The impact of fatigue on neuromuscular activity during a lifting task
University of New Brunswick
Lifting tasks in the workplace have been associated with a variety of musculoskeletal disorders including disorders of the shoulder and back. The exact mechanisms leading to injury are still not completely understood. Fatigue is a concern while lifting as it may result in a less efficient lifting technique, thereby, increasing the risk of injury (Gandevia, 2001). The purpose of this study was to investigate the fatigue related neuromuscular changes that occur while lifting. 32 participants (16 male and 16 female) between the ages of 20 and 40 performed three different symmetrical lifting protocols consisting of a sagittal lift from floor to shoulder height at a rate of six lifts per minute with a box weighing 10 percent of the participants’ predetermined lifting capacity. The general fatigue protocol consisted of 75 minutes of continuous lifting. The shoulder and back fatigue protocols consisted of a five minute period of baseline lifting followed by a shoulder specific or back specific fatiguing task and then an additional five minutes of post-fatigue lifting. Electromyographic (EMG) activity was recorded at eight locations including the anterior and posterior deltoid, biceps, triceps, upper trapezius, latissimus dorsi as well as the thoracic and lumbar erector spinae musculature. Results indicated that participants were fatigued in all three protocols. Participants had significant increases in perceived exertion for all three protocols (P < 0.05). The general protocol was perceived to be significantly more difficult than the shoulder protocol and the shoulder protocol was perceived to be significantly more difficult than the back protocol. Maximal voluntary isometric exertion (MVIE) forces decreased significantly for all three protocols. Males decreased significantly more than females in the total force drop for the shoulder MVIEs, however, there was no difference between genders when the decreases were examined as a percentage decrease relative to their initial maximal capacity. The relative time to peak values decreased significantly in five of the eight muscle locations monitored in the general fatigue protocol. Few other clear patterns of change in EMG activity were noted. The lack of consistent changes in EMG may be indicative of the redundancy in the variety of ways the participants were able to accommodate to accomplish the lifting task while fatigued.