Insulin-like Growth Factor I In Skeletal Muscle After Weight-Lifting

Aug 31, 2021

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Maria A. Fiatarone Singh, Wenjing Ding, Thomas J. Manfredi, Guido S. Solares, Evelyn F. O'Neill, Karen M. Clements, Nancy D. Ryan, Joseph J. Kehayias, Roger A. Fielding, and William J. Evans


To assess muscle remodeling and functional adaptation to exercise and diet interventions, 26 men and women (aged 72-98) underwent a quadriceps (vastus lateralis) biopsy before and after a 10-week study. These subjects were part of a study of 100 men and women (age 72-98) who participated in one of four treatment groups including; a placebo control condition, progressive resistance training, multi-nutrient supplementation, or both resistance training and supplementation.


Analysis of biopsies showed Type II atrophy, Z band, and myofibril damage were present at baseline. Combined resistance training and nutritional supplementation increased strength by 257+ 62% (P = 0.0001) and type II fiber area by 10.1+ 9.0% (P = 0.033), with a similar trend for type I fiber area (+12.8 + 22.2%). Resistance training alone was associated with a 2.5-fold increase in neonatal myosin staining (P = 0.0009) and an increase of 491 + 137% (P<0.0001) in IGF-I staining. Ultrastructural damage (a step in the remodeling process) increased by 141 + 59% after exercise training (P = 0.034). Strength increases were largest in those with the greatest increases in myosin, IGF-I, ultrastructural damage, and caloric intake during the trial.


This study provides the first evidence of skeletal muscle remodeling in response to resistance training in frail individuals of extreme old age. Age-related sarcopenia appears largely confined to type II muscle fibers suggesting that interventions aimed specifically at stimulating type II fibers (e.g., contractions demanding high force output, i.e. power) may be most effective in the prevention and treatment of sarcopenia. Muscle hypertrophy was linked to higher caloric intake suggesting that adequate energy balance is a critical component of treating sarcopenia with exercise in frail elders.

Keiser Equipment Used

Leg press and leg extension 

Published in the American Journal of Physiology-Endocrinology and Metabolism, 1999; vol. 277, issue 1, E135-E143

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