Neck and Shoulder Fatigue
Neck and shoulder muscle fatigue can seriously impact work efficiency and quality of life. The definition of muscle fatigue in many studies focuses on fatigue-induced action potential changes or changes in power. Bigland-Ritchie et al. (1986) suggested that reduced maximal capacity of the central nervous system or muscle fatigue from exercise may cause muscles to fail to generate normal force, leaving them unable to maintain the required or desired power output (Gandevia, 2001; Huang et al., 2009). Other scholars have interpreted fatigue from a dynamic perspective as the reduction of maximal power output or maximal capacity to generate force, or failure to maintain a required force or output of power during sustained or repeated muscle contraction (Vøllestad, 1997; Vøllestad et al., 1988).
Fatigue is any reduction in the maximal capacity to generate force or power output; it may be caused by obstructed transmission of motor signals and may result in reduced motor performance and power output. Failure in motor signals in different areas induces different types of fatigue. Failure in neuromuscular transmission between the cerebral cortex and the spinal cord is referred to as central fatigue, while failure in neuromuscular transmission between the spinal cord and muscle fibers is referred to as peripheral fatigue (Edwards, 1981; Benwell et al., 2006).
Neck muscles are divided into anterior/posterior and deep/superficial muscles. Muscles contract and relax in a coordinated manner and play an important role in maintaining cervical spine stability and exercise. Neck muscles are relatively small compared to other muscle groups and, during wakefulness, tend to stay in a contracted state to maintain body position and posture, and this long-term contraction can easily induce muscle fatigue (Edmondston et al., 2011). In addition, smaller muscles are more prone to fatigue for sustain contraction (Harrison et al., 2009).