Introduction- Weightlifting probably puts higher loads on the body, for longer periods of time, than any other sport. The arms, the spine and the knees are all highly stressed, and injuries in all three areas are common. In order to estimate the load on the knee, it is necessary to estimate the moment to which the joint is subjected. We describe the use of a television/force platform/computer system to measure the angle of the knee and the moments in the sagittal plane during a series of Olympic 'clean-and jerk' lifts.