Phase relation and breathing pattern during locomotor/respiratory coupling in uphill and downhill running.

Differential effects of uphill and downhill running on phase relation between locomotor and respiratory cycles were studies in nine experienced runners who were instructed to run uphill and downhill on a sloped surface at comfortable and constant speeds (actually 1.7-4.4 m s-1). Timings of footstrike and onsets of inspiration and expiration were measured to compute respiratory cycle duration (Ttot), inspiratory time (Ti), duty cycle (Ti/Ttot), and stride time (Ts). Incidence of locomotor/respiratory coupling (LRC) was determined based on steadiness of Ttot and Ts (within +/- 0.1 s in SD) and Ttot/Ts (LRC ratio, integer or a half-integer multiples). Both in the uphill and downhill running, LRC ratio observed was 1:1, 2:1, and 2.5:1. Ti/Ttot during LRC was 0.41-0.49, which depended on the combinations of Ts and LRC ratio but not on the running conditions. In the uphill running, the onset of inspiration subsequent to footstrike was seen during the first half period (corresponding to the support phase) of the step interval (Ts/2, the time interval between the right and left footstrikes) in 7 of the 9 subjects, while in the downhill running it occurred during the last half period of the step interval (the floating phase) in all subjects. For onset of expiration, no consistent relation to footstrike was observed. These results suggest that the mechanical constraints of running on the respiratory system affect the phase relation between locomotor and respiratory cycles but not Ti/Ttot during LRC.