Myonuclear content and domain size in small versus larger muscle fibres in response to 12 weeks of resistance exercise training in older adults

Abstract

Aim: To assess the relation between muscle fibre hypertrophy and myonuclear accretion in relatively small and large muscle fibre size clusters following prolonged resistance exercise training in older adults. Methods: Muscle biopsies were collected before and after 12 weeks of resistance exercise training in 40 healthy, older men (70 ± 3 years). All muscle fibres were ordered by size and categorized in four muscle fibre size clusters: ‘Small’: 2000-3999 µm2, ‘Moderate’: 4000-5999 µm2, ‘Large’: 6000-7999 µm2 and ‘Largest’: 8000-9999 µm2. Changes in muscle fibre size cluster distribution were related to changes in muscle fibre size, myonuclear content and myonuclear domain size. Results: With training, the percentage of muscle fibres decreased in the Small (from 23 ± 12 to 17 ± 14%, P