Definition: "An ergogenic aid is any substance or phenomenon that enhances performance "

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Grit your teeth and you'll be stronger

If you clench your jaw while doing your sets, it'll make you stronger. The same happens if you grip the weights or handles harder. American sports scientists at Marquette University have researched the effect known as concurrent activation potentiation.

This is the effect in which muscle A becomes stronger if you contract muscle B at the same time. If you're doing bench presses to train your pecs, delts and trics, then you'll be stronger if at the same time you clench your jaw muscles for example.

That's the theory at least. Little research has been done on the effect of 'concurrent activation potentiation' on the strength of large muscle groups. The studies that have been done, however, go little further than showing that subjects can squeeze a hand-grip 15 percent more if they clench their jaw at the same time. [Kokubyo Gakkai Zasshi. 2003 Jun; 70(2): 82-8.]

Grit your teeth and you'll be stronger
So the researchers designed an experiment that they performed on 12 men, all of whom used weights regularly to train their lower body.

The researchers got the men to train their quads on a leg-extension machine. This was a special machine, on which the researchers could also measure the maximum voluntary isometric contraction. The subjects had to generate as much power as they could, while the machine itself did not move.

On one occasion the subjects exercised their quads only [NO RVC]. On the other occasion they had to squeeze hand-grips as hard as they could at the same time [GRIP2]. On another occasion they were given a mouthpiece that they had to bite on [JAW]. And on yet another occasion the subjects had to make all the movements at the same time, and on top of that also hold their breath and contract their stomach muscles [JAW/GRIP2/VAL]. The latter you may recognise as the Valsalva manoeuvre. Strength athletes should be careful with this.

Grit your teeth and you'll be stronger

When the subjects gritted their teeth, they became 10 percent stronger.

If they also clenched their fists and contracted their stomach muscles, they became 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", the researchers conclude.

Med Sci Sports Exerc. 2008 Oct; 40(10): 1805-9.

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