An acute bout of resistance exercise (RE) and dietary protein consumption stimulate muscle protein synthesis (MPS). This anabolic effect is believed to be attenuated with resistance exercise training (RET), however, the mechanism for this plateau" is unknown. In addition, the ideal timing for protein consumption to optimize MPS is not well characterized. The central hypothesis of this research is that RE stimulates cumulative (measured over 24-36 h) MPS in rats and humans. Study one determined whether an acute bout of RE in rats enhances MPS when assessed with the traditional flooding dose (~ 25 min) and 2H2O (4 and 24 h measurements); thus a comparison of the two methodologies was made. An acute session of RE did not result in an elevation in MPS when quantified by either the flooding dose or 2H2O over 4 and 24 h (methods compared qualitatively). Therefore, an acute bout of RE in rats does not appear to be anabolic and adaptation resulting from multiple bouts is likely necessary. Study two determined if RET in rats results in attenuation in MPS (plateau effect) 16 h following the final RE session (peak anabolic window) and if it is due to an increase in 4E-BP1 (a key regulator of mRNA translation initiation) activity; or if the timing in anabolism changes, which could be detected with a cumulative assessment (2H2O). MPS at 16 h was unchanged following RE training. Consistent with this finding, there were no differences in 4E-BP1 activity. Conversely, cumulative MPS was significantly increased with RET, suggesting a temporal shift in anabolism. Study three determined if dietary protein consumed immediately following RE augments cumulative (24 h) MPS in young adult human males when energy and macronutrients are controlled. RE and post-RE protein had no effect on mixed MPS; however, myofibrillar MPS was significantly increased with RE suggesting specific changes within a heterogeneous protein pool. Collectively, these are the first studies to assess changes in cumulative MPS with RE in rats and humans. The long term goals of this research are to understand muscle protein anabolism in "free-living" mammals and the mechanisms that regulate this process.
