|Abstract||INTRODUCTION: Whole-body vibration during helicopter flight can result in adverse health effects, such as neck
strain, which can impact performance and safety. The current ISO-2631 whole-body vibration standard does not
account for vibration effects on the head and neck. Furthermore, it is unclear as to the extent to which vibration
mitigating countermeasures, such as seat cushions, affect vibration transmission to the pilot and reduce head
movement and neck strain. This study examined the impact of vibration level and a mitigating cushion on pilot
neck strain and head movement.
METHODS: Using a human rated shaker facility, the physiological responses of 12 pilots were examined during
15-minute exposures to three levels of vibration (Low=0.23, Normal=0.30, High=0.36 grms) which are representative
of forward flight in NRC’s Bell 412 and CF Griffon helicopters. Responses were also compared using either a
standard original equipment manufacturer (OEM) or vibration mitigating (MIT) cushion at each vibration level.
Electromyography (EMG), as an indicator of neck strain, and seat and head acceleration were recorded continuously.
RESULTS: Normalized EMG amplitude was significantly higher during High (OEM= 0.201±1.023, MIT= -
0.008±0.983) compared to Low (OEM = -0.197±0.859, MIT= -0.193±0.991) vibration for both cushions, and
amplitude was also higher during Normal (OEM= 0.245±0.914, MIT= -0.048±0.947) compared to Low vibration
for the OEM cushion. During Normal and High, the EMG amplitudes were significantly lower, and median frequency
significantly higher, with the MIT compared to OEM cushion. Head acceleration was significantly lower with the
MIT (1.187±0.261 m∙s⁻ ²) compared to the OEM (1.108±0.234 m∙s⁻ ²) cushion.
DISCUSSION: The EMG changes occurring with increased vibration may be indicative of higher neck strain, highlighting
the deficiency in ISO-2631 which suggested that the tested vibration levels and durations were within accepted
exposure limits. The vibration mitigating cushion was effective in reducing such effects, as well as reducing