The beauty of any form of training is that over time, your capacity for the work increases. "Practice makes perfect" can refer not only to your ability to play a piano sonata mistake-free but can also refer to your skills in executing a flawless 200-meter freestyle swim race. It all comes back to muscle memory, and with swimming, building muscle memory-as well as strengthening the muscles themselves to improve strength, speed, and endurance-is the central physical aspect of the sport. Any physical activity, when engaged in consistently, can build muscle. But a key selling point of swimming that sets it apart from other forms of exercise that also build muscle is that swimming engages all the major muscle groups throughout the body in a low-impact way. This means you can build strength and stamina without putting excessive stress on the joints, such as can occur with weight-bearing activities such as running.