Physical activity is known to enhance the mechanical competence of bones. However, previous related studies provide little information regarding the optimum exercises for the prevention of osteoporosis in the lumbar region, including the hip joints. Physical activities can be evaluated by simultaneously collecting acceleration data from accelerometers worn on different parts of the body. We attached three triaxial accelerometers to the ankle, knee, and lumbar points of 20 young women subjects in order to perform acceleration measurements while walking (a flat surface and a stairway) and jumping rope. The acceleration at the lumbar point while walking a flat surface, ascending stairs, and descending stairs were 1.96 ± 0.28, 1.92 ± 0.29, and 2.88 ± 0.66G, respectively. On the other hand, jumping rope provided an acceleration of 5.4G at the lumbar point. This value is higher than the threshold acceleration necessary to induce an osteogenic response in the lumbar region of young subjects, namely 3.5G. Descending stairs provided the second-highest intensity of acceleration in the lumbar region; however, it also produced excess impact acceleration at the ankle and knee points. Jumping rope, in contrast, provided sufficient intensity of acceleration in the lumbar region, but the acceleration imparted to the ankle and knee points remained at a tolerable level. Moreover, correlation analyses of the acceleration at the ankle, knee, and lumbar points during each physical activity showed that the knee joints solely regulated the strong landing impact force while the subjects were descending the flight of stairs. In comparison, while jumping rope, the ankle and hip joints regulated the large landing impact force cooperatively, without overloading themselves. Our results suggest that jumping rope can provide sufficient acceleration to induce an osteogenic response in the lumbar region without causing an overload to any joints. Thus, jumping rope is one of the most optimum exercises for bone mineral gain in the proximal femur and lumbar vertebrae regions in young subjects.
2010 by Japanese Society for Biological Sciences in Space