Summation of forces is simply to time the links of the skeletal segments in an orderly fashion from the ground up. This is a simple concept as many events in sport movement occur this way. Training needs to encourage summation of forces as much as possible as the strength ratios of muscle groups must be cultivated in harmony. Many times athletes will hear working on the posterior chain catch phrases or doing corrective exercises with lousy progressions. An example of this is the psoas major being treated with isometric holds at the end ranges. If one looks at gait and fine wire EMG studies of the muscle group many of the beliefs don’t hold water in regards to corrective exercise. The above link is Hector doing elastic medball throws in order to handle eccentric stress in deep leg joint angles. We also do half turn shotput throws, various cleans and snatch work, and will integrate jump activities in a few weeks. Coaching efforts need to see how the start of the movement is initiated and linked (timing of the motions) as athletes are great finishers and tend to fool the eye of observers.