276P Exploring muscle endurance in a neuromuscular population: insights from the assisted 6-minute cycling test combined with cardiopulmonary exercise testing and near-infrared spectroscopy

Abstract

Assessing muscle endurance in weak individuals with neuromuscular disease (NMD) is challenging given physiological limitations. By integrating Cardiopulmonary Exercise Testing (CPET) and Near-Infrared Spectroscopy (NIRS) with the Assisted 6-Minute Cycling Test (A6MCT), we can explore the interplay of muscle oxygenation dynamics and metabolic demands during exercise. We collected data from 56 individuals with SMA (n=41,73.2%) and DMD (n=15,22.8%). Patients were 15-74 years (avg=30.5±13.2) and ranged in function (non-sitters=35.7%; sitters=44.6%; walkers=19.6%). Fatigability (%fatigue) during a maximal effort A6MCT was assessed by calculating the percent change in revolutions between first and last minute, while total work was determined by total revolutions. Peak aerobic capacity (peak VO2) was measured using a metabolic cart (K5 COSMED USA), while changes in deoxygenated hemoglobin were measured by NIRS sensors placed on biceps and triceps (ΔHHbb;ΔHHbt). Perceived exertion at the end of the 6-minutes (OMNI score) was collected, as were peak heartrate (peak HR) during exercise and Forced Vital Capacity (FVC%) at rest. Baseline analysis revealed that total revolutions positively correlated with FVC% (r=0.663; p=0.003), peak VO2 (r=0.753; p<.001), and peak HR (r=0.500; p=0.008). Meanwhile, OMNI score is correlated with peak VO2 (r=0.444; p=0.034) and peak HR (r=0.700; p<0.001). When assessing NIRS, mean HHb in biceps during exercise is positively correlated with peak VO2 (r=0.537; p=0.008), while mean HHb recovery in biceps is inversely correlated with %Fatigue (r=-0.475; p=0.011). The observed correlations between ventilation and muscle oxygen uptake in individuals with NMD reveal a distinctive mechanistic relationship that potentially influences endurance and fatigability. Further exploration combining these exercise testing modalities may yield valuable insights for assessing the metabolic demands of muscle performance during aerobic exercise. In addition, these findings may provide future direction for identifying underlying causes in the mismatch between ventilatory and peripheral oxygen uptake that leads to the increased fatigability in the NMD population.