OnlyFans Models Brittney Lefevre, Kristina Santa Workout in Tiny Bikinis Before Fights

Brittney Lefevre and Kristina Santa are usually lovers ... but it's clear they're quickly turning themselves into fighters -- working out on a beach in a pair of tiny bikinis.

The OnlyFans stars hit Miami Beach this weekend before their bouts at The Knockout Queen ... a multi-day festival in Coachella Valley later this month that will feature OF models using their hands in a decidedly different way than usual.

Brittney and Kristina rip sit-ups and pull-ups in the clips, throw punches and even run sprints -- all while baring pretty much everything in barely-there bathing suits.

Check out their jumping squats, too ... it's a move that'll knock you out.

While these two ladies are training together, they won't be fighting one another ... Kristina's taking on Blondie Moto in one of the undercard matches -- while Brittney's fighting Rebecca McLeod as the main match.