Abstract

Maximal voluntary contractions (MVC) were performed by five male subjects as repeated knee extensions separated by 13-s rest periods for the purposes of studying performance capability, physiologic responses, and recruitment patterns among fast-twitch (FT) and slow-twitch (ST) extrafusal muscle fibers forthis type of exercise. Exercise was performed on an isokinetic ergometer as 4 MVC per min for 1 h. Biopsies taken from the m. vastus lateralis were analyzedfor ATP, CP, lactate, and glycogen. Fiber type was determined by staining sections for myofibrilar ATPase and fiber glycogen content by PAS stain. Ability to produce force declined from an average of 250 Nm during the first minute to 200 Nm during the last minute of exercise. Oxygen uptake and heart rate were relatively constant for each subject and averaged 0.94 1 x min and 110 beat x min throughout exercise. Muscle values in mmol x kg at rest, at midpoint, and at end of exercise were for ATP 5.3, 5.4, and 4.1 for CP 19.4, 15.7, and 12.1 and for lactate 1.7, 3.9, and 4.5, respectively. It was estimated that one third of the energy requirement for exercise was obtained from the endogenous muscle glycogen. Glycogen depletion patterns indicated theinvolvement of both FT and ST fibers in this type of exercise. Verf.-Referat