H-13K Free Communication/Poster Exercise Training
Type II fibers are predominantly recruited during eccentric exercise.
To find out if myosin heavy chain (MHC) isoform distribution determine the magnitude of functional impairment after eccentric exercise.
The force generated during countermovement jumps (CMJ) was measured with a plate force before and 1h after a squat eccentric exercise session (10 series of 25 repetitions each, at 95% of maximal isometric force, measured with the knees bent at 90°) in 10 active men (25.5 ± 1.1 yr, mean ± sem). The height jump (Hj), peak force (Fp), rate of force development (RDF) and positive mechanical impulse (IMP+) were calculated from the recorded forces. The MHC isoforms and fiber type composition, and fiber size of the vastus lateralis muscle, were analysed by electrophoresis (SDS-PAGE), ATPase histochemistry and immunocytochemistry from muscle biopsies.
The Hj and relative IMP+ during CMJ strongly correlated with IIa MHC isoform (r = 0.75 and r = 0.79, p = 0.05), and the relative area occupied for IIa fiber as well (r = 0.76 and r = 0.80, p = 0.05). The magnitude of HJ and IMP+ impairment 1h after the eccentric exercise was closely related with the IIa MHC percentage in vastus lateralis (both r = 0.79, p = 0.05).
Strenuous squatting eccentric exercise reduces jumping performance, being the effect the more accentuated the higher the percentage of MHC IIa fibers. Granted by Consejo Superior de Deportes (2002).