Biomechanical Analysis of Lumbar Spinal Motion and Coordination in Nordic Skiers During Double Poling

A technique with increasing utilization in Nordic ski competition is double poling, in which the skier stands in set tracks and applies force to both poles during forward torso rotation (poling phase) followed by a return to upright posture (recovery phase). While other aspects of this technique (such as limb kinematics and pole force) have been studied, torso movement during double poling is typically modeled as a rigid body rotation. This study tested the hypothesis that double poling involves significant lumbar flexion, by tracking twenty collegiate Nordic ski racers (10 male and 10 female) using wearable sensors while double poling around a loop of track composed of varied terrain. The tracking data indicated complex coordination between pelvic and thoracic rotations, which follow different paths through the poling and recovery phases. These paths varied between individual skiers, between male and female populations, and often between slopes for the same skier. Clustering analysis indicated that skiers adopted one of three movement patterns depending primarily on degree and timing of thorax-dominant motion. Peak lumbar flexion was found to be as high as 65° in some subjects. Lumbopelvic coordination is indicated as an important consideration in whole-body modeling of the double poling technique.