Fitness is the body's ability to perform daily tasks, exercise and recreational activities effectively, without excessive fatigue, while keeping enough energy for other activities and unexpected physical demands. It depends on how well the heart, lungs, muscles, joints and nervous system work together.
Fitness is commonly described through 6 components:
| Fitness Component | What It Means | Examples |
|---|---|---|
| Cardiorespiratory endurance | How efficiently the heart and lungs supply oxygen during sustained activity | Brisk walking, running, cycling, swimming |
| Muscular strength | The maximum force a muscle or muscle group can produce | Lifting a weight or performing one push-up |
| Muscular endurance | The ability of muscles to work repeatedly or for an extended period | Repeated squats, climbing stairs, holding a plank |
| Flexibility | The range of movement available at a joint | Stretching, yoga, reaching overhead |
| Body composition | The proportions of fat, muscle, bone and other tissues in the body | The balance between muscle and fat |
| Balance and coordination | The ability to control body position and movement | Standing on one leg, dancing, playing sports |
These components work together, but they measure different abilities. Someone may have strong muscles but limited cardiovascular endurance. Another person may run well but have limited flexibility.
What Is the Difference Between Fitness, Physical Activity and Exercise?
Physical activity is movement, exercise is planned physical activity, and fitness is the body's resulting ability to perform physical tasks.
Physical activity is any movement produced by the skeletal muscles that requires energy. Walking to work, gardening, cleaning, playing with children and climbing stairs all count as physical activity.
Exercise is planned, structured and repetitive physical activity performed to improve or maintain fitness. Weight training, a scheduled run and a cycling workout are examples.
Fitness describes the body's capacity to perform physical tasks. Regular physical activity and exercise can improve fitness, but fitness itself is not an activity.
Why Is Fitness Important?
Fitness helps people perform everyday activities more easily, including carrying groceries, walking uphill, climbing stairs and maintaining balance. Regular physical activity also supports immediate and long-term health.
For adults, consistent physical activity can:
- Improve sleep quality
- Reduce feelings of anxiety and depression
- Support brain health
- Strengthen bones and muscles
- Improve blood pressure and cardiovascular health
- Reduce the risk of type 2 diabetes and several cancers
- Help maintain a healthy weight
- Improve physical function and reduce the risk of falls, especially in older adults
Fitness is not determined by body size or appearance. Someone can be thin, muscular or athletic-looking without having balanced cardiovascular, strength, mobility and coordination abilities.
How Can You Improve Your Fitness?
You can improve fitness by combining several types of activity:
- Aerobic activity: brisk walking, cycling, swimming, jogging or dancing.
- Muscle-strengthening activity: weights, resistance bands, push-ups, squats and other bodyweight exercises.
- Flexibility and mobility work: stretching, yoga and controlled joint movements.
- Balance and coordination practice: single-leg exercises, tai chi and movement-based sports.
For most adults, the U.S. Physical Activity Guidelines recommend 150 to 300 minutes of moderate-intensity aerobic activity each week, or 75 to 150 minutes of vigorous-intensity activity, along with muscle-strengthening activities on at least two days each week. The guidelines also recommend moving more and sitting less.
You do not have to begin at the full target. Any amount of moderate-to-vigorous physical activity can provide health benefits. You can build gradually by increasing workout time, frequency or intensity.
How Is Fitness Measured?
Fitness is measured with tests that assess specific abilities, such as:
- Walking or running tests for cardiorespiratory endurance
- Repetition or lifting tests for muscular strength and endurance
- Joint range-of-motion tests for flexibility
- Balance and movement tests
- Body-composition measurements
The appropriate assessment depends on a person's age, health, goals and activity level. Fitness is specific, so a running test will not fully measure strength, flexibility, balance or body composition.
Bottom Line
Start with physical activity you can perform safely and repeat consistently. Over time, include aerobic, strengthening, mobility and balance work to develop a broader level of fitness.