I heard I should use one all the time and I've also heard it can make my core weaker.
Weight belts are one of THE most abused pieces of training equipment in the gym and can actually cause more problems than they prevent. There are a number of types of belts ranging from Velcro-attached nylon belts to heavy-duty leather belts to air bladder, pump-up belts.
They are simply not necessary for most of the exercises people use them on. Repeated overuse of belts will weaken your back and core IF you continually rely on them unnecessarily.
The reason for this is that you are no longer relying on your own natural weight belt: your abdominals (specifically the DEEP muscles of the core - your Transverse Abdominis and your Internal and External Obliques).
The purpose of the belt is to push your abs OUT against the belt to develop intra-abdominal pressure, helping to stabilize the core. This is also known as "bracing" and it's something you can actually do without the belt.
When to use a weightlifting belt and when not to use a weightlifting belt:
Bottom line, unless you're doing very heavy training, I wouldn't recommend relying on a belt. Learn how to properly brace with your core instead. Because once you do, the belt will be that much more effective.
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