Age related differences in mechanical demands imposed on the lower back by manual material handling tasks.

The prevalence of low back pain (LBP) increases with age, yet the underlying mechanism(s) responsible for this remains unclear. To explore the role of biomechanical factors, we investigated age-related differences in lower-back biomechanics during sagittally-symmetric simulated manual material handling tasks. For each task, trunk kinematics and mechanical demand on the lower back were examined, from among 60 participants within five equal-sized and gender-balanced age groups spanning from 20 to 70 years old. The tasks involved lowering a 4.5kg load from an upright standing posture to both knee height and a fixed height and then lifting the load back to the initial upright posture. During these tasks, segmental body kinematics and ground reaction forces were collected using wireless inertial measurement units and a force platform. Overall, older participants completed the tasks with larger pelvic rotation and smaller lumbar flexion. Such adopted trunk kinematics resulted in larger peak shearing demand at the lower back in older vs. younger participants. These results suggest that older individuals may be at a higher risk for developing lower back pain when completing similar manual material handling tasks, consistent with epidemiological evidence for higher risks of occupational low back pain among this cohort.