Basal muscle amino acid kinetics and protein synthesis in healthy young and older men.
Level 4 - case-series / case-control
Cross-sectional physiological comparison of two age cohorts
PubMed 11559266 · doi:10.1001/jama.286.10.1206
What was done
A cross-sectional study evaluated whether basal muscle protein turnover differs between young and older healthy men. Participants included 26 young men (mean age 28 years) and 22 older men (mean age 70 years) who were healthy, independent, and free of chronic organ disease or steroid use. Basal muscle protein and amino acid kinetics were quantified using stable isotope infusions, femoral arteriovenous catheterization, and muscle biopsies, analyzed across three kinetic models: arteriovenous balance, a three-pool model, and fractional synthesis rate.
What was found
Older men had lower mean total leg volume than younger men (9.60 vs 10.83 L). Net muscle protein balance was similar between older and younger men (-19 vs -21 nmol/min per 100 mL leg volume; P = .51). Fractional synthesis rate did not differ significantly between older and younger men (0.0601 vs 0.0578 %/h; P = .73). Absolute muscle protein synthesis was higher in older men by arteriovenous balance (48 vs 32 nmol/min per 100 mL; P = .004) and three-pool model (58 vs 43 nmol/min per 100 mL; P = .04). Protein breakdown was higher in older men by arteriovenous balance (66 vs 53 nmol/min per 100 mL; P = .045) but not significantly different by three-pool model (76 vs 64 nmol/min per 100 mL; P = .14).
Why it matters
This study demonstrates that age-related sarcopenia is not explained by basal deficits in muscle protein synthesis or balance, pointing attention toward postprandial responses or physical inactivity rather than fasting turnover.
Limits
The sample was relatively small (48 men total) and included only healthy, functionally independent men, limiting generalizability to women, frail populations, or individuals with chronic illness. The cross-sectional design only evaluated fasting basal state kinetics and did not measure fed-state or exercise-stimulated responses.
Cited by
- supports Human muscle protein turnover (breakdown and synthesis) occurs at a rate of 1 to 2% per day, independent of age.