The purpose of this study was to utilize a rodent model to test the hypothesis that
creatine (Cr) supplementation during
resistance training would influence the pattern of slow-twitch muscle
myosin heavy chain (MHC)
isoforms expression. Male Wistar rats (2-3 months old, 250-300 g) were divided into 4 groups: Nontrained without
creatine supplementation (CO), nontrained with
creatine supplementation (CR), trained without
creatine supplementation (TR), and trained with
creatine supplementation (
TRCR). TR and
TRCR groups were submitted to a
resistance training program for 5 weeks (5 days/week) for morphological and biochemical analysis of the soleus muscle. Weightlifting exercise involved jump sessions into water, carrying progressive overload equivalent to percentage of
body weight. CR and
TRCR groups were given
creatine at 0.5 g/kg(-1)/d(-1). Both Cr supplementation and
resistance training alone or associated did not result in significant alterations (p > 0.05) in
body weight gain, food intake, and muscle weight in the CR, TR and
TRCR groups compared to the CO group. Also compared to the CO group, the CR group showed a significant (p < 0.02) increase in MHCI content and a reduction in MHCII; inversely, the TR group increased the MHCII content and reduced MHCI (p < 0.02). When combined, both
creatine and
resistance training did not promote significant (p > 0.05) changes in MHC content of the
TRCR group compared to the CO group. The data show that Cr supplementation provides a potential action to abolish the exercise-induced MHC
isoform transitions from slow to fast in slow-twitch muscle. Thus, Cr supplementation might be a suitable strategy to maintaining a slow phenotype in slow muscle during
resistance training, which may be favorable to maintenance of muscle oxidative capacity of endurance athletes.