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! The passengers are your upper body, whilst the car is the lower half of the bowling action.
Just to reiterate the importance of the BFC and how it sets up the subsequent key attractor of braced front leg. This is an extract from my bowling matrix
‘The greater the vertical displacement of the hips without losing horizontal momentum the greater the gravitational momentum into the delivery. However this increases the dynamic complexity of the sequence. Neutral pelvis setting up the correct position on FFC to optimise the GRF [ground reaction forces] Pelvis remains neutral while trunk slightly rotates towards bowling arm to produce torque . STIFF Back foot LANDING [see above consequences-crossed extensor reflexes]-Accelerate back foot to front foot .If you land and unable to be in control of the PRE-TURN due to the fact you either ‘Sink’ laterally or have heel contact [meaning you’re on the back foot too long] the whole sequence is out of time. The upper body continues whilst the back leg has yet to pivot and allow the hip to square up. Correct timing of the pre-turn- allows the extension of front leg towards target and subsequent hip shoulder separation’
While back leg after BFC [back foot contact] doesn’t necessarily or directly correlate with increased ball velocity, lead leg posterior force does. To achieve the correct sequence leading into FFC does however depend on BFC effectiveness.
This “clawback” mechanism can also be seen on world class sprinters. Notice how they make contact with the ground when producing maximum force
Now the question is: How do you train this mechanism not only mechanically, but using training modalities in the weight room and track to ensure it transfers properly to fast bowling and develops strength/power over the range of motion expressed in the delivery
‘Swing-leg retraction can improve the stability of spring-mass running. With retraction, the spring-mass model is stable across the full range of biological running speeds and can overcome larger disturbances in the angle of attack and leg stiffness. In the stabilization of running humans and animals, we believe both stance-leg dynamics and swing-leg rotational movements are important control features’
– André Seyfarth, Hartmut Geyer, Hugh Herr
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