Name: Backward Power Datafield
Rating: 3.7 (9 reviews)
Author: takura87

**** CAUTION: STILL IN BETA PHASE. PLEASE DOWNLOAD ONLY AFTER READING AND UNDERSTANDING POSSIBLE ISSUES DESCRIBED BELOW. ****


Have you ever wondered how much your legs are braking your forward movement on their upstroke ... and found no good answer in the torque efficiency percentages from your power meter?

This data field shows you the unintended backward (or negative or lost or braking) power during the upstroke - in Watts! (This is probably the same as what is called Gross Power Absorbed (GPA) in Training Peaks / WKO4.) 

A torque efficiency of, for example, 50% at 100W effective power actually means that you are braking with 100W while pushing forward with 200W: 
(200W forward power - 100W backward power) / 200 W forward power = 50% torque efficiency

In such a case, this data field will show you that your backward power is 100W, together with the left and right component. You could use this data for example as motivation to work on pedaling technique through single leg drills, variations of which could for example include doing them not just with both hands on the tops but with just a single hand on the handlebars or both hands in the drops, but also strength training like sumo squats to improve your ability to pull up your legs and stretching to improve flexibility.

Notes:
- Requires a power meter supporting left-right balance and torque effectiveness (e.g. Garmin Vector, Powertap P1 or Pioneer SGM-PY910 in ANT+ power meter mode).
- Though unlikely, in theory you could of course be braking on the down stroke as well. That would be included in the displayed number.
- The cover image shows force vectors with tangential and radial component for illustration of the force applied to the pedal. The advanced metrics defined by Garmin uses only the tangential component.
- There can be a slight delay compared with the native power data fields which may lead to momentarily negative backward power being displayed.
- Looking at datasets from the P1 and from the Pioneer I noticed that it's not just a delay but the refresh cycle for the advanced metrics seems inconsistent, slower and not synchronized with the other power data and to be in the range of above 3 but more typically between 5 and 10 seconds, whereas the normal power data is generally updated every second except for drops due to wireless communication. The P1 seems to still send the (same) data every second, whereas the Pioneer might only be sending when there is new data. Might have to look at this in more detail and possibly implement at least some averaging or better some correction algorithm. I have not looked yet at the Vector.

************** CAUTION **************
This app uses the AntPlus BikePower and BikePowerListener classes - that were than still new - in order to access the advanced metrics. Unluckily, I only found out later that running two apps using these classes simultaneously may lead to system instabilities. I have posted a bug report and Garmin acknowledged issues on their side but stated that it's complex and require some time to solve. The last I heard was in May; it might or might not have been resolved since then. As I was not yet able to confirm the current situation, AT THIS MOMENT I RECOMMEND NOT USING THIS TOGETHER WITH ANY CIQ APP.

If you have run into problems, deleting the apps folder usually helps. You will need a PC/Mac to do that as well as a few other tricks: Long power button press to reset the device if frozen, and booting with pressed lap button to get into mass storage mode. I recommend making a backup of all files on your Garmin to your PC/Mac before experimenting with this app to be on the safe side.