MHC Isoforms Are Associated with Acute Neuromuscular Performance Changes Induced by Prolonged Jumping Exercise

Abstract

Prolonged fatiguing exercise has been demonstrated to cause ultrastructural changes in skeletal muscle and its metabolism that may further cause decreases in neuromuscular performance. PURPOSE: To investigate changes in maximal performance and muscle activity (EMG) and their associations with myosin heavy chain isoforms (MHC). METHODS: Ten young men (age 26±6 yrs; height 180±8 cm; body mass 77.8±11.2 kg) volunteered to participate. Prolonged unilateral jumping exercises were performed on a sledge apparatus (jump time varied from 3:20-30:12 min, and number of jumps from 61-1248). Measurements for isometric maximal voluntary contraction (MVC), maximal drop jumps (MDJ), blood analyses, and muscle biopsies were obtained at pre, immediately post, 3 and 20 hours post jumping exercises. The pre muscle biopsy was taken from the control (left) leg ~3 hours prior to the fatiguing exercise, and subsequent biopsies from the exercised (right) leg immediately and 3 hours post exercise. RESULTS: The vastus lateralis muscle contained MHC isoforms analyzed from the pre-samples as follows: I 41.2±8.8%, IIA 35.4±7.5% and IIX 22.4±5.7%. After the fatiguing exercise, the mean (±SD) peak blood lactate concentrations were 7.8±3.3 mmol/l and creatine kinase activity 1043±442 U/l. MVC decreased by 43.7±15.8% (from 2505±1070 to 1343±511 N) from pre to immediately post, with a simultaneous 14.9±25.5% increase in EMG of the vastus medialis muscle. Rate of force development decreased by 24.6±31.0%, and take-off velocity in MDJ by 18.1±8.6% in the fatigued leg. MHCI was associated with relative changes in MVC (r=-0.73, p<0.01) and EMG (r=-0.71, p<0.01), and the changes in MVC and EMG were correlated (r=0.65, p<0.05). No respective changes and associations were noticed in the control leg. CONCLUSIONS: The fatiguing stretch-shortening cycle exercises induced muscle damage and large reductions in neuromuscular performance that were associated with respective changes in EMG of the activated muscles. MHCs were associated with decrements in performance: lower MHCI had more substantial reductions in performance. Maximal neuromuscular performance acutely decreases mainly due to impaired functions of fatigued type II fibers.