Muscle fibre capillarization is a critical factor in muscle fibre hypertrophy during resistance exercise training in older men.
Level 3 - non-randomized controlled study
Prospective cohort study with non-randomized baseline-stratified group comparisons
PubMed 27897408 · doi:10.1002/jcsm.12137
What was done
Twenty-two healthy older men (71 ± 1 years) completed 24 weeks of progressive resistance exercise training. Percutaneous biopsies of the vastus lateralis muscle were obtained before and after 12 and 24 weeks of training. Participants were stratified at baseline into LOW and HIGH groups based on type II muscle fibre capillary-to-fibre perimeter exchange index (CFPE). Immunohistochemistry was used to assess type I and type II muscle fibre size, satellite cell content, capillary content, and satellite cell-to-capillary distance.
What was found
Overall, 24 weeks of training increased type II muscle fibre size (5150 ± 234 to 6719 ± 446 µm², P < 0.05) and satellite cell content (0.058 ± 0.006 to 0.090 ± 0.010 satellite cells per fibre, P < 0.05). These hypertrophic gains were restricted to the HIGH baseline capillarization group (type II fibre size increased from 5170 ± 390 to 7133 ± 314 µm², P < 0.05; satellite cells increased from 0.059 ± 0.009 to 0.102 ± 0.017 per fibre, P < 0.05), with no significant changes observed in the LOW group. Neither group exhibited significant changes in type I or type II muscle fibre capillarization at 12 or 24 weeks.
Why it matters
Baseline muscle fibre capillarization may be a critical prerequisite determining whether older adults experience muscle fibre hypertrophy and satellite cell expansion following resistance training.
Limits
The sample size was small (n = 22) and restricted exclusively to healthy older men. It was a non-randomized, baseline-stratified observational subgroup comparison within a single training cohort, and exact numerical values for the LOW group were not reported in the abstract.
Cited by
- supports Endurance exercise promotes capillarization in skeletal muscle, enhancing blood flow and nutrient delivery, and activates satellite cells to donate nuclei that support hypertrophy from resistance exercise.