Gym members who beat the hell out of each other with exercise equipment are now in serious trouble ... they've been banned from the facility for life and cops say they're now investigating.
The wild fight all went down shortly after noon on Nov. 7 at Ab Salute Gym in England ... and video of the scene -- which just surfaced this week -- shows a violent affair.
Unclear what kicked off the skirmish ... but several members grabbed gym equipment and weaponized it, swinging it at each other wildly.
You can see in the footage .