In situ rat fast skeletal muscle is more efficient at submaximal than at maximal activation levels.
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 degrees 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/micromol 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.
Abbate
F
F
Institute for Fundamental and Clinical Human Movement Sciences, Faculty of Human Movement Sciences, Vrije Universiteit, 1081 BT Amsterdam, The Netherlands.
De Ruiter
C J
CJ
Offringa
C
C
Sargeant
A J
AJ
De Haan
A
A
D000255:Adenosine Triphosphate / Q000032:analysis / Q000378:metabolism; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D003401:Creatine / Q000032:analysis / Q000378:metabolism; D004558:Electric Stimulation; D004734:Energy Metabolism; D007291:Inosine Monophosphate / Q000032:analysis / Q000378:metabolism; D019344:Lactic Acid / Q000032:analysis / Q000378:metabolism; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000737:chemistry / Q000502:physiology*; D010725:Phosphocreatine / Q000032:analysis / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D010725:Phosphocreatine; D007291:Inosine Monophosphate; D019344:Lactic Acid; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D003401:Creatine