This page explains the basics of the Principles of Training:
Every exercise has a specific effect on your body. For example a biceps curl with a heavy weight will strengthen your arm muscle. One with a light weight will improve their endurance. But neither will effect your leg muscles at all.
This means you must first decide what muscle you want to work on and then use the correct exercise. To improve in a sport, you must exercise the muscle and joints used in the sport and the speed you them. A training programme must be devised to suit you.
To improve the fitness of a part or the body, you need to overload it. That means that you need to make it work harder than usual. Over time, it adapts to meet the increased demand by getting fitter.
Increase the frequency of exercise - how often you do it. For example start by exercising twice a week, then move up to three or four times.
Your body takes time to adapt to increased demands on it. So you should build up your exercise level gradually or progressively. Otherwise you risk torn muscles and other injuries.
You will notice the biggest changes early in your training programme. The fitter you get, the harder it is to gain further improvement. This shows you are getting close to your full potential. If you keep exercising at a constant level your fitness will stay at the same level.
Sadly, improvements in fitness are reversible. Exercise harder and your body gets fitter. Stop exercising and it loses fitness again.
It takes only three or four weeks to get out of condition. You lose endurance, strength, flexibility and speed. You rapidly get worse at things like jogging and swimming because your muscles get poorer at using oxygen. Muscles that are not used will waste away or atrophy.
Increasing the intensity of the exercise – how often you do it. For example run faster or lift heavier weights.
Increasing the time you spend on exercise. If you are very unfit, you may start jogging for about five minutes per session and work up week-by-week to thirty minutes per session.
by Jez Green