Defining Physical Fitness

What is physical fitness (and why is it important)?

Physical fitness is an ideal state of health. When you're physically fit, you can perform physical tasks (such as running up a staircase or lifting a heavy box) without becoming fatigued or incurring injuries. There are five key components to fitness: muscular strength, muscular endurance, aerobic fitness, flexibility and body composition. The following article unpacks what each of these five components is and why fitness is important.

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The five key components to fitness

As we mentioned above, there are five key components to fitness. These are:

  1. Muscular Strength (Power)
  2. Muscular Endurance
  3. Aerobic Fitness
  4. Flexibility 
  5. Body Composition 

In order to be optimally physically fit, we need to train and work on all five components. We’re now going to define each component, so that you understand where each one fits in to overall health and fitness.

What is muscular strength?

Muscular strength (power) is the amount of force a muscle (or group of muscles) can produce, with a single maximal effort. Muscular strength could be measured by the amount of weight you could lift in a single motion - such as lifting a heavy box and putting it on a shelf.

What is muscular endurance?

Muscular endurance is the ability of a muscle or muscle group to exert force repeatedly against resistance, without becoming fatigued. If we use the same real-world example of the heavy box, muscular endurance could be measured by your ability to repeat the motion of lifting the box and putting it down, over and over again.

Both muscular strength and endurance are improved with resistance training such as weight lifting, push ups or squats.

What is aerobic fitness?

Aerobic fitness (or cardiovascular fitness) is your heart and lungs' ability to supply sufficient oxygen to your muscle tissue, to produce the energy needed to move. Aerobic fitness is measured by your VO2 max (maximal oxygen intake), which gradually declines with age. 

Cardio training (such as cycling, running or swimming) is one of the most important forms of exercise as it improves your VO2 max. It also helps maintain healthy lungs and heart.

What is flexibility?

Flexibility is essentially your range of motion (your ability to move your joints freely, without stiffness or pain). Flexibility training (such as yoga, tai chi or hiking) helps to improve mobility and stability, and improves oxygen circulation to your muscles.

What is body composition?

Body composition is the overall percentages of fat, muscle, bone and water which make up your body. A healthy body composition requires a high lean muscle and bone mass percentage, and a low body fat percentage. Your body composition is affected by all of the other fitness components (muscular strength, muscular endurance, aerobic fitness and flexibility) as well as your genes (your height, for example).

Why physical fitness is important

Physical fitness is important because it reduces your risk of developing diseases and improves your quality of life. Physical fitness increases your cardiovascular health, respiratory function and longevity. It promotes strong bones, muscles and joints, and helps maintain a healthy weight. Physical fitness also boosts your immune system, and helps improve your sleep quality, energy levels and mood.

Physical fitness is achieved through exercise and an active lifestyle.

Long-term benefits: how improving your fitness level leads to better overall health

Regular exercise and physical activity can help prevent diseases, such as:

  • Cardiovascular disease (heart disease)
  • Certain types of cancer
  • Depression and anxiety
  • Heart attacks
  • High blood pressure
  • High cholesterol
  • Insomnia
  • Obesity
  • Osteoporosis
  • Stress
  • Strokes
  • Type 2 diabetes

Exercise is proved to assist your body’s production of chemicals such as serotonin and endorphins and decrease levels of harmful stress hormones (like cortisol). 


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