The effect of acute back muscle fatigue on postural control strategy in people with and without recurrent low back pain

Abstract

Back muscle fatigue decreases the postural stability during quiet standing, but it is not known whether this fatigue-induced postural instability is due to an altered proprioceptive postural control strategy. Therefore, the aim of the study was to evaluate if acute back muscle fatigue may be a mechanism to induce or sustain a suboptimal proprioceptive postural control strategy in people with and without recurrent low back pain (LBP). Postural sway was evaluated on a force platform in 16 healthy subjects and 16 individuals with recurrent LBP during a control (Condition 1) and a back muscle fatigue condition (Condition 2). Back muscle fatigue was induced by performing a modified Biering-Sørensen test. Ankle and back muscle vibration, a potent stimulus for muscle spindles, was used to differentiate proprioceptive postural control strategies during standing on a stable and unstable support surface, where the latter was achieved by placing a foam pad under the feet. Ankle signals were predominantly used for postural control in all subjects although, in each condition, their influence was greater in people with LBP compared to healthy subjects (p < 0.001). The latter group adapted their postural control strategy when standing on an unstable surface so that input from back muscles increased (p < 0.001). However, such adaptation was not observed when the back muscles were fatigued. Furthermore, people with LBP continued to rely strongly on ankle proprioception regardless of the testing conditions. In conclusion, these findings suggest that impaired back muscle function, as a result of acute muscle fatigue or pain, may lead to an inability to adapt postural control strategies to the prevailing conditions.

Figures

Fig. 1

Experimental setup. Lumbar multifidus vibration during upright standing on an unstable support surface (“foam”)

Fig. 2

The back endurance test

Fig. 3

Means and standard deviations of the anterior–posterior sways for the muscle vibration trials in Condition 1. Note that the negative center of pressure displacements indicate posterior sway and positive displacements indicate anterior sway. TS vibr, triceps surae muscles vibration; TS vibr F, triceps surae muscles vibration while standing on a “foam” support; MF vibr, lumbar multifidus muscles vibration; MF vibr F, lumbar multifidus muscles vibration while standing on a “foam” support; LBP, low back pain; ** p < 0.01; *** p < 0.001

Fig. 4

Means and standard deviations of the changes with time in mean power frequency of the lumbar multifidus muscle in healthy subjects and people with LBP during the back muscle endurance test

Fig. 5

Means and standard deviations of the anterior–posterior sways for the muscle vibration trials in Condition 2. TS vibr, triceps surae muscles vibration; TS vibr F, triceps surae muscles vibration while standing on a “foam” support; MF vibr, lumbar multifidus muscles vibration; MF vibr F, lumbar multifidus muscles vibration while standing on a “foam” support; LBP, low back pain; ** p < 0.01