Skeletal muscle adaptation in adolescent boys

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Abstract
Effects of 3-mo. sprint and endurance training programs on the vastus lateralis muscle fiber area and the activities of glycolytic (phosphofructokinase; PFK) and oxidative (succinate dehydrogenase; SDH) enzymes were investigated in adolescent boys. Enzyme activities were also determined after a subsequent 6-mo. detraining period. Endurance training resulted in significant increases in .ovrhdot.VO2 max [maximal O2 uptake] (58.4-64.3 ml .cntdot. min-1 .cntdot. kg-1), in ST [slow twitch] and FT [fast twitch] a fiber area (6.0-7.3 and 8.0-10.4 .mu.m2 .times. 103, respectively) and in SDH activity (6.4-9.1 IU). After detraining, .ovrhdot.VO2 max and SDH activity returned to pretraining levels. Sprint training resulted in a significant increase only in PFK activity (28.1-33.9 IU), which was also abolished in the detraining period. In adolescent boys skeletal muscle enzyme changes are specific to the mode of training, and they are similar in direction but different in magnitude to those found in adults.