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J Appl Physiol 92: 2089-2096, 2002; doi:10.1152/japplphysiol.00498.2001
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Vol. 92, Issue 5, 2089-2096, May 2002

In situ rat fast skeletal muscle is more efficient at submaximal than at maximal activation levels

F. Abbate1, C. J. De Ruiter1, C. Offringa1, A. J. Sargeant1,2, and A. De Haan1,2

1 Institute for Fundamental and Clinical Human Movement Sciences, Faculty of Human Movement Sciences, Vrije Universiteit, 1081 BT Amsterdam, The Netherlands; and 2 Neuromuscular Biology Research Group, Manchester Metropolitan University, Alsager ST7 2HL, United Kingdom

The influence of stimulation frequency on efficiency (= total work output/high-energy phosphate consumption) was studied using in situ medial gastrocnemius muscle tendon complexes of the rat. The muscles performed 20 repeated concentric contractions (2/s) at 34°C. During these repeated contractions, the muscle was stimulated via the severed sciatic nerve with either 60, 90, or 150 Hz. The muscle was freeze-clamped immediately after these contractions, and high-energy phosphate consumption was determined by measuring intramuscular chemical change relative to control muscles. The average values (±SD) of efficiency calculated for 60, 90, and 150 Hz were 18.5 ± 1.5 (n = 7), 18.6 ± 1.5 (n = 9), and 14.7 ± 1.3 mJ/µmol phosphate (n = 9). The results indicate that the efficiency of the muscles that were submaximally activated (60 or 90 Hz) was higher (+26%, P < 0.05) than that of those maximally activated (150 Hz). Additional experiments showed that the low efficiency at maximal activation levels is unlikely to be the result of a higher energy turnover by the Ca2+-ATPase relative to the total energy turnover. Therefore, alternative explanations are discussed.

stimulation frequency


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