Peak and kinetic cardiorespiratory responses during arm and leg exercise in patients with spinal cord injury

Study design: A paired comparison of the peak and submaximal responses of oxygen uptake and heart rate in patients with spinal cord injury (SCI) performing voluntary arm cycle exercise and functional electrical stimulation (FES) leg cycling exercise. Objectives: To test if the blunted heart rate response and slower rate of adjustment of oxygen uptake seen in patients with SCI performing FES leg cycle exercise are also characteristic of arm exercise in these patients. Methods: Eight paraplegics performed incremental and constant work rate (CWR) exercise with the legs and arms. Mean response times (MRT) for (V) over dotO(2) during exercise (on) and in recovery (off) were calculated from the breath-by-breath (V) over dotO(2) profile. Results: Peak heart rate was higher during incremental arm exorcise, and uncorrelated with that observed during incremental FES leg cycling. For the same increase in (V) over dotO(2), constant work rate arm exercise was associated with faster (and normal) (V) over dotO(2) kinetics, greater increase in heart rate, and lower end-exercise blood lactate, compared to FES leg cycling, Conclusions: The consistently higher peak heart rate and (V) over dotO(2), and faster (V) over dotO(2) kinetics, for voluntary arm compared to FES leg cycle exercise suggest no intrinsic dysfunction of heart rate control in these paraplegics. Rather, these data suggest that during FES leg cycling the changes seen are due to some characteristic specific to the injury, such as reduced muscle mass and/or deconditioning of the remaining muscle. Sponsorship: This research was supported by The Department of Veterans Affairs, Rehabilitation Research and Development Project #B603-RA.