‘Breaking’ usually refers to the slowing effect of over-striding. By over-striding I am speaking about extending the lead leg to far foward of your center of gravity. By sticking a leg out in front it not only acts like a ‘break’ but also forces you to expend energy ‘climbing’ up and over the lever arm that is being created by your leg.
An effecient way to extend stride length is to extend the kick which has the side effect of causing more flexion of the knee. This is effect shortens the length of the leg while it is moving forward. The ‘shoter’ leg, like a shorter pendulum, can move forward faster and with less energy.