You are stronger than you think, you can take on more than you ever could, and you have the ability to reach past your full potential. I found this article on The New York Times that demonstrates how your body can handle more than you think. As the saying goes ‘No pain, No gain’. How will we know what our limits are if we do not set out to find them?
I suggest you take a look at GRETCHEN REYNOLD’S article about physical limits and be open to the idea of pushing yourself to reach your goals.