Transcriptomic time course of skeletal muscle disuse and rehabilitation in middle-aged adults.

Disuse drives rapid muscle atrophy and metabolic dysfunction. This study aimed to characterize phenotypic and transcriptomic skeletal muscle changes in middle-aged individuals during disuse and rehabilitation. Eleven healthy middle-aged adults (6 males, 5 females; age; 57 ± 5 years) underwent 7 days of unilateral lower limb suspension (ULLS). Following disuse, participants participated in a rehabilitation program consisting of either a lower-body resistance exercise (RE) or walking control (WC) three times weekly for 2 weeks. Bilateral skeletal muscle biopsies were collected at Day 0 and Day 7 of disuse and 2 h post-exercise on Days 7, 9, 11, and 21. Strength testing was conducted, and RNA sequencing was performed on muscle samples. Seven days of disuse reduced knee extension strength (14%; p < 0.05) and isometric force (13%; p < 0.05). Over-representation analysis revealed a downregulation of mRNAs related to cellular respiration and NADH dehydrogenase complex assembly. Resistance exercise induced robust, but different, transcriptional changes in both disuse- and control-legs. Walking had minimal effect on the muscle transcriptome. We conclude that 7 days of disuse reduced leg strength, decreased mitochondrial gene expression, and increased inflammation and apoptosis-related genes. We also conclude that resistance exercise enhanced recovery from disuse by improving strength, associated with significant transcriptomic changes.