Pilot study of the effect of low-cadence functional electrical stimulation cycling after spinal cord injury on thigh girth and strength.

OBJECTIVE: To investigate the long-term effects of functional electrical stimulation (FES)-evoked cycle training cadence on leg muscle hypertrophy and electrically evoked strength. DESIGN: Open intervention study. SETTING: Laboratory setting. PARTICIPANTS: Untrained individuals with chronic spinal cord injury (N=8). INTERVENTIONS: Six weeks (3d/wk) of training on an isokinetic FES cycle ergometer. For each subject, 1 leg was randomly allocated to cycling at 10 revolutions per minute (rpm) (LOW) for 30min/d, and the other cycling at 50rpm (HIGH) for 30min/d. MAIN OUTCOME MEASURES: Pre- and posttraining measurements of lower limb circumference were performed at the distal and middle position of each thigh. Electrically evoked quadriceps muscle torque during an isometric contraction was also assessed. RESULTS: Six weeks of FES cycle training significantly increased thigh girth in both LOW and HIGH groups. At midthigh, girth increases induced by LOW (6.6%±1.2%) were significantly greater than those by HIGH (3.6%±0.8%). LOW also produced greater gains in electrically evoked isometric torque than HIGH after training. CONCLUSIONS: These results suggest that lower pedaling cadences evoke greater muscle hypertrophy and electrically stimulated muscle strength compared with higher cadences.

Impact of sleep disordered breathing severity on hemodynamics, autonomic balance and cardiopulmonary functional status in chronic heart failure.

BACKGROUND: Despite advances in medical therapy, sleep disordered breathing (SDB) remains highly prevalent in chronic heart failure (CHF). The impact of severity of SDB on sympathovagal balance, central hemodynamic responses and cardiopulmonary functional status in these patients is uncertain. METHODS: Thirteen patients with stable CHF (mean age+/-10 years; 12 NYHA Class II, 1 Class III) identified with SDB (apnoea-hypopnoea index [AHI] >or=5) by polysomnography underwent echocardiography, standard hemodynamic and functional assessment, heart rate variability analysis and treadmill cardiopulmonary testing. RESULTS: Mean AHI of study cohort was 32+/-19, with predominant hypopnoea. Anthropomorphic measurements of obesity correlated positively with increasing AHI severity (p<0.05). NYHA functional class, 6-minute walk distance, measures of left ventricular systolic and diastolic function, serum brain natriuretic peptide levels, cardiac output and VO(2)peak at baseline did not differ with SDB severity. Although SDB severity did not impact on VE/VCO(2)-slope, patients in the highest AHI tertile (AHI>35) demonstrated significantly greater respiratory effort (VE), despite similar VO(2)peak during exercise. Increasing SDB severity was associated with higher resting and post-exercise heart rates, reduced heart rate variability, and possibly slower post-exercise heart rate recovery, consistent with autonomic imbalance. CONCLUSIONS: SDB severity was most closely associated with the degree of autonomic dysfunction, and abnormal ventilatory response during and post-exercise in a group of stable ambulant patients with similar severity of CHF on contemporary therapy.

Muscle oxygenation during prolonged electrical stimulation-evoked cycling in paraplegics.

This study investigated cardiorespiratory responses and muscle oxygenation during prolonged electrical stimulation (ES)-evoked leg cycling in individuals with paraplegia (PARA). Four PARA and 6 able-bodied (AB) persons participated in this study. Subjects performed 10 min of passive cycling and 40 min of active cycling (PARA, ES cycling; AB, voluntary cycling) at workloads selected to elicit an equivalent oxygen uptake between groups. Cycling power output, cardiorespiratory responses, mechanical efficiency, and quadriceps muscle oxygenation (measured with near-infrared spectroscopy) were measured over the duration of the exercise. Oxygen uptake was similar in both groups during active cycling (PARA, 737+/-177 mL.min(-1); AB, 840+/-90 mL.min(-1)). The cycling power output for PARA individuals commenced at 8.8 W, but varied considerably over 40 min. PARA individuals demonstrated markedly lower gross mechanical efficiency (approximately 1.3%) during ES cycling compared with AB individuals performing voluntary exercise (approximately 12.6%). During ES cycling, muscle oxygen saturation (SO2) decreased to approximately 72+/-19%, whereas SO2 during volitional cycling was unaltered from resting levels. Muscle oxygenated haemoglobin initially decreased (-23%) during ES cycling, but returned to resting levels after 10 min. Deoxygenated haemoglobin initially rose during the first 5 min of ES cycling, and remained elevated by 28% thereafter. Upon cessation of ES cycling, lower-limb muscle oxygenation increased (+93%), suggesting reactive hyperaemia in PARA individuals after such exercise. During ES cycling, muscle oxygenation followed a different pattern to that observed in AB individuals performing voluntary cycling at an equivalent VO2. Equilibrium between oxygen demand and oxygen delivery was reached during prolonged ES cycling, despite the lack of neural adjustments of leg vasculature in the paralyzed lower limbs.