Originally from AquaVolo.com
USA Swimming recently posted a short article titled “The Key to Freestyle Balance: Breathing and Kick”  in which the author, Matt Barbini, suggests that a lack of balance is the root of most common flaws in freestyle. The author finds that the key to balance is a “strong steady kick” and early breathing. While I agree that lack of balance is the root of most common flaws and that inconsistent kick and late breathing can throw off your balance, a strong, steady kick and early breathing alone will not make you a balanced and efficient swimmer. A strong and stable core is the foundation upon which everything else is built.
To maintain balance in the water the swimmer must have a strong and stable core. The core links the arms and the legs together and orchestrates the coordination between different parts of the body. If the core is weak, a stronger, steadier kick will not improve balance or efficiency significantly because the body cannot maintain balance. Salo and Riewal had a good analogy—a strong kick with an unstable core is like trying to push cooked spaghetti across the table. “It’s very difficult to push the wet noodle because of it’s floppiness. This is like trying to use your kick to push you across the pool when you have poor core stability”.  A strong, steady kick in isolation will not improve balance; you need a strong and stable core to attain balance and efficiency.
Late breathing is one of the most common flaws in swimming. As Barbini points out, it “causes a delay in returning to a clean body-line and necessitates a corrective motion – like an outward hand sweep”. Learning how to breath early will eliminate these problems. However, it’s the balance attained by strong and stable core that makes the early breath possible, not vice versa. Just like with kicking, an early breath with a weak unstable core will not improve balance.
Barbini’s article makes a lot of sense, pointing out that a lack of balance can lead to many problems. However, the most fundamental aspect of balance is a strong core. While flawed technique such as an inconsistent kick or late breathing can throw off your balance, strong and stable core is what allows you to attain balance and achieve the correct technique.
 Complete Conditioning for Swimming. Dave Salo and Scott A. Riewald (2008)