Elevations in myofibrillar protein fractional synthesis rates following 5-weeks of dynamic resistance exercise
Anabolic responses to a single bout of high intensity exercise are elevated, but these responses appear to be diminished with chronic training. PURPOSE: To determine the effects of resistance exercise (RE) training on cumulative (36 hour) fractional synthesis rates (FSR) in gastrocnemius muscle of the Sprague-Dawley rat. METHODS: Fifteen rats were assigned to one of three groups: resistance exercise (RE; n=6), exercise control (EC; n=5), or sedentary cage control (CC; n=4). RE and EC animals were then operantly conditioned to perform the exercise regimen which consisted of a movement similar to a traditional "squat" exercise. Over a 5 week period, RE and EC performed 15 incremental resistance exercise sessions consisting of 50 repetitions for the first session with a 5% decrease in total volume per week. EC group performed sessions with an 80g vest while RE group started with only the vest and progressively increase weight to 410g by session 15. All cohorts were euthanized 16 hours following the final session and muscle tissues were collected. Cumulative FSR (%/day), as determined by a 2H2O primed-continuous method, was measured in red and white portions of the gastrocnemius. Isolation of myofibrillar, mitochondrial (subsarcolemmal or intermyofibrillar) and cytosolic protein subfractions were obtained through differential centrifugation. RESULTS: This study demonstrated that cumulative FSR in the myofibrillar subfraction maintained an exercise response with training, and was incrementally dependent on intensity (CC < EC < RE; p<0.05) in both red and white portions. No other subfractions of the muscle were responsive to high intensity exercise after 5-weeks of training (p>0.05). CONCLUSION: Results suggest that elevations of muscle protein synthesis with chronic training are selectively targeted to the myofibrillar fraction and are not a generalized response. Further, our data suggest that cumulative FSR responses may be dose-responsive in an intensity-dependent manner.
Dobson, J; Nilsson, M; Gasier, H; Fluckey, J
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American College of Sports Medicine
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