The Effect of Muscle Fatigue on the Muscular Response to a Sudden Load of the Spine

Low back injuries are frequent among employees in the health-care sector. The combined effect of sudden unexpected trunk loading (SL) and accumulated fatigue of the erector spinae muscles (ES) has been suggested as a risk factor for low back injuries. SL incidents such as slips and falls are common among employees in the health care sector who handles patients (Radebold et al, 2000). Andersen et al (2001) reported that nursing aides in average were exposed to 2.5 (0-8) sudden trunk movements during a workday. Moreover, nurses working in a geriatric ward developed signs of neuromuscular fatigue (i.e. a significant drop in initial median frequency and slope of the EMG signal) in the ES muscle during an 8 hours workday (Ling Hui et al, 2001). Fatigue in the ES may affect the muscle spindle system and muscle reflex mechanism involved in the maintenance of spinal stability, thus leaving the spine vulnerable to external perturbations. The combination of SL’s and the development of lumbar muscle fatigue during a workday may in this way expose employees in the health care sector to an increased risk of low back injuries.