THE EFFECTS OF DIETARY SUPPLEMENTS CREATINE AND WHEY PROTEIN ON INDICES OF MUSCLE OXIDATIVE CAPACITY

Graeme J. Smith, Matthew B. Cooke, Andrew D. Williams, Alan Hayes, Michael F. Carey, Exercise Metabolism Unit, Centre for Rehabilitation, Exercise & Sport Science, Victoria University, Footscray, Vic.

A number of disorders are characterized by reduced muscle oxidative capacity leading to impaired exercise tolerance. The aim of this study was to examine possible interventions that may increase skeletal muscle oxidative capacity. Female Sprague Dawley rats were supplemented with creatine (Cr, n=8) or whey protein (WP, n=8) for 6 weeks, while control rats (n=10) received a standard diet. Mitochondrial ATP production rate (MAPR), citrate synthase (CS) activity and fibre type proportions were evaluated in oxidative (soleus) and glycolytic (extensor digitorum longus, EDL) muscles. MAPR is a reliable index of oxidative capacity as it measures the direct production of ATP from the mitochondria. Cr supplementation resulted in an increase in total Cr levels in the soleus, but not EDL, while WP did not alter metabolite levels. Compared to control animals, MAPR was significantly (P<0.05) higher in the soleus, but not EDL, muscle after Cr supplementation. In contrast, MAPR was significantly (P<0.05) higher in the EDL, but not soleus muscle, after WP supplementation when compared to control animals. These changes were not caused by fibre transitions, as muscle fibre type proportions were not different between control and supplemented groups. Similarly, it is unlikely that there were any increases in mitochondrial volume or density, as CS activity was also unaltered after supplementation. Increased MAPR in the soleus after Cr supplementation may be due to regulation of oxidative phosphorylation in oxidative muscle being closely related to muscle Cr concentration. Whereas the effects of WP may be due to enhanced levels of the antioxidant glutathione provided by the high levels of glutamine found in WP. While further work is required to fully elucidate the mechanisms, these results clearly demonstrate that Cr and WP can increase oxidative capacity in oxidative and glycolytic muscles, respectively.