Twitch interpolation in the assessment of the maximum force-generating capacity of the jaw-closing muscles in man.

The method of twitch interpolation was employed to study the maximum potential bite forces of humans. Transcutaneous electrical stimuli were applied to parts of one or both masseter muscles in eight volunteers while they bit with a variable but controlled isometric force on a unidirectional force transducer held between the anterior teeth. In all participants the twitch force produced by a single 1-ms pulse, of 25 50 mA intensity, was inversely and linearly related to the voluntary bite force. For each participant the slope of the regression between twitch force and bite force depended on the stimulus intensity and not on whether the stimulus was applied to one or both masseters. Extrapolation of the regression lines to zero twitch force showed that they converged towards a bite-force value that, for any given participant varied only a small amount between different stimulus intensities. For most participants this bite force lay above the maximum that they produced voluntarily: voluntary maximum bites ranged from 153 to 593 N, while the extrapolations predicted a narrower and higher potential range of 282-629 N. It was concluded that, for the masseters at least, there is often spare force-generating capacity which individuals are either unable or not prepared to utilize. This method is non-invasive and may help to define better the maximum bite-force potential of humans.