Surface electromyography as a tool to study the head rest comfort in cars

In this study, two methods were presented in order to evaluate objectively the comfort of head rests in cars using surface electromyography (SEMG). First, the Amplitude Probability Density Function (APDF) was computed. Extremely low level intensity activities were measured. No significant differences were observed on SEMG global activity between experiments with and without a head rest. Second, instead of computing one APDF, several APDF were calculated over time. Analyses focused on the rate of evolution of APDF parameters. This was a time varying APDF (TAPDF). This last method allowed a better diagnosis than the first one. For drivers, significant decreases in SEMG activity were observed when using a head rest. For passengers, a contradictory increase in SEMG activity was observed during experiments with a head rest. This observation was explained by the seat back angle chosen by passengers.