Time-frequency analysis of chewing activity in the natural environment.

The aim of this observational study was to investigate the features of the chewing activity and the variability of the human chewing pace, as assessed in the natural environment. It was hypothesized that the chewing pace is relatively constant within individuals across different days but is variable across individuals. Electromyographic surface activity was recorded unilaterally from the masseter in 21 participants for 3 hours over 3 recording days, in the natural environment, by means of portable recorders. The time-frequency properties of chewing activity were assessed with a previously validated algorithm. Repeated-measurements ANOVA was used for statistical analysis. Chewing activity mainly occurred in the range of 0.94 Hz (5(th) percentile) and 2.17 Hz (95(th) percentile). Mean and median chewing frequencies were 1.57 Hz and 1.58 Hz, respectively (95\% confidence intervals: 1.45-1.68 Hz). The mean duration of chewing episodes was 13.0 sec, the 5(th) and 95(th) percentiles being 2.7 sec and 34.9 sec, respectively. Variability of the mean chewing frequency between individuals was much greater than that within individuals (F = 29.8; p < 0.001). The individual chewing paces were stable across different days (intraclass correlation coefficient = 0.88; 95\% confidence intervals = 0.79-0.94). Our findings provide evidence that each individual, in the natural environment, chews with a consistent pace across different days. Abbreviations: ANOVA, analysis of variance; CPG, central pattern generator; EMG, electromyography; ICC, Intra-class Correlation coefficient; SD, standard deviation.