Mouthguards being fairly hard are not made to extend collision time between the teeth and the source of impact. They act on the principle of distribution of force. Once there is a blow to the mouth all the teeth are involved at once, minimizing possible dental damage. Wearing a mouthguard is exactly what athletes should do and be encouraged to do.
Many conditioning coaches introduce the mouthguard in summer conditioning so the athlete gets used to exercising with something that for many feels like an obstruction in their mouth. Running with an unaccustomed mouthguard initially cause the athlete to feel an unexpected dryness during activity. Many have thought mouthguards negatively effects performance and take measures to use it as sparingly as possible.
The truth is that mouthguards have no effect on ventilation, that is, the rate at which gas enters or leaves the lungs. The mouthguard has no effect on maximum oxygen uptake, the ability of an individual's body to transport and use oxygen during exercise. Nor do mouthguards effect an individuals ability to give maximum effort while playing sport.
Wear those mouthguards and Get Strong.
3 Way Rows Headed 1 Way to Notre Dame