I started using Under Armour’s Bite Tech Permformance Mouthwear about a year ago after my company signed an exclusive distribution deal. You can read all about the technology and science here, but basically by aligning your jaw properly, this mouthpiece limits the amount of cortisol (stress hormone) your body releases when clenching your teeth during strenuous activity. I’ve always said I feel more relaxed when I wear it. No matter what the workout, I’m able to focus on my breathing and just settle in.
Here’s what some of the pros who wear one say:
“The ArmourBite Mouthpiece helps me train harder, recover faster and ski stronger.”
Lindsey Vonn, U.S. Olympic Downhill Skier
“If I don’t have it in, I feel naked. It has become part of my uniform.”
Michael Cuddyer, Minnesota Twins
“I tried it, not only on the field but off the field during workouts. I could feel the difference in my endurance. I was stronger, my body felt better.”
Adrian Peterson, Running Back, Minnesota Vikings
“It has increased my strength, power and heightened my accuracy.”
Hunter Mahan, PGA Pro
“The weights didn’t feel so heavy.”
David Ortiz, Boston Red Sox
“I have noticed feeling more relaxed while riding. ”
Sarah Haskins, Pro Triathlete
“I am always looking for that extra edge. From the moment I put my Under Armour Performance Mouthpiece in my mouth, I could feel a difference.”
Chris McCormack, Pro Triathlete, 2-Time Kona World Champion
Go The Distance 
Do you know of any runners who use this? I’m curious
There are some testimonials from Triathletes on the site. I won’t leave home without it at this point. I’m not sure I can point to a specific effect it’s had (never done any testing), but I get the sense I’m more relaxed. I could just be mental, but I’m a believer.