What gels the three elements together to make the complete product is a combination of technique, power and flexibility. Although equally important, today we will look at, as promised, two simple technical points.
After the bound, the back leg should land and bend at the knee. This allows you to conserve your run-in energy through the back-leg landing.
Imagine that the cricket field is a scale; your back foot landing should make the reading on the scale as small as possible.
On the other hand, the front leg must be as straight as possible. This action stops a huge proportion of the straight line speed of the bowler, but by the 'conservation of energy', this kinetic energy is transferred to the upper body.
'Conservation of energy' is simply the idea that energy will stay constant. For example when two balls hit each (ignoring friction for a moment), energy is transferred from one ball to the other, but the total energy of both the balls stays constant. As a fast bowler you are keeping your front leg straight to transfer the energy from your legs to your upper body (and eventually the ball).
By doing this with your legs, you set yourself up to bowl ridiculously fast. Let's look again at Brett Lee doing just that:
We are not going to push off our back leg onto the front leg. The reason is that pushing off requires you to register that you've pushed off. By the time your brain has told you that you've pushed off, it's already too late: you've lost your run-in energy.
All we want to do on back foot landing is to allow our energy to keep on travelling towards the batsman until our front foot lands. We then want to decelerate as rapidly as possible, which is achieved by the braced front leg.
Watch a long jumper. They don't push off the board; they just allow their run-in energy to propel themselves through the air.
By positioning your legs in this way you won't want to follow through much at all. If you feel like you have to follow through right down the pitch, it is clear that you are not transferring run-in energy to your upper body very well. In other words, you need to practise keeping your front leg straighter.
While much of bowling is an art, there is definitely a very important place for science in cricket. I hope that with time, we will all be able to improve the quality of the cricket we play by accepting a little bit of physics into our lives.