Changes in jaw muscles activity with age: effects on food bolus properties.

Bolus formation depends on chewing process that evolves with age. This study aims to analyze the effect of age on chewing behavior (recorded by EMG) and the consequences on bolus formation for meat products. Twenty-five young adults (age range: 25-30) and 20 healthy elderly (age range: 68-73) having at least six pairs of natural postcanine teeth participated. From two different textures of bovine meat, boli were characterized by shear force measurements. Saliva incorporated into the bolus was quantified. Chewing duration was significantly longer in the elderly group for both textures, but muscle activity was significantly lower for the toughest texture only. Moreover, muscle activity was less accurately adapted to food texture in elderly than in young. In order to control that changes in EMG reflect changes in bite force, EMG was recorded during static bite forces. Slopes were fairly similar for both groups suggesting that EMG/bite force relationships do not vary with age. Elderly subjects could partly compensate for a weaker chewing efficiency by increasing the number of chewing cycles before swallowing. It is hypothesized that lengthening of chewing duration results from a decrease in muscle activity during healthy aging. After chewing, the mechanical resistance of the bolus was always higher for the elderly than for the young subjects. No significant age effect was found on the amount of saliva incorporated in the bolus. Elderly subjects, despite the lengthening of the chewing sequence, were less efficient to comminute a meat bolus than young subjects and swallowed less comminuted boli.