Remember, no single form of exercise delivers all these benefits. Walking for example, which we all know to be healthy, does little for balance and flexibility. Swimming does nothing for bone density because the water is taking our weight. Yoga does little for the cardiovascular system. That is why exercise specialists recommend that we 'pick and mix' types of exercise to get a broad range of benefits.

Strength

We need enough muscle power to perform everyday tasks such as walking, climbing stairs, lifting and, ultimately, getting out of the bath or a chair and even breathing efficiently. Loss of muscle strength alone will lead to disability and loss of independence. Women are particularly vulnerable because they have less muscle mass to begin with and so lose strength more quickly.

It is vital to maintain strength in the main functional muscles - the legs, arms, ankles and back. You can improve strength by holding a movement for a slow count of five and repeating it on a regular basis. For example, while washing up, strengthen your ankles by rising onto your toes and holding it for a count of five, then gently lower yourself and repeat it.

Bone density

Loss of bone makes fractures more likely and can cause the upper spine to collapse, which in turn makes breathing difficult. When bone thins to a certain degree we call it osteoporosis. Bone density can only be maintained by weight-bearing exercise - it is the stress on bone and the jarring repetition of movement that builds bone mineral density. We particularly need to maintain bone at three sites - the wrist, hip and spine. Squeezing a tennis ball ten times a day, holding each squeeze for five seconds, will help improve bone density at the wrist within six months.

Stamina

Stamina, or cardiovascular fitness, is vital to ensure that the heart and arteries are supplying energy, giving oxygen to all the cells to help keep the whole system free from disease. Any exercise that makes you warm and increases your rate of breathing (also called aerobic exercise) will benefit your cardiovascular system. We need stamina to avoid undue tiredness, which is often attributed to medical conditions rather than unfitness. The benefits only occur, however, if the activity is maintained for at least half an hour and on a regular basis, namely three times a week or more.