This is important for increasing body strength and endurance. It also plays an important role in increasing bone density and preventing diseases such as osteoporosis. Resistance exercise can be achieved with free weights or the resistance machines common in most gyms. Aerobic exercise is that which increases the body's demand for oxygen over an extended period of time and provides energy at the same rate it is used. This produces many longlasting benefits to the heart and lungs.
Aerobic exercise includes cycling, jogging, and swimming.
For general fitness a combination of resistance and aerobic training should be combined. The greatest cause of injury is lack of fitness and flexibility. Anaerobic metabolism takes over when exercise intensifies and provides a fast supply of energy, produced by the breakdown of the carbohydrate glycogen which is stored in the liver and the muscles. Pain is a warning that the body has had enough and can indicate a rapid rise in lactate causing muscle burn, excessive strain on a previous injury, or perhaps actual tissue and cell damage. At this stage the athlete should slow down with some loose rhythmical swinging or walking on the spot, accompanied by controlled breathing, which will restore normality so that the muscles can continue working.