Peak ACL force during jump landing in downhill skiing is less sensitive to landing height than landing position

Background Competitive skiers face a high risk of sustaining an ACL injury during jump landing in downhill skiing. There is a lack of knowledge on how landing height affects this risk. Objectives To evaluate the effect of varied landing height on peak ACL force during jump landing and to compare the effect of the landing height with the effect of the landing position varied by the trunk lean of the skier. Methods A 25-degree-of-freedom sagittal plane musculoskeletal model of an alpine skier, accompanied by a dynamic optimisation framework, was used to simulate jump landing manoeuvres in downhill skiing. First, a reference simulation was computed tracking experimental data of competitive downhill skier performing a jump landing manoeuvre. Second, sensitivity studies were performed computing 441 landing manoeuvres with perturbed landing height and trunk lean of the skier, and the corresponding effects on peak ACL force were determined. Results The sensitivity studies revealed that peak ACL force increased with jump height and backward lean of the skier as expected. However, peak ACL was about eight times more sensitive to the trunk lean of the skier compared with landing height. The decreased sensitivity of the landing height was based on the lower effects on the knee muscle forces and the shear component of the knee joint reaction force. Conclusion Preventive measures are suggested to focus primarily on avoiding trunk backward lean of the skier, and consequently on proper jump preparation and technique, and secondarily on strategies to reduce landing height during jumps.