If you start exercising incorrectly, it can actually cause harm to your body, be it through physical injury or as damage to the heart and circulatory system, which can eventually lead to death.
A Guide to Proper Running Form
Body-Weight Exercises for Arms, Legs, Core, and More
How to Improve Your Running Form
5K Race Tips - ASICS Runkeeper
3 Ways to Prepare for a Run - wikiHow
Proper Running Form: 9 Tips To Perfect Your Running Form
Effects of Running on the Female Body (by a Medical Doctor
The Basics of Running: Proper Running Form
Runner's Diet Johns Hopkins Medicine