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

Mako Fujita; Kiyotaka Kamibayashi; Tomoko Aoki; Masahiro Horiuchi; Yoshiyuki Fukuoka

doi:10.3389/fphys.2022.820666

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

Front Physiol. 2022 Apr 12:13:820666. doi: 10.3389/fphys.2022.820666. eCollection 2022.

Authors

Mako Fujita¹, Kiyotaka Kamibayashi¹, Tomoko Aoki², Masahiro Horiuchi³, Yoshiyuki Fukuoka¹

Affiliations

¹ Faculty of Health and Sports Science, Doshisha University, Kyoto, Japan.
² Faculty of Environmental Symbiotic Science, Prefectural University of Kumamoto, Kumamoto, Japan.
³ Division of Human Environmental Science, Mt. Fuji Research Institute, Fujiyoshida, Japan.

Abstract

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^-1 with periods from 10 to 1 min. Using a customized sound system, we fixed the SF at 120 steps⋅min^-1 with SL variation (0.83-0.41 m) (SF _fix ) or fixed the SL at 0.7 m with SF variation (143-71 steps⋅min^-1) (SL _fix ) during the subjects' sinusoidal walking. Both the subjects' preferred locomotion pattern without a sound system (Free) and the unprompted spontaneous locomotor pattern for each subject (Free) served as the control condition. We measured breath-by-breath ventilation [tidal volume (VT) and breathing frequency (Bf)] and gas exchange [CO₂ output ( $\dot{V}$ CO₂), O₂ uptake ( $\dot{V}$ O₂)]. The amplitude (Amp) and the phase shift (PS) of the fundamental component of the ventilatory and gas exchange variables were calculated. The results revealed that the SF _fix condition decreased the Amp of the Bf response compared with SL _fix and Free conditions. Notably, the Amp of the Bf response under SF _fix was reduced by less than one breath at the periods of 5 and 10 min. In contrast, the SL _fix condition resulted in larger Amps of Bf and $\dot{V}$ _E responses as well as Free. We thus speculate that the steeper slope of the $\dot{V}$ _E - $\dot{V}$ CO₂ relationship observed under the SL _fix might be attributable to the central feed-forward command or upward information from afferent neural activity by sinusoidal locomotive cadence. The PSs of the $\dot{V}$ _E , $\dot{V}$ O₂, and $\dot{V}$ CO₂ 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.

Keywords: breath frequency; entrainment; step frequency; stride length; ventilation.