The start times for the hip extension, knee extension, and ankle plantarflexion torques are as follows:
- Hip extension torque starts at time stamp 0:06.439
- Knee extension torque starts at time stamp 0:07.907
- Ankle plantarflexion torque starts at time stamp 0:08.775
I selected the frame at time stamp 0:06.439 as the start of the hip extension torque because the jumper's hip joint and his head begin to move upward. Now, the hip joint and the head moving upward could be caused by a hip extension torque, a knee extension torque, or an ankle plantar flexion torque. So, why did I conclude this was the beginning of the hip extension torque? To answer this question, you have to look at the three joints. Only the hip joint is moving upward. The knee joint and the ankle joint are stationary. If there was an ankle plantarflexion torque all three joints, as well as the head, would all be moving upward. If there was a knee extension torque, the knee and hip joints, as well as the head, would be moving upward. The only torque that can cause only the hip joint and the head to be move upward is a hip extension torque.
The same analysis can be made in determining the start time of the knee extension torque. At the frame with time stamp 0:07.907. The knee joint starts moving upward and the ankle joint is still stationary. The only torque that can cause this to occur is a knee extension torque. Finally, at the frame with time stamp 0:08.775, the ankle joint starts moving upward. The only torque that can cause this to occur is an ankle plantarflexion torque.
I'll let you think this over. On my next post, I will tell you when the torques end.