THE EFFECTS OF DIETARY SUPPLEMENTS WHEY PROTEIN AND CREATINE ON STRENGTH AND FATIGUABILITY IN RAT SKELETAL MUSCLE

Matthew B. Cooke, Graeme Smith, Michael F. Carey, Alan Hayes, Exercise Metabolism Unit, Centre for Rehabilitation, Exercise and Sport Science, Victoria University, Vic.

Athletes from a variety of sports have endeavored to increase their muscle mass, and muscle strength, in such a way as to enhance exercise performance. This study examined the effects of whey protein and creatine on muscle force production, fatigue and fibre type. Female Sprague-Dawley rats were randomly separated into 3 groups: i) control (n=10), ii) creatine supplemented (n=8), and iii) whey protein supplemented (n=8) and fed normal or supplemented chow for a period of 6 weeks. Animals were deeply anaesthetised with sodium pentobarbitone (60 mg/kg body weight i.p.) and both the fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscles were removed and tested.

Creatine supplementation resulted in a significant increase in both creatine (P<0.001) and total creatine (P<0.05) levels in the soleus muscle, while no significant changes were observed in the EDL muscle. Despite this, both EDL and soleus muscles generated significantly higher (P<0.001) absolute and specific forces after creatine supplementation. Furthermore, creatine treated animals exhibited a 17% improvement in fatigue recovery in the EDL muscle. There were no significant differences in fibre type proportions in the EDL muscles after creatine supplementation, whereas there was a significant decrease in type I and an increase in type IIA fibre percentages (P<0.05) in soleus muscles compared to controls. Whey protein supplemented muscles also displayed higher absolute and specific forces, which was achieved with no alterations in metabolite or fibre type proportions.

The major finding of this investigation was an increase in skeletal muscle force output after creatine and whey protein supplementation, and an improved recovery after creatine supplementation without the influence of exercise training. While these changes could be a result of alterations in fibre type proportions, it's likely that both supplements are also exerting effects at the metabolic and molecular level.