Lumbar back muscle activity of helicopter pilots and whole-body vibration

Several studies have attributed the prevalence of low back pain (LBP) in he licopter pilots mainly to poor posture in-flight and whole-body vibration. with the latter hypothesis particularly related to a cyclic response of the erector spine (ES) muscle to vibration. This work aims to determine if hel icopter vibration and the pilot's normal posture during flight have signifi cant effects on the electromyogram (EMG) of the ES muscle. The bilateral su rface EMG of the ES muscle at the L3 level was collected in 10 young pilots before and during a short flight in UH-50 helicopters. The vibration was m onitored by a triaxial accelerometer fixed to the pilots' seat. Prior to th e flight, the EMG was recorded for relaxed seated and standing postures wit h 0 degrees (PO) and 35 degrees (P35) of trunk flexion. The effect of the p osture during the flight was tested by comparing left and right EMG (normal ized with respect to P35). The in-flight muscle stress was evaluated by his tograms of EMG activity, and compared to PO values. Only one pilot in ten s howed significant (p <0.05) correlation between the vibration and the EMG o ver cycles of vibration, and no consistent causal effect was found. The pil ots' posture did not show significant asymmetric muscular activity, and low EMG levels were observed during most of the duration of the flight. The re sults do not provide evidence that LBP in helicopter pilots is caused by ES muscle stress in the conditions studied. (C) 2001 Elsevier Science Ltd. Al l rights reserved.