From Fellrnr.com, Running tips
comment: batch update
* '''Cadence (+ stride length)'''. As you'd expect, the measure of cadence is pretty accurate. Cadence is one of those things that fairly trivial to measure if you have a sensor on your feet or torso. It's only wrist based sensors that tend to have problems. The SHFT system will also calculate your stride length from your pace and your cadence. Unfortunately, SHFT does not get any pace information from the Footpod, relying on a GPS data from the smartphone. That means that if you run on a treadmill, your pace information is just the random noise from GPS inaccuracies, and your stride length is meaningless.
* '''Ground Contact Time (+ time in air)'''. Ground Contact Time is how long each foot spends on the ground, and this some research indicating that a lower Ground Contact Time is correlated with a better [[Running Economy]]. However, I've found no evidence so far that training can improve Ground Contact Time, and my personal suspicion is that the differences in the Running Economy are more to do with Cadence. A higher cadence will naturally result in a lower Ground Contact Time, and I'd like to see Ground Contact Time as a percentage of overall starts at time rather than an absolute value. The SHFT estimate of Ground Contact Time is too high, something I verified using [[High Speed Video Analysis]].
* '''Vertical Osculation'''. It seems intuitively obvious that excessive vertical movement is a sign of an inefficient runner, but I've not found any research indicating if there is an optimal value for Vertical Oscillation. A runners' vertical movement is partly based around the elastic properties of the leg muscles and tendons, so not all vertical motion is bad. SHFTs measurement of Vertical Oscillation, which they call "body balance" is far too low. I measured my Vertical Oscillation using [[High Speed Video Analysis]] to be 3.5"/8.75cm, but SHFT said it was 2.2"/5.5cm. Worse, the real time display on the smartphone app showed less than 1"/2.5cm.
* '''Impact'''. SHFT calls [[Impact]] "G-Landing" and says it's "the maximum force of impact upward through the body from when the foot hits the ground to flatfoot" and they talk about this impact being "normalized." I find this all confusing on several levels, not least of which is the value displayed for my running seems a rather low at generally less than 2.0g. I'm not sure if this is the impact forces measured on the chest strap on the Footpod, or combination of the two.
* '''Landing angle'''. Unlike other systems, SHFT provides an angle of landing rather than a simple classification or in the case of [[RunScribe]] an arbitrary numeric indicator. The results look pretty good based on [[High Speed Video Analysis]].