Meeting Abstract
Human lumbar lordosis (LL) is an adaptation for bipedalism that helps position the center of mass of the upper body over the lower limb, reducing the mechanical and metabolic costs associated with upright posture. However, fossil evidence indicates there has been considerable LL variability among hominin groups, perhaps suggesting that postural variations serve other functions. This study investigates the effects of LL on impact-related shock attenuation (SA) in the human lumbar spine during walking and running. During bipedal locomotion, each step generates a shock wave that propagates up through body toward the head, and repeated shocks can lead to pathology without active or passive mechanisms for attenuation. To test the hypothesis that LL increases SA, 27 participants (14 male, 13 female) walked and ran on a treadmill with two lightweight, tri-axial accelerometers affixed to the skin overlying T12/L1 and L5/S1. Sagittal plane accelerations were analyzed across frequencies using power spectral density analysis, and SA was measured in the impact frequency range. 3-D kinematics quantified natural standing and dynamic LL, and the effects of intervertebral discs on SA were tested using MRI scans. Results showed no correlation between LL and SA during walking, but LL correlated with SA during running (p<0.01, R2=0.30). Multiple regression models showed that higher amplitudes of dynamic LL displacement and slower rates of displacement during running were associated with higher levels of SA (p=0.008, multiple R2=0.41). Thicker discs were also associated with higher SA (p=0.02, R2=0.22), but LL was a stronger predictor of SA than disc thickness when controlling for both variables (p=0.001, multiple R2=0.44). Results support the hypothesis that a more curved lordosis reduces impact-related shock accelerations transmitted through the human lumbar spine during dynamic activities such as running.
