Dynamic Characteristics of Ventilatory and Gas Exchange during Sinusoidal Walking in Humans

Abstract

Our present study investigated whether the ventilatory and gas exchange responses show different dynamics in response to sinusoidal change in cycle work rate or walking speed even if the metabolic demand was equivalent in both types of exercise. Locomotive parameters (stride length and step frequency), breath-by-breath ventilation (V̇E) and gas exchange (CO2 output (V̇CO2) and O2 uptake (V̇O2)) responses were measured in 10 healthy young participants. The speed of the treadmill was sinusoidally changed between 3 km·h-1 and 6 km·h-1 with various periods (from 10 to 1 min). The amplitude of locomotive parameters against sinusoidal variation showed a constant gain with a small phase shift, being independent of the oscillation periods. In marked contrast, when the periods of the speed oscillations were shortened, the amplitude of V̇E decreased sharply whereas the phase shift of V̇E increased. In comparing walking and cycling at the equivalent metabolic demand, the amplitude of V̇E during sinusoidal walking (SW) was significantly greater than that during sinusoidal cycling (SC), and the phase shift became smaller. The steeper slope of linear regression for the V̇E amplitude ratio to V̇CO2 amplitude ratio was observed during SW than SC. These findings suggested that the greater amplitude and smaller phase shift of ventilatory dynamics were not equivalent between SW and SC even if the metabolic demand was equivalent between both exercises. Such phenomenon would be derived from central command in proportion to locomotor muscle recruitment (feedforward) and muscle afferent feedback.

Differential kinetics of the cardiac, ventilatory, and gas exchange variables during walking under moderate hypoxia

“…In the case of mild sinusoidal exercise such as slower walking (average HR ≤ 100 beats·min −1 ), the HR response will reflect mostly the parasympathetic nervous system [ 6 , 16 ]. Yamamoto et al .…”

“…This study was carried out on a motor-driven treadmill (modified TMS 2200; Nihon Kohden, Tokyo). All 13 subjects performed a series of submaximal exercise tests as described [ 16 ]. The inspired oxygen fraction (FiO 2 ; %) was set at either normobaric normoxia (20.9% FiO 2 ) or moderate normobaric hypoxia (15.0% FiO 2 ) [ 17 – 19 ].…”

“…Following a 4 min warm-up by the subject consisting of walking at a constant speed at the midpoint of the sinusoid (4.5 km·h -1 ), we changed the treadmill speed with a sinusoidal pattern from 3 km·h -1 to 6 km·h -1 at a periods ( T ) of 10, 5, 2 or 1 min ( Fig 1 ). Before the sinusoidal pattern, a stepwise manner (steady-state) pattern at speeds of 3 km·h -1 and 6 km·h -1 for 5 min and 3 min each was carried out [ 3 , 16 , 20 ]. The sinusoidal loading was repeated for six cycles at 1-min period and continued for three cycles at 2-min period after a warm-up at a constant work load at the midpoint between maximum and minimum.…”

“…All HR, ventilatory and gas exchange data were analyzed using a standard Fourier analysis as described previously [ 2 , 5 , 6 , 16 , 20 ]. In brief, the variation of the treadmill speed was regarded as the input function.…”

Effect of acute ambient temperature exposure on cardio-pulmonary and respiratory kinetics in men

“…Typically, V _ O 2 is non-invasively measured at the mouth by the application of repeated step responses in WR and is analysed with multiple exponential mathematical equations and fitting procedures [15,21]. In this regard, multi-exponential approaches cannot be applied for fast changes in WR by definition [22][23][24][25]. Alternatively, the application of pseudorandom binary sequence (PRBS) WR protocols with a time-series analysis (e.g.…”