One of the new kinematic terminology made popular and reintroduced into athletic preparation recently thanks mainly to the work of Frans Bosch is 'swing leg retraction. So, what is it and how is it relevant for fast bowlers?
Swing leg retraction can be seen as a feed-forward motion where the swing-leg is retracted at constant angular velocity throughout the second half of the swing phase during sprinting or any high velocity locomotive motion like fast bowling. The stiffness on back foot contact has a direct impact on the effectiveness of this motion. Crossed extensor reflex due to the stiffness of the contralateral leg sets up a sequence concluding with swing leg retraction and foot plant form above. Foot plant above guarantees a stable pelvis and a fulcrum at the hip joint as opposed to at the knee joint. This is why I place a premium on training the stiffness on back foot contact and the isometric and eccentric strength on front foot contact.
The idea is that the footstrike should not “slide into” contact with the ground but rather should be directed from above with the line of expected Ground Reaction Forces (GRFs) we are hoping to create.
The most important direction for a fast bowler isn’t the vertical but rather the anterior/posterior direction. Here is a direct quote from a recent study. “Force imparted by the stride leg against the direction of the throw appears to contribute strongly to achieve maximum throwing velocity”
Stride Leg Ground Reaction Forces Predict Throwing Velocity in Adult Recreational Baseball Pitchers (McNally, Borstad, Onate, Chaudhari; JSCR Oct 2015)
The fact that the stride leg is applying force AGAINST the direction of the delivery means that this force is being applied in a posterior direction. The back leg keeps the momentum going towards the batter in an anterior direction but the bowler must “slam on the brakes” and stop the momentum by applying force backwards with the front leg- negative acceleration. Think of the car analogy and the passengers in the back seat. A sudden emergency stop will send the passengers hurtling forward!