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Performance Condition with Rally Pedals

DavidJJones
over 1 year ago

This is really a data algorithm question (I think)....

I have two pairs of Rally RS100 pedals, one on my hybrid commuter bike (straight bar, 11.5kg) and one on my road bike (full carbon, 7.5kg).  My issue is that although the power feels about right (calibrate before most rides), when I'm on the hybrid commuting to work (24km each way), my performance condition is regularly -5 / -10 for a ride.  When I then jump on the road bike, its +2/+5.

Does anybody know what the algorithm for Performance Condition is, and how this could be affected so heavily by the environment?  Surely if I'm on a heavier bike with a rucksack, the speed is irrelevant as the power is what matters?  I know I'll ride home tonight with no rucksack (wind break!), in a tailwind, and the performance condition will be nearer zero.

This seems at odds with the logic of having a power meter, and incidentally, also appears to have a knock-down effect to FTP, that has started reducing ever since I bought the second set of Rallys - even though my pace / HR on the road bike for 50-100km is basically identical.

Any help would be gratefully received.

  • 0 over 1 year ago

    I don't know for sure but I think I can shed some light on this. I have a exercise/thermal physiology background so this isn't entirely out of my comfort zone. 

    Based on my own experience and what you mentioned there, I beleive the performance condition uses the relationship between power output and heart rate and not much else. For example, when on your commuter you may not be sending it so power outoput will be lower than on your roadbike, but your heart rate will still respond to the power output on the commuter/during an easier ride. I honestly doubt that it takes speed into account as there are too many factors that can influence this, as you have mentioned rucksack, bike weight, road surface, tyres, wind etc etc. 

    If I were designing such an algorithm I would only use the relationship between heart rate and power output (aboslute and rate of change for power and heart rate). During low-moderate power outputs your heart rate when you are not pushing it will still rise pretty quickly, and then when you are doing a tempo or higher intesnity ride, your heart will go up more of course, but if you are well trained, your power output can be substantially greater. 

    I have a similar thing that on Zone 1-2 recovery/endurance rides my performance condition is usually -5-0 then on higher power output rides my performance condition is 5+ until the end of long long rides as I get tired and the amount of power I can put out compared to my heart rate response due to dehydration, fatigue etc is reduced. For example on an easy ride, your power output might be 150Watts and your heart rate might be 135bpm, but on a hard ride you might get up to 230Watts and an average heart rate of 150bpm. The magnitude of the increase is much higher for power output compared to the ride in heart rate between the easy ride and the hard ride. 

    Hope this helps. 

  • 0 over 1 year ago

    Garmin has information around how PC works at a very high level on their website, the exact inner workings are likely to be Firstbeat IP:

    - https://support.garmin.com/en-US/?faq=A28UA4k16v1qjjGuvSFgo8

    - https://www.garmin.com/en-US/garmin-technology/running-science/physiological-measurements/performance-condition/

    In my anecdotal experience it seems to pivot mostly around HRV. I would suspect that factors like time-of-day, position on the bike, clothing (choice, which could impact movement, heat retention, etc), rucksack (which would add metabolic load), and hydration probably play a bigger role than the type of bike (although the type of bike would impact position).

    Anything that changes your metabolic load will impact HRV and HR, which would impact PC. I regularly have better PC, and VO2 Max calculations (which is driven off the relationship between HR and power) riding the trainer compared to my riding outside. I suspect that this is an artifact of riding in a much more relaxed position (no reason to ride aero when your not moving :)), which increases air intake and lowers metabolic load.

  • 0 over 1 year ago

    Hi, the other answers here already covered it I think. I just wanted to stress that Performance Condition has nothing to do specifically with the Rally pedals, or any other power meter that you use. As  mentioned, these are proprietary algorithms developed by FirstBeat (now owned by Garmin), which are implemented in the Garmin Edge units (and I assume their watches as well). As others mentioned, it's primarily based on heart rate monitoring, including HR variability (time between beats), supplemented with power data, and it's calculated in real time during your activity (not at the end).

    I've noticed similar variations that you mention. I find it's easy to underestimate the load that commuting etc puts on us! Clothing, packs, posture, route (frequent stops, etc), bike type, etc, all degrade how efficiently our bodies are working. In other words, our body is under greater strain for the amount of work we're doing than if we were doing the same on an efficient road bike/kit. So the algorithm sees it as reduced performance.

    And this kinda highlights some of the drawbacks of these FirstBeat secret-sauce algorithms. I think it helps to compare apples to apples to get the most benefit out of them (or the least misleading info). And it's very difficult for *everything* to stay the same over a period of time, even in the same ride style such as road riding. So comparing commute rides is probably okay, or comparing road rides, but comparing commute rides to road rides encounters the problems you have. They're simply not comparable.

    I find Performance Condition might help show me a strong/fresh day vs a fatigued one, but aside from that it hasn't been terrifically useful for me. And to be honest it simply confirms what I already feel. And it also usually requires some high exertion periods in the activity to give a useful value. If I just putt around at recovery pace, the PC value will be bad. If I do some sprints, it will be (much) higher. So it's very sensitive to what you're doing. Take it all with a hugeee grain of salt!

    Cheers!