Gait-Specific Pulmonary Oxygen Uptake Kinetics During Gait Transitions Reflect the Energetics of Walking and Running in Humans.

Abstract

Human terrestrial locomotion involves a transition between walking and running. While the energetics of steady-state walking and running have been well characterized, cardiac, ventilatory, and gas-exchange kinetics during gait transitions remain poorly understood. In this study, we used a sinusoidally changing speed of locomotion to investigate cardiac, ventilatory, and gas-exchange kinetics ( beat-by-beat heart rate, breath-by-breath pulmonary ventilation [ ], CO 2 output [ ], and O 2 uptake [ ]) as well as step frequency adjustment across three gait conditions: walking (Walk), running (Run), and the walk-run transition (WRtrans). In each condition, the treadmill speed was varied sinusoidally in a range of mid-speed ± 1.5 km·h with two different frequencies: the periods of 2 and 5 min. The in the WRtrans condition was intermediate between walking and running, whereas the amplitude of the in the WRtrans was significantly greater than in the other two conditions (both P < 0.001). The and heart rate response during running was significantly delayed, as showing larger phase shifts, compared with walking. Notably, the observed response in the WRtrans closely matched the estimated response, reconstructed from the amplitude and phase shift values individually obtained in the Walk and Run conditions. Additionally, the average step frequency of all participants abruptly increased at gait transition and remained constant during the running phase of the WRtrans condition. These results suggest that: 1) the kinetics during gait transitions reflect the integration of walking- and running-specific energetic responses, and 2) gait transitions are accompanied by adjustments in step frequency and length that are consistent with energetically optimal locomotor patterns.