The effects of intermittent exposure to hypoxia during
endurance exercise training on the ventilatory responses to
hypoxia and hypercapnia in humans.
Katayama K, Sato Y, Ishida K, Mori S, Miyamura M
Research Center of Health, Physical Fitness and Sports, Nagoya University, Japan.
The present study was performed to investigate the effects of a combination
of intermittent exposure
to hypoxia during exercise training for short periods on ventilatory
responses to hypoxia and
hypercapnia (HVR and HCVR respectively) in humans. In a hypobaric chamber
at a simulated
altitude of 4,500 m (barometric pressure 432 mmHg), seven subjects
(training group) performed
exercise training for 6 consecutive days (30 min x day(-1)), while
six subjects (control group) were
inactive during the same period. The HVR, HCVR and maximal oxygen uptake
(VO2max) for each
subject were measured at sea level before (pre) and after exposure
to intermittent hypoxia. The post
exposure test was carried out twice, i.e. on the 1st day and 1 week
post exposure. It was found that
HVR, as an index of peripheral chemosensitivity to hypoxia, was increased
significantly (P < 0.05) in
the control group after intermittent exposure to hypoxia. In contrast,
there was no significant increase
in HVR in the training group after exposure. The HCVR in both groups
was not changed by
intermittent exposure to hypoxia, while VO2max increased significantly
in the training group. These
results would suggest that endurance training during intermittent exposure
to hypoxia depresses the
increment of chemosensitivity to hypoxia, and that intermittent exposure
to hypoxia in the presence
or absence of exercise training does not induce an increase in the
chemosensitivity to hypercapnia in
humans.