Comparing fatigue responses between healthy individuals and asymptomatic low back pain sufferers - implications for return-to-work : a pilot study

Although most LBP episodes are acute, research suggests that up to two-thirds of people suffer pain relapses within a year. As muscle fatigue is considered a risk factor for the development of work-related musculoskeletal disorder, it was hypothesised that workers, who have seemingly recovered, i.e. are asymptomatic, display premature fatigue responses and may therefore be at elevated risk of re-injury. 30 volunteers were recruited: 10 without LBP history, 10 participants who experienced their last bout of symptoms between 9 and 12 months ago, and 10 participants who had been injured within the last 3 months. All groups were matched for basic demographic variables and individuals with LBP history were pain-free. Participants performed a self-paced repetitive lifting and lowering task until they reached a rating of perceived exertion (RPE) for the back of 17. Isometric back strength and joint position sense (deviation from 45o trunk flexion) were measured pre and post protocol. Task duration, back RPE, and sEMG of selected trunk and leg muscles were recorded throughout the protocol. Statistical significance was identified at p<0.05 using a one-way ANOVA with Tukey Post-hoc analyses. Although the groups with a LBP history displayed greater decrements in relative back strength, time to exertion and perceptions of effort, compared to the uninjured group, spectral analyses indicated that fewer LBP participants exhibited fatigue of the assessed muscles, and no differences were found for joint position sense compared to the uninjured participants. These results imply that previously injured participants displayed exaggerated subjective responses to the lifting task, which can be attributed to “fear avoidance behaviour”.Keywords: Fatigue, injury history, low back pain, re-injury, return-to-work