Even if you are a triathlete who competes only in freestyle, it is important to train more than one stroke. Swimming, is the perfect example of a repetitive motion activity. Even a sprinter, who in general, does fewer overall yards than other freestylers, does thousands of shoulder rotations in their career.
It is important to balance the muscle develop and wear with different movements. While I prefer my swimmers to do at least back and breast, I will accept just one additional stroke from more beginner level swimmers.
Swimming multiple strokes also improves your overall conditioning. Our bodies are great at adjusting to routine and one of the best ways to force your body to breakout is to add additional strokes to the routine.
It may not be today, or even tomorrow, but swimming exclusively freestyle will slowly create a muscular imbalance that will lead to pain or injury. So, don’t fight it, just swim more than one stroke as part of your training.