We will explored the effect of cross education training on different cortex functional connectivity, cortex and muscle functional connectivity, and maximal voluntary contraction.

Healthy participants receive cross education training of the elbow flexor (12 rep./set, 3sets, 60%MVC, 180°/s, eccentric).Maximal voluntary contraction, electroencephalogram and electromyogram will record during cross education tasks to determine the effects of cross education training on cortical network and muscle functional connectivity

Cross education (CE) training was observed in 1894, when unilateral strength training of single limb was found to increase in strength of untrained muscle group. CE has potential clinical relevance in rehabilitation for patient who have acute injuries of the limb, post-surgical limb immobilization and certain neurological disorders with unilateral muscle weakness. Although CE has several potential clinical application, the precise physiological mechanisms underlying CE remains unknown. Previous studies reported that CE may involve bilateral cortical activity in both contralateral primary motor cortex (cM1), and ipsilateral primary motor cortex (iM1).In addition, neuroimaging studies have demonstrated that bilateral supplementary motor area, but CE immediate change of functional connectivity in cortical network remains unknown.

The purposes of this study are to investigate the immediate effect of CE training of biceps brachii (1) Immediate change of functional connectivity in cortical network; (2) Immediate change of functional connectivity in cortex and target muscle; (3) Explore immediate change of corticomuscular functional connectivity on maximal voluntary contraction. We hypothesize that (1) Bilateral cortical motor network that exhibit changes in functional connectivity during cross education; (2) Cross education would immediately enhance functional connectivity between cortex and target muscle; (3) Cross education would immediately change corticomuscular functional connectivity on maximal isometric voluntary contraction.

Inclusion Criteria:

1. Healthy adults who are 20-40 years old

Exclusion Criteria:

1. Upper extremity (UE) pain or discomfort
2. Medical condition that substantially influenced their UE strength
3. Experience of UE surgery
4. Paresthesia in UE
5. Open wound on UE