Low-frequency fatigue, post-tetanic potentiation and their interaction at different muscle lengths following eccentric exercise

J. M. Rijkelijkhuizen
2005 Journal of Experimental Biology  
Low-frequency fatigue (LFF) and post-tetanic potentiation (PTP) were quantified at different muscle lengths in rat medial gastrocnemius (GM) muscle. In situ experiments were performed on GM muscle-tendon complexes of anaesthetised (urethane, 1.5·g·kg -1 i.p.) Wistar rats (N=8). Force-length characteristics were determined at maximal (200·Hz) and submaximal (60·Hz) stimulation. Data for submaximally stimulated muscle were obtained in a non-potentiated and in a potentiated condition. LFF was
more » ... ed by a series of 40 eccentric contractions. Post-exercise (40-80·min), data for the force-length relationships were obtained once more. Whereas force loss at 200·Hz-stimulation was least at optimum muscle length, L 0,200Hz , (17.0±1.4%, mean ± S.E.M.), force loss at 60·Hz-stimulation was maximal near L 0,200Hz (55.1±4.3% at L 0,200Hz -1·mm). When the muscle was potentiated, force loss at 60·Hz-stimulation was maximal at short muscle length: L 0,200Hz -4·mm (53.5±3.8%). The extent of LFF, quantified by a decrease in the 60:200·Hz force ratio, varied with muscle length: LFF increased with decreasing muscle lengths when muscles were potentiated. However, in the non-potentiated condition, LFF was maximal at a length just below L 0,200Hz ; the 60:200·Hz force ratio had decreased to 54.6±5.9% of the pre-exercise ratio at L 0,200Hz -1·mm. Compared with the non-potentiated condition, LFF was less pronounced in the potentiated condition. PTP counteracted LFF particularly at long muscle lengths. However, at short muscle lengths, LFF was still observed in potentiated muscles.
doi:10.1242/jeb.01329 pmid:15601877 fatcat:euwqho6wfzaxpbadh7qxl5oebq