The Overload Principle

Aerobic and anaerobic exercise use the overload principle for training. The overload principle states that to improve your fitness, you need to work your body harder than it is used to working. Research has found that your body adapts to the stress of working harder by becoming stronger.

For example, if you walk two miles fives days a week, eventually walking those two miles will get easier, and you'll be able to work longer or faster or both. Your heart becomes stronger and more efficient using the overload principle, but you can apply this principle to the other components of physical fitness, including muscle strength, muscle endurance, and flexibility.

Muscles and Overload

By systematically overloading your muscles in both strength and endurance (lifting more weight or lifting weight for longer), as well as in flexibility (stretching further and more extensively) you will also be able to make gains in those fitness elements. Lifting weights and stretching in a regular strengthening program allows you to create a body that is more capable and fitter than it was before.

The American College of Sports Medicine (ACSM) is the largest sports medicine and exercise-science organization in the world, with over 15,000 members in more than seventy-two countries. ACSM members include doctors, educators, scientists, personal trainers, group-exercise instructors, and other health and fitness professionals. The recommendations in this book follow ACSM guidelines.

Your fitness level determines how much overload you will use when you exercise. If you have been sedentary, here is some good news: it won't take much to overload your heart and other muscles, so your fitness will improve quickly. If you have been exercising for a while but haven't seen improvements, it may be due to a lack of overload in your activity. So once you start working harder, you'll see improvements, too.

FITT and Overload

To properly incorporate the overload principle into your fitness routine, you can rely on FITT. FITT is an acronym for the four elements that make up an effective exercise program:

  • Frequency — how often you exercise
  • Intensity — how hard you exercise
  • Time — how long you exercise
  • Type — mode or type of exercise

Frequency, Intensity, Time, and Type of Exercise

As mentioned previously, frequency refers to how often you exercise. You'll need to do 30 minutes of moderate activity daily (which can be broken up into 10-minute sessions) to stay healthy, and three or four high-intensity workouts each week to stay truly fit. The more you exercise, the more calories you burn, and the stronger your heart and muscles are.

Keeping the overload principle in mind, you'll need to be aware of your intensity level to make sure you are working hard enough to overload your heart and your muscles while you exercise. Moderate-intensity exercise gets your heart pumping, but not in an overly stressful, breathless way. This kind of exercise helps you develop endurance. High-intensity exercise is tough; you breathe heavily and are overloading your heart and muscles. You need a mixture of both kinds of intensity to stay fit. When you push your intensity levels, your body responds by becoming stronger and burning more calories.

How long are you working out? Is it enough to build endurance and allow for proper overloading? The more time you spend exercising, the greater the results in terms of strength and endurance.

The fittest bodies and healthiest people get that way due to a variety of types of exercises, such as walking, weightlifting, and yoga; or bicycling, swimming, and gardening. The more variety in your exercise program, the more likely it is that your body will increase its strength, endurance, and flexibility — and the less likely it is that you'll suffer from overuse injuries.

What is the difference between moderate-intensity and high-intensity exercise?

Intensity refers to how hard your heart and muscles are working during a given activity. In practical terms, a stroll is low intensity, a brisk walk is moderate intensity, and a fast walk/jog program is high intensity. Likewise, playing in the pool is low intensity, swimming laps is moderate intensity, and racing is high intensity. To provide one last example, gardening on your knees is low intensity, raking is moderate intensity, and moving shrubs and young trees is high intensity.

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