To investigate the effect of teeth clenching on isokinetic knee extension at various velocities, isokinetic muscle strength during knee extension was measured in association with teeth clenching at 30, 60, 150, 300 and 450 degrees per second (deg/s) using the Cybex 6000 isokinetic dynamometer. The volunteer subjects were 9 healthy males (26.2±0.97 years) . The peak torque per body weight and average power per body weight were statistically analyzed. Our results demonstrated that the peak torque per body weight with teeth clenching at 30, 60 and 150 deg/s significantly increased by 7.0%, 7.4% and 4.9%, respectively (p<0.05), but no significant differences were found at 300 and 450 deg/s. While the average power per body weight with teeth clenching at 30, 60 and 150 deg/s significantly increased by 6.5%, 6.1% and 6.9%, respectively (p<0.05), no sig-nificant differences were found at 300 and 450 deg/s. A significant negative correlation was shown between the isokinetic angular velocity and the difference in peak torque per body weight derived from with and without teeth clenching (r=-0.699; p<0.05) . These findings suggested that the effect of teeth clenching on isokinetic muscle strength of knee extension was dependent on the angular velocity, and at lower angular velocities teeth clenching had the effect of increasing the isokinetic muscle strength during knee extension.

The purpose of this study was to investigate the effect of teeth clenching on isokinetic knee extension force during repeated voluntary contractions. We assessed isokinetic muscle strength in association with teeth clenching during 100 consecutive knee extensions at 60 degrees per second (deg/s) using a Cybex 6000 isokinetic dynamometer. In this study, 8 healthy male volunteers (28.4 ± 3.89 years) were asked to perform isokinetic contractions in an extended cycle of five contractions without teeth clenching followed by five contractions with the teeth clenching. The peak torque per body weight was statistically analyzed. In our results, the peak torque per body weight with teeth clenching were significantly greater than those without teeth clenching in the first 70 cycles; however, no significant differences were shown at 71-100 cycles. There was a significant negative correlation between the number of knee extensions and the difference in peak torque per body weight derived from with and without teeth clenching (r=-0.475, p<0.0001) . Our findings reveal that the effect of teeth clenching on the isokinetic muscle strength of knee extension is dependent on muscular fatigue, and that the improving effect of teeth clenching on isokinetic muscle strength declines with increasing muscular fatigue.

Previous research has demonstrated that the concentric muscle strength of knee extension exerted at slow to medium angular velocities is increased by teeth clenching. This study evaluated the isokinetic eccentric strength of knee extensors at 4 angular velocities (60, 120, 180 and 240 degrees per second) with and without teeth clenching on the Cybex 6000 Extremity Testing and Rehabilitation System. Twelve healthy adult male (26.8±1.8 years) volunteered for the study. Peak torque per body weight and average power per body weight were analyzed. The results demonstrated that peak torque per body weight accompanied by teeth clenching was significantly increased at 60, 120, 180 and 240 deg/s by 9.5%, 8.2%, 8.2% and 9.8%, respectively (p<0.01) . Similarly average power per body weight during teeth clenching was significantly higher at 60, 120, 180 and 240 deg/s by 9.1%, 9.5%, 9.4% and 7.7%, respectively (p<0.05) . These findings suggest that teeth clenching is a factor that leads to augmented eccentric strength of knee extensors. Its effect appears to be independent of angular velocity.

One is inclined to imagine that the incidence of respiratory diseases will be negligible among rural people who live and work in fresh and clean air. On the contrary, however, we have reports on the high incidence of chronic obstructive pulmonary diseases and on the existence of a variety of specific respiratory diseases which are incidental to farm work. To clarify this situation, the Japanese Association of Rural Medicine organized a special study group and carried out various studies with grants from the Ministry of Health and Welfare. This is the study group's summary report of the four year research project prepared in conclusion of the project.
The actual state of respiratory diseases among rural people, as investigated by the present study group, can be summarized as follows:
1) In rural districts, in spite of its freedom air-pollution, there exist in high percentages people suffering from respiratory symptoms and patients of obstructive pulmonary diseases. As the important cause of this phenomenon, farm operations, especially thrashing, rice-hulling, compost preparation, scattering of agricultural chemicals can bementioned, which invite the development of symptoms and their aggravation.
2) Pathologically, farmer's pneumoconiosis attributable to farm operation dust was evidenced, crying for the necessity of dust prevention measure during farm operations.
3) In connection with atopic asthma the study group proved the antigenicity of rice-straw, wheat-straw, celiae of tea-sprout, young leaves, and chrysanthemum leaves. There are also anumber of already known antigens. It is necessary to establish measures for its prevention and treatment.
4) In rural districts of Japan, esp. in stock-raising farm houses, there are in comparatively high percentages those who react positive to fungous antigens which are the causes of farmer's lung. However, there have hitherto been reported only two cases, and the study group added one more. In the future, more extensive practice of immunological tests and clinical follow-ups of the positive cases will be necessary.
5) In view of the results reported above, it is considered that there are numerous questions concerning respiratory troubles and diseases in rural districts which are awaiting further study.