Influence of Step Frequency on the Dynamic Characteristics of Ventilation and Gas Exchange During Sinusoidal Walking in Humans

We tested the hypothesis that restricting either step frequency (SF) or stride length (SL) causes a decrease in ventilatory response with limited breath frequency during sinusoidal walking. In this study, 13 healthy male and female volunteers (mean ± SD; age: 21.5 ± 1.8 years, height: 168 ± 7 cm, weight: 61.5 ± 8.3 kg) participated. The walking speed was sinusoidally changed between 50 and 100 m⋅min with periods from 10 to 1 min. Using a customized sound system, we fixed the SF at 120 steps⋅min with SL variation (0.83-0.41 m) ( ) or fixed the SL at 0.7 m with SF variation (143-71 steps⋅min) ( ) during the subjects' sinusoidal walking. Both the subjects' preferred locomotion pattern without a sound system () and the unprompted spontaneous locomotor pattern for each subject () served as the control condition. We measured ventilation [tidal volume (VT) and breathing frequency (B)] and gas exchange [CO output ( CO), O uptake ( O)]. The amplitude () and the phase shift (PS) of the fundamental component of the ventilatory and gas exchange variables were calculated. The results revealed that the condition decreased the of the B response compared with and conditions. Notably, the of the B response under was reduced by less than one breath at the periods of 5 and 10 min. In contrast, the condition resulted in larger Amps of B and responses as well as . We thus speculate that the steeper slope of the - CO relationship observed under the might be attributable to the central feed-forward command or upward information from afferent neural activity by sinusoidal locomotive cadence. The PSs of the , O, and CO responses were unaffected by any locomotion patterns. Such a sinusoidal wave manipulation of locomotion variables may offer new insights into the dynamics of exercise hyperpnea.