That people get the positive effects from regular exercise?
Most importantly, what do people get from physical activity is health. Strengthening of all body muscles and improve the function of internal organs, tone the vascular system - all that one acquires, if engaged in sports at least twice a week. Adverse effects with proper adherence to technique exercises and balance loads of sport has not, although we should not forget that post-workout muscle formation of lactic acid, which makes itself felt pain.
What about those who train six or more times a week?
Such people are called "professional athletes". They train on schedule with the coach. Professional athletes are not only interested in building muscle or a beautiful figure, all workouts are focused on results, which they will show at the event. On the medical examination, you can see that they even after an intense workout, calm heartbeat, it is well-trained, so as the heart pumps enough blood to support the blood circulation and the normal condition of the body at the proper level.
Professionals body more resilient and well developed, but still human performance is limited. There is in the sport and such a term as occupational diseases. For example: in swimming - LOR-diseases, and in athletics - diseases of knee and hip joints. They are not protected no athlete. Such diseases can develop at any age just when playing any sport, but it's nothing compared to the victories and achievements which athlete wins. The assertion that professional sports cripple - it's true, but whoever wants to win will win, even self-mutilation, and the one who trains not for himself but for the coach or parents, will not achieve anything either in life or in sports.