To assess muscle oxygenation during exercise and associations with aerobic capacity and body composition in spinal muscular atrophy (SMA) patients.

Nine ambulatory SMA participants, 6 healthy and 3 disease controls with mitochondrial myopathy were evaluated. Change in deoxygenated hemoglobin from rest to peak exertion, using near-infrared spectroscopy measured on the vastus lateralis, was used to determine muscle oxygenation (ΔMOx). Peak aerobic capacity (VO_2peak) and workload (W_peak) were measured using a cardiopulmonary exercise test performed on a recumbent ergometer. LBM was estimated with Dual Energy X-ray Absorptiometry.

Control groups were combined for analyses due to the small disease control sample. Independent samples t-tests were used to determine group differences. Bivariate relationships among ΔMOx, VO2_peak, W_peak and LBM were examined using Pearson correlation coefficients.

Mean ΔMOx was lower in SMA (-1.1 ± 3.6) than in controls (9.1 ± 6.7) (p = 0.002). VO_2peak was associated with LBM in controls (r = 0.82; p = 0.007) and in SMA (r = 0.65; p = 0.06).  ΔMOx was associated with VO_2peak (r = 0.92; p < 0.001), LBM (r = 0.84; p = 0.005), and W_peak (r = 0.88; p = 0.002) in controls but not in SMA.

Individuals with SMA demonstrate diminished muscle oxygenation during exercise. SMA patients appear to rely on anaerobic pathways resulting in fatigue and exercise intolerance. Targeted treatments may be needed to address apparent mitochondrial disturbance in SMA.