Effect of Hip Bone Mineral Density / Content on Vibration-Induced Hip Adductors Muscle Electrical Activity in Postmenopausal Women

It is usually reported that there is a parallelism between changes in the bone structure and function and the muscle structure and function. Sarcopenia is frequently observed in osteoporotic patients. Bone formation increases or bone resorption decreases with exercise.

One of the most important functions of bone bear mechanical loads include body weight. Bone must be strong enough to resist the mechanical loading. Mechanisms need to protect bone when bone is subject to excessive mechanical loading. These mechanisms may mainly focus on strengthening the bone and/or changing vectorial properties of mechanical loading applied bone.

The vectorial properties of mechanical loading applied bone may be controlled by muscle contractions. Bone contains wide mechanoreceptor net constructed by osteocytes. So,distribution of the mechanical loading on bone cross-sectional area is possible to perceive. It may be also possible that inappropriate distribution of mechanical loading on bone crosssectional area is optimized by muscle contractions. To get this regulation, there should be a mechanism that muscle activity is controlled by central nervous system based on mechanical loading distribution on bone cross-sectional area. The investigators previously showed that bone can regulate muscle activity, based on its bone mineral density. According to this study result, it can be suggested there may exist a mechanism that bone sensing mechanical stimuli can send the signals to central nervous system and neuronally regulate muscle activity (bone myo-regulation reflex). (It is also well known that load-induced adaptive bone formation is neuronally regulated. Taken together, a general mechanism, bone reflex, may be defined that bone subjected to loading can neuronally regulate bone formation and muscle activity) Vibration has a strong osteogenic effect. Vibration-induced bone formation is neuronally regulated. Vibration can also effectively enhance muscle strength and power. Previous studies have shown that vibration increases muscle electromyographic (EMG) activity. It has been showed that bone has an effect on the increase in muscle EMG activity caused by vibration in healthy young adults in a study. In this study, it was reported that vibrations-induced increases in muscle electrical activity of flexor carpi radialis (FCR) was related to ultradistal radius bone mineral content (BMC) and the FCR H-reflex was suppressed or depressed during vibration. This findings were reported to support the assumption that the bone exposed to cyclic mechanical loading may neuronally regulate muscle activity.

The aim of this study is to investigate effects of femur exposed to vibration on the rest muscle electrical activity of hip adductors in cases with postmenopausal osteoporosis.