Quadriceps muscle deoxygenation during functional electrical stimulation in adults with spinal cord injury

Study design: Cross-sectional study comparing healthy subjects with age and gender matched subjects with spinal cord injury (SCI, injury levels from C 5 to T12). Objectives: To compare the acute cardiorespiratory responses and muscle oxy genation trends during functional electrical stimulation (FES) cycle exerci se and recovery in the SCI and healthy subjects exercising on a mechanical cycle ergometer. Setting: Seven volunteers in each group participated in one exercise test a t the Rick Hansen Center, University of Alberta, Edmonton, Canada. Methods: Both groups completed a stagewise incremental test to voluntary fa tigue followed by 2 min each of active and passive recovery. Cardiorespirat ory responses were continuously monitored using an automated metabolic cart and a wireless heart rate monitor. Tissue absorbency, an index of muscle o xygenation, was monitored non-invasively from the vastus lateralis using ne ar infrared spectroscopy. Results: The healthy subjects showed significant (P<0.05) increases in the oxygen uptake ((V)over dot O-2), heart rate (HR) and ventilation rate (VE) from rest to maximal exercise. The SCI subjects showed a twofold increase i n (V) over dot O-2 (P>0.05), a threefold increase in (V) overdot (E) (P<0.0 5) and a 5 beats/min increase in HR (P>0.05) from the resting value. The SC T subjects demonstrated a lesser degree (P<0.05) of muscle deoxygenation th an the healthy subjects during the transition from rest to exercise. Regres sion analysis indicated that the rate of decline in muscle deoxygenation wi th respect to the (V) over dot O-2 was significantly (P<0.05) faster in the SCI subjects compared to healthy subjects. Conclusions: FES exercise in SCI subjects elicits: (a) modest increases in the cardiorespiratory responses when compared to resting levels; (b) lower degree of muscle deoxygenation during maximal exercise, and (c) faster chan ges in muscle deoxygenation with respect to the (V) over dot O-2 during exe rcise when compared to healthy subjects.