Purpose: This study compared acute exercise responses during arm cranking, functional electrical stimulation (FES)-assisted leg cycling, and combined arm and leg ("hybrid") cycling in individuals with spinal cord injury during maximal and submaximal exercise.
Methods: Nine male subjects with long-standing neurological lesions from C7 to T12 were recruited. All subjects performed arm crank ergometry (ACE), FES leg cycle exercise (FES-LCE), combined ACE + FES-LCE, and cycling on a hybrid FES tricycle (HYBRID). They were assessed for their peak exercise responses in all four modalities. Subsequently, their submaximal heart rates (HR), cardiac outputs (Q), stroke volumes (SV), and arteriovenous oxygen extractions (Ca-Cv)O2 were measured at 40%, 60%, and 80% of mode-specific V˙O2peak.
Results: Arm exercise alone and arm + leg exercise resulted in significantly higher V˙O2peak and HRpeak compared with FES-LCE (P < 0.05). Submaximal V˙O2 during FES-LCE was significantly lower than all other modalities across the range of exercise intensities (P < 0.05). ACE elicited 70%-94% higher steady-state V˙O2, and HYBRID evoked 99%-148% higher V˙O2 compared with FES-LCE. Steady-state FES-LCE also produced significantly lower Q, HR, and (Ca-Cv)O2. ACE evoked 31%-36% higher Q and 19%-47% greater HR than did FES-LCE. HYBRID elicited 31%-49% greater Q and 23%-56% higher HR than FES-LCE.
Conclusions: Combined arm and leg exercise can develop a higher oxygen uptake and greater cardiovascular demand compared with ACE or FES-LCE alone. These findings suggested that combined arm + leg FES training at submaximal exercise intensities may lead to greater gains of aerobic fitness than would arm exercise alone. These data also proffered that FES leg cycling exercise by itself may be insufficient to promote aerobic fitness in the spinal cord injury population.