CONTRACTION DURATION AFFECTS METABOLIC ENERGY-COST AND FATIGUE IN SKELETAL-MUSCLE

It has been suggested that during a skeletal muscle contraction the me tabolic energy cost at the onset may be greater than the energy cost r elated to holding steady-state force. The purpose of the present study was to investigate the effect of contraction duration on the metaboli c energy cost and fatigue process in fully perfused contracting muscle in situ. Canine gastrocnemius muscle (n = 6) was isolated, and two co ntractile periods (3 min of isometric, tetanic contractions with 45-mi n rest between) were conducted by each muscle in a balanced order desi gn. The two contractile periods had stimulation patterns that resulted in a 1:3 contraction-to-rest ratio, with the difference in the two co ntractile periods being in the duration of each contraction: short dur ation 0.25-s stimulation/0.75-s rest vs. long duration 1-s stimulation /3-s rest. These stimulation patterns resulted in the same total time of stimulation, number of stimulation pulses, and total time in contra ction for each 3-min period. Muscle O-2 uptake, the fall in developed force (fatigue), the O-2 cost of developed force, and the estimated to tal energy cost (ATP utilization) of developed force were significantl y greater (P < 0.05) with contractions of short duration. Lactate effl ux from the working muscle and muscle lactate concentration were signi ficantly greater with contractions of short duration, such that the ca lculated energy derived from glycolysis was three times greater in thi s condition. These results demonstrate that contraction duration can s ignificantly affect both the aerobic and anaerobic metabolic energy co st and fatigue in contracting muscle. In addition, it is likely that t he greater rate of fatigue with more rapid contractions was a result o f elevated glycolytic production of lactic acid.