Inquiry about Stair Threshold Definition in ActiPass

[Crescent1999]

In Acti4, I noticed that the stair threshold appears to be not user selectable and stair-walking outcome of ActiPass is based on Acti4. I would greatly appreciate it if you could kindly clarify how this threshold is defined in the software, and whether there is a specific numeric value used internally for this parameter.

[pasan-h]

Short answer is, yes, there exist angle cut-offs and movement cut-offs for activities like cycling and stair-walking. But Acti4 algorithm is not just a simple decision-tree based on such cut-offs. Acti4 activity detection is sequential (one after the other), and after each detection the time series is filtered with median filter with different time-windows corresponding to different activities. Then another activity is detected, and the time-series again filtered. In addition to the sequential nature of the algorithm, activities like cycling and stair-walking has further complicated error corrections. Therefore it is not advised, to assume a behaviour/activity is detected using only simple cut-offs, nor change existing cut-offs without fully considering the implications. If one really needs it's possible via a special configuration file. Be aware that after you change any algorithm parameter (by using the source code or config files) you have to explicitly declare that you did that in a subsequent publication 😊.

1. For more information about changing algorithm parameters, finding default values and changing configuration files; see similar discussion here: Adding additional cadence cut-offs to use ActiPASS results for children #114.
2. For activity detection algorithm source code see: https://github.com/Ergo-Tools/ActiPASS/blob/main/algorithms/ActivityDetect.m

[pasan-h]

If it's not clear from the other discussion thread I linked above, in order to change algorithm parameters and thresholds we need to use a special config file. Non of the thresholds are user adjustable using the GUI (this is by design). At the moment ActiPASS released version (2025.04) uses config files in CSV format. The next release version will use the more readable JSON format. The thresholds used in algorithms are available in the file:
https://github.com/Ergo-Tools/ActiPASS/blob/main/conf/AktDetect_UI.conf

[Crescent1999]

Thank you very much!