Creatine but not betaine supplementation increases muscle phosphorylcreatine content and strength performance

We aimed to investigate the role of betaine supplementation on muscle phosphorylcreatine (PCr) content and strength performance in untrained subjects. Additionally, we compared the ergogenic and physiological responses to betaine versus creatine supplementation. Finally, we also tested the possible additive effects of creatine and betaine supplementation. This was a double-blind, randomized, placebo-controlled study. Subjects were assigned to receive betaine (BET; 2?g/day), creatine (CR; 20?g/day), betaine plus creatine (BET?+?CR; 2?+?20?g/day, respectively) or placebo (PL). At baseline and after 10?days of supplementation, we assessed muscle strength and power, muscle PCr content, and body composition. The CR and BET?+?CR groups presented greater increase in muscle PCr content than PL (p?=?0.004 and p?=?0.006, respectively). PCr content was comparable between BET versus PL (p?=?0.78) and CR versus BET?+?CR (p?=?0.99). CR and BET?+?CR presented greater muscle power output than PL in the squat exercise following supplementation (p?=?0.003 and p?=?0.041, respectively). Similarly, bench press average power was significantly greater for the CR-supplemented groups. CR and BET?+?CR groups also showed significant pre- to post-test increase in 1-RM squat and bench press (CR: p?=?0.027 and p?p?=?0.03 and p?