Here are links to two very insightful New York Times articles. They both focus on how the human body can endure long distance exercise and still remain injury free. Long distance exercise can become complicated when the body starts to fatigue. When muscles tire out, proper form is compromised which can lead to injury. Some people may feel that the human body isn't meant for long duration exercise because of all the harmful risks.
These risks of injury can be prevented if you listen to your body. Distinguishing between the difference of joint pain and muscle pain is the first step. If your joints consistently ache, you should probably go to a doctor and get them checked out. If your muscles fatigue while training, you should learn to work through it. Allowing the body to fight past the exertion of pain will help reduce muscle fatigue and increase muscle tissue regeneration if done correctly. The article Pushing Past the Pain of Exertion touches upon how to respond to muscle fatigue and understanding lactate thresholds. When our muscles feel "the burn", it's typically because of the "lactic acid" build up in our muscles. That pain is OK to feel. Lactic Acid is formed when our muscles don't receive enough oxygen. It aches, but it isn't going to create an injury. Increasing our Lactate threshold will help the body endure more of this pain which will allow us to train longer and harder. Accepting the pain rather than fighting it will be monumental for any aspiring goals.
The second article The Human Body Is Built for Distance talks about how our bodies are more equipped for long distance activity than other mammals in the world. The bipedal movement of humans doesn't make us the fastest sprinters, but it does allow us to run for longer periods of time. It's remarkable. If you think your body isn't meant to run a marathon or half marathon, please read this article.
Pushing Past the Pain of Exertion
The Human Body Is Built for Training
Hope you enjoy the articles. If you happen to come across any other cool fitness related write-ups, please share them!