Here's what your belt is suppose to be used for
"Gear is a supplement to improve your fitness, not a crutch to cover up pain."
First off, if you do have back pain, the most important thing to do would be to contact your coach, trainer, doctor, physical therapist, or local wizard to help fix your movement... or at least help you get to the bottom of why it hurts versus covering it up.
And secondly, a back brace is designed to limit motion in the spine. I see patients in the clinic with back braces who have spinal fractures and/or scoliosis. The brace runs from the pelvis/hips all the way to the lower chest region.
That's the opposite of something you'd want when performing heavy squats followed by burpees.
Burpees suck enough as is... no need to make them worse.
A belt can absolutely minimize back pain, but that's not the main function of a belt.
A belt is designed to increase the pressure within your abdomen and provide tactile (touch) feedback to the skin and muscles around the abdomen and back.
The belt serves as secondary reinforcement for the abdominal muscles, low back muscles, and lower ribs. That means the first line of defense are the abs. That's why training belt-less during specific phases of training is so important.
Now think about this, if the muscles around that area are not able to contract appropriately at the correct time, there will be a decrease in stability around your pelvis and spine.
That decrease in stability leads to some tight hips, a tight low back, squat depth issues, and possibly knee pain. Other areas get tight to try and compensate for lack of abdominal contraction.
Throwing a belt on in this case will work to cover up some issues and underlying deficiencies, but it's not the fix.
The belt is designed to optimize intra-abdominal pressure, not serve as a back brace.
Quote of the Day
"Strength is the product of struggle, you must do what others don't to achieve what others won't." Henry Rollins