Risk factors for lower back injury in male dancers performing ballet lifts.

Lower back injuries are common in ballet dancers. Allegedly there is a higher incidence in males than in females due to their lifting requirements. This study analyzes the estimated forces generated at the L5/S1 joint in five professional and three pre-professional male dancers performing full press (FP) and arabesque (AR) ballet lifts. The estimated peak lumbar anterior shear force (PLASF) was identified using a 3D motion analysis system, and was found to occur at the beginning of each lift, approximately 0.01 seconds prior to the ballerina moving vertically into the lift. Data representing the male dancers' posture at the point of PLASF were input into a 3D Static Strength Prediction Program (3DSSPP, University of Michigan, Centre for Ergonomics, 2006) to calculate the PLASF and corresponding compression forces. The compression forces identified in this way were found to be greater than the National Institute of Occupational Safety and Health, Back Compression Design Limit (3400N). This suggests that administrative controls such as monitoring the number of lifts performed daily are required to reduce the risk of lower back injury in male dancers. Comparison of the two lifts found significantly (p < 0.05) higher compression forces in the FP versus the AR lift. This could be attributed to a significantly (p < 0.05) larger horizontal distance between the male dancer and the ballerina, or the eccentric loading of the male dancers' lower limb and trunk musculature in the preparation phase of the FP. Retrospective regression analysis indicated that peak trunk extension velocity and the horizontal distance between the male dancer and the ballerina were significant (p < 0.05) predictors of PLASF.