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

Figures

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  FIGURE 1. Two sinusoidal locomotion protocols at a sinusoidal speed between 50 and 100 m⋅min–1 at the period of 1⋅2 min (A) and 5⋅10 min (E). The stride length (SL) was fixed at 0.7 m with step frequency (SF) variation (143–71 step⋅min–1) (SLfix) (B,F) and the SF was fixed at 120 steps⋅min–1 with stride variation (0.83–0.41 m) (SFfix) (C,G). The control (Free) condition was the subjects’ preferred locomotion pattern (D,H).

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  FIGURE 2. Time course of the locomotion responses at a 5-min period. Example from a representative subject of the locomotion pattern of the step frequency (SF) and the stride length (SL) divided under SLfix (A), SFfix (B), and Free (C). The oscillating line is the superimposed SL and SF for a 5-min period. The lower sinusoidal curve is the sinusoidal change of the speed between 50 and 100 m⋅min–1.

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  FIGURE 3. The amplitude (Amp), phase shift (PS), and mean (Mx) values in the step frequency under SLfix (A–C) and in the stride length under SFfix (D–F) compared with Free. The Amp under both SLfix and SFfix became significantly higher compared with those at Free at any period (p < 0.001). The PS values for SL were quite small and virtually close to zero at each period (E). The Mx under SLfix tended to be lower and the Mx under SFfix was significantly lower than that under the Free condition at each period. **p < 0.01, ***p < 0.001 vs. Free. T, time periods (1, 2, 5, and 10 min). Data are mean ± SD.

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  FIGURE 4. Time course of the ventilatory responses to the sinusoidal change in treadmill speed at the period of 5 min. Examples highlighting characteristic responsiveness of the ventilatory variables of ventilation (V.E), breath frequency (Bf), and tidal volume (VT) responses under SLfix locomotion (A–D) and SFfix locomotion (E–H) in a representative subject. The oscillating line is the superimposed gas exchange variables data. The smooth blue and red lines are the sine-wave fundamental component of these dynamics.

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  FIGURE 5. Comparisons of Amp and PS in V.E (A,E), Bf (B,F), VT (C,G), and end-tidal PCO2 (PETCO2) (D,H) dynamics under SLfix, SFfix, and Free. *p < 0.05 between SLfix vs. SFfix within the same period. †p < 0.05 between Free vs. SFfix within the same period. T, time periods (1, 2, 5, and 10 min). Data are mean ± SD.

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  FIGURE 6. Comparisons of Amp and PS in heart rate (HR) (A,D), O2 uptake (V.O2) (B,E), and CO2 output (V.CO2) (C,F) dynamics under SLfix, SFfix, and Free. *p < 0.05 between SLfix vs. SFfix within the same period. †p < 0.05 between Free vs. SFfix within the same period. T, time periods (1, 2, 5, and 10 min). Data are shown in mean ± SD.

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  FIGURE 7. Relationship between the Amp ratio in V.E and V.CO2 under SLfix, SFfix, and Free, respectively. The slope of the regression lines of the V.E-V.CO2 relationship was steeper at SLfix than SFfix. SLfix: y = 1.19x + 0.05, r = 0.83 (p < 0.001). SLfix: y = 0.70x + 0.09, r = 0.92 (p < 0.001). Free: y = 0.97x + 0.08, r = 0.88 (p < 0.001).