Determination of chewing efficiency using muscle work.

OBJECTIVE: A new method was proposed to evaluate 'true' chewing efficiency in which the 'cost' of chewing was accounted for.
DESIGN: Twenty-three subjects were asked to chew an almond for 5 cycles, after which the chewed particles were air-dried and passed through a 1.4-mm aperture sieve. The activity of both superficial masseter muscles was simultaneously recorded with surface EMG. Integrated EMG (IEMG) was used to calculate burst amplitude, burst duration and maximum voluntary contraction (MVC). The percentage weight of particles passing the sieve was used to represent the conventional chewing efficiency (or masticatory performance). Muscle work (integral of IEMG bursts), muscle effort (muscle work normalized to maximum work) and masticatory effectiveness (the ratio between masticatory performance and muscle work) were also calculated.
RESULTS: The results showed that (1) masticatory performance was significantly correlated with muscle work (R=0.45; p<0.005), MVC (R=0.31; p=0.04), but not correlated with muscle effort; (2) masticatory effectiveness was significantly correlated with MVC (R=0.58, p<0.001), but not correlated with masticatory performance.
CONCLUSION: Persons with good masticatory performance were not necessarily effective (or efficient) chewers. They seemed to have larger MVCs and use more muscle work during the chewing task.