To investigate the relationship between teeth clenching in Intercuspal position and isometric shoulder adduction movement in 12 normal subjects, the muscle strength and electromyogram (EMG) of the seven muscles concerned were measured by using Cybex 6000 Extremity Testing and Rehabilitation System and surface EMG analyzing system. Normalized peak torque (n-PT) and normalized average torque (n-AT) were analyzed to find muscle strength. Normalized integrated EMG (n-iEMG) was analyzed to find muscle activity.
The results were as follows :
1. For n-AT, the value in 100 %MVC significantly increased by 5.4% as compared with that in the rest position (RP) .
2. There was a significant positive correlation between biting force of intercuspal position (ICP), 20%MVC, 50%MVC and 100%MVC and muscle strength of n-PT and n-AT.
3. For n-iEMG, the value of latissimus dorsi, teres major, triceps brachii and forearm extensor muscles in 100%MVC significantly increased by 8.4%, 13.0%, 9.3% and 18.9% respectively as compared with that in RP.
4. There was a significant positive correlation between biting force of intercuspal position (ICP), 20%MVC, 50%MVC and 100%MVC and muscle activity of pectralis major, latissimus dorsi, teres major, biceps brachii, triceps brachii, forearm extensor and forearm flexor muscles.