Degree of coordination between breathing and rhythmic arm movements during hand rim wheelchair propulsion

This study aimed (i) to quantify the spontaneous coordination between breathing and hand rim wheelchair propulsion, (ii) to manipulate arm movement frequency and assess its effects on spontaneous coordination, and (iii) to investigate the hypothesis that entrainment of breathing improves economy of locomotion and leads to a lower rate of perceived exertion (RPE) compared with spontaneous breathing. Nine male, able-bodied participants completed four bouts of 6 min submaximal steady state exercise at 60 % of maximal propulsion velocity on a wheelchair ergometer, with spontaneous breathing and arm frequencies (Fspont), with 20 % higher and lower arm frequencies (F +20 and F -20, respectively) compared to Fspont accompanied with spontaneous breathing frequency, and by synchronising expiration phase with pushing time and inspiration phase with upper limb recovery time (C). Oxygen uptake and propulsion frequency were continuously recorded. The degree of coordination was expressed as a percentage of inspiration starting in the same phase of the wheelchair propulsion cycle (i.e. pushing and recovery times). No difference in degree of coordination was observed between Fspont, F -20 and F +20 conditions (49.2 +/- 12.1 %, 49.1 +/- 29.0 % and 48.2 +/- 29.4 %, respectively). Oxygen uptake increased significantly during C condition while RPE was significantly lower for C and F -20 (p < 0.05) compared to F +20 conditions. Contrary to what we expected, entrainment of breathing using a monofrequency ratio (C) induced a higher energy cost probably due to the mechanical properties of the wheelchair propulsion activity itself. In conclusion, this study showed that the same locomotor-respiratory coupling occurred during hand rim wheelchair propulsion regardless of the arm movement frequency, and that entrainment of breathing did not improve economy of locomotion.