Effect of exercise-induced muscle fatigue on reaction times under postural perturbation conditions in individuals with and without chronic low back pain.

BACKGROUND: Total reaction time (TRT), composed of premotor time (PMT) and electromechanical delay (EMD), is susceptible to muscle fatigue and can be affected by pain. Limited evidence is available regarding the postural control capacity of patients with chronic low back pain(cLBP) following muscle fatigue-induced postural perturbation. This study aimed to examine the impact of pain and muscle fatigue on reaction time, so as to gain insights into the neuromuscular control strategy changes associated with muscle fatigue effect of cLBP. METHODS: Twenty-four subjects with cLBP (cLBP group) and twenty-two healthy individuals (HC group) were tested by Biering-Sorensen Test to generate exhaustive muscle fatigue. TRT, PMT and EMD were recorded by surface electromyography during the arm raising task with visual cues prior to and following muscle fatigue. The mean difference (MD) of reaction time was calculated before and after muscle fatigue, denoted as MDTRT, MDPMT, and MDEMD, respectively. Besides, the fear avoidance beliefs questionnaire (FABQ) and visual analogue scale (VAS) was evaluated before muscle fatigue in cLBP group. RESULTS: The TRT and PMT were significantly prolonged after muscle fatigue in the cLBP group compared with before muscle fatigue (Z = -3.371, P < 0.001; Z = -3.286, P < 0.001, respectively). Meanwhile, the cLBP group had significantly shorter TRT and PMT before muscle fatigue than HC group (Z = -3.299, P < 0.001; Z = -3.256, P < 0.001, respectively). Additionally, the correlation analysis manifested that MDPMT and MDTRT were positively correlated with FABQ (r = 0.422, P = 0.040; r = 0.418, P = 0.042) and VAS (r = 0.546, P = 0.006; r = 0.564, P = 0.004) separately. CONCLUSIONS: The reaction time would be altered by chronic pain in neuromuscular control processes, and muscle fatigue could further induce it delay. Besides, this reaction time delay was positively correlated with pain level and fear-avoidance beliefs. These findings highlight the importance of the muscle fatigue effects with cLBP, such as avoiding exhaustive muscle fatigue and paying more attention to fear-beliefs and pain during rehabilitation. TRIAL REGISTRATION: This trial is registered at [chictr.org.cn], number [ChiCTR2300074348]. Registered August 4, 2023.