Building your own swim session is easy. The key to making a good workout is to have an intention, a singular focus for the session itself be it speed, endurance, form, force/power, or pacing. Endurance will have longer distances at more controlled efforts while sprint...
Stand beside a road sometime and watch a race instead of running it. You will see in the passing parade what you might not have noticed from the middle of it, focusing only on yourself and the runners within sight. If you wouldn’t have been one of the lead...
In short, it depends on the experience of the athlete and the type of session you are performing. It’s the question all athletes want to know the answer to: “How long will it be before I see the benefits from my workout?” How quickly will I adapt to training that...