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Ground Reaction Force Explained (For Coaches)

What is Ground Reaction Force?

Ground reaction force is the force generated by the ground against a person’s body in motion. It revolves around Newton’s third law of motion, which states that for every action, there is an equal and opposite reaction. When a person is walking, their feet touch the ground lightly and don’t generate that much GRF. However, if the same person begins to sprint, each strike is more forceful and generates much higher GRF––the equal and opposite reaction.

What Does Ground Reaction Force Mean For Coaches?

Ground reaction force is typically measured using specialized tools like triaxial force platforms and motion capture software and hardware. These and other tools are useful during a biomechanical analysis but are not accessible to most coaches.

That said, understanding GRF is still crucial, even if you can’t readily measure it and compare the values over time.

Having a good understanding of the body’s interaction with the ground can help you:

  • Assign movements that suit individuals. For example, running might be ideal for an experienced trainee looking to do hybrid training. However, low-impact activities like swimming, cycling, and using an elliptical machine might be better for someone who is overweight.
  • Teach proper form. This is one of the primary pillars of coaching, but understanding ground reaction forces can help you communicate the importance of proper form with your athletes and develop strategies to optimize technique and limit joint stress.
  • Optimize power output. Understanding how GRF works can help you teach activities and drills focusing on explosive starts, deceleration, and change of direction for superior athletic performance.

FAQ

1. Why is GRF important in sports?

Ground reaction force is crucial for understanding how athletes develop force, how various activities could stress the body, and how to optimize the trainee’s workout plan and technique for optimal performance, progression, and injury prevention.

2. Can ground reaction force play a role in injury prevention?

By understanding the ground reaction force generated by specific movements, coaches can help athletes improve their technique to reduce the stress generated during training and competition. This can reduce the risk of nagging aches and injuries.

3. Does footwear impact ground reaction force?

Special footwear, such as running shoes, can reduce the force impact of each foot strike by providing cushioning, leading to more comfort, fewer aches, and a lower risk of overuse injuries.

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