Each man's ability to be fit is affected by their physical abilities. In other words, each man has different physical abilities that depend on their strength, their endurance and their speed. There are three main factors that limit men's potential Fitness; their sex, their age and their health.

Age affects fitness
Anyone of any age can be considered fit. But age does matter as it affects strength, speed and endurance. Age does tend to define aspects of fitness as we reach peak potentials at different times in our lives. As we age, so our physical efficiency declines. For example:

# speed is at its optimum in early adulthood

# we are at our strongest in our late 20s

# endurance is most evident in later life

To maintain fitness at different ages men have to find ways to maximize their potential without compromising their health. Keeping fit has to be tailored to do that.

Sex differences affect fitness
Men have a greater potential to be stronger and faster. This is just a fact. Although on an individual basis women can be as strong or as fast, they start off from a point where their body design favors different things. Men's musculature favors strength and speed, women's bodies mean they live longer and can withstand greater extremes of temperature. Men are about 30-50% stronger than women in total muscle force on the basis of absolute force extended.

Health Affects Fitness
We tend to think that fitness and health go together, but that is not true. It is quite possible to be ill and not be aware of it.
Physical and mental well-being contribute to our overall fitness. If we are healthy then our weight, our diets, our sleep patterns and exercise patterns all have to be satisfactory to make us fit.

Nutrition and fitness. A healthy, balanced diet is central to maintain fitness
Weight and Fitness.
Being overweight or underweight reduces our levels of fitness. Being overweight or obese means our bodies have to work harder for it to function properly. Being underweight is not necessarily any healthier as it means the body lacks the capacity to perform efficiently.
Exercise and fitness We can only be fit if our bodies take regular exercise. Without exercise our muscles waste and our joints lose their flexibility. Our bodies become unable to burn calories effiently to control weight and body function and our sleep patterns suffer too.