Effects of neck extensor muscles fatigue on balance

Objective. Measure the effects of cervical extensor muscle isometric contraction on cervical surface electromyographic spectral shift and balance in healthy subjects. Design. Experimental within-subject design. Background. Postural instability can be induced by mechanically stimulating cervical muscle spindles. Postural changes are also observed in individuals who suffer from chronic neck pain or whiplash injury. Furthermore these subjects appear to experience neck musculature fatigue more quickly, which in turn not only affects the neck function but also seems to affect the balance in a standing posture. Methods. Using a force platform, balance was measured, in 10 blindfolded college students before and after isometric voluntary contraction in neck extension at 5% and 25% maximum voluntary isometric contraction for a period of 5, 10 and 15 min. Paired posturographic data were analysed for differences. Control measurements were performed on the same subjects by measuring balance before and after subjects sitting quietly for 5, 10 and 15 min without performing isometric contraction. Results. The results indicate that a 25% maximal isometric contraction of the neck extensors for 10 and 15 min duration produced significant changes in some posturographic parameters in young healthy males. Furthermore, this contraction also produced a significant cervical muscle electromyography median frequency spectrum shift of the lower frequencies. Conclusions. Balance was affected by 15 min of 25% maximal isometric contraction of the extensor cervical muscles. Posturographic parameters affected are similar to parameters observed in subjects that have suffered a whiplash injury.