Myofibrillar and collagen protein synthesis in human skeletal muscle in young men after maximal shortening and lengthening contractions

Abstract

-We aimed to determine whether there were differences in the extent and time course of skeletal muscle myofibrillar protein synthesis (MPS) and muscle collagen protein synthesis (CPS) in human skeletal muscle in an 8.5-h period after bouts of maximal muscle shortening (SC; average peak torque ϭ 225 Ϯ 7 N⅐ m, means Ϯ SE) or lengthening contractions (LC; average peak torque ϭ 299 Ϯ 18 N ⅐ m) with equivalent work performed in each mode. Eight healthy young men (21.9 Ϯ 0.6 yr, body mass index 24.9 Ϯ 1.3 kg/m 2 ) performed 6 sets of 10 maximal unilateral LC of the knee extensors on an isokinetic dynamometer. With the contralateral leg, they then performed 6 sets of maximal unilateral SC with work matched to the total work performed during LC (10.9 Ϯ 0.7 vs. 10.9 Ϯ 0.8 kJ, P ϭ 0.83). After exercise, the participants consumed small intermittent meals to provide 0.1 g ⅐ kg Ϫ1 ⅐ h Ϫ1 of protein and carbohydrate. Prior exercise elevated MPS above rest in both conditions, but there was a more rapid rise after LC (P Ͻ 0.01). The increases (P Ͻ 0.001) in CPS above rest were identical for both SC and LC and likely represent a remodeling of the myofibrillar basement membrane. Therefore, a more rapid rise in MPS after maximal LC could translate into greater protein accretion and muscle hypertrophy during chronic resistance training utilizing maximal LC. eccentric; concentric; resistance exercise; z-band streaming ATTEMPTS BY PREVIOUS WORKERS to determine the influence of contraction types on rates of protein synthesis provided no evidence of any difference in either mixed muscle (6, 19) or myofibrillar (5) protein synthesis after shortening or lengthening contractions. Greater force can be generated during maximal muscle lengthening contractions (LC) than during maximal muscle shortening contractions (SC). Thus less active muscle is required to move a given load with LC than with SC. Whereas this may represent an increase in the force per active muscle fiber, it suggests a reduction in the number of fibers subjected to a potentially hypertrophic (i.e., resistive) stimulus during LC compared with SC. Because high-threshold motor units that innervate fast-twitch muscle fibers are preferentially recruited during submaximal (18) but not maximal LC (2), the conclusion made in previous reports (19) of no difference between the extent or time course of rates of muscle protein synthesis after SC and LC (5, 6, 19) may be due to differences in the amount of active muscle, the muscle tension, and/or the pattern of muscle activity during these studies.Traditional isotonic resistance training programs require subjects to perform both SC and LC of particular muscles. Training programs exclusively comprising LC are generally agreed to result in greater hypertrophy than those comprising SC alone (9); however, this finding is not exclusive (10 -12). LaStayo et al. (14) showed that 8 wk of training on an eccentric (muscle lengthening) but not a concentric (muscle shortening) cycle ergometer were sufficient to increase muscle fiber area by ϳ52% i...

Heat shock response and autophagy—cooperation and control

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Circulating protein synthesis rates reveal skeletal muscle proteome dynamics

“…Fractional synthesis rates (FSRs) of mixed muscle proteins or protein subfractions are typically measured in rodents and humans through short-term infusions of stable isotope-labeled amino acids (12)(13)(14)(15)(16). These methods have demonstrated the anabolic effects of exercise (6,7), dietary supplements (17,18), or treatment with anabolic agents such as testosterone (8)(9)(10) or clenbuterol (19,20).…”

Contraction intensity and feeding affect collagen and myofibrillar protein synthesis rates differently in human skeletal muscle

“…The importance of the collagen matrix for skeletal muscle function is exemplified by the severe functional abnormalities when pathologies in collagen structures are present (7, 67). Skeletal muscle collagen proteins increase their synthesis rate acutely after exercise (5,23,70,71). Few and conflicting data exist on whether the temporal changes in collagen protein synthesis rates are similar to those of the contractile proteins.…”