Muscle Collagen Synthesis in Human Quadriceps in Response to Maximal Shortening and Lengthening Contractions

2321 Epimysial collagen provides external structure support to skeletal muscle cells through a fibrous network. While a bout of strenuous exercise stimulates protein synthesis in myofibrillar and sarcoplasmic protein fractions, the synthesis of proteins outside the muscle fibre (e.g collagen) is also stimulated (Miller et al. 2003. FASEB J. 17: LB136) and is potentially more rapid after a bout of submaximal lengthening contractions (Babraj et al. 2003. Scand. Congr. Physiol. Pharmacol.). PURPOSE: We aimed to determine if there was any difference in the extent and time course of muscle collagen fractional synthetic rate (FSR) after maximal muscle shortening (SC, average peak torque = 225 ± 7 N.m, means ± SE) or lengthening (LC, average peak torque = 299 ± 18 N.m) contractions, when total work performed during each contraction protocol was equivalent. METHODS: Eight healthy young men (21.9 ± 0.6 y, BMI 24.9 ± 1.3 kg/m2) performed 6 sets of 10 maximal unilateral LC as knee extensions on an isokinetic dynamometer. Then, with the contralateral leg they performed 6 sets of maximal SC with work matched to the total work performed during LC by adding an additional number of repetitions in each set to match total work (SC = 10.9 ± 0.7, LC = 10.9 ± 0.8 kJ; P = 0.83). The subjects received a primed constant infusion of [1,2-13C] leucine over 8.5 h, in the fed state, with bilateral quadriceps muscle biopsies at 1.5, 4.5, and 8.5 h. Tracer incorporation into protein was measured by gas chromatography – combustion – ratio mass spectrometry and plasma α-KIC labeling by GCMS. Muscle collagen FSR was calculated as the incorporation over time divided by the plateau α-KIC labeling, which we have found gives identical results to use of 13C proline flood. RESULTS: At 4.5 h post-exercise, collagen FSR was significantly (P: <0.01) elevated above resting values (0.015 ± 0.001 % h−1) with no difference between modes (SC 0.061 ± 0.003 and LC 0.061 ± 0.002 % h−1). Collagen FSR remained elevated at 8.5 h (SC 0.061 ± 0.002 and LC 0.058 ± 0.002 % h−1). CONCLUSIONS: Muscle collagen FSR is elevated after strenuous resistance exercise suggesting muscle fibroblasts are stimulated to a similar extent at least 4.5 h following maximal SC and LC. The increase in endomysial collagen synthesis is likely to be a beneficial adaptive response to resistive exercise, which would provide a more extensive external support lattice for muscle fibres. Supported by Experimental and Applied Sciences (EAS™), NSERC Canada, The Wellcome Trust, UK MRC and BBSRC

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