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Abstract
To study the effects of resistance exercise on strength, muscle size and hormonal levels in older adults ($>$60 years old), four studies were designed. The first addressed the growth hormone response to resistance exercise in young and old. There were no significant differences in basal GH levels between groups (1.76 versus 2.61$\mu$g/L respectively). Serum GH concentrations rose significantly in the young, and decreased toward baseline values during recovery. GH concentrations in elderly subjects did not rise above 6$\mu$g/L.
The second project investigated changes in muscle strength and structure after 12 weeks of resistance training in older women. Exercisers trained for 12 weeks. Significant increases in muscle strength were observed in the exercisers (28-115%) in all muscle groups. Cross-sectional area of type II muscle fibers increased in the exercisers (20.1 $\pm$ 6.8%, p $<$ 0.02), whereas no change in strength and size was observed in the controls.
The third and fourth studies assessed the effects of prolonged resistance training on hormonal and muscle adaptations in older adults (68.2 $\pm$ 1 yrs). Serial muscle biopsies were taken. The subjects underwent provocative GH testing after 15, 30 and 52 weeks. The exercisers trained for 1 year. With exercise, muscle strength increased rapidly over 3 months, and then plateaued. Increases in strength ranged from 30% (hip extensors) to 97% (hip flexors). The controls were retested every 15 weeks. Cross-sectional area of type I muscle fibers increased in exercisers by 15 weeks (29.4 $\pm$ 1%, p $<$.02) and after 30 weeks (58.5 $\pm$ 13.7%, p $<$.002). Type II fiber area increased by 30 weeks (66.6 $\pm$ 9.5%, p $<$.0002). Exercise training did not change basal or acute GH response to exercise. We conclude that healthy older adults may successfully participate in moderately intense resistance training. Such training leads to increases in strength and hypertrophy.
