Clenching your teeth under a heavy bar is partly reflex and partly technique. When you brace hard for a squat, deadlift or press, the jaw muscles tend to switch on along with everything else, and some lifters bite down on purpose because it feels stronger. A few seconds of that is harmless. Years of it, set after set, can show up as wear on the teeth and tired, sore jaw muscles.
You do not need to stop lifting, or change a bracing technique that keeps your back safe. It helps to know the signs, to mention your training to your dentist or OHT, and to think about whether a mouthguard makes sense for the way you train.
Surveys of lifters keep finding high rates of clenching
The research here is still small, but it points the same way. A 2026 study in Dental Traumatology examined 272 professional weightlifters in Chennai, India (Riyaz and colleagues). About 68% reported awake bruxism, meaning clenching or grinding while awake, and around 64% showed some tooth wear when examined. A smaller Brazilian study of 57 CrossFit participants (Ribeiro and colleagues, Dental Press Journal of Orthodontics, 2024) found that about 61% said they clenched their teeth during training.
These are single groups of people, not a measure of every gym member, and they do not prove that lifting caused the wear they found. They do suggest that clenching is common among people who train with heavy loads, and that many of them have signs of it in their mouths.
Bracing and biting tend to happen together
Most lifters brace by taking a breath, holding it against a closed throat and tightening the trunk around it. This is the Valsalva manoeuvre, and it helps keep the spine stiff under load. At maximal effort the body rarely tightens one muscle group in isolation. Grip, shoulders, neck and jaw often come along for the ride, which is why many people find their back teeth pressed together at the hardest point of a rep without ever deciding to do it.
Some lifters clench on purpose. Exercise scientists call this a remote voluntary contraction. In a small study of 13 young men (Ebben and colleagues, Journal of Strength and Conditioning Research, 2010), squatting while biting on a mouthguard, gripping the bar hard and using the Valsalva manoeuvre together produced higher force readings than squatting without them. That study tested the combination, not jaw clenching alone, and it did not look at the teeth.
Signs that clenching is starting to cost you
Damage from clenching builds slowly, so early signs are easy to miss. Things worth noticing include:
- jaw muscles that feel tight, tired or achy after a heavy session, or a headache around the temples
- a clicking or stiff jaw joint, or difficulty opening wide the day after training
- front teeth whose edges look flatter, shorter or slightly chipped
- teeth that have become more sensitive to cold
- a filling or crown that has cracked or come loose without an obvious reason
- ridges on the inside of the cheeks or scalloped marks along the sides of the tongue
Some of these also have other causes, such as grinding during sleep, acid wear from sports drinks or reflux, or an old filling reaching the end of its life. That is one reason to have them checked rather than assuming the gym is to blame. If jaw pain is the main problem, our article on orthodontic treatment and TMJ explains how jaw joint problems are assessed.
Teeth that already have large fillings are the most vulnerable
A healthy, intact tooth copes well with short bursts of heavy force. A tooth that has lost a lot of its own structure to decay or a big filling is a different matter, because the remaining walls of the tooth have less support. Repeated hard clenching can add to the stresses that lead to a cracked tooth, especially in back teeth. Cracks often start as a sharp pain when biting on something firm, or a twinge that is hard to pin to one tooth.
If you train hard and you have a lot of existing dental work, tell your dentist. They can look at those teeth more closely and talk with you about whether any of them need extra protection.
What to do about it
Keep the brace, relax the jaw where you can
The Valsalva manoeuvre is a widely taught way to protect the back under heavy loads, and there is no dental reason to abandon it. Some lifters find they can keep the trunk braced while letting the teeth sit slightly apart, or resting the tongue on the roof of the mouth. This is a skill that takes practice, and it may not hold up on a true maximal attempt. Between sets, it helps to check in and unclench.
Think about a mouthguard
A mouthguard puts a layer of material between the upper and lower teeth, so the teeth are not grinding directly on each other when you bite down. A guard made by a dentist from a scan or impression of your teeth usually fits more closely and feels more comfortable than a boil-and-bite guard from a sports store, which matters because a loose, bulky guard is the one people take out halfway through a session. There is limited research comparing the two types for heavy lifting specifically, so this is a practical choice rather than a proven one. A guard for the gym is also different from a night splint for grinding in your sleep. Your dentist can tell you which, if either, fits your situation.
Look at the rest of your routine
Frequent sips of sports drinks, pre-workout drinks and acidic flavoured waters can soften enamel, and a softened surface wears faster under clenching. Water between sets is kinder to your teeth. If you also grind at night, the two habits add together, and our guide to teeth grinding in adults covers that side of the problem. Clenching while concentrating is not limited to the gym, either: the same pattern shows up in people who play video games for long stretches, as described in our article on gaming and jaw clenching.
Common questions from lifters
Does this only matter for competitive lifters?
The more often you train close to your limit, the more clenching your teeth are exposed to, so people who lift heavy several times a week carry more of the load than occasional gym-goers. The mechanism is the same for everyone, though, and anyone with jaw pain or new tooth sensitivity is worth checking.
Will a mouthguard make me stronger?
Possibly a little, but the evidence is shaky. A 2023 systematic review of 41 small studies (Cao and colleagues, Journal of Science and Medicine in Sport) found that athletes performed somewhat better in some tests while wearing a mouthguard, and the authors cautioned that the studies varied widely and often lacked important details. The main reason to wear one is to protect your teeth, not to add kilos to the bar.
How can I tell if I clench during a lift?
Pay attention to your jaw at the top of a hard rep, or ask a training partner to watch your face. Tired jaw muscles after a session, or noticing that your back teeth are pressed together while you brace, are both strong hints.
If you train with heavy weights and would like your teeth and jaw checked for signs of clenching, our dentists and OHTs can take a look and talk through whether a mouthguard would help. You can see our current offers or read more about general dental care at Lumi Dental in Melrose Park.
This article is general information and does not replace individual dental advice.
