Author(s): TØIEN, T., EIK, M., NIELSEN, J.L., BERG, O.K., BROBAKKEN, M.F., FRANDSEN, U., AAGAARD, P., WANG, E., Institution: MOLDE UNIVERSITY COLLEGE, Country: NORWAY, Abstract-ID: 304

INTRODUCTION:
Ageing is associated with muscle fibre atrophy, particularly of type II fibres, with reductions in the satellite cell and myonuclei pool suggested to be partly responsible. Short-term strength training interventions in older adults have shown promising results, yielding increased type II fibre cross sectional area (CSA) along with increased satellite cell and myonuclei content. However, evidence from strength training of longer duration is scarce. Thus, the aim of the present study was to examine the effects of lifelong strength training (OS) on satellite cells and myonuclei content compared to lifelong endurance training (OE) and recreationally active old (OC) and young (YC) adults.
METHODS:
Immunofluorescent staining was used to visualize satellite cells (Pax7+-fibres) and myonuclei (DAPI) on muscle biopsy samples from vastus lateralis, along with muscle fibre CSA.
RESULTS:
Only OS had similar type II fibre CSA as YC (p>0.05), along with higher myonuclei content in type II fibres than all other groups (p<0.05). Across all groups, myonuclei content was highly correlated with muscle fibre CSA in both fibre types (r=0.807-0.848, p<0.001). No between-group differences were observed in satellite cell content (p>0.05). OE demonstrated higher satellite cell (p<0.01) and myonuclei (p<0.001) density (per fibre area) and myonuclei per perimeter (p<0.001)), however, this was restricted to type I fibres only.
CONCLUSION:
These results from two exceptionally well-trained groups of older adults suggest that only lifelong strength training can maintain type II fibre CSA, likely in part because of elevated myonuclei content. Strength training therefore seems paramount to counteract the age-related atrophy of type II fibres.