Nothing to Do With the Mouth Guard Itself
Back in the early 1980s, supposedly tech-savvy lifters began using high-tech mouth guards to increase their strength. Clenching down on the mouth guard was supposed to align the jaws and increase nervous system efficiency, allowing them to move heavier weights.
You couldn't just buy a plastic mouth guard from the local sporting goods store, though – it had to be fitted and manufactured by a dentist.
Custom-fit mouthpieces are still around, but the current theory behind them is that they improve breathing and prevent you from clenching the jaws in a way that pinches the nerves that run through the temperomandibular joint. This supposedly prevents performance-hampering cortisol from being released.
The cortisol theory is quite likely bunk, but the early mouth guard adapters from the 80's were onto something, only it probably had nothing to do with jaw alignment. In fact, it probably had nothing to do with the mouth guard itself. Instead, it had to do with simply clenching the jaws.
Researchers from Marquette University discovered that the mere act of clenching your teeth during a lift, along with gripping the weights or handles harder, dramatically increases strength.
The researchers procured a leg-extension machine that measured the force of maximum voluntary isometric contractions. They then recruited 12 previously weight-trained men. The subjects were then put through four tests:
- The first time, the subject simply exerted as much force as possible against the leg-extension machine.
- The second time, they squeezed some hand grips as hard as they could while pushing against the leg-extension machine.
- The third time, they were given a generic mouth guard and told to bite down on it as hard as possible while exercising the quads against the machine.
- The fourth time, the subjects had to push against the machine while squeezing the hand grips and biting down on the mouth guard, along with doing a Valsalva movement (where you hold your breath and contract the abdominal muscles).
What They Found
Gritting the teeth made the subjects 10 percent stronger, and when they clenched their teeth, gripped the handles, and did the Valsalva movement at the same time, they were 15 percent stronger.
"The present study demonstrates that jaw clenching as well as the aggregate effect of gripping, jaw clenching, and the Valsalva maneuver potentiates leg extensor mean and peak torque," concluded the scientists.
What This Means to You
Many of you know this phenomenon as "concurrent activation potentiation" or CAP. It's simply the phenomenon by which you can increase the force production of muscles through the contraction of muscles that are remote to the prime mover.
In practice, that means that gripping the bar tightly and simultaneously clenching your jaw should improve your bench press, deadlift, squat, or any other lift by a considerable degree.
While potentiation isn't a new concept, it's woefully underemployed, especially since it's such an easy and productive way to improve your performance in the gym.
One word of caution, though: If you want to use this method, get yourself a mouth guard. It's not for proper alignment of the jaws and it's not to prevent the release of cortisol; it's simply to protect your teeth as you clench down hard. (I've cracked two molars through overly exuberant jaw clenching.)
Cheap mouth guards are widely available and they don't need to be custom-fitted.
Related: Strength-Training Tricks: What Works?
Related: Cutting-Edge Muscle Science
- Ebben WP1, Leigh DH, Geiser CF. "The effect of remote voluntary contractions on knee extensor torque," Med Sci Sports Exerc. 2008 Oct;40(10):1805-9.