This week: Can you tell your ashtanga from your jivamukti?

Madonna's renowned muscular physique, currently on show in the Sticky and Sweet tour and in hundreds of press photos, results from an intensive daily exercise regime which includes ashtanga yoga, one of several forms of the exercise. Yoga is ideal for the winter months when inclement weather prevents as much outdoor activity and is also calming at times of stress or worry.

What does "yoga" mean?
Yoga is a term which refers to a Hindu system of philosophy aimed at the mystical union of the self with the Supreme Being, something which is achieved through mental and physical exercises. It's all about promoting a healthy body in order to clear the mind for the path to enlightenment. The word comes from the Sanskrit meaning yoking or union.

So it isn't just about exercise, then?
Many people in Britain today approach it primarily as a form of exercise; most of us think of yoga as being a series of asanas - postures - which strengthen and tone the musculature. But yoga also aids relaxation. In a typical class, 10 minutes is given over to relaxation while in "savasana" (lying on your back and relaxing all limbs), when it's very easy to fall asleep. Centred, controlled breathing, which is calming and encourages you to focus, is also key. Yoga is claimed to lower blood pressure and improve flexibility.

What are the different types?
Hatha yoga focuses on doing asanas and regulating your breathing, typically with short pauses between the postures.

Other forms are often seen as different to hatha, though there are sometimes sub-forms of it. One is ashtanga vinyasa, as preferred by Madonna. This is vigorous exercise in which the postures are linked. It gets up a sweat and utilises a special, audible form of breathing. You require a basic level of fitness to do ashtanga. Power yoga closely resembles ashtanga, but the interpretation is looser.

Then there's iyengar yoga, in which you hold the individual postures for longer and precision and alignment are particularly important. Iyengar yoga also makes use of props, such as straps and wooden blocks. Another is kundalini yoga, a more spiritual form, in which there is meditation and chanting. Then there's hot yoga, which is a vigorous form of the exercise done in a room where the heating is turned up to 95 or 100 degrees to promote further perspiration designed to rid the body of toxins.

Jivamukti yoga classes, popularised in New York, incorporate vigorous yoga with discussions of how you can apply yogic principles in your life. Other forms include sivananda, in which a heavy emphasis is placed on diet.

Is it aerobic?
It won't get your heart rate up like running, brisk walking or swimming, but it can be quite demanding.

Do you have to be flexible?
"Everyone can practice yoga, regardless of age, sex or ability," says the British Wheel of Yoga, the UK governing body for yoga. Not all yoga fans are contortionists, in spite of what the photographs might imply. So even if you have trouble touching your toes to your fingertips, never mind your ear, you can give yoga a try. Most gyms and many community centres offer classes; you'll also find it on offer in church halls, residential care homes and private studios, and there are plenty of DVDs and books to help you learn at home.