This study investigates how helmet inertial properties-mass and centre of mass (COM)-influence neck muscle fatigue to support the biomechanical design of firefighter helmets. Thirty-six firefighters (18 males, 18 females) performed sustained neck flexion and extension tasks under three conditions: no-helmet, US, and European-style (EU) helmets. Neck angles, endurance time, discomfort ratings, and electromyography (EMG) data from eight neck muscles were collected. Fatigue was assessed as an increase in normalised mean absolute value (NMAV) and decrease in median frequency (MF) of EMG signals, segmented into four intervals (0-25%, 26-50%, 51-75%, 76-100%).Piece-wise regression and ANOVA analyses of NMAV and MF slopes for each interval showed that the US helmet led to greater muscle activation, faster fatigue, and reduced endurance. These findings highlight the importance of optimising COM location-not just the weight-when designing a helmet to reduce neck injury risks.
Wei et al. (Tue,) studied this question.