Read what Glen Mills, Usain Bolt's coach, had to say about the importance of proper training. I have highlighted certain passages. Read this carefully!
Usain is an extremely gifted athlete. When I started working with him, one of the things that stood out like a sore thumb was his poor mechanics. He was running behind the centre of balance. This resulted in a negative force against his forward drive and it was affecting other areas. For example, his body position put pressure on his lower back and there was a continual shift of his hip girdle and a pull on his hamstring. He was continually having hamstring problems and my assessment was that one of the things that contributed to it was his poor mechanics. Our first task was to get him to run with his upper body core in line with his centre of mass or a forward lean of somewhere around 5-10°. We set about doing drills then we took videos of his workouts and broke them down on the screen in slow motion to show him exactly what he was doing. I would draw diagrams and show him the position that we are working to achieve. Part of his poor mechanics was because