Purpose <p>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.</p> Method <p>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.</p> Results <p>After fatigue, individuals with CLBP exhibited greater variability in sway velocity in the mediolateral direction on the foam surface with eyes closed (<i>p</i> = 0.035) and a larger sway area in the eyes closed condition (<i>p</i> = 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) (<i>p</i> &lt; 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 (<i>p</i> &gt; 0.05).</p> Conclusions <p>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.</p>