13/01/2026
BUILDING PERFORMANCE: A Mechanical Foundation from Newton to Usable Force
Building athletic performance isn’t magic; it is a blend of fundamental physics and neurology.
Here is a mechanical foundation for understanding how we move from basic laws of motion to producing “Usable Force” in sport.
The Foundation:
Movement starts with Newton’s laws. Every action applied to the ground creates an equal and opposite Ground Reaction Force (GRF). This GRF is essential because force is what creates acceleration (F=ma), and acceleration is required to change velocity. No force, no change in motion.
The Neurological Boost:
We don’t just rely on conscious muscle contraction. The Stretch-Shortening Cycle (SSC) utilizes the stretch reflex. It’s a neurological loop where rapid stretching triggers an immediate reflex contraction, enhancing concentric force output.
The Real-World Constraints:
Force doesn’t exist in a vacuum. In sport, it is constrained by:
* Time: Impulse (Force x Time) dictates momentum change, but ground contact times are short.
* Load: Force must always overcome gravity and inertia.
Defining “Usable” Force:
Because of these constraints, not all force capability is accessible. “Usable Force” is the specific range where you can apply sufficient force, in the right direction, within the limited available time to actually affect motion.
The Critical Takeaway:
This is why strength is the key adjustable variable. Increasing raw strength builds capacity, lifting the entire force-velocity curve. This expands the “Usable Region,” allowing you to produce more impulse under time pressure.
Patrick Stephensen | Exercise Physiology |
