Analysis of Compression Force in the Hip Joint during Impulsive Exercises: A Preliminary Study for Developing Exercise Protocol for Osteoporosis.

Past intervention studies on bone remodeling for preventing osteoporosis in elderly women often lack sufficient description of the intensity of the exercise, though bone remodeling is dependent on applied force at specific sites. The effectiveness of exercise in increasing bone density cannot be defined without sufficient description of the intensity and targeted site of the exercise. We conducted kinetic and kinematic analyses of the lower extremities in order to categorize exercise in terms of compression force applied at the proximal end of the femur, to formulate guidelines for prescribing exercise to elderly women. Thirty healthy women aged 18-24 participated in the study. Joint compression force at the proximal end of the femur was measured with the aid of motion analysis devices under several conditions of impulsive loading. Joint compression force at the proximal end of the femur was estimated for twenty-two exercise regimes varying from low to high-impact exercises, including jumping off, stepping down, vertical jumping, and dropping down after heel raises. Some exercises appear to be inappropriate for exercise intervention, because the variability for these exercises is high. Most of the jumping exercises, with coefficients exceeding 0.36, were excluded from further analysis. Of the remaining exercises, four were categorized as statistically different loads, as determined by a posthoc test of one-way analysis of variance of joint compression force. These included jumping off a 10 cm platform, stepping down from a 20 cm platform with the knees in the extended position, stepping down from a 20 cm platform with the knees in a relaxed position, and heel dropping at 80 cycles per minute with the knees in a relaxed position. The joint compression forces during these exercises were 2.32 ± .81, 1.81 ± .59, 1.45 ± .59, and 1.00 ± .27 times as much as the subject's body weight, respectively.