Back Muscle Activity During One Hour of Vertical Vibration Simulating a Helicopter Flight.

Purpose: Back pain is detected at high rates in helicopter aircrew members, leading in some cases to flying incapacitations. The cause of this pain remains unclear in this population. The goal of this research is to better understand how muscles respond over time (1 h) in a seat that vertically vibrates simulating a helicopter flight.

Methods: Surface electromyography (EMG) data at six locations (middle trapezius, erector spinae, longissimus, iliocostalis lumborum, and multifidus) was collected in 14 subjects during 1 h of vertical whole-body vibration (0.2 g at 4 Hz). To simulate a helicopter flight, a rigid seat with the dimensions of an H-60 helicopter was used, including pedals and hand controls of a flight simulator, HGU-56/P helmets and a 5-point harness. The EMG readings were collected at 0, 15, 30, 45, and 60 min during the vibrational exposure.

Results: Low muscle activity was seen in all the tracked muscles with insignificant changes over time (middle trapezius and erector spinae increased the EMG amplitude less than 0.5 %MVC, longissimus decreased the median frequency 3.75 Hz). Muscle activity was below 10 %MVC (maximum voluntary contraction) in most of the cases, with average values between 2 and 7 %MVC. The average median frequency ranged from 33 Hz to 53 Hz.

Conclusion: The muscle activity of the back remained unaltered during the vibrational exposure of 1 h. A better understanding of how whole-body vibrations affect back muscles during flights would help in reducing the high prevalence of pain in aircrew members.