terrymorse 

Is anyone using Efficiency Factor (avg. power divided by avg. heart rate) to track their aerobic fitness?

It seems like an obvious and easy way to tell if your aerobic system is improving or not, but I can't find much in writing about it.

Joe Friel writes in Efficiency Factor and Decoupling: "By comparing the resulting [Efficiency Factor] ratios for similar workouts over several weeks you can measure improvements in aerobic efficiency."

And again here on The Efficiency Factor in Running, "If your EF is rising then you are becoming more efficient and therefore more aerobically fit."

That's all I could find, so I guess we have to take Joe's word for it.

Veloviewer displays a handy graph of Efficiency Factor by week. Here's mine for the last few years:



Each year starts with a low EF that rises quickly to a plateau, with a few short bumps throughout the season.

I'm trying something different this year by getting on the bike earlier, and doing almost all of my rides in that "awesome aerobic" zone 2 that's getting so much attention. This year's "starting point" EF is higher (yay), and it looks like I've already gotten back up to my best EF from last year (also yay).

Encouraging -- unless this EF stuff is just a bunch of hooey.

Carbonfiberboy 

I watch it for Z2 roller rides because those are at steady power, not counting warmup. I haven't been charting it, but I do look at it. Every little pat on the back helps. Definitely not hooey in that narrow application, but that's all I have data for right now. My pedals feel lighter as that EF goes up, no surprise.

RChung

Interesting that in 2019-2021 you returned to the same baseline ratio (~ 0.6) each year.

Combining this with your other thread on VO2 and power, does this mean you were delivering more O2 per beat (i.e, stroke volume)?

Rather than the ratio, what were the trends in actual HR and power?

I never look at this ratio.

terrymorse 

Yeah, I guess that 0.6 figure corresponds with my completely detrained state, as I did no exercising to speak of between those two years.

I guess that's what it means. More power per heart beat --> more O2 consumption --> larger cardiac output.

Unfortunately, I don't see a clean way to display average weekly HR and power. Veloviewer shows weighted average power, back to 2021 (when I started using a power meter):

RChung

What is "weighted average power"?

terrymorse 

It’s a number that Strava spits out. Their description sounds a lot like “Normalized Power®”.

From Strava glossary:

Weighted Average Power

When you ride with a power meter, you'll notice how your power jumps all over the place based on the terrain, grade, wind, and other factors. Weighted Average Power looks at all of this variation and provides an average power for your ride that is a better indicator of your effort than simply taking your average power. It is our best guess at your average power if you rode at the exact same wattage the entire ride.

RChung

Ah. If it's Strava's, it's Skiba's xPower, which is a slightly smoothed version of Normalized Power. Golden Cheetah uses Skiba's xP. (There's a story about putting that "®" on “Normalized Power”).

For the purposes of looking at the power/HR "efficiency" ratio, you probably don't want to look at something like NP or xP (though Coggan talked about doing just that back when he first introduced NP -- back before it was even called NP).

[Edited to add] As an aside, this is the 20th anniversary of when Coggan first introduced the concept of NP to the public.

mschwett 

i think this is a very interesting question!

i track heart rate and power pretty religiously, but unfortunately (due to different power meters, occasionally finnicky HRM, and impact of medications) my data doesn't show a clear trend over a long period of time. the most consistent data i have (same power meter, same methodolgy) is affected by the first 3-4 months of the year with the PM only reading the left side, and then being post-corrected. my balance is in the 44-56 range, so that's a huge difference and the correction is not that accurate. the last 6 months of the data is the most reliable, but there are dropouts for some rides where my HRM was misbehaving, and for rides less than an hour long. what i track is the "strongest hour" of the ride, otherwise the average numbers are too strongly affected by rides with breaks, starts and stops, etc. most of my routes have at least one fairly hard uninterrupted hour, maybe with a descent or two.

there is a subtle reflection in the somewhat spiky charts of my general riding trend, which was a bit of a slump through december, but improving since the new year. strava's "fitness and freshness" shows something similar, but way exaggerated.

the other thing i find useful is a scatter chart (first chart below) of heart rate vs power, showing the relationship for a longer period of time. in my case, there are sort of two trend lines, a lower one for rides later in the day where my heart rate is higher, and a higher one for early rides where my heart rate is lower. heart rate varies by 10-15%, but power only varies by 5-10%. a morning ride or a ride closer to having taken meds shows a slightly lower power, a much lower HR, and a slightly higher "efficiency."

the second chart has heart rate and power on the left axis, and the "efficiency" number on the right axis, in gold, with moving average line. it doesn't vary much and is very spiky, but you can see the slump and upswing.

RChung

20-ish years ago on the old Wattage List most of us had come from HR training and were switching to power meters, and trying to correlate HRM and PM readings. There were discussions about what HR and power together could tell you that neither could tell you alone, and some of those discussions were pretty heated. I think the "efficiency factor" dates back to that time, as well as "decoupling."

Back then I was more interested in "what can these data tell me right now that I can do something about" rather than long term trends. With 20-20 hindsight, I think there may be longer term trends that HR and HRV may be able to tell you that power alone cannot, but I'm still not sure if the information is actionable on a day-to-day basis. But not everything has to be actionable on a day-to-day basis for it to be interesting and thought-provoking.

terrymorse 

It seems that Training Peaks followed Coggan's advice, as this is how they define Efficiency Factor:

RChung

No doubt.

