What evidence in Chapter 6 of Night that the prisoners are stronger than the guards?

The prisoners who are able to survive run the entire forty-two miles. Their desire for survival makes them stronger than the guards.... their will to live keeps them mentally sharp and physically numb.

"We were masters of nature, masters of the world. We had forgotten everything-death, fatigue, our natural needs. Stronger than cold or hunger, stronger than the shots and the desire to die, condemned and wandering, mere numbers, we were the only men on earth."