In this “forward-backward animation” we see this crucial moment within the stroke phase, which is all about acceleration. The forearm muscle is briefly stretched before it is contracted (shortened). Through this reversal movement from eccentric to concentric work (stretch-shortening cycle) and by storing mechanical energy, all the energy of the body’s overall movement (coordination of the partial impulses) is transferred into the forearm in the last part of the stroke movement to be released afterwards.

In video Grigor Dimitrov at Mutua Madrid Open