Changes

* Loading Rate is how rapidly the forces build up and can either be averaged over parts of this section of the graph or an instantaneous peak can be used. This is a measure of how steep the curve is during this initial landing.

=Acceleration =

* '''Axis'''. Accelerometers can be either a 3-axis or 9-axis sensor. A 3-axis sensor simply measures acceleration in each of the three directions, which is sufficient for simple impact evaluation. A 9-axis sensor adds the ability to measure rotational movement in the three axis. (A 9-axis sensor also include a 3 axis compass.) This ability to measure rotation can be useful for understanding things like [[Foot Strike]]. For instance, if the foot rotates so the toes continue to descend after the initial impact then you know that the runner landed on the heel.

* '''Jerk'''. Just like Ground Reaction Forces, the impact can be evaluated as the peak acceleration or it can be based on how quickly the acceleration builds up. This rate of change of acceleration is called [https://en.wikipedia.org/wiki/Jerk_(physics) Jerk in physics]. (It's also called the third derivative of position, but "Jerk" is more entertaining and more intuitive.) There is some evidence that Jerk may be more relevant to injury rates than acceleration on its own. However, I don't think the evidence is compelling enough to form any definite conclusion. That said, it's important to know if your sensor is showing you impact has acceleration or Jerk. I suspect that Jerk could be a little misleading, as relatively low acceleration that builds up very quickly would be considered a higher impact than relatively high acceleration the builds up more gradually. It seems to me to be possible that the 2 values might be combined in some way, but I've not seen that approach used. Sensors that use Jerk include the [[Wahoo TICKR Run]] ("Smoothness") and [[MilestonePod]] ("Rate Of Impact (ROI)").