I see alot of random stuff on Japanese TV. Today's was the claim that biting on a tissue increases your strength. Take a tissue, fold it in half, then once again, then again, then the last 2 times fold in half the short way so you end up with a tissue pad about 4 inches wide by 1/2 an inch thick. Now put it between your teeth and as you do something strenuous, bite down on the tissue, just like most people clench their teeth when straining say to pick something up.
The TV program showed some guy who claimed he couldn't lift some boulder then he bit the tissue and was able to lift it. They then showed a bunch of people do a grip pressure test with and without the tissue. Finally they showed a 5 grade vs 6th grade tug−o−war test. The 6th grade easily beat the 5th graders the first time but then all the 5th graders were given tissues to bite on and they managed to win.
Is it true? Well, I tend not to buy it but some doctor was on at the end claiming that in clenching your teeth, the brain interprets the pressure on your teeth as a signal to put out more strength in the muscles. The thing is, because everybody's teeth are not perfectly aligned you don't actually get pressure on all the teeth so the signal to the brain is smaller. Putting the tissue between your upper and lower teeth allows you to put pressure everywhere and therefore send a stronger signal resulting in stronger muscles. Do you buy it?