Insulin-like growth factor I in skeletal muscle after weight-lifting exercise in frail elders

To assess muscle remodeling and functional adaptation to exercise and diet interventions, 26 men and women aged 72-98 yr underwent a vastus lateralis biopsy before and after placebo control condition, and progressive resistan ce training, multinutrient supplementation, or both. Type II atrophy, Z ban d, and myofibril damage were present at baseline. Combined weight lifting a nd nutritional supplementation increased strength by 257 +/- 62% (P = 0.000 1) and type II fiber area by 10.1 +/- 9.0% (P = 0.033), with a similar tren d for type I fiber area (+12.8 +/- 22.2%). Exercise was associated with a 2 .5-fold increase in neonatal myosin staining (P = 0.0009) and an increase o f 491 +/- 137% (P < 0.0001) in IGF-I staining. Ultrastructural damage incre ased by 141 +/- 59% after exercise training (P = 0.034). Strength increases were largest in those with the greatest increases in myosin, IGF-I, damage , and caloric intake during the trial. Age-related sarcopenia appears large ly confined to type II muscle fibers. Frail elders respond robustly to resi stance training with musculoskeletal remodeling, and significant increases in muscle area are possible with resistance training in combination with ad equate energy intakes.