What does the sensor measure exactly?

To explain this, we need to go back to the biomechanical basics, without making it too complicated. 

Every time your foot hits the ground, the ground exerts a force on your body, which is called the ground reaction force (GRF; see the figure below). There are two important load measures in the GRF related to overuse injuries in running:

1. The impact is the shock your body experiences the instant your foot hits the ground, and is expressed in G-forces.
   
   
2. Peak GRF is the maximal load your body experiences the moment your foot 'caries' your entire body, and is expressed in body weight (BW). 
   

Impact is mainly related to stress fractures and plantar fasciitis, while the peak GRF is mainly related to Achilles and Patellar tendon overuse injuries, as well as bony injuries at the ankle or knee. 

The OnTracx sensor measures the acceleration of the tibia (or the shin bone). Scientific research shows that the peak of this tibial acceleration (or PTA) is strongly related to the shock or impact runners experience during running. We’re currently working on developing algorithms to also calculate peak GRF. 

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