A few years ago I was training for a marathon, and I was feeling great throughout my training. I had just run my best half marathon time while training a couple weeks prior, and I was excited to get outside to do a 12 mile training run. The run felt great, the weather was beautiful, and I was in the zone. Then at mile 10, without changing anything in my stride, a sharp pain went straight through my ankle and I could barely walk. As a runner, I still tried to power through and managed to jog about another half mile, until finally I gave up and limped the rest of the way home.
So what happened? The short answer is I stress fractured my ankle from overuse. The longer answer dives into the anatomy of the human body, the stresses that are exerted on it, and the limitations of what we can endure without injury. After my injury (and a second stress fracture a couple months later), I began to wonder what kind of forces act of the human body while running, and whether or not it’s good for us to run for longer distances.
Any time you take a step, your body experiences a force that is greater than what it experiences while standing. A typical jog/run will exert between 2 and 4 times your standing force on your body. This means if you weigh 100 pounds, a single impact during a run will cause enough force to make you feel like 400 pounds. Your body does its best to absorb this shock to your body. The muscles in your legs act as a shock absorber, and the stronger your muscles, the less impact you will have loaded straight to your skeletal structure. This is why it’s important to weight train your lower body. Having weak or tight ankles or calves could lead to stress fractures in the foot and lower legs, which is what happened to me.
Shock absorbing shoes and insoles can help reduce the impact on your body, and has been scientifically proven that it helps reduce injury, but there could be some downsides to this. When you put on supportive shoes, the support and shock absorption that your muscles are adapted to provide are no longer needed. This triggers your body to weaken those muscles, and if you’re not careful, if you lose support in your shoes your muscles may not be ready to support the impacts of jogging the next time you go.
Another common technique runners use is they will run on softer surfaces to reduce the impact on their bodies. Scientists from the University of Calgary wanted to test this and see if impacts on harder surfaces such as concrete caused more injuries than softer surfaces, such as running on grass. The results were fairly surprising. They discovered that there wasn’t a noticeable difference in injury frequency when running on a softer surface rather than a harder surface. This could be because the cause of injury is more centered around an individual’s muscular and skeletal structure, rather than the force of the impact.
If you’re a walker or a runner it’s impossible to avoid the impact forces of the exercise, but you can reduce them by wearing supportive shoes or insoles. Also, impact activities such as basketball, running, or dancing typically produce an increase in skeletal mass, and are good ways to increase bone density to decrease your chance of stress fractures. Perhaps the best way to keep yourself from a running injury is to keep your lower body muscles strong and loose. The smaller muscles such as the ones in your ankles and calves are perhaps the most forgotten and important when it comes to preventing impact injuries. So for my runners and walkers out there, make sure you are staying ahead of any potential injuries by training your lower body muscles. If not you may end up like me, doing every cardio session on a stationary bike for months while my ankles healed.
Thank you for reading! If you want to learn more about the science behind walking and running impacts, check out these two peer-reviewed articles that I referenced when writing this article: