Training-induced bioenergetic improvement in human skeletal muscle is associated with non-stoichiometric changes in the mitochondrial proteome without reorganisation of respiratory chain content

Mitochondrial defects are implicated in multiple diseases and aging. Exercise training is an accessible and inexpensive therapeutic intervention that can improve mitochondrial bioenergetics and quality of life. By combining a multi-omics approach with biochemical and in silico normalisation, we removed the bias arising from the training-induced increase in human skeletal muscle mitochondrial content to unearth an intricate and previously undemonstrated network of differentially prioritised mitochondrial adaptations. We show that changes in hundreds of transcripts, proteins, and lipids are not stoichiometrically linked to the overall increase in mitochondrial content. We demonstrate that enhancing electron flow to oxidative phosphorylation (OXPHOS) is more important to improve ATP generation than increasing the abundance of the OXPHOS machinery, and that training-induced supercomplex formation does not confer enhancements in mitochondrial bioenergetics. Our study provides a new analytical approach allowing unbiased and in-depth investigations of training-induced mitochondrial adaptations, challenging our current understanding and calling for careful reinterpretation of previous findings.