One issue with using NP (or xP) for this is that they can be sensitive to the composition of training over time. That is, if you're looking at the EF for a single ride, it can tell you one thing but over the course of a season, we often start off doing fairly "easy" training and then ramp up the intensity distribution as the season progresses. If so, because NP (and xP) are intensity-weighted, you could see a trend in NP/HR that tells you more about the intensity than about cardiac remodeling.

mschwett 

this was my thought in relying on the average (un-normalized) power for the strongest hour of the ride, rather than the whole ride. a 6 hour ride obviously doesn’t have the same average power as a 1 hour ride. the simple fact of the lower power doesn’t represent lower fitness, and i don’t think the relationship between power and heart rate is linear.

but i am interested in whether people think that relationship is meaningful. the other/original EF (ejection fraction), stroke volume, lung capacity and a bunch of other biomechanical things i don’t understand must play a very large role.

terrymorse 

I think you can see this "exercise intensity" weighting factor in my EF graph. There's a substantial "jump" in 2021 and 2022, after the early season ramp-up, which I suspect matches up with my switch-over to higher intensity rides. See the red arrow jumps:



No "jump" so far in 2023--just a steady-ramping up--as I haven't yet started doing higher intensity rides.

I guess a really smart EF would exclude all of the LT/anaerobic efforts in every ride, calculating EF on just the fully aerobic segments.

RChung

That's pretty damn cool.

I suspect that even if you were looking at un-normalized power, you'd still see a trend, just not as sudden a jump. I think there may be some changes due to stroke volume (though I'd sorta kinda be surprised if LVEF were changing that much) but I also suspect that increasing "efficiency factor" also reflects changes in mitochondrial density. But while I think it does reveal something going on, I'm still uncertain how to use this information day-to-day. It's descriptive but not prescriptive so you can use it to monitor progress but not to tell you what to do next.

terrymorse 

Yeah, I don't see how EF can tell you what type of training to do next, but it seems to tell me the effect of my recent training. I think of EF as a sanity check on whether I'm currently improving, plateauing, or declining. Also, comparing my current value to prior years gives me idea of where I am in this year's fitness trend.

For example, this year my starting EF was higher than in past years, and after just 5 weeks my current EF is roughly where it was at last year's peak. I suspect that's due to spending fewer weeks in detraining, doing strength workouts during the detraining period, and maybe doing much more zone 2 volume.

RChung

So, as I said above, I don't track this metric. What I do try to track is my power, and use that to tell if I'm improving, plateauing, or declining. Mostly, declining, dammit.

GhostRider62

I don't use TP anymore, GC user. For me (long endurance type rider), the concept of EF and Decoupling are very important and something I look at closely. I just do it differently. Let's say my RHR is 55 and my first ventilation threshold is 115 and I make 180 watts at that power. This gives me 3 watts per beat. So, I better be making about 270 watts at 145 BPM. If I am unsure of my recovery, I warm up well and then put it on 180 watts and if my HR is not around 115 BPM, let's say 125 bpm, I know I need more rest. As stroke volume and all the goodness in the mitochondria improve, the power increases at that HR. WRT decoupling, I like to see very little difference between the first half and second half unless it is very hot and then some decoupling is unavoidable for a lard bottom like me. I used to measure lactate but can't afford the strips anymore and it is a bit tedious.

terrymorse 

The issue I see with looking solely at power is that it's tough to tell how hard you actually went. Unless you're doing regular time trials, and even those can be variable. Were you drilling it or taking it easy? Adding in heart rate takes some of the variability out of the result.

Back in the pre-power days, I would monitor VAM over heart rate on longer climbs. If my number was 25 or better, I could tell I was in good form. If it was less than 20, I figured I had some work to do. The thing that got that number up was more climbing volume at a moderate pace, similar to the "lots of training in zone 2" that's become popular today.

RChung

I don't really look at decoupling. Does it take into account length of the halves, or do you just split the ride into two parts whether the ride is short or long?

I usually take note of my RPE when it's unusually high (or low). I felt that gave me enough context to evaluate changes in power even in the long period when I wasn't wearing a HRM (I started up again about a year ago so I could get HRV measurements). I rarely do formal tests -- though "rarely" doesn't mean never. GC does a pretty good job of updating my CP and W', especially when I'm disciplined enough to mark max efforts. When I'm not doing max efforts, I usually consider that "base" so I'm not particularly worried about tracking power changes anyway. As an aside, Dan Connelly originally coded up that CP/W' finding algortihm.

GhostRider62

GoldenCheetah seems to divide the ride in two by time and compares the two halves. I can usually tell I am wilting. When I get home, GC confirms. In temperate conditions, decoupling on a 3-4 hour ride might be zero or sometimes slightly negative when fit. When unfit, it can be 20%. I don't look at it for long rides because inevitably it seems the heart also gets tired, but that is just a SWAG. I also only look at it if the ride was homogeneous in efforts and aerobic in nature. Perhaps, once per week not every ride.

RChung

So, "decoupling" is just a quickie way to look at HR drift using a ride that's split in two halves rather than a finer (continuous) set of intervals? Hmmm. That's interesting too.

MoAlpha

I track it for the endurance power band too, where the HR response is linear-ish. At high effort, the HR response asymptotes and a flatter response or lower max can look like increased efficiency when it’s just decrepitude.

mschwett 

what i notice when i'm wilting is that both my heart rate and power are down. it just feels like more work, and i can gradually watch the average power for the ride decreasing a watt every five minutes or so.

chaadster

So how do you have an EF chart for ‘19 and ‘20 if you didn’t start using a power meter until ‘21? Where is the power data part of the EF equation coming from?

terrymorse 

I can’t tell for sure, but I suspect the 2019 and 2020 power values are Strava’s “estimated power”, which are probably not that accurate.

These graphs are from Veloviewer, which I assume takes Strava data and doesn’t manipulate them.