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First published online December 15, 2004
Journal of Experimental Biology 208, 55-63 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01329

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

J. M. Rijkelijkhuizen^1,*, C. J. de Ruiter¹, P. A. Huijing^1,2 and A. de Haan^1,3

¹ Institute for Fundamental and Clinical Human Movement Sciences, Vrije Universiteit, Van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands
² Integrated Biomedical Engineering for Restoration of Human Function, Instituut voor Biomedische Technologie, Faculteit Construerende Wetenschappen, Universiteit Twente, Postbus 217, 7500 AE Enschede, The Netherlands
³ Institute for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Crewe & Alsager Faculty, Cheshire ST7 2HL, UK

View larger version (11K): [in a new window]   Fig. 1. Typical example of length and force traces of eccentric contractions as imposed during the eccentric exercise. Length (top panels) and force (bottom panels) traces during eccentric contractions of a medial gastrocnemius (GM) muscle. The first (A), 20th (B) and last (C) contraction of the eccentric fatiguing protocol are shown. The length of the muscle-tendon complex is expressed relative to the isometric optimum length for maximal stimulation (L0,200Hz). The bold line below the force trace indicates stimulation.

View larger version (13K): [in a new window]   Fig. 2. Sustained effect of eccentric exercise on isometric force-length characteristics for maximally stimulated muscle. (A) Maximal isometric force-length relationships before (pre-exercise, closed circles) and 40-60 min after a series of eccentric contractions (post-exercise, open circles). Maximal force, obtained at a stimulation frequency of 200 Hz, was significantly reduced post-exercise at all muscle lengths. (B) Maximal isometric force-length relationship post-exercise, expressed relative to the pre-exercise values. Force loss was less pronounced at L0,200Hz compared with both shorter and longer lengths. Note that post-exercise (open circles in Fig. 1A and 1B), the muscle was set on the new (1 mm longer) L0,200Hz. Data are presented as mean ± S.E.M.

View larger version (21K): [in a new window]   Fig. 3. Sustained effect of eccentric exercise on isometric force-length characteristics for submaximally stimulated muscle. (A) Submaximal isometric force-length characteristics before (pre-exercise, closed symbols) and 80 min after a series of eccentric contractions (post-exercise, open symbols) (mean ± S.E.M.). Data were collected before (circles) and after (triangles) a potentiating tetanus, which caused post-tetanic potentiation (PTP). Exercise reduced submaximal force (obtained with a stimulation frequency of 60 Hz), whereas the potentiating tetanus raised force at most muscle lengths. (B) Submaximal isometric force-length relationship post-exercise, expressed relative to the pre-exercise values. Different effects of muscle length were found in the potentiated (triangles) compared with the non-potentiated (circles) condition. *Significant difference between non-potentiated and potentiated condition.

View larger version (12K): [in a new window]   Fig. 4. Sustained effect of eccentric exercise on post-tetanic potentiation (PTP) at different muscle lengths. The increase in submaximal force (F) of muscles in the potentiated compared with the non-potentiated condition was calculated before (closed triangles) and 80 min after (open triangles) eccentric exercise. Different effects of muscle length were found in the pre-compared with the post-exercise condition. On average, PTP had similar effects (P>0.05) preand post-exercise. However, post-exercise, PTP was significantly lower at short and higher at long muscle lengths than pre-exercise. Data are presented as mean ± S.E.M. *Significant difference between pre- and post-exercise condition.

View larger version (23K): [in a new window]   Fig. 5. Length-dependent effects of eccentric exercise and post-tetanic potentiation (PTP) on the 60:200 Hz force ratio. (A) 60:200 Hz force ratios before (pre-exercise, closed symbols) and 80 min after (post-exercise, open symbols) eccentric exercise. The ratios were calculated for the non-potentiated (circles) as well as for the potentiated (triangles) condition (mean ± S.E.M). Exercise decreased the 60:200 Hz force ratio whereas PTP increased the 60:200 Hz force ratio significantly at most muscle lengths. (B) Post-exercise 60:200 Hz force ratios expressed as a percentage of the pre-exercise ratios at different muscle lengths (circles: non-potentiated condition, triangles: potentiated condition). Significantly less LFF was present in the potentiated condition than in the non-potentiated condition at most muscle lengths. *Significant difference between non-potentiated and potentiated condition.