Local bone mineral response to brief exercise that stresses the skeleton.

OBJECTIVE To compare grip strength and bone mineral content in the forearm in women and to test the effects on bone mineral content of short periods of exercise that stresses the skeleton. DESIGN Assessment of both wrists in 69 volunteers and of the non-fractured wrist in 30 patients followed by an exercise regimen entailing squeezing a tennis ball as hard as possible for 30 seconds each day for six weeks. SETTING Old people's homes and outpatient departments of Hammersmith and Northampton general hospitals. PATIENTS 99 Women, of whom 69 were volunteers and 30 had a fractured forearm. MAIN OUTCOME MEASURE Grip strength and bone mineral content after six weeks and at six months after the exercises had stopped. RESULTS The bone mineral content of the women's forearms was measured with a densitometer and the grip strength with a semi-inflated bag connected to an anaeroid barometer. Measurements before exercise showed that the two variables correlated closely, irrespective of age, and that there were significant differences in both between the dominant and non-dominant arms of the volunteers. After six weeks of exercise there was a mean increase in grip strength of 14.5% (95% confidence interval 9.9 to 19.2%) and in bone mineral content of 3.4% (1.4 to 5.3%) in the stressed forearms of the 77 women who attended for examination. After six months without exercise the improvements in the 33 women who attended for follow up had reversed. Women who had had a fractured forearm (n = 13), however, had continued to gain grip strength and bone mineral content in the arm that had not been injured. CONCLUSIONS Grip strength in the forearm is a good indicator of bone mineral content. Both variables may be increased by brief periods of stressful exercise. If this principle can be applied to the whole skeleton it may provide a means of reversing osteoporosis.