Fig. 2: Skeletal muscle alterations are associated with exercise capacity in patients with long COVID.
From: Muscle abnormalities worsen after post-exertional malaise in long COVID
A and B examples of skeletal muscle capillaries; no group-differences in capillary density (p = 0.11) or capillary:fiber ratio (p = 0.08) were observed (n = 26 long COVID, n = 21 healthy control). C A significant association was found between capillary-to-fiber ratio and V̇O2max for both groups (n = 23 long COVID, p-value: 0.048, n = 21 healthy control, p-value: 0.007). D Patients with long COVID (n = 25) had a higher percentage (p-value: 0.036) of glycolytic type IIx compared to healthy controls (n = 21). E For a given fiber cross-sectional area (FCSA), patients with long COVID (n = 25) had a significantly lower peak power output (p-value: 0.045) as compared to healthy individuals (n = 21). F Succinate dehydrogenase (SDH) activity in sections (see also Fig. 3) was associated with maximal oxygen uptake consumption (V̇O2max) in healthy controls (n = 21, p-value: 0.0014), but not in long COVID patients (n = 23, p-value: 0.66), with significant different correlation coefficients. Continuous parametric data were analyzed using a two-sided t-test (B, D). Correlations were calculated using two-sided Pearson (C, E, F). The difference in intercept was calculated with a linear regression using a two-sided ANOVA (E). Correlation coefficients were compared using the R package cocor. *p < 0.05; **p < 0.001. Bar: 100 μm. Box plots show the median (centerline), the first and third quartiles (the lower and upper bound of the box), and the whiskers show the 1.5× interquartile range. Source data are provided in the Source Data File.
