Muscle oxygenation during prolonged electrical stimulation-evoked cycling in paraplegics

Abstract

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.

Health and Fitness Benefits of Functional Electrical Stimulation-Evoked Leg Exercise for Spinal Cord–Injured Individuals

“…123,124 Evidence that did not adhere either to randomization or controlling the treatment has explored FES-evoked exercise responses among persons with tetraplegia 38,41,72,125 ; children with SCI 126 ; and an individual's fatigue responses, 23,127 gas exchange kinetics during exercise involving aerobic and anaerobic metabolism, [128][129][130][131][132] and muscle deoxygenation and leg metabolism. 29,76,82,101,133 A consistent finding in this less rigorous research has been the observation that work rate and load of exercise are important determinants of metabolic responses 55,73,110,134 and, in particular, the power output production of the legs. 42,64,65,130 In general, and in agreement with the prior two categories of physiological outcomes, the empirical evidence lends support to positive metabolic responses and increased aerobic fitness for people with SCI who participate in FES-induced exercise training programs.…”

“…The whole-body metabolic responses of SCI individuals during leg exercise are quite different from the able-bodied population due to their considerably smaller leg muscle mass and the inherent differences of FESevoked muscle contractions compared to voluntary muscle activation. 37,101,102 SCI does not affect the ability of the central nervous system to elicit metabolic responses during FES exercise, 69 particularly those dependent upon baroreflex activity during voluntary effort. 103 However, some studies that have investigated submaximal and graded FES exercise have revealed different metabolic responses among SCI subjects.…”

The use of muscle near-infrared spectroscopy in sport, health and medical sciences: recent developments

“…Cardiorespiratory and muscle oxygenation responses to electrical stimulation-evoked leg cycling were measured using NIRS in patients with paraplegia [53]. The study observed that equilibrium between oxygen demand and delivery was reached during prolonged electrical cycling, despite the lack of neural adjustment of leg vasculature in the paralysed lower limbs.…”

Muscle oxygenation during hybrid arm and functional electrical stimulation–evoked leg cycling after spinal cord injury

“…[ 10 ] As such, muscle oxidative metabolism during FES-evoked exercise is physiologically interesting (and infrequently investigated in person with SCI), because the muscle metabolic pattern during FES is dissimilar to voluntary contractions and may vary under different stimulation protocols. [ 11 , 12 ]…”