IMPACT OF RESISTANCE AND ENDURANCE EXERCISE AND INGESTION OF VARYING PROTEIN SOURCES ON CHANGES IN HUMAN SKELETAL MUSCLE PROTEIN TURNOVER

Abstract

Both resistance and endurance exercise elicit an increase in muscle protein synthesis during recovery from exercise. Ingestion of amino acids augments the exercise-induced stimulation of muscle protein synthesis following resistance exercise. Our work showed that 8 wk of unilateral resistance training induced muscle hypertrophy only in the exercised limb. Importantly, using this unilateral model we showed that muscle hypertrophy was confined to the exercised leg and occurred without measurable changes in circulating anabolic hormones. We then went on to use the unilateral leg resistance exercise model to study how animal-derived (milk) and plant-derived (soy) proteins impacted acute post-exercise protein turnover. We observed that ingestion of soy or milk protein resulted in a positive net protein balance following resistance exercise. Moreover, milk promoted a greater net protein balance and muscle protein synthesis than soy protein. In the final study, a key finding was that acute endurance and resistance exercise differentially stimulated myofibrillar and mitochondrial protein synthesis and also differentially affected cellular signaling proteins involved in the regulation of the protein synthetic response. Specifically, the acute, untrained state response showed that resistance exercise stimulated myofibrillar and mitochondrial protein synthesis while endurance exercise stimulated mitochondrial protein synthesis. Following resistance training only myofibrillar protein synthesis increased after exercise, while mitochondrial protein synthesis was unchanged. Endurance exercise training did not affect the acute protein synthetic response and so following training mitochondrial protein synthesis was stimulated as it was acutely, prior to training. In conclusion, the studies within this thesis provided novel insights on the impact of intact dietary proteins and differing modes of exercise on the control skeletal muscle protein metabolism.