Jump distance of dance landings influencing internal joint forces: II. Shear forces

Little is known about shear loading patterns during dance movements. The purpose of the study was to investigate the effect of jumping distance (JD) on contributors of ankle and knee shear forces (SF) generated during the landing phase of traveling jumps. Six female dancers performed 10 trials each at 30, 60, and 90% maximum jump distance (JD) and 15 jumps ranging from 35 to 100% JD. A sagittal view of the right leg landing onto a force platform was filmed using a high-speed cine camera. Greater ankle and knee joint reaction shear forces (JRSF) and quadriceps SF (QuadSF) were observed (P < 0.05) at increased JD. Although the triceps surae SF (TriSurSF) also increased at greater JD for all but one participant, the effect on minimizing the increase in the ankle SF was minor. The peak QuadSF magnitude and rate of loading were always greater than the corresponding knee JRSF variables. However, the increased QuadSF that occurred at longer jumps led to increased knee SF for only half of the participants.