Aerobic exercise training induces skeletal muscle hypertrophy and age-dependent adaptations in myofiber function in young and older men.
Level 3 - non-randomized controlled study
Non-randomized pre-post comparative cohort intervention without an untrained control group
PubMed 22984247 · doi:10.1152/japplphysiol.00786.2012
What was done
Seven young men (20 ± 1 years) and six older men (74 ± 3 years) completed 12 weeks of cycle ergometer aerobic training. Vastus lateralis muscle biopsies were taken pre- and post-training to evaluate single-fiber contractile physiology (MHC I and MHC IIa), fiber cross-sectional area (CSA), myosin heavy chain (MHC) composition, and total and myofibrillar protein concentrations. Quadriceps muscle volume was assessed by MRI and aerobic capacity was measured.
What was found
Aerobic capacity increased by 16 ± 2% in young men and 13 ± 3% in older men (P < 0.05). Quadriceps volume increased by 5 ± 1% in young men and 6 ± 1% in older men (P < 0.05), accompanied by an increase in MHC I myofiber CSA regardless of age. MHC I peak power rose in both groups (P < 0.05), whereas MHC IIa peak power increased only in older men (P < 0.05). In older men, peak and normalized force (peak force/CSA) were preserved for MHC I and IIa fibers; in young men, MHC I normalized force and MHC IIa peak force decreased (P < 0.05). Total and myofibrillar muscle protein concentrations were unchanged (P > 0.05). The proportion of MHC IIx isoform decreased in both cohorts (P < 0.05).
Why it matters
This study demonstrates that cycle exercise can induce modest skeletal muscle hypertrophy and myofiber functional adaptations in healthy older adults comparable to young adults, countering the assumption that aerobic exercise cannot stimulate muscle growth.
Limits
The sample size was very small (n=13 total: 7 young, 6 older) and limited to healthy men, preventing generalization to women or frail populations. There was no non-exercising control group to account for time-dependent variation, and long-term functional or clinical outcomes were not evaluated.
Cited by
- supports In deconditioned elderly individuals, aerobic-style interval training on a stationary bike can stimulate muscle protein synthesis and increase muscle fiber size.
- contradicts Aerobic exercise has minimal effects on strength, muscle hypertrophy, and bone development compared to resistance training.