Author(s): BETZ, M., KAISER, J., MONSEGUE, A., HENDRIKS, F., VERDIJK, L., VAN LOON, L., SNIJDERS, T., Institution: MAASTRICHT UNIVERSITY, Country: NETHERLANDS, Abstract-ID: 1309

INTRODUCTION:
Skeletal muscle satellite cells are essential in muscle fiber regeneration, repair, and growth. Aging is accompanied by specific loss of type II muscle fiber size and associated satellite cell content and function. Muscle fiber capillarization has been suggested to play a key role in satellite cell function. We assessed whether 8 weeks of aerobic exercise training, to increase muscle fiber capillarization, improves the acute type II muscle fiber satellite cell response to a single bout of resistance exercise in healthy older adults.
METHODS:
In a randomized parallel design, n=26 healthy older (70±5 y) adults participated in 8 weeks of aerobic exercise training (AER, n=14), 3 times per week for 45 min at 65% VO2peak or no-exercise control (CON, n=12). Aerobic capacity (VO2peak tests on cycling ergometer) and body composition (DXA-scan) were assessed at baseline and following 8 weeks of AER or CON intervention. Resting vastus lateralis muscle biopsies were collected at baseline and following the 8-week AER or CON intervention. To assess the acute satellite cell response, two additional biopsies were obtained at 24 and 48 h following a single bout of resistance exercise after the 8-week AER or CON intervention. Immunohistochemistry was used to assess type I and type II muscle fiber size, capillarization, and satellite cell content. Data were analyzed by two-way repeated-measures ANOVA. Post-hoc testing was performed in case of a significant time x treatment interaction effect. Statistical significance was set at P<0.05. All data are expressed as mean±SD.
RESULTS:
Aerobic exercise training increased VO2peak (9±6%, P<0.05), with no changes in leg lean mass. VO2peak and leg lean mass remained unchanged in response to the 8-week CON condition. Whereas type I muscle fiber size remained unchanged, a main effect of time (P<0.05) was observed for type II muscle fiber size, which was mainly driven by hypertrophy observed in the AER group (24±48%, P<0.05). Type I (33±25%, P<0.05) and type II (37±40%, P<0.05) muscle fiber capillarization increased in the AER group, with no changes in the CON group. Aerobic exercise training increased type I (97±65%, P<0.05), but not type II muscle fiber satellite cell content. Type I and II muscle fiber satellite cell content remained unchanged in the CON group. The acute type I and II muscle fiber satellite cell response was not different between the AER and CON group (interaction effects, P>0.1) at 24 and 48 h following the single bout of resistance exercise.
CONCLUSION:
Aerobic exercise training increases type I and II muscle fiber capillarization and satellite cell content in type I muscle fibers in healthy older adults. The type II muscle fiber satellite cell response to an acute bout of exercise is not modified by prolonged aerobic exercise training. An increase in muscle fiber capillarization does not improve post-exercise muscle satellite cell function in healthy older adults.