Save Your Joints - Get to Know Ground Reaction Force

Trainer Question:  I am a trainer in Florida and I run my program in a school yard.  Some of my heavier clients complain of knee pain.  Do you think that the black top is contributing to higher impact?
Answer:  It certainly could, Shane. Especially if you have your clients doing moderate-to-high impact moves like jogging or plyometric exercises.
Remember Newton’s Laws—For every action, there is an equal and opposite reaction?  In our case, it's known as Ground Reaction Force. We use this force as propulsion to initiate and to our control movements. And Outdoor Trainers - you need to know about it.

The ground reaction force is the external force that acts against our body in motion.
•    Reaction force is supplied by the ground.
•    The heavier the client, the greater the reaction force.
Here is a list of surfaces from the hardest to the softest:

  1. Concrete
  2. Pavement
  3. Blacktop—school yards
  4. Firm pack dirt
  5. Soft dirt
  6. Grass
  7. Sand

Bottom Line:
Avoid hard surfaces (#1-3) for moderate-to-high impact moves such as, jogging, running, and jumping.
For plyometric exercises like jumping and leaping, teach "soft landings" - landing through the toes and forefoot first, and absorbing through the muscles, not the joints.

Outdoor Fitness BookOutdoor Fitness ShopOutdoor Fitness NewsOutdoor Fitness PodcastOutdoor Fitness Newsletter