BACKGROUND: There is a widespread notion among physical education teachers, physical therapists and orthopedists that, during any type of squatting, the knee should not be brought forward too much in relation to the tip of the foot, so as to reduce the mechanical loading on the knee. However, there is little quantitative evidence to corroborate this notion. OBJECTIVE: To estimate the forces and torque on the knee joint in healthy individuals during free squatting exercises using weights performed in two different ways: a) knee not going beyond a vertical line going through the toes; b) knee going beyond this vertical line. METHOD: Three-dimensional analysis using video cameras and a force platform was performed on squatting movements performed by ten healthy young adults. Fifteen repetitions of each of the two squatting conditions were performed by each subject on the force plate. The forces and joint torque at the ankle, knee and hip were calculated using an inverse dynamic procedure. RESULTS: The results obtained showed that the mean peak torque on the knee was around 38 ± 31% greater, and the mean patellofemoral force was around 28 ± 27% greater, when the knee went beyond the tip of the foot, than when it did not. CONCLUSIONS: These results demonstrate that, when the knee does not go beyond the line of the foot, the patellofemoral compression force is less, which leads to lower mechanical demand on this joint.
knee; injury; inverse dynamics; three-dimensional kinematics
