Post by John A. Casler on Jul 14, 2009 11:28:27 GMT -8
FULL TEXT HERE:
jap.physiology.org/cgi/content/full/100/5/1443
IN THE LAST DECADE, there was a dramatic increase in our knowledge of the molecular events that accompany changes in skeletal muscle mass in response to resistance exercise training or to chronic unloading. For example, the role of myostatin in limiting skeletal muscle growth during development was dramatically demonstrated in knockout animals, and myostatin's role in modulating growth of adult muscle was demonstrated by the administration of anti-myostatin antibodies (14). The key autocrine and paracrine roles of muscle insulin-like growth factor I [or mechano-growth factor (9)] in stimulating muscle hypertrophy were clearly established, and many details of the intracellular signaling cascades that link insulin-like growth factor I -receptor binding to increased muscle protein synthesis and satellite cell activation were worked out (8, 15). Similarly, other signaling pathways by which either mechanical force (10) or calcium changes (6) might regulate muscle growth were identified. Conversely, the loss of muscle mass during chronic unloading is now understood to arise not just from the downregulation of hypertrophic signals but also from the activation of additional intracellular signaling cascades that specifically activate muscle protein degradation (8, 15).
Concurrent with these molecular advances, there was also a dramatic increase in applied research aimed at devising exercise programs to optimize muscle hypertrophy or to minimize atrophy in response to muscle unloading. Much of this applied research was directed toward counteracting the sarcopenia of normal aging or the muscle loss that occurs during prolonged spaceflight or bed rest. Thanks to these applied studies, the response of human muscle to almost every conceivable variation in resistance exercise training paradigm (e.g., number of repetitions, number of sets, interval between sets, interval between training sessions, eccentric vs. concentric motions, etc.) has been explored by at least one study