What is a Ground Reaction Force (GRF)?
Imagine that you’ve got a pea sized pebble in your shoe as you’re out on a walk or a hike. Not real comfortable, is it? Now imagine that you’re running or stepping off a big rock with your pack on with that same pebble in your shoe. Now it’s even more uncomfortable! Thankfully we can easily remedy this problem by taking the pebble out of our shoe.
If you’re a runner or a hiker or backpacker, you’ve maybe been in a conversation that brought up ground reaction forces (GRF). If you’re like most people who haven’t heard of GRFs and just smiled and nodded your head or changed the subject, you’ll appreciate getting the rundown on GRFs for that next conversation or that next run or hike.
First things first - what is a GRF? GRF is the force exerted by the ground on a body in contact with it. GRF is right in step with Newton’s 3rd law of motion - for every action, there is an equal and opposite reaction. In layman’s terms think of it like this - if your muscles aren’t strong enough to counter the GRF and carry you to that next step, something is going to give. GRF can be up to 2-7x your body weight! In the most extreme sense, your leg may buckle like you just jumped off a high fence. In the more common case, your knee or foot and ankle or hip may get a little extra stress placed on them that could lead to pain or an injury or inefficiency if left unaddressed.
Just like you can take the pebble out of your shoe, there’s plenty that you can do to counter the GRF on your next run or hike. First thing first, you want to make sure that you have the appropriate strength to support your run or hike. There’s a really simple way to test it. Watch your knee as you’re running or stepping up or down on a trail. Does your knee move inward toward your other knee? Or does it stay in line over your 2nd and 3rd toe? If your knee is moving inward, that is often a sign that you are putting more load on it than it is able to efficiently handle.
Before you try to buy Forest Gump’s leg braces, let’s look into how you remedy GRF when you’re running or hiking or backpacking. First, get stronger. A great place to start is with functional movements like squats, lunges, and hip hinges. While you’re not going to squat 7x your body weight, the stronger you are with these movements, the better support your body is going to have while you’re running or hiking or backpacking.
Runners - in addition to strength training you’ll want to pay attention to plyometric movements also. Some of our favorite plyometric exercises are box jumps, jump rope, jumping lunges, and lateral step ups (for speed).
If you’re wanting a more customized approach to address any pain issues or to maximize your runs or hiking and backpacking, give us a call!
