1) Investigations of human protein metabolism rely on the assumption that all muscles in the body are equivalent in terms of protein turnover. However, it is known that in animals the rate of protein synthesis is higher in red, slow-twitch, oxidative muscles than white, fast-twitch, glycolytic muscles. We now have evidence that neither anatomical location nor fibre-type composition are major determinants of the rate of human muscle protein synthesis. Data will be presented that demonstrate that the basal (overnight fasted) and amino acid stimulated rates of myofibrillar and sarcoplasmic protein synthesis are very similar in human muscles of vastly different fibre-type composition (triceps, vastus, soleus); although statistically significant (P<0.05), the differences in protein synthesis rates between muscles are not big enough to be considered biologically significant: triceps protein synthesis rate is ~15% and vastus protein synthesis rate ~7% smaller than that of soleus. Therefore, (i) extrapolating the findings from one muscle to whole-body skeletal muscle is valid, at least during fasted and fed conditions, (ii) differences in fibre-type composition will not substantially confound the data obtained from studies in subjects with distinct muscle fibre-type composition (e.g., sedentary persons and athletes; the young and elderly; men and women), and (iii) rodents are poor models for investigations of the effects of interventions and conditions that affect human muscle protein turnover. 2) The investigation of human muscle protein metabolism has been limited largely to measurements made in men; hence, little is known about sexual dimorphism in the regulation of muscle protein kinetics. However, it is well known that men have more muscle mass than women, and there is evidence that resistance exercise training leads to a greater increase in muscle mass in men than in women, probably because of a more pronounced stimulation of muscle protein synthesis to either exercise alone or exercise plus nutrition. The proposed differential responses of muscle protein metabolism could be due to sex per se (i.e., male versus female genotype) or otherwise sex-related differences such as the hormonal milieu and body-composition and their possible interaction with exercise. Evidence for sexual dimorphism in the response to exercise/nutrition available so far and the importance of various factors associated with sexual dimorphism will be presented.