PDKL45

So I have a training route that I'm currently using. I'm tracking my training with a heart rate monitor and a Strava phone app subscription. I get that people have a lot of issues with the Strava app and the use of algorithms etc to provide fitness stats. I accept all of that and I understand that things may not be 100% accurate.

That said, the issue I am having is relative effort discrepancies in what are similar rides. On that route I ride fasted both at dawn and at lunchtime. The route's 26 kilometers/16 miles, give or take a meter or two, 139 meters/456 feet elevation gain. I'm using rate of perceived effort (RPE) to gauge if I'm in Zone 2 or 3, and it seems to be working okay. Still, I can never seem to replicate lunchtime rides in the morning and it's really bugging me.

For example:
Wednesday @11:45 am: 26.1 kms, 1:00:35, 149 watts estimated average power, 543 kj energy output: Relative Effort: 93 (2% Zone 1, 26% Zone 2, 64% Zone 3 & 8% Zone 4)
Thursday @ 6:45 am: 26.05 kms, 1:01:45, 147 watts estimated average power, 544 kj energy output: Relative Effort: 44 (7% Zone 1, 75% Zone 2, 18% Zone 3)

The RPE was roughly the same for both rides and there were even physiological factors telling me the efforts were very similar, like ropey saliva strands, similar breathing etc. The only real variable is temperature. Lunchtime is around 33C/91F while morning is around 23C/73F.

I'm genuinely baffled. Has anyone else ever come across something like this? Or has an explanation as to why the heart rates would be so different?

RChung

What were your average HR for those two rides?

PDKL45

I can't find the averages, but parsing the data, the answer lies therein.

2% Zone 1, 26% Zone 2, 64% Zone 3 & 8% Zone 4 as opposed to 7% Zone 1, 75% Zone 2, 18% Zone 3.

Maybe it's a fault with my RPE? The numbers are fairly clear, but the two rides--in my mind at least--were all but identical.

MoAlpha

I can’t follow that, but if the measure is based on HR, higher numbers in the heat are expected.

shelbyfv

You get heart rate zones with the Strava subscription, default or custom. Why guess? And yes, heat really makes a difference.

RChung

You're saying the (7%, 75%, 18%) had RE=93? Or did you switch the ordering?

Harold74

I do something similar. Same 27km, tempo-ish ride, similar temperatures, similar times of day. Trainer Road estimates my effort as a TSS score based on my heart rate (no power data).

I'll see the heat in the data but it might be 5 pts on a 60 TSS ride. Certainly not a doubling.

I don't know how Strava does it's RPE but it almost seems as though your HR is close to the z2/z3 boundary and gets tipped over into a different bucket by the heat. I would hope that it would be a more graduated thing than that of course.

I will say that I seem to do quite well in the high temperatures relative to other people that I know. As long as I've got sections of high enough speed that it feels like a faux breeze, my subjective RPE isn't much more than at lower temperatures.
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Harold74

Your degree of fasting might be another variable that comes into play. An overnight "while you sleep" fast won't actually be fasted in the sense that it won't draw down your muscle glycogen stores. What you do with your waking, fasted hours in the morning might.

pdlamb

Have you considered old-school, where RPE=Relative PERCEIVED Exertion? Skip the opaque mathematical ************ Strava does, and record how hard it felt like you were riding.

RChung

RPE is fine, but Strava's Relative Effort isn't *that* nutty. It's basically Bannister's TRIMP, which was the inspiration for Coggan's development of TSS. If you have power data, many people use TSS; if you only have HR data, many people use TRIMP.

I have a power meter so, basically, I ignore Strava's RE.

Iride01 

The difference in temperature will make a big difference. Especially if you've lost your heat acclimatation. I'm assuming your 93 relative effort is high effort and the 44 is low.

I just posted about this in the old peoples forum, but last week I rode 4 days in the morning cool temps instead of the midday temps I normally ride of 90-95°F. And this week, back doing the midday ride, halfway through what is normally a short ride, I was worn out. So I feel that those few days of lower temperature riding let me lose some of my heat acclimation.

And on a different thought about it, Sometimes rides I perceive as very easy rides turn out to be rides where I put out the most power and have a few PR's for some segments. And that comes from just having your riding loads from previous rides giving you the ideal stuff you need to be at your best for that days ride.

PDKL45

Sorry, I switched the order. I'll edit.

PDKL45

Sorry, I may not have made it clear. That is my issue.

In relying on my own RPE, I got two very different results from rides that, in my mind, had almost identical rates of perceived exertion.

RChung

OK, so I can more easily see why you're puzzled. The elapsed time is almost the same, the average power is almost the same, your RPE was similar, but the time in HR zones are very very different. For the morning ride, you spent 18% of your time above Zone 2; for the noon ride, you 72% of your time above Zone 2. So, if your HR monitor was working properly, I can easily understand that your average HR was higher for the noon ride, and if we're to believe those zone proportions, the Relative Effort difference looks believeable.

So, the first question is: was your HRM flaky on one of the rides or on both, or was RPE off so much (or, I suppose, but less likely, was your heart doing something weird)? The temperature was 10C hotter, and that's a lot.

I think I'd probably track another ride or two to figure out whether it's the HRM, or the heat.

PDKL45

I think it was the heat? I just did a lunch ride with the same RPE and it was 88. I think it's a combination of things, the heat at midday and my RPE perception being a bit off. I don't think it's the HRM, I trust the numbers. I guess I was just puzzled by the large discrepancy before really digging into things, and I suspect it's more of a perception issue than anything else.

It's just strange for me. I have really gotten into measuring my performance lately and I can really put down heavy efforts on that route at lunchtime. I find it very hard to replicate those numbers on other routes at other times of the day, but I also think it's more to do with me than my tech playing up.