Effect of resistance exercise and growth hormone on bone density in older men.

OBJECTIVE

The purpose of this study was to evaluate whether 16 weeks of heavy resistance exercise training combined with daily growth hormone administration (GH) increases bone mineral density in 64-75-year-old men greater than resistance exercise training without GH supplementation.

DESIGN

Eighteen healthy, elderly men (67 +/- 1 year) followed a 16-week progressive resistance training programme (75-90% maximum strength, 5-10 repetitions/set, 4 sets/day, 4 days/week) after double-blind, random assignment to either a GH (12.5 or 18 micrograms/kg/day, equivalent to 25 or 36 mU/kg/day, n = 7) or placebo (n = 11) group.

MEASUREMENTS

Before and at the end of 16 weeks of resistance exercise with or without GH administration, body composition, whole body and regional bone mineral density (BMD) were determined by dual-energy X-ray absorptiometry. Serum osteocalcin and IGF-I were determined by radioimmunoassay before, during and at the end of treatment.

RESULTS

Increments in fat-free mass and training-specific maximum voluntary muscle strength were similar in both groups after training. Serum insulin-like growth factor-I (IGF-I) and osteocalcin levels were increased (P < 0.05) after exercise training plus GH. In comparison to initial measures, bone mineral density (g/cm2) of the proximal femur (Ward's triangle) was increased (P < 0.05) after 16 weeks of exercise training plus placebo treatment. Sixteen weeks of exercise training plus GH treatment did not increase whole body, spine or hip (femoral neck, trochanter, Ward's triangle) bone mineral density more than exercise plus placebo treatment.

CONCLUSIONS

These findings suggest that in these older men with normal bone mineral density, short-term resistance exercise training increased regional bone mineral density, but the addition of daily GH administration did not enhance whole body or regional bone mineral density despite GH-induced increments in serum IGF-I and osteocalcin. This implies that GH administration during a 16-week resistance exercise training programme may increase bone turnover without increasing bone mineral accumulation.