Today after school before my real run, I ended up running for a few minutes with my heavy backpack on. I couldn't help but notice how much more of a workout that I got, but afterwards on my run, my stride felt kind of imbalanced. So here's my question: could running with a heavy backpack a couple times a week for no more than 10 minutes be beneficial? I know it could lead to injury, but a small amount of it could be beneficial.