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 induced 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, L0,200HZ, (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 L0,200Hz-1 mm). When the muscle was potentiated, force loss at 60 Hz-stimulation was maximal at short muscle length: L0,200Hz-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 L0,200Hz; the 60:200 Hz force ratio had decreased to 54.6±5.9% of the pre-exercise ratio at L0,00Hz-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.
CITATION STYLE
Rijkelijkhuizen, J. M., De Ruiter, C. J., Huijing, P. A., & De Haan, A. (2005). Low-frequency fatigue, post-tetanic potentiation and their interaction at different muscle lengths following eccentric exercise. Journal of Experimental Biology, 208(1), 55–63. https://doi.org/10.1242/jeb.01329
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