If the skeleton fails to stand poised and well-balanced when upright, then our joints won't work properly. A simple parallel is a skyscraper standing at an angle - the lifts won't run smoothly up and down their shafts, the doors and windows won't open properly, the desks will inch across floors. The better your joints run, the better you run, and vice versa, so it's important to keep them supple and watch out for signs of trouble.

1 Don't ignore stiffness

One of the first signs of any joint wearing out is generalised stiffness, particularly after being in one position for too long. With the larger weight-bearing joints such as the hips you might - for example, getting out of the car after a long drive - find it difficult to get upright and take the first few steps. But you can also get a similar sense with non-weight-bearing joints such as an elbow after being bent for a long time.

2 Stretch

Lack of multidirectional joint looseness, otherwise known as "joint play" makes it much easier for joints to be traumatised by an incidental jolt during daily life. Stretching makes joints more compliant and less susceptible to injury and arthritis. A knee, for example, or an ankle, which has more joint play, will be able to cope better with uneven ground.

3 Test your joints to their limits

All joints are wont to get trapped in their middle range of functional movement and losing end-of-range freedom is an early indicator of trouble - even if there is no pain. You rarely have a reason for taking your arm right up over your head but making sure it can go there, at least once a day, means that it will be "looser and freer" to move, and work with precision, in its functional inner range. For this reason it is important to exercise the extremes of "non-useful" movement at every joint, whether it be your big toe or your lower back. With the big toe, for example, separating it out as far as you can from the other toes helps prevent bunions.

4 Exercise with care

Poorly crafted gym regimes often leave the joints out of balance because they concentrate on repetitive joint activity in their middle range which simply emphasises the patterns of every-day use. Dumbbell routines to strengthen biceps do this, when really the elbow needs to be opened out fully to keep you from developing "tennis elbow".

5 Don't be afraid to bend

The lumbar spine is designed to bend forward and doing so gives the spine's discs a drink by moving fluid around them. This becomes more necessary with age.

• How to Keep Your Joints Young by Sarah Key is published on Thursday by Vermillion at £11.99.