Alterations in step frequency and muscle activities using body weight support influence the ventilatory response to sinusoidal walking in humans

Abstract

Abstract The use of body weight support (BWS) can reveal important insights into the relationship between lower-limb muscle activities and the ventilatory response during sinusoidal walking. Here, healthy participants (n = 15) walked on a treadmill while 0%, 30%, and 50% of their body weight was supported with BWS. The walking speed was varied sinusoidally between 3 and 6 km h−1, and three different frequencies, and periods ranging from 2 to 10 min were used. Breath-by-breath ventilation ( $${\dot{\text{V}}}_{{\text{E}}}$$ V ˙ E ) and CO2 output ( $${\dot{\text{V}}}\text{CO}_{{2}}$$ V ˙ CO 2 ) were measured. The tibialis anterior (TA) muscle activity was measured by electromyography throughout the walking. The amplitude (Amp), normalized Amp [Amp ratio (%)], and phase shift (PS) of the sinusoidal variations in measurement variables were calculated using a Fourier analysis. The results revealed that the Amp ratio in $${\dot{\text{V}}}_{{\text{E}}}$$ V ˙ E increased with the increase in BWS. A steeper slope of the $${\dot{\text{V}}}_{{\text{E}}}$$ V ˙ E – $${\dot{\text{V}}}\text{CO}_{{2}}$$ V ˙ CO 2 relationship and greater $${\dot{\text{V}}}_{{\text{E}}}$$ V ˙ E / $${\dot{\text{V}}}\text{CO}_{{2}}$$ V ˙ CO 2 values were observed under reduced body weight conditions. The Amp ratio in TA muscle was significantly positively associated with the Amp ratio in the $${\dot{\text{V}}}_{{\text{E}}}$$ V ˙ E (p < 0.001). These findings indicate that the greater amplitude in the TA muscle under BWS may have been a potent stimulus for the greater response of ventilation during sinusoidal walking.