The effects of isometric exercise on maximum voluntary bite forces and jawmuscle strength and endurance

The effects of training and exercise on the strength and endurance of limb muscles has been investigated extensively, but the response of the jaw musc les to exercise remains poorly known. The purpose of this study was to dete rmine whether short-term isometric training increases strength and enduranc e of the superficial masseter and anterior temporalis muscles. Maximum and submaximum voluntary bite forces and corresponding electromyographic (EMG) activity were measured in 28 young adults, randomly divided into exercise a nd nonexercise (control) groups. Subjects in the exercise group performed i sometric clenches against a soft maxillary splint for five 1-min sessions p er day over a 6-week period. After exercise, subjects increased their maxim um bite forces by 37%, but control subjects' bite forces also increased by 25%. After exercise, EMG levels per unit of bite force generally decreased, but similar decreases were also seen in the non-exercised controls. Masset er muscle activity levels during standardized 10-kg bites decreased after 6 weeks of exercise. Fatigue resistance increased significantly with exercis e but did not differ significantly from control values after 6 weeks of exe rcise. The results of this study indicate that increases in maximum bite fo rce can be easily produced with training, but that actual strengthening of the jaw muscles is more difficult to achieve.