We obsess over every single detail of our gear.
If you are a runner, you probably know your exact foot strike pattern and have spent hours researching the perfect shoe drop. If you lift, you likely have a specific belt, wrist wraps, and sleeves. We track our sleep, measure our macros to the gram, and spend hundreds on smartwatches that tell us exactly how recovered we are.
But there is one piece of equipment that almost every athlete neglects. It is usually an afterthought—a cheap, boil-and-bite piece of plastic tossed into a gym bag and forgotten until sparring day or game time.
I’m talking about your mouthguard.
Most of us view a mouthguard as nothing more than a “tooth saver.” While protecting your smile is critical, the wrong mouthguard is doing something else entirely: it is acting as an obstruction to your airway and a trigger for physiological stress.
Here is exactly how a bad mouthguard ruins your endurance, and the science behind why upgrading this one piece of gear could be the easiest performance hack you make this year.
Restricting Airflow
The most obvious way a generic mouthguard hurts your performance is by stealing your air.
Endurance is, at its core, an oxygen game. Your muscles need a constant supply of oxygen to break down glucose and create ATP (energy). The harder you work, the more oxygen you need. This is why VO2 max (the maximum amount of oxygen your body can utilize) is such a gold standard metric for fitness.
The “Drinking Straw” Effect
Imagine trying to run a 5K while breathing through a narrow drinking straw. That is effectively what happens when you wear a bulky, ill-fitting mouthguard.
Generic “boil-and-bite” guards are often made of thick, uniform rubber. When you bite down, that material bulks up in the roof of your mouth and against your soft palate. This reduces the volume of your oral cavity and narrows the airway passage.
When you are deep in a workout, your body naturally switches from nasal breathing to oral breathing to get air in faster. If your mouthguard is blocking that pathway, you have to work harder just to breathe. This increases the energy cost of respiration. You are burning precious energy just to move air in and out of your lungs, rather than using that energy to move your body.
The Science of Airflow
Research supports the idea that mouthguard design significantly impacts ventilation.
A study published in the British Journal of Sports Medicine examined the physiological effects of wearing different types of mouthguards. The researchers found that wearing standard mouthguards significantly reduced Forced Expiratory Volume (FEV1) and Peak Expiratory Flow (PEF) compared to not wearing one.
In simple terms, the wrong guard makes it harder to exhale fully and forcefully. If you can’t get the old air (CO2) out efficiently, you can’t get new, oxygen-rich air in. This leads to a faster buildup of carbon dioxide in the blood, triggering that gassed-out feeling much earlier than necessary.
The Cortisol Spike
A bad mouthguard stresses your body out.
Think about what happens when you put a loose object in your mouth. Your natural, subconscious reaction is to bite down to keep it in place. If you are wearing a cheap mouthguard that doesn’t lock onto your teeth, you are likely micro-clenching your jaw throughout your entire workout.
This might seem harmless, but the jaw is a neurological heavy hitter. The Temporomandibular Joint (TMJ) is packed with nerve endings. When you clench your jaw, you send a signal to your brain that you are under threat. This triggers the “fight or flight” sympathetic nervous system.
When your body enters this stress state, it releases cortisol. Cortisol is a catabolic hormone. While you need some of it to exercise, chronically elevated levels during a workout can be counterproductive. High cortisol levels can accelerate fatigue and increase the production of lactic acid.
Conversely, keeping the jaw relaxed and aligned can lower this physiological stress.
A randomized controlled trial involving Division I football players looked at the effects of a custom mouthpiece on cortisol levels during intense resistance exercise. The results were striking. The athletes wearing the proper mouthpiece had significantly lower cortisol levels 10 minutes post-exercise compared to those who didn’t.
The Solution: Custom-Fit Protection
So, if stock mouthguards are suffocating you and stressing you out, what is the alternative?
The answer lies in custom-fit protection.
Unlike boil-and-bite guards, which are essentially thick rubber trays you mold yourself, custom guards are crafted from a dental impression of your actual teeth. This makes a massive difference for three reasons:
- Retention: They snap into place. You can open your mouth, speak, and breathe heavily without the guard falling out. This eliminates the clench reflex, lowering tension in the jaw and neck.
- Profile: Because they are made for your specific bite, there is no excess material bulking up the roof of your mouth. Your airway remains open.
- Oxygen Intake: With a secure fit, you can focus on deep, rhythmic breathing without obstruction.
In the past, getting a custom guard meant an expensive trip to the dentist. However, direct-to-consumer options have made pro-level protection accessible to everyone.
For example, getcheeky.com offers a streamlined way to get a dentist-grade custom guard without the dentist’s office price tag. You take your own impression at home, send it in, and get a guard that is perfectly trimmed to maximize airflow and comfort.
Once you switch to a custom fit, you escape the physical obstruction of a bulky guard and the physiological stress of clenching.
Conclusion
Endurance is hard enough.
If you are using a generic mouthguard, you are essentially training with a handicap. You are restricting your air, spiking your cortisol, and wasting energy on jaw tension.
Don’t let a $20 piece of rubber ruin the gains you have worked months to achieve. Treat your mouthguard with the same respect you treat your running shoes. Upgrade to a custom fit that opens up your airway and stops the energy leaks.