AbstractsBiology & Animal Science

Work-related musculoskeletal disorders impose a substantial economic burden on society. Low back pain represents one of the most common and costly health issues in the workplace. Previous research suggests that cytokines play a key role in the development of back pain. However, how biomechanical loading acting on various tissues in the low back initiates cytokine response is not clear. The purposes of this study were to assess whether there are acute biochemical responses to physical work that stresses the low back and to identify specific tissue loading that might lead to the biochemical responses through advanced biomechanical modeling techniques. Twelve healthy male subjects completed three sessions of experimental tasks (control, lifting and lowering 5 lbs and 25 lbs for 2 h at a frequency of 12 exertions per minute). Blood was sampled before, immediately after, 2 h, and 24 h after the physical work. Plasma was analyzed for IL-1ß, IL-10, TNF-a, IL-6, IL-8, and PGE2. Blood was also analyzed for WBC counts with differential and creatine kinase (CK) level. Biomechanical data were collected during the tasks and used as inputs into an EMG-assisted lumbar spine model to calculate three-dimensional end plate loading at each lumbar disc level and trunk muscle forces. The plasma concentrations of IL-1ß and TNF-a increased significantly 2 h after the 25 lbs task compared to their baselines (p < 0.05). The plasma IL-6 level elevated from the baseline immediately after the 5 lbs lifting task (p < 0.05), while it also significantly increased immediately after and 2 h after the 25 lbs lifting task (p < 0.0001). The magnitude of changes in IL-6 levels was greater for the 25 lbs task when compared with the 5 lbs task and the control condition. The WBC and granulocyte counts all significantly increased immediately after and 2 h after both the 5 and 25 lbs tasks (p < 0.001), with the latter condition showing the greatest changes. The plasma CK levels continued to increase immediately after the task until 24 h later for both weight lifting conditions (p < 0.05). Correlation analysis demonstrated that the changes of most biochemical variables were moderately correlated with the maximum spinal loads and muscle forces (Pearson’s r = 0.3 ~ 0.7). Multiple regression analysis found that the combinations of biomechanical and individual variables were able to predict 40-50% of the variability in biochemical responses. In conclusion, the current study indicates that there are acute inflammatory responses which involve various cytokines, especially IL-6, after physical work at the occupational level. It may be possible to use inflammatory cytokines as biomarkers to monitor the physiological responses of the human body to biomechanical loading. Identifying the possible sources of cytokine up-regulation using an advanced biomechanical model may help develop more effective interventions to reduce the risk of low back pain in the workplace.