Connect with Ground Reaction




In late May 2017 I teamed up with a local marathon runner to attempt an extended period outdoor running gait analysis. At 12 hours it was by far the longest continuous assessment that I had tried to perform. The longest full suite analysis I had conducted before this was approximately 2 hours, with most analyses being up to 60mins.

The format for the data recording was an ultra marathon event hosted on asphalt pathways using a looped course. Key to my planning was ensuring that all the recording sensors had the necessary battery life to go to at least 12 hours, in fact to go even further than this. The sensor array that I used was relatively simple to ensure there was no excess bulk or issues with ergonomics given the long duration. I attached tibial sensors to the left and right legs and 2 sensors to each shoe (1 on the back and 1 on the laces). All of the real time wireless signals were collected by either a wrist watch or a separate RFD unit.

What I present below are snapshot results from 3 points during the event, showing data collected from just the tibial sensors. Due to the size of the dataset that was collected over the 12 hour period it was better to break the recorded data up into segments and analyse each of these. For simplicity I chose to create segments for each hour interval.

It’s important for me to note that going into the event the runner picked up a minor hip injury to the right side.

1st Hour

5th Hour

10th Hour

High Level Thoughts

I won’t go into the detailed evaluation of the all of the results, but rather just use the 3 snapshots presented above to stimulate thought and give an example of what can be performed. I haven’t used hours 11 and 12 because there was a significant amount of walking and this affects the interval results and makes the comparison between hour intervals less clear.

[It’s worth noting that more detailed analysis could only be performed with data from the other sensors.]


  • Firstly and most obviously there is a consistent tendency to weight the left side more and although the exact asymmetry value changes the asymmetry is pretty significant all the way from hour 1 to hour 10. If we didn’t already know about the right side hip injury then this would be a great indicator that something on the right side was not right.


  • Secondly the force, cadence and the speed drop by hour 10 (more specifically between hour 5 and hour 10). A clear indication of the fatigue related to such a long distance ultra endurance event. Whilst contact times stay approximately the same its the ability to output force and to sustain a higher turn over that are affected by the increasing fatigue.


  • Thirdly the change in symmetry does not adhere to one of the simple patterns of increasing, decreasing or staying the same. Rather it drops at hour 5 and then has increased again at hour 10. We might expect that during the event the hip injury would worsen for example and that asymmetry would increase. However when looking through all 12 hours of the data it appears that during this event the runner experienced changing degrees of hip functionality and changing effects on gait mechanics.


So that’s a very brief look at some of the data that was collected during the 12 hour recording period of the event. I’m still not 100% sure whether any other practitioner has performed a longer continuous outdoor running gait analysis to date. So far I have not found anything published that suggests anyone has, but I could be wrong.



M.Sc, MSci, B.Sc, CSCS, NSCA-CPT, XPS, CGS. Malc Kent is a professional coach, internationally respected applied scientist and former world class athlete that has represented Great Britain 31 times internationally. His services include personal coaching and mentoring, running gait and biomechanical analysis and running strength coaching.

Click to comment

Leave a Reply

Your email address will not be published. Required fields are marked *