The effect of acute plantar flexor muscles fatigue on postural control of upright stance in people with chronic low back pain

Purpose This study aimed to investigate the differences in postural control effects due to plantar flexor fatigue between individuals with chronic low back pain (CLBP) and healthy controls. Method A total of 36 individuals with CLBP and 36 healthy participants took part in the study. Postural stability was evaluated using a force plate before and after a fatigue protocol that involved heel raises. Center-of-pressure (CoP) data were recorded during quiet standing on a rigid surface with eyes open (EO), a rigid surface with eyes closed (EC), and a foam surface with eyes closed (FC). Measurements included mean velocity, the area of the 95% confidence ellipse, and the standard deviation of velocity in both the anteroposterior and mediolateral directions. Results After fatigue, individuals with CLBP exhibited greater variability in sway velocity in the mediolateral direction on the foam surface with eyes closed (p = 0.035) and a larger sway area in the eyes closed condition (p = 0.027) compared to healthy controls. All participants demonstrated increased postural sway after fatigue in the more challenging task (EC) compared to the easier task (EO) (p < 0.01). However, the reduction in postural stability due to plantar flexor fatigue was not influenced by the increased difficulty of the postural task in the foam condition compared to the EO condition (p > 0.05). Conclusions Localized fatigue in the plantar flexor muscles negatively affected postural control in both CLBP and healthy groups, with a more significant impact observed in individuals with CLBP. This effect was particularly pronounced when visual input was removed.