Sports Bras

Muay Thai asks more of a sports bra than running does. There is impact from the front, there is grappling and framing in the clinch, and there is a lot of overhead movement — and a bra designed for treadmills tends to shift on all three.

What to look for

High impact support. Kicking, kneeing and punching involve a lot of rotation and sudden deceleration. Medium-support bras are not built for it.
Nothing that digs in. You will be clinched, framed against and hit in the body. Rigid underwiring and thick plastic clasps become a problem quickly.
Full coverage across the back. A racerback or cross-back holds position far better than thin straps when someone is pulling on your neck.
Fabric that wicks. This is the item in closest contact with your skin, for the longest, in a very hot room.

Fit

It should be firm without restricting your breathing. You will be working at a high heart rate for long stretches, and anything that constricts the ribcage will cost you rounds.

Test it properly before you train in it: throw a few punches, raise your arms fully overhead, and drop into a clinch position. If it moves, it will move worse when you are sweating.

Sizing

Thai-manufactured brands cut smaller than UK sizing, so do not assume the size you wear on the high street carries across. Check the measurements on the individual product.