Aerobic exercise training improves whole muscle and single myofiber size and function in older women.
Level 4 - case-series / case-control
Uncontrolled before-and-after interventional study in a single small cohort.
PubMed 19692660 · doi:10.1152/ajpregu.00354.2009
What was done
Seven older women (mean age 71 ± 2 years) completed 12 weeks of cycle ergometer aerobic exercise training. Before and after the intervention, researchers measured aerobic capacity, quadriceps muscle volume via MRI, and knee extensor power. Vastus lateralis muscle biopsies were analyzed for single slow (MHC I) and fast (MHC IIa) myofiber size, contractile properties (peak force, contraction velocity, peak power), myosin light chain (MLC) composition, and myofibrillar protein concentration.
What was found
Aerobic capacity increased by 30 ± 6% (P < 0.05). Quadriceps volume increased by 12 ± 2% (P < 0.05) and knee extensor power increased by 55 ± 7% (P < 0.05). At the cellular level, MHC I fiber size increased by 16 ± 5% (P < 0.05) and MHC I peak power rose by 21 ± 8% (P < 0.05) driven by increased contraction velocity, whereas MHC IIa size and power did not change. Peak force was unchanged, but normalized force (force per cross-sectional area) decreased by 10% (P < 0.05) in both fiber types alongside a significant reduction in myofibrillar protein concentration. Proportion of MLC(1s) in MHC I fibers decreased from 0.62 ± 0.01 to 0.58 ± 0.01 (P < 0.05), with no changes in MLC(2s) or MLC(3f).
Why it matters
Shows that aerobic cycling exercise can induce whole-muscle hypertrophy and improve single slow-twitch myofiber contractile velocity and power in older women, supporting its role in counteracting age-related muscle loss.
Limits
The sample size is very small (n = 7) and lacks a non-exercising control group. The study evaluated only healthy older women on a cycle ergometer, limiting generalizability to men, frail populations, or other exercise modalities. Normalized single-fiber force paradoxically declined, likely due to reduced myofibrillar protein concentration.
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.