Skeletal muscle adaptations to training under normobaric
hypoxic versus normoxic conditions.
Melissa L, MacDougall JD, Tarnopolsky MA, Cipriano N, Green HJ
Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada.
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.