I've had one knee replacement and am about to have one on the other knee. What should I do to aid my recovery and get moving again?

To some extent, you can protect your knees by keeping the muscles that support them strong, so avoid bending the knee when it is not aligned correctly. Both before and after knee replacement operations, it is important to strengthen the quadriceps at the front of the knee and the hamstring at the back of the thigh - these are the main muscles responsible for bending and straightening the knee joint.

Try this exercise. Arrange a pile of pillows so you can lie on your back with your right leg resting over the pillows, your left leg bent and your left foot resting on the floor by the pillows. Breathe in, then, as you breathe out, contract your abdominals to provide stability while you extend the right leg until it's straight. Flex the foot. Breathe in, still contracting your abdominals, and point the foot. Flex the foot again, then breathe in as you lower it to the floor. Repeat five times on each leg.

For hamstrings, do lying glute squeezes. Lie face down with a folded towel between your thighs and another under your abdomen. Breathe out, squeeze your buttocks towards each other and you should feel your abdominals contract and your lower back gently lengthen. Make sure the legs do not turn in. Repeat 10 times.

You'll find more knee exercises, with excellent diagrams, in Pilates Plus, by Alan Herdman with Gill Paul (£14.99, Gaia Books).

· Joanna Hall is a fitness expert (joannahall.com). Send your exercise questions to Weekend, 119 Farringdon Road, London EC1R 3ER (weekend@theguardian.com).