Effects Of Unilateral Forearm Vibration On The Loss Of Muscle And Bone Of Contralateral Forearm

The structure of a bone and the muscles surrounding it changes in a temporally synchronized fashion. Skeletal muscles have positive effects on bone structure and function. It is well-known that exercise training of muscles improves the resistance of bone to mechanical loading and that physical activity is also important for treating and preventing osteoporosis. Resistance and impact training can induce bone formation and/or prevent bone resorption. Immobilization frequently leads disuse osteoporosis in patients with a bone fracture.

Vibration has a strong osteogenic effect. The cyclic mechanical loading to the bone stimulates osteocytes. 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. Based on the bone myoregulation reflex, bone is sensitive to mechanical stimuli and can send mechanical input signals to central nervous system and so can neuronally regulate the muscle activity.

Previous studies have documented the impact of unilateral training of limb muscle on the untrained contralateral homologous muscle.

The aim of the present study is to investigate the effects of vibrating the forearm bone in the free limb on muscle strength and bone mineral density of the forearm in patients with forearm/elbow fracture.

The study will include a total of 80 patients with forearm/elbow fractures. The participants meeting inclusion criteria will be randomized into one of two groups: a training group (40 cases) and a control group (40 cases). Patients in the control group will receive standard care for provided for fractures, including fixation and rest.

Forearm Vibration: Training group will exercise 5 times a week for six week period using a forearm vibration device. The forearm vibration device consists of a joystick unit, a weight-pulley system and a control panel. The subject will be seated in a chair. The right forearm will be placed on the vibration device with the shoulder in 10 degrees abduction, the elbow in 90 degrees flexion and the forearm and wrist in the neutral position. The axis of rotation of joystick unit will be aligned with that of the wrist joint of the free arm. The joystick unit will be capable of performing both an angular and a sliding motion simultaneously. The angular motion obtained the vibration effect and the sliding motion obtained the compression effect. The angular motion of the joystick unit will be provided by an electric motor. The range of angular motion will be 6 degrees. The weight is attached to the joystick with a rope and pulley system to provide mechanical loading to the forearm (compression effect). This weight is defined as vibration load. Maximum vibration load tolerated will be applied during vibration. The amplitude of vibration (range of motion of the wrist) will be 6 degree and the frequency of the vibration will be 40 Hz. The exercise duration and intensity will be low at the beginning but increased systematically over the 6-week training period. The subjects will be asked to report negative side effects or adverse reactions in their training diary.

Bone Densitometry: Before trails and after six weeks, bilateral bone density of distal radius will be measured by DXA. The bilateral bone density will be evaluated by bone densitometer (Norland).

Grip Strength Measurement: Before the start of the study, grip strength of wrist muscles in the free limb will be measured. After six weeks, bilateral grip strength will be measured by a hand dynamometer (Jamar digital plus hand dynamometer).

Surface EMG: Surface EMG of the right and left wrist muscles will be recorded using disposable self-adhesive bipolar Ag/AgCl electrodes (Kendall Arbo ) placed on its belly. The small disc electrodes (10-mm in diameter, inter-electrode distance of 20 mm) arranged in the direction of the muscle fibers. All cables will be carefully taped to the skin.

The skin overlying the muscle will be shaved, light abrasion will be applied, the skin will be cleaned using 70% alcohol and, conductive paste will be used to reduce electrode resistance before placing the electrodes.

Motor unit potentials will be amplified and recorded on a computer for off-line analyses at a sampling frequency of 2k using a data acquisition and analysis system (Powerlab data acquisition system, ADInstruments, Australia).

Twenty seconds of myoelectrical activity will be recorded from wrist muscles at rest. The mean myoelectrical activity will be calculated as the root mean squared (RMS) using the EMG device software, and defined as the "resting myoelectrical activity". The resting myoelectrical activity will be expressed as microvolt.

Power spectral analyses will be done. They will be conducted using Hamming windowed, 2048 point epochs, resulting in a frequency resolution of 0.98 Hz.

This is a prospective, randomized, controlled, single blind trial