For thousands of years, physical activity has been associated with health. Today, science has confirmed the link, with overwhelming evidence that people who lead active lifestyles are less likely to die early, or to experience major illnesses such as heart disease, diabetes and colon cancer.

But it's often difficult to change exercise habits, or even to get into the habit in the first place. Thinking about your motivation can help.

Evidence shows that regular exercise can:

• increase levels of HDL or "good" cholesterol,
• lower high blood pressure,
• help improve body composition by burning fat,
• promote healthy blood sugar levels,
• promote bone density,
• boost the immune system,
• improve mood and reduce the chance of depression.

Despite the strong case for staying active, many people find it difficult to adapt their daily lives to incorporate physical activity. With cars on most driveways and the decline in the number of physically active jobs, 70% of the adult population is sufficiently inactive to be classed as "sedentary".

Being sedentary increases the risk of a heart attack or stroke by the same amount as smoking, yet even the threat of a future illness is often not enough motivation for people to change their habits.