The ground answers every step
When a runner pushes into the ground, the ground pushes back. That response is ground reaction force (GRF). In running, the vertical force rises and falls while the foot is in contact, creating a distinct curve for every step.1,3
Peak vertical GRF marks the curve's highest point. Expressing it in body weights makes the number personal: 2.0 BW means the ground pushed upward with a force equal to twice the runner's body weight at that instant.
Two equal peaks can be completely different landings
Two steps can reach the same peak while one builds force gradually and the other arrives sharply. Vertical loading rate describes that early rise—the speed at which load is introduced to the system.1,2
That is why STRIV shows peak force and loading rate together. One describes magnitude; the other describes delivery. Neither tells the full story alone.
- Peak force: how high did the curve rise?
- Loading rate: how quickly did it rise?
- Contact time: how long did the foot stay connected to the ground?
One landing becomes a load profile
Plantar-pressure models have reconstructed continuous vertical and braking–propulsive GRF across multiple running speeds and slopes. Wearable motion models have also estimated structure-specific peaks, impulses, and loading rates for the Achilles tendon, patellar tendon, ankle, and knee.3,4
That research points to the larger opportunity: the signals captured at every foot strike can help translate an invisible mechanical event into a profile runners can follow outside the lab.
What STRIV sees across the whole run
STRIV combines underfoot pressure and motion signals to estimate peak vertical GRF and vertical average loading rate for each foot. It aligns those readings with contact timing, cadence, pace, and run progression.
The result is not one scary impact score. It is a moving comparison: left versus right, early miles versus late miles, easy pace versus hard pace, and one shoe or surface versus another.
The useful question is: what changed?
Speed, slope, cadence, footwear, and running strategy all reshape the force curve. A personal baseline lets those changes become information instead of noise.1,3
Did loading become sharper while pace stayed steady? Did one side begin taking more peak force? Did a cue soften the early rise without slowing the runner down? STRIV makes those questions visible—and makes the next run an experiment rather than a guess.