LONDON • Yoga may have taken 5,000 years to evolve into a Western phenomenon, but its 21st-century profile has rocketed at lightning speed. The number of American practitioners has doubled in just a few years, reaching 37 million in 2016, while there are half a million in Britain.
Pilates, yoga's more modern associate, has seen similarly rapid growth since it was devised almost 100 years ago.
Increasing stress levels, coupled with a greater focus on physical health and well-being, are cited as factors in the growth of both, as well as celebrity endorsements.
Singers Madonna and Geri Halliwell have long sworn allegiance to yoga while singer Beyonce and actress Emma Stone fly the flag for pilates.
But despite the longevity and global popularity, confusion persists about yoga and pilates, compounded by the increasing variety of classes offered in each discipline.
Ashtanga, iyengar and vinyasa are all considered relatively modern incarnations of yoga. Inevitably, new variants of pilates have sprung up, as the market has become more commercialised.
Teachers of both yoga and pilates say they are routinely asked to explain the difference between them.
"The simple answer is that they're both low intensity, low impact and inclusive, unlike many other forms of exercise," said Professor Greg Whyte, a former Olympian and now a leading authority on sports science.
"Generally speaking, yoga is much more about flexibility and stability, pilates is strength and stability."
But for every flashy gym offering yoga classes to burn calories and sculpt bodies, there are many more teachers committed to its traditional spiritual principles.
Yoga was originally practised by holy ascetics in India, to focus the mind, connect with a higher consciousness and, through this newfound compassion, end suffering in the world. Although pilates is not a spiritual pursuit, its origins are rooted in healing and rehabilitation.
Ms Suzi Power teaches yoga and pilates at community studio East Of Eden in London, and sees the benefits of both.
She advocates pilates as a safer option for those prone to injury or those who are exploring this type of exercise for the first time.
"I trained in yoga first, but I was drawn to pilates because I had a yoga injury. Pilates helped me to rehabilitate."
Yoga uses the body to connect with the mind and the inner self, while pilates uses mindfulness to connect to the inner workings of the body.
"I practise both and love both - I think they complement each other well," said Ms Lottie Murphy, a former ballet dancer turned pilates teacher. "The main difference is the focus on the spiritual element in yoga. Some of the actual poses are similar. It's just that in pilates, we tend to build up to some of those moves more slowly than you might in yoga."
Yoga teacher Lily Silverton said: "Both pilates and yoga target muscle groups that you won't access in many other forms of exercise.
"You can be an incredibly fit runner or boxer and come out of a yoga or pilates class in agony because you've worked muscles you don't usually engage."
When professional athletes come to Prof Whyte asking about yoga and pilates, which discipline does he recommend?
"Often, I suggest a combination of the two. Pilates has become the mainstay of rehab, particularly for back problems. But it's also great for other conditions, such as urinary incontinence.
"You're focusing on the core, whereas yoga tends to be more the whole body. Both are great in pregnancy, although the key advice to remember is that pregnant women should look to maintain fitness, not improve it."
Ultimately, it might just be down to personal preference.
Ms Power said the choice is as much in the mind as the body.
"People who are more logical tend to like pilates. People with a creative brain often find more freedom in yoga."