moment a gym user in Indonesia was thrown off a treadmill and plunged out of a third-floor window.

The video, from the busy facility in Pontianak, West Kalimantan, shows a row of treadmills being used on June 18, when the woman suddenly stumbles backwards.

The woman, who has only been identified with the initials FN and was reportedly 22 years old, attempts to grab on to the window frame but then disappears out of sight as she falls through.

Picture is believed to show the victim, who is 22 and has only been identified with the initials FN

Her boyfriend had reportedly asked her to exercise with him on the second floor, but she wanted to work out on the treadmills on the third floor.

The woman had been exercising for just 30 minutes when she reportedly slowed to a walk, before the tragic fall took place, according to local media reports.

She was reportedly rushed to hospital with serious head injuries, but doctors were unable to save her life, according to local media reports.

An autopsy reportedly revealed that she had suffered extensive bruising and lacerations to her head.