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at moderate altitude (~1800m) is often used by athletes to stimulate
muscle hypoxia. However, limited date is available on peripheral muscle
oxidative metabolism at this altitude (1800AL). The purpose of this
study was to determine whether acute exposure to 1800AL alters muscle
oxygenation in the vastus lateralis muscle during resistance exercise.
Twenty young active male subjects (aged 16 - 21 yr) performed up to
50 repetitions of the parallel squat at 1800AL and near sea level
(SL). They performed the exercise protocol within 3 h after arrival
at 1800 AL. During the exercise, the changes in oxygenated hemoglobin
(OxyHb) in the vastus lateralis muscle, arterial oxygen saturation
(SpO2), and heart rate were measured using near infrared continuous
wave spectroscopy (NIRcws) and pulse oximetry, respectively. Changes
in OxyHb were expressed by Deff defined as the relative index of the
maximum change ratio (%) from the resting level. OxyHb in the vastus
lateralis muscle decreased dramatically from the resting level immediately
after the start of exercise at both altitudes. The Deff during exercise
was significantly (p < 0.001) lower at 1800AL (60.4 ± 6.2 %) than
at near SL (74.4 ± 7.6 %). SpO2 during exercise was significantly
(p < 0.001) lower at 1800AL (92.0 ± 1.7 %) than at near SL (96.7
± 1.2 %). Differences (SL - 1800AL) in Deff during exercise correlated
fairly strongly with differences in SpO2 during exercise (r = 0.660).
These results suggested that acute exposure to moderate altitude caused
a more dramatical decrease in peripheral muscle oxygenation during
leg resistance exercise. It is salient to note, therefore , that peripheral
muscle oxygenation status at moderate altitude could be evaluated
using NIRcws and that moderate altitudes might be effectively used
to apply hypoxic stress on peripheral muscles.
KEY
WORDS: NIRcws, muscle oxygenation, moderate altitude, parallel
squat, SpO2
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