This study examined some of the physiological and performance effects of three different tapers in highly trained athletes. After 8 wk of training, nine male middle-distance runners were randomly assigned to one of three different 7-day tapers: a high-intensity low-volume taper (HIT), a low-intensity moderate-volume taper (LIT), or a rest-only taper (ROT). After the first taper, subjects resumed training for 4 wk and performed a second taper and then resumed training for 4 wk and completed the remaining taper, so that each subject underwent all three tapers. Performance was measured before and after each taper by a treadmill run to fatigue at a velocity equivalent each subject's best 1,500-m time. Voluntary isometric strength and evoked contractile properties of the quadriceps were measured before and after each taper, as were muscle glycogen concentration and citrate synthase activity (from needle biopsies) and total blood and red cell volume by 125I and 51Cr tagging. Maximal O2 consumption was unaffected by all three tapers, but running time to fatigue increased significantly after HIT (+22%). It was unaffected by LIT (+6%) and ROT (-3%) procedure. Citrate synthase activity increased significantly with HIT and decreased significantly with ROT. Muscle glycogen concentration increased significantly after ROT and HIT, and strength increased after all three tapers. Total blood volume increased significantly after HIT and decreased after ROT.(ABSTRACT TRUNCATED AT 250 WORDS)

This study examined whether training under normobaric hypoxic conditions (simulating medium level altitude) would enhance physical performance and selected muscle adaptations over and above that which occurs with normoxic training. Ten healthy males (19-25 yr) underwent 8 wk of unilateral cycle ergometry training so that one leg was trained while breathing an inspirate of 13.5% O2 and the other while breathing normal ambient air. Pre- and post-training measurements included single leg VO2max and time to fatigue at 95% VO2max. Needle biopsies from quadriceps were assayed for oxidative and glycolytic enzyme activity and analyzed for capillary density, fiber area, % fiber type, and mitochondrial and lipid volume density. VO2max, time to fatigue, citrate synthase (CS), succinate dehydrogenase, and phosphofructokinase activity increased significantly (P > 0.05) in both legs following training. The increase in CS activity in the hypoxically trained leg was also significantly greater than that in the normoxically trained leg. It thus appears that training under moderate normobaric hypoxic conditions enhances muscle citrate synthase activity to a greater extent than training under normoxic conditions.

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