You and your hypothetical twin brother have a competition to see who can beat the other at the next New York City marathon. You are identical in physicality and fitness level. He trains by running 26.2 miles three days a week, going all out. You also train three days a week, running 3 to 5 mile sets followed by wind sprints. As a result, you are going to crush your brother at the marathon next year. Why? Because you trained in multiple energy zones and he only trained in one. It works the same way in the pool.
Training specific energy zones with different durations and intensities will make you a faster and stronger swimmer. The seven training zones we use in our sport are based on the three main ways that muscle cells recycle energy during exercise: non-aerobic, anaerobic, and aerobic metabolism.