# The association of mitochondrial morphology and supercomplex redistribution with skeletal muscle oxidative capacity in older adults

## TL;DR

Higher muscle energy production in older adults is linked to longer mitochondria and better organization of energy-producing complexes, which improves with exercise.

## Contribution

This study shows that mitochondrial elongation and supercomplex redistribution are associated with skeletal muscle oxidative capacity in older adults.

## Key findings

- ATPmax was positively associated with mitochondrial elongation and specific supercomplex assemblies.
- Exercise training increased ATPmax and was accompanied by mitochondrial elongation and redistribution of complex III.
- Mitochondrial elongation was linked to the formation of higher-order supercomplexes.

## Abstract

Skeletal muscle maximal oxidative capacity (ATPmax) is a key component of age‐related sarcopenia and muscle health. The contribution of mitochondrial morphology and electron transport chain supercomplex (SC) assemblies to ATPmax has yet to be determined in human muscle. ATPmax measured in vivo by 31phosphorus magnetic resonance spectroscopy in the quadriceps femoris of nine volunteers (65.5 ± 3.3 years old) was correlated with muscle biopsy outcomes before and after 4 months of supervised exercise. Mitochondrial morphology was assessed in electron micrographs, and SCs were measured by blue native gel electrophoresis. In the sedentary conditions, ATPmax was positively associated with complex (C) I and CIII in SC I+III2+IVn and negatively associated with CI and CIII in SC I+III2. Regarding mitochondrial morphology, ATPmax was positively associated with markers of mitochondrial elongation. Exercise training‐induced increases in ATPmax were accompanied by mitochondrial elongation and by the redistribution of free complex III. Indicators of mitochondrial elongation were associated with the redistribution of specific complexes to SC I+III2+IVn. Higher skeletal muscle oxidative capacity in older adults is associated with mitochondrial elongation and the redistribution of electron transport chain complexes into higher rank SCs in the same muscle. Further, we provide evidence that mitochondrial elongation favors mitochondrial SC assembly.

ATPmax is positively associated with mitochondrial elongation and the redistribution of electron transport chain complexes into higher‐order supercomplex assemblies in the skeletal muscle of elderly volunteers, both before and after a 4‐month supervised exercise intervention.