Forty healthy, sedentary, premenopausal women were entered into a randomized, single-blind, controlled study to determine the effects of capacitively coupled electrical stimulation on the strength of the lumbar paraspinal muscles and the bone mineral in the lumbar spine. All were between 35 and 45 years of age and had normal physiologic estrogen. The study group received electrical stimulation over the lower lumbar paraspinal muscles for 30 minutes twice a day. Isometric strength of the lumbar paraspinal muscles was assessed with a strain-gauge dynamometer at entry and again after 3, 6, 9, and 12 months. Bone mineral was measured in the lumbar spine by dual-energy x-ray absorptiometry at entry and at 6 and 12 months. After 3 months, the median increase in isometric strength was 8.1% in the study group and 1.6% in the control group (P < 0.03). This initial difference was maintained during the remainder of the study. No further changes were seen between the two groups at 6, 9, and 12 months. It was concluded that capacitively coupled electrical muscle stimulation can, throughout a 1-year period, improve and maintain isometric strength of the lumbar paraspinal muscles independent of exercise, but it has no measurable effect on bone mass in the lumbar spine.