PubMed, Web of Science, Cochrane Library, Embase, and EBSCO from database inception through April 21 2025, and performed backward citation tracking to identify additional relevant trials. Hedge's g (g) served as the summary effect size for each outcome. Meta-analysis was performed using a three-level random-effects model in the metafor package (R). Potential moderators were explored via subgroup analyses and meta-regression.

Sixty-three studies (n = 1489) were included. Compared with resistance training alone (RT), resistance training plus creatine (RT + CR) produced significant increases in upper-body strength (g = 0.54, p < 0.001), lower-body strength (g = 0.55, p < 0.001), lean mass (g = 0.30, p < 0.001), and body mass (g = 0.12, p = 0.04), and a significant reduction in body-fat percentage (g = -0.14, p = 0.02). No significant difference emerged for fat mass (g = -0.10, p = 0.14). Exploratory subgroup analyses suggested that age may be associated with strength gains, with statistically significant between-subgroup differences observed for both upper- and lower-body strength. These findings should be interpreted cautiously because multiple moderator analyses were conducted and the age subgroups were unevenly represented. Exploratory meta-regression also suggested an inverse association between age and strength effects, with larger effects observed in studies involving younger participants. Neither subgroup nor meta-regression analyses identified consistent moderators for body composition outcomes.

Compared with resistance training alone, resistance training combined with creatine supplementation significantly enhanced muscle strength and lean body mass, without a significant effect on fat mass. The modest increase in total body weight was primarily attributable to gains in lean body mass, contributing to a slight reduction in body fat percentage. Among participant characteristics, age appeared to be associated with the magnitude of strength effects, although this exploratory finding should be interpreted cautiously given the uneven representation of age subgroups. Intervention-protocol variables did not significantly influence the outcomes. These conclusions should also be interpreted within the context of heterogeneous and incompletely reported nutritional intake and training backgrounds across the included trials.