If you've ever seen models of some of our early ancestors like the homo erectus, one of the first things you notice about them is their strong, broad jawlines.

We've come a long way since then both structurally and biologically speaking, and our bones have become much more slight and fragile in modern times. The jaws of the modern man are becoming increasingly narrow and short, and many people require excessive dental work ranging from tooth extractions to palate expanders to braces.

As the shape of our jaws continue to change, our physiology and biology have had to adapt. In the human body, every structure and system affects one another, for better or for worse. The jaw is a linchpin that has a massive impact (either positive or negative) on overall health and movement mechanics.

Let's review several ways that jaw position and function might interfere with alignment or performance and look at some tools you can use to help mitigate the effects.

The Jaw and Posture

There are 36 bones and over 50 muscles in the head and neck. All of those tiny muscles are responsible for many different tasks like chewing, swallowing, moving the eyes, stabilizing the head, and more. Let's focus on the masseter and the lateral and medial pterygoid muscles.

The masseter is one of the strongest jaw muscles and one of the most easily visible on the face. This powerful muscle originates at the cheekbone (zygomatic arch) and attaches to the jawbone (mandible). The primary functions of the masseter are to close or clench the jaw and to protrude the jaw forward.

The medial pterygoid is a thick muscle that connects the mandible to the maxilla (the upper jawbone). The lateral pterygoid has two heads and sits on top of the medial pterygoid. The pterygoid muscles assist in opening the jaw and moving the jaw from side-to-side.

When any of these muscles are imbalanced or tight, it can have a profound effect on your overall posture and movement patterns. If your masseter and/or pterygoids aren't functioning properly, you may notice an excessive tracking of the jaw to one side, or you might have an underbite. Many issues like temporomandibular joint (TMJ) pain, excessive clenching, teeth grinding (bruxism), and tension headaches can arise from poor jaw tracking and alignment.

The position of the jaw will ultimately influence tension of the muscles in the neck, which can in turn influence the position of the shoulder girdle and inevitably affect everything else in the kinetic chain.

For example, an overbite pushes the mandible back and the head forward. The rest of the body follows suit. The ribs shift forward and the pelvis rotates anteriorly.

Conversely, if you have a significant underbite you'll likely maintain a slouched posture and a posteriorly rotated pelvis. The same goes for someone with a jaw that's shifted dramatically towards one side: the muscles on that side will be preferentially recruited. When the mandible is properly positioned, however, the rest of the kinetic chain can function as intended.

How to Minimize Jaw Imbalances

While more extreme jaw issues may require significant interventions like surgery or braces, there are several tips you can use to address your imbalances at home.

The first approach to minimizing jaw imbalances is to release any overactive muscles. In many clients that I've worked with, the occipital muscles (underneath the base of the skull) and the masseter on either side are the typical culprits of jaw dysfunction or pain. Use one or two fingers and apply moderate pressure (no need to press too hard) as you massage those areas to encourage them to relax. Spend 20-30 seconds on your tight spots. For some people, this alone will create a huge difference.

The next thing to be mindful of is the tracking of your mandible when you talk or yawn. If you notice that you favor one side or the other, start to be more mindful of your movements. Practice opening and closing your mouth without deviating your jaw to one side. I also like to stretch out the tighter side by shifting the jaw laterally in the opposite direction.

Finally, focus on chewing more on the opposite side. For example, if you've found that the right side of your jaw is exceedingly tight, then chew more frequently on the left side. These strategies can help you maneuver the jaw back to a more neutral position.

The Jaw and Performance

Our breath is at the foundation of every movement we make. The position of our jaws significantly affects our breath. To breathe most efficiently, breathe through the nose with the mouth closed. Someone who has an underbite, for example, will almost certainly breathe through their mouth because of the position of their jaw. The tongue should ideally rest on the roof of the mouth behind the front teeth.

Studies have shown that mouth breathing is far less efficient for oxygen uptake than nasal breathing. One study compared bronchoconstriction (tightening of the airways) in mouth breathing versus nasal breathing. Effectively, nasal breathing results in less bronchoconstriction post-exercise when compared with mouth breathing (Shturman-Ellstein et.al. 1978). So, nasal breathing is preferable for exercise performance.

Additionally, nasal breathing is crucial when considering recovery after exercise. Simply by closing or opening the jaw while breathing, you can influence your body's physiological response to exercise. The breath regulates the state of the central nervous system.

Shallow breaths through the mouth send your body into the sympathetic (fight or flight) mode, whereas deep nasal breathing results in a parasympathetic (rest and digest) response. Pranayamic breathing in yoga, for example, has been found to have a profound effect on the state of the CNS.

One paper that analyzed pranayama breathing (yogic breath control work) concluded that nasal breathing increased grip strength in controls (Raghuraj 1997). As such, breathing through the nose with a proper jaw position may have a significant effect on strength.

Other researchers have sought to prove the efficacy of wearing a mouth guard during sports to improve speed and strength measures. The idea is that a mouthguard effectively encourages the athlete to generate more tension throughout the muscles of the face and neck.

One study found that taekwondo athletes who wore a customized mouth guard saw increases in peak power on both a Wingate aerobic test and in peak hamstring isokinetic torque (Cetin 2009). Another study noted that participants who wore a performance mouth guard demonstrated significantly greater power in the bench throw exercise.

When it comes to aerobic performance, jaw posture also seems to be important. Researchers performed a three-year study of long distance runners to note if improvements in jaw posture affected endurance. Surprisingly, they found that performance markers on hill runs, perceived exertion, and endurance levels all improved dramatically (Garabee et.al. 1981).

Jaw posture at the end of (or even in the beginning of) a race can be indicative of the athlete's breathing patterns and bodily alignment which will ultimately dictate his or her performance.

The Jaw and Your Hormones

Finally, jaw posture may influence hormone secretion. Jaw position can affect breathing strategies and thus the CNS. This seems to ultimately alter hormone levels.

One study tested post-exercise cortisol levels in participants who were either wearing a mouth guard or not wearing one. The findings were significant: the group that wore the mouth guard had no increase in cortisol levels 10 minutes after exercising. While the group without the mouth guard's cortisol levels continued to increase as more time elapsed, the mouth guard group actually saw decreases in cortisol (Garner et. al. 2011).

If you struggle to breathe properly during exercise, a mouth guard could be a beneficial investment. Much of the research available seems to note huge performance enhancements across many different parameters. This is an easy intervention you can make that will reap massive benefits.

Related: The Posture Cure

Related: Mouth Guards for Bodybuilding?

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