Health versus Fitness

To distinguish between internal arts such as Taiji, Bagua and Xingyi from external practicies its important to distinguish between health and fitness.
When you are healthy you can achieve a high level of fitness. If you overtrain, however, you will injure your health. Fitness is supported by health.
External styles require fitness. But as we age or if we injure ourselves, our bodies are slower at recovering. The demands of external styles can then be too hard to maintain or can contribute to eroding health.
Internal styles, in contrast, link directly to our health. The training methods are different because the intent is to build health rather than draw on fitness. The result is a practice that cultivates health. On the martial side of things, the effectiveness of internal styles comes from a strong vitality. The more the mind and body are coodinated and integrated, the more effective the techniques.
This distinction is easy to overlook. But unless it is recognized, your training in internal styles will always be limited.