Encouraged by A-listers such as Trudie Styler and Christy Turlington, who claim they owe their perfectly honed bodies to yoga, around half a million of us now regularly attend yoga classes.
And the popularity of yoga shows no signs of waning, with the growth rate set to reach 25 per cent this year. But, last week, one of Britain"s leading fitness experts, celebrity personal trainer Matt Roberts, suggested that yoga isn"t doing much for our fitness levels, at all.
"You may feel that you are keeping fit by doing a weekly yoga class, but you aren"t," Roberts said. "The reason why everyone likes yoga is that it isn"t very hard.
"Yes, there are individual parts of your body that are being worked hard, but with every form of exercise you should ask yourself is it intensive enough? Is my heartbeat raised? Am I out of breath and sweating for at least 25 to 30 minutes at a time? The answer when you"re doing yoga is, I suspect, no."
His comments will undoubtedly unsettle yoga enthusiasts everywhere. Yet, Roberts isn"t alone in suggesting that yoga offers less of a workout than we have been led to believe.
John Brewer, professor of sports science at the University of Bedfordshire, is keen to debunk the myth that celebrities achieve their streamlined appearance solely through endless sessions on a yoga mat.
"You just can"t achieve weight loss and a high level of fitness through doing yoga alone," he says. "These people probably devote hours a day to running, cycling, the gym and do yoga on top of that for its relaxation and flexibility benefits."
Brewer says that other than leaving you with better balance and flexibility, yoga doesn"t provide too many benefits, because the most important muscle in the body is the heart and this workout doesn"t really work the cardiovascular system at all.
Quite how limited a workout yoga provides was put to the test when the U.S. consumer watchdog, the American Council on Exercise (ACE), commissioned researchers at the University of Wisconsin"s human performance laboratory to investigate its fitness benefits.
What the exercise scientists found was surprising. In their trial, a group of 34 previously sedentary women were asked to take part either in three 55-minute hatha yoga classes ― the most popular variety in the West ― a week for two months, or to abstain from exercise altogether.
"You get changes in strength and muscular endurance, flexibility and balance ― all those types of things ― but, in order to improve aerobic capacity, essentially the efficiency of your heart and lungs, you really need to be working in the training zone where your heart rate reaches 70 to 80 per cent of your maximum," says Professor John Porcari, who led the study. "Based on what we found, the intensity just wasn"t there."
Many yoga fans argue that they don"t do yoga simply for fitness or weight loss. Some claim that it eases back pain by keeping their spines supple and strengthening the muscles that support it. But what"s the evidence?
In a study published by U.S. musculoskeletal specialist Dr Karen Sherman, it was shown that a gentle yoga class seemed a better alternative to "either general exercise or a self-help book" for back pain. But, worryingly, Dr Sherman also found that more vigorous types of yoga, such as ashtanga, and classes led by poorly qualified instructors, could make problems worse.
"People should be careful about doing yoga when they have bad back pain," says Matt Todman, consultant physiotherapist at Six Physio in London"s Harley Street. "It can be helpful in some cases, but many of the postures place strain on the back."
"If you feel any pain you should stop or if you have any pre-existing physical vulnerability, then you should always get medical advice before trying it," he says. "Yoga can reduce stress levels. But anyone who thinks they are going to get in shape sitting in the lotus position or any other pose is deluded. They should jump off their mat and go for a run if it"s pounds they are looking to lose."