Chelle - I've dug out a massive chunk of concrete from 2' down with my fiberglass shovel. It creaked & groaned, but didn't snap. And I *doubt* you're anywhere near my size (I'm what you can call a "generously proportioned individual"
which is a lot nicer than saying I'm a fat butt) so I wouldn't honestly worry about it. Look at the main shaft of the handle. Fiberglass, when it gives, shatters just like wood (trust me on this) and you can actually see splintering in the handle much like old old old wood.