The assessment of in vivo protein synthesis following chronic resistance exercise using 2H2O
Protein synthesis (PS) in rats is preferentially assessed using labeled amino acids over a short period of time. We previously observed in our lab (unpublished) that 15 resistance exercise (RE) sessions over 5 weeks stimulated hypertrophy, but not PS when assessed 16 h following the final RE bout. Sixteen h represents the peak ‘anabolic window’ in rats following acute RE; however, this may not be indicative of an ‘integrative’ response over time. The purpose of this study was to determine if anabolic responses to RE could be observed if assessed over 1.5 days. Rats (n=27) were operantly conditioned to engage in ‘squat-like’ exercise and assigned to either RE or NoRE groups. Resistance was progressively increased from 80g (50 repetitions) during session 1 to 410g during session 15, and repetitions were adjusted to maintain a constant volume of work (repetitions x resistance). Thirty six hours prior to muscle harvest, animals were injected with 1.5 ml of 2H2O and provided 4.0% 2H2O drinking water for the assessment of deuterium incorporation into skeletal muscle protein (PS). PS was increased in RE versus NoRE (p<0.001) in the plantaris, but not soleus, which corresponded to the hypertrophic responses in these muscles, respectively. Our results suggest that total anabolic responses are augmented in exercised muscle after training, which may represent a temporal shift in the ‘anabolic window’ with chronic training.
