Effect of teeth clenching on force-velocity relationships in isokinetic knee extension

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 significant 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.