Good physical condition is required for competing athletes and does not insure good health. A trained athlete can have cancer and die from a heart attack. Arnold Schwarzenegger needs to have a heart valve replaced.
Strenuous exercise produces toxins and free radicals, which can harm the body.
Most people do not have enough time to train properly and so rapid movements can injure muscles and joints. Repetitive strain can lead to chronic injuries and disease. Slow, nonstrenuous Qigong can improve your health. However, there is an overlap between these branches. Qi can be translated as life energy.