LOS ANGELES, May 29 — Yet another fitness craze is spreading on Instagram, thanks to yoga devotees demonstrating a new exercise which involves contorting their stomach into a strange pose.

Dubbed "alien yoga” on Instagram because of how your stomach looks while doing the movement, the practice is traditionally known as "nauli”. It was apparently first mentioned around 500 years ago, and in some yoga traditions, was among one of the first exercises taught to new students. It is still fairly uncommon in Western yoga — though that might be changing.

But what exactly is nauli, and is it a fitness trend we should be following?

According to nauli.org, nauli is a yogic cleansing exercise, or "kriya”, which cleanses the internal organs and strengthens the abdominal area. It involves rolling the abdominal muscles from side to side in a wave-like movement. It may look difficult, especially in some of the Instagram videos, but this movement can be practiced by most yogis and by any age group.

The nauli exercise comprises a series of four movements in total — and nauli.org says you must master uddiyana bandha before attempting the next three: