Sagittal and Frontal Plane Knee Angular Jerk Effects During Prolonged Load Carriage

Introduction: Musculoskeletal injuries are a costly military problem that routinely occur during training. Quantifying smoothness of knee motion, or angular knee jerk, may be an effective measure to monitor injury risk during training, but to date, the effects of body borne load and prolonged locomotion on angular knee jerk are unknown. Purpose: This study sought to quantify angular knee jerk for frontal and sagittal plane motion during prolonged load carriage. Methods: Eighteen participants had peak and cost of angular jerk for frontal and sagittal plane knee motion quantified while they walked (1.3 m/s) 60-minutes with three body borne loads (0, 15, and 30 kg). Statistical Analysis: Peak and cost of angular jerk for sagittal and frontal plane knee motion of stance phase (0 % - 100%) were derived from motion capture and IMU data and submitted to a repeated measures linear model to test the main effects and interaction of load (0, 15, and 30 kg) and time (0, 15, 30, 45, and 60 min.). Two one sided t-tests (TOSTs) were used to compare the motion capture- and IMU-derived measures of angular jerk for sagittal and frontal plane knee motion. Results: For the motion capture-derived jerk measures, body borne load increased peak and cost of angular jerk for sagittal (p < 0.001, p < 0.001) and frontal (p < 0.001, p < 0.001) plane knee motion, while time increased jerk cost (p = 0.001) of frontal plane knee motion. While the IMU-derived jerk measures exhibited similar increases in peak and cost of angular jerk for sagittal (p < 0.001, p < 0.001) and frontal (p = 0.027, p < 0.001) plane knee motion with addition of load, and in cost (p = 0.015) of angular jerk for frontal plane knee motion with time, they were not statistically equivalent to motion-capture derived measures (p > 0.05). Conclusion: Prolonged load carriage may lead to jerkier knee motion and increased knee musculoskeletal injury risk. Specifically, the jerkier knee motions exhibited with the addition of body borne load and longer walking time may increase the joint loading that leads to greater knee musculoskeletal injury risk.