| Besides neuro-mechanical constraints, chemical or metabolic stimuli
have also been proposed to interfere with the coordination between
respiratory and locomotor rhythms. In the light of the conflicting
data observed in the literature, this study aimed to assess whether
acute hypoxia modifies the degree of coordination between respiratory
and locomotor rhythms during rowing exercises in order to investigate
competitive interactions between neuro-mechanical (movement) and chemical
(hypoxia) respiratory drives. Nine male healthy subjects performed
one submaximal 6-min rowing exercise on a rowing ergometer in both
normoxia (altitude: 304 m) and acute hypoxia (altitude: 2877 m). The
exercise intensity was about 40 % and 35 % (for normoxia and hypoxia
conditions, respectively) of the individual maximal power output measured
during an incremental rowing test to volitional exhaustion carried
out in normoxia. Metabolic rate and minute ventilation were continuously
collected throughout exercise. Locomotor movement and breathing rhythms
were continuously recorded and synchronized cycle-by-cycle. The degree
of coordination was expressed as a percentage of breaths starting
during the same phase of the locomotor cycle. For a same and a constant
metabolic rate, acute hypoxia did not influence significantly the
degree of coordination (mean ± SEM, normoxia: 20.0 ± 6.2 %, hypoxia:
21.3 ± 11.1 %, p > 0.05) while ventilation and breathing frequency
were significantly greater in hypoxia. Our results may suggest that
during rowing exercise at a moderate metabolic load, neuro-mechanical
locomotion-linked respiratory stimuli appear "stronger"
than peripheral chemoreceptors- linked respiratory stimuli induced
by hypoxia, in the context of our study.
KEY
WORDS: Control
of breathing, locomotor-respiratory coupling, neuro-mechanical entrainment,
chemical drive.
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