How Exercise Works

Exercise Factors

If you exercise regularly or if you are an athlete in training, you are trying to make your muscles work better. You want to be stronger if you are a weightlifter, you want to be able to throw a blistering fast ball if you are a baseball pitcher or you want to be able to finish strong at the end of a 26-mile race if you are a marathon runner. Those three activities illustrate three major factors in muscle performance:

  • strength
  • power
  • endurance

Muscle strength is the maximal force that a muscle can develop. Strength is directly related to the size (that is, the cross-sectional area) of the muscle. Muscle fibers are capable of developing a maximal force of 3 to 4 kg/cm2 (average = 3.5 kg/cm2) of muscle area. So, let's say that you have increased your muscle size from 100 to 150 cm2, then the maximal resistance that you could lift could be increased from 350 kg (770 lb) to 525 kg (1,155 lb).


The power of muscle contraction is how fast the muscle can develop its maximum strength. Muscle power depends on strength and speed [power = (force x distance)/time]. A person can have extreme power from muscles (7,000 kg-m/min) for a short period of time (about 10 seconds) and then power reduces by 75 percent within 30 minutes; this aspect is important for sprinters because it gives them great acceleration. Muscle endurance is the capacity to generate or sustain maximal force repeatedly.