Most people know that it's important to brace their core while lifting weights, especially when doing heavy squats or deadlifts. But knowing you should do something, and actually doing it (and doing it correctly) are two very different things. When I ask the athletes that I work with about bracing their core, I am often told that they don't know what that means or how to do it. And it's true, for as much as we (trainers, coaches, PTs) tell our athletes that it's important to brace their core, we often don't teach them HOW to do it.
Even athletes that think they are bracing their core correctly are often using a core bracing strategy that is less than ideal. The error I see most commonly is people flexing their rectus abdominis (six-pack muscle) instead of collectively engaging all of the abdominal muscles. The role of the rectus abdominis is to flex the trunk (think about the movement during a sit up), which is exactly what you don't want your trunk doing when you're doing heavy squats. The goal with bracing your core is to create a stiff trunk, not one that bends under load.
So how should you brace your core?
Lie on your back with your knees bent.
Put a couple fingers an inch or two inside your hip bone. As you brace your core, you should feel the muscles here contract.
Think about pulling your hip bones/pelvis together. (Your legs shouldn't move at all.)
If your low back gently flattens into the floor, that's a sign that you've done it correctly.
Once you get the hang of it in this position, try it while sitting/standing/etc and then while lifting weights.
Do not:
Suck in your stomach. If you do this, you'll see the chest rise and the belly sink. But no significant contraction of the abdominals will occur.
Flex your six-pack. If you do this, your six-pack muscles with contract and bulge out. You likely won't feel the muscles inside your hip bone contract, and you may feel your back round into the table.
**This is the core bracing strategy that works best for myself and the majority of the athletes I work with, but keep in mind that everyone is different. Also, I find that this is often best taught in-person. So if you are struggling with this, I recommend seeking out a local PT to work with. You are also always welcome to reach out to me with any questions.**
If you give this a try, let me know how it goes and if you feel a difference during your lifts!