Extension. The second principle of an efficient stroke. Become a longer, leaner, taller swimmer by making sure your exchange your lead arm. Newer swimmers often churn and take too many strokes. Remember the fastest portion of your stroke is the pull and the glide. If you start your pull before the recovery hand comes in for the exchange you are losing that gif to the glide. Reach your extender or lead hand towards the other side of the pool until you to the other hand as the lead that will reach towards the other end of the pool.