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Twitch potentiation is greater after a fatiguing submaximal isometric contraction performed at short vs. long quadriceps muscle length

Institut National de la Santé et de la Recherche Médicale/Equipe de Recherche et d'Innovation Technologique 207, Motricité-Plasticité Laboratory, Faculty of Sport Sciences, University of Burgundy, Dijon, France

Submitted 25 June 2004 ; accepted in final form 7 October 2004

Endurance time of a submaximal sustained contraction is longer when the muscle is fatigued in a shortened position. The aim of the present study was to compare central and peripheral mechanisms of fatigue after an isometric contraction of the knee extensor muscles performed at 20% maximal voluntary contraction (MVC) at two knee angles (35°, short length vs. 75°, long length; 0° = full extension) until exhaustion. Eleven men (24 ± 4 yr) attended two experimental randomized sessions. Endurance time was greater at 35° compared with 75° (974 ± 457 vs. 398 ± 144 s; P < 0.001) despite a similar reduction in knee extensor MVC (–28.4 ± 16.0%, P < 0.001 vs. –27.6 ± 18.8%, P < 0.001, respectively). Voluntary activation level was similarly depressed after the fatiguing contraction performed at the two muscle lengths (–19 ± 16.7% at 35°, P < 0.01 vs. –13.7 ± 14.5% at 75°, P < 0.01). After the fatiguing contraction, peak twitch potentiation was observed only at the short length (+31.8 ± 17.6% at 35°, P < 0.01 vs. +6.4 ± 21.3% at 75°, P > 0.05), whereas M-wave properties were similarly altered for the two angles. These results suggest that 1) central fatigue at task failure for a sustained isometric contraction was not dependent on the muscle length, and 2) the longer endurance time of a sustained isometric contraction performed at a shortened length is related to potentiation. It is suggested that the greater endurance time of a sustained isometric contraction observed at 35° is related to the occurrence of potentiation at this short length, because central fatigue is similar at task failure for both tasks.

sustained contraction; central activation; muscular twitch; M wave

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