Toning

Astanga, pronounced ashtanga, is an energetic form of yoga developed by K Pattabhi Jois. It is well known for developing a taut, strong physique, especially in the arms. 5 stars.

Iyengar (named after the man who developed it) will also lengthen and strengthen muscles - the practice of holding the poses (asanas) for a certain amount of time builds strength in the arms and legs. 4 stars.

Aerobic stamina

A: Classes begin with sun salutations designed to heat you up and stimulate sweating, which is believed to purify your body. After that, you perform a series of asanas which will get your heart rate up.

I: While Iyengar will increase your stamina as you maintain asanas for longer periods, it's not as intensely physical as astanga and won't get your heart racing in the same way.

Flexibility

A: Gives you a greater range of motion in your joints and loosens tight muscles. Self-practice (doing the exercises alone) is a strong feature of astanga, and will make you more flexible more quickly.

I: Also gives great flexibility, but may take a little more time. With practice and the use of props (belts, wooden blocks), you will get deeper into the stretches and reap the benefit as you learn to hold them.

Peace of mind

A: Emphasises deep, rhythmic breathing (ujjayi) and a focused gaze (drishti). Flowing in and out of the asanas can put you into a meditative state. You'll leave a class feeling calm and energised.

I: Breathwork (pranayama) in Iyengar will initially be more basic as it's believed you need to build strength and precision in the asanas first. Classes will still leave you feeling super-relaxed, though.

Injuries

A: Because the asanas are performed in a continuous flow, it's more physically demanding than other forms of yoga.

I: This is a slower form of yoga and great emphasis is placed on correct positioning in the postures. An American study has showed that it can actually ease back pain.