The number one thing you can do is refine your stroke. The more efficient your technique, the less energy it's going to require to travel more distance in the water. Another way to think about it: If your stroke is inefficient, it takes you more energy to travel the same speed with more strokes.
Beyond that, you need strength and stability to maintain proper technique. Clearly, you need to train your whole body, but here are few keys to prevent pain and boost speed and endurance in the water:
- Rotational power If you use proper technique, your torso should rotate as you slice through the water. Improve rotational power with moves like rotational medicine ball throws.
- Shoulder protection Shoulder injuries are common for swimmers because of the overhead motion. To protect your shoulders, train the muscles that support your shoulder bladesyour "scapular stabilizers"with Ys and Ts, for example.
- Craig Friedman, Performance Specialist, Athletes' Performance