Effect of Radius Subjecting to Mechanical Loading on Alpha Motor Neuron Excitability

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.

To date, the effect of bone on the muscle activity is not investigated. 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. We 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)

This study hypothesize that radius subjecting to mechanical loading may affect excitability of alpha motor neuron innervating muscle, based on its bone mineral density.