Effects of volitional spine stabilization and lower extremity fatigue on landing performance in a recurrent low back pain population
Lower extremity injury during dynamic physical activity is a significant problem in society. Fatigue is as a major risk for injury. A volitional preemptive abdominal contraction (VPAC) is commonly used to improve lumbar spine stabilization in individuals who have spine dysfunction, but little is known about the ability of VPAC to reduce the effects of fatigue. The purpose of this study was to determine whether VPAC can modulate the effects of lower extremity fatigue on lower extremity and trunk mechanics and neuromuscular control during landing in people with and without recurrent low back pain (LBP). Two studies were conducted. The first study used correlation to explore the interrelationships among kinematic, kinetic and electromyographic (EMG) variables in order to determine a parsimonious subset of dependent variables that explain the greatest amount of unique variance, and regression to predict kinetic variable values from representative kinematic variables during 0.30 m drop vertical jump (DVJ) landing in healthy subjects. The second study used a 2x2x2 design to examine differences in selected kinematic, kinetic and EMG variables between healthy and LBP subjects with and without VPAC and lower extremity fatigue during 0.30 m DVJ landing. Seven of 49 variables were found to explain unique variance using correlation: maximum knee angle in the sagittal plane, maximum pelvic angle in the frontal plane, pelvic angle in the sagittal plane at initial contact, lower lumbar angle in the sagittal plane angle at initial contact, maximum knee flexion moment in the sagittal plane, maximum vertical GRF, and semitendinosus onset. Stepwise regression predicted maximum vertical GRF (R2=0.42; p=0.001) and maximum knee moment in the sagittal plane (R2=0.50; p=0.001). VPAC and fatigue altered landing mechanics in the healthy and LBP subject groups and there were differences between groups. Semitendinosus onset exhibited a significant (p=0.001) three-way interaction effect between groups, and the VPAC and fatigue conditions. Maximum pelvic obliquity angle exhibited a significant (p=0.045) two-way interaction effect between VPAC and fatigue conditions. Our results provide evidence that a VPAC strategy that is performed during a fatigued landing decreases exposure to biomechanical factors that may contribute to lower extremity injury. Incorporating VPAC during stressful activities with fatigue appears to improve sensorimotor control and landing mechanics.