Here some intersting information on how the Tonic Neck Reflex (Tonic Labyrinthine Reflex) and Asymmetrical Tonic Neck Reflex increases strength. Most lifters/athletes do it without thinking about it, it is a reflex.
One of the prime examples of the Tonic Neck Reflex occurs in the bench press. (Journal of Strength & Conditioning Research. 5(4):188-191, November 1991.Berger, Richard A.; Smith, Kirby J.)
When most lifters bench, they drive their head into the bench as they push the bar up. Doing so elicits the Tonic Neck Reflex.
This reflex causes the arms to straighten, thus producing a stronger pushing movement when bench pressing.
In my observations, many heavyweight lifters evoke an even more pronounced Tonic Neck Reflex of driving the head into the bench when bench pressing. These heavyweight lifters will lift their head up off the bench as the bar is lowered to the chest.
Just as the bar touches thier chest, they simultaneously drive their head in to the bench. This appears to increase the Tonic Neck Reflex, producing more drive in pushing the weight up.
In a bilateral (two hand) pulling movement, the Tonic Neck Reflex is elicited when the lifter pulls their head forward, tucking their chin into their chest.
An example of this is cable rows or barbell curl. As you pull the weight into you, tucking you head into your chest causes your muscle to flex. Thus, you pull more weight.
In unilateral (one arm) movements, the Assymetrical Tonic Reflex increase strength. This reflex is know as the "fencing reflex." The movement like that of a fencer with a sword.
Turning the head to the right side, extends the right arm while flexing the left arm, and vise versa.
So, when performing a dumbbell over head press with your right hand, turning your head to the right causes the reflex of your right arm straighten, increases you strength.
By the same token, when performing a dumbbell curl with your left arm, turning your head to the right cause a reflex of your left arm flexing (curling into you), thus increasing how much you curl.
You can see Asymmerical Tonic Reflex in bikers when they pull on the handle bars with their arms. Instinctively, as they pull with their left arm they turn their head to the right. Then as they pull with their right arm they turn their head to the left.