To take firmly with the hand and maintain a hold on
An act or means of holding something
The thought made her chest clench so tight, she almost stopped walking.
Taran strode away, turmoil making his gut clench.
This condition, which is known as sleep bruxism, occurs when you grind your teeth together or clench your mouth while asleep.
If you clench or grind your teeth while sleeping, using teeth grinding protection can help prevent complications.
As you begin to develop your balance, you will not need to clench your toes, and the cramping will not be an issue.