P.161 - Local muscle strength, oxygen extraction capacity, and exercise capacity in adults with RYR1-related myopathies: Exploratory study

Abstract

Skeletal muscle weakness and fatigue are primary symptoms in patients with RYR1-related myopathies (RYR1-RM). In this patient population, there is skeletal muscle fatty infiltration and oxidative stress affecting muscle function. Near infrared spectroscopy (NIRS) allows for the measurement of maximal oxygen extraction capacity and local muscle desaturation when used with arterial occlusion (AO) and exercise, respectively. The purpose of this study was to determine the influence of local muscle oxidative metabolism and strength on overall exercise capacity. 14 participants > 18 years of age. Maximal desaturation of vastus lateralis was determined using AO with NIRS. Participants performed cycle ergometry to the limit of their exercise tolerance. Two days later, participants performed sustained isometric knee extension at max effort (peak torque) to the point of fatigue. Tissue oxygenation index was recorded using NIRS during both cycle ergometry and sustained isometric exercise. Participants demonstrated an average of 33.8% (+28.0) relative muscle O2 desaturation. Relative O2 desaturation was related to VO2peak (r = .772, p < .01) and anaerobic threshold (r = .629, p < .05). Peak torque was related to peak power (r = .885, p < .01) and VO2peak (r = .844, p < .01) determined during cycle ergometry. Local muscle oxygen extraction capacity and muscle strength may be determinants of exercise capacity in participants with RYR1-RM.