Cross-Education Of Contralateral Antagonists

It has been reported that strength training of unilateral limb causes an increase in voluntary strength not only in the trained limb, but also in the contralateral untrained limb. This phenomenon is known as "cross-education, cross-training or contralateral strength training effect" . Cross-education of muscle strength can occur in both upper and lower limb muscles.It is not gender and age specific and can occur with training accomplished by voluntary effort, electrical stimulation of muscles or mental practice of unilateral contractions. Electrostimulation is one of the most efficient methods to induce cross-education.

Although it is clear that unilateral training has a contralateral effect, the mechanisms behind this effect remain unclear. Because of the specific nature of cross education, modification in neural function is the more likely mechanism underlying this effect. The potential neural mechanisms can be broadly categorized as either ''central" or ''peripheral (spinal)" adaptations. Central neural mechanisms involved in the excitation of the relevant part of the cortex during voluntary contraction of the trained limb are thought to produce contralateral facilitation. The cross-extension reflex is the primary spinal neural mechanism for cross-education.

In the studies performed up today, the contralateral effects of unilateral training were evaluated in the contralateral homologous muscles. However it's not reported whether a change in the muscle strength have been observed in the antagonists of the contralateral homologous muscles. In a study, after one session of unilateral surface electrical stimulation of the rectus femoris, an increase in the isometric force and EMG activity of the contralateral rectus femoris, but a decrease in the EMG activity of the contralateral biceps femoris was reported in adult men. It's proposed that, the EMG activity decrease in the biceps femoris may be explained by cross-extension reflex. The effect of long-time exercise or electrical muscle stimulation on the antagonists of the contralateral homologous muscles is not clear.

The aim of this study is to evaluate whether the electrical muscle stimulation on the dominant wrist flexors for 6 weeks cause an increase in the muscle strength of the contralateral wrist extensors in healthy adult men.

Inclusion criteria

• young-adult healthy volunteer
• male
• right hand dominant

Exclusion criteria

• a chronic disease such as metabolic/endocrine bone disease (osteoporosis, osteomalacia, paget's disease etc)
• myopathy
• tendinopathy
• neurologic disorders (hypoesthesia/anesthesia, epilepsy, paralysis)
• dermatologic disease
• peripheral vascular disease
• joint disease
• cardiac pacemaker
• noncooperative
• professional sportsman
• regular sportive activity such as tennis, volleyball
• heavy worker