Yet Another Cycling Forum

General Category => The Knowledge => Health & Fitness => Topic started by: riddon on March 24, 2019, 02:03:46 pm

Title: Heart Rate on Audax
Post by: riddon on March 24, 2019, 02:03:46 pm
I have recently invested in an Heart Rate strap which I am using with a wahoo. I rode a 200km yesterday and noticed that, towards the end, I had difficulty raising my heart rate anything like as high as it went earlier in the ride. Strangely I also noticed that for the last 50k or so I was going really well, having gone through quite a dip in performance between 50 and 150k. . I have noticed similar performance anomalies on other similar rides. Is this something others have noticed? i.e feeling stronger and with a lower heart rate towards the end. Seems odd.
Title: Re: Heart Rate on Audax
Post by: FifeingEejit on March 24, 2019, 08:40:16 pm
Certainly notice the HR drop as distance increases, feeling stronger possibly mental boost from being so close to home?

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Title: Re: Heart Rate on Audax
Post by: Chris S on March 24, 2019, 08:50:17 pm
Pretty much my experience. Given a hill early in a ride, and I can hit MHR, but by the end of the day will be loitering around MHR-40.

This doesn't end there. On PBP, my HR decayed throughout the first 36hrs, and then languished in the MHR-60 area for the rest of the event.
Title: Re: Heart Rate on Audax
Post by: hellymedic on March 24, 2019, 09:45:18 pm
i don't KNOW but suspect this is related to the fuels you are burning, low heart rates going with fat and ketones, whereas carbs and lactate go with the highest heart rates.
Title: Re: Heart Rate on Audax
Post by: Kim on March 24, 2019, 10:09:55 pm
Pretty much my experience. Given a hill early in a ride, and I can hit MHR, but by the end of the day will be loitering around MHR-40.

+1

As to whether I feel that I'm going better later on, that's certainly something I've experienced, but I've had enough counter-examples that I don't think there's any particular pattern to it.

I'm a subscriber to the "The last 20km of any ride is always a bit of a slog" school of thought, but I think that's as much about psychology and geography as much as physiology.
Title: Re: Heart Rate on Audax
Post by: chrisbainbridge on March 25, 2019, 10:02:14 am
This is a known "thing" of cardiac decoupling.  I did not know about it until 700km into my LEL when I got worried enough that i bailed.  Research since then has shown that this is well known in endurance circles.  I suspect that low heart rate or Maffetone training will help and i have now switched to doing all my endurance training at the HR he prescribes. 

I will tell you if it has helped on my next 600km ride!
Title: Re: Heart Rate on Audax
Post by: rob on March 25, 2019, 10:15:33 am
Fatigue causes cruising HR to drop as does fuelling.   I can keep my HR in zone for a 200 these days but I need to be properly fuelled so I keep my carbs topped up.

For distances over 400 I only wear my HR strap for the first day as it helps me to keep a lid on my early efforts.   After that it doesn't give me any meaningful data so I leave it in the bag.
Title: Re: Heart Rate on Audax
Post by: Peat on March 25, 2019, 10:27:16 am
Heart rate always decreases with fatigue. I first noticed it on a cycling holiday, by day 4 I was blowing out of my arse and barely able to get my HR to my 'safe' level I normally used to cap my efforts on long climbs.

As an aside, I did a 200 last year where I decided to actively ride at a far lower intensity than I usually would. The thinking being that I would be able to maintain that effort far more consistently over the distance. What I actually found was that my HR/Power dropped off at a similar rate to usual but of course I was then unable to recoup any of the time I had lost taking it easy in the first half because I was reduced to a crawl. Is that a 'thing'?
Title: Re: Heart Rate on Audax
Post by: T42 on March 25, 2019, 10:50:17 am
I asked my cardiologist about it and he said "adaptation".  Apparently you start using oxygen more efficiently (mitochondrion population hike?) so your heart doesn't need to pump as hard. On 1000+ k rides I used to notice that I was flying on the 3rd day.  And ready for the morgue on the 4th.
Title: Re: Heart Rate on Audax
Post by: simonp on March 25, 2019, 11:38:46 am
Yes to both the heart rate cap and to the dropping energy levels turning around.

On the HR cap, I simply put it down to fatigue. Long endurance riding is hard on the heart. For the improvement in energy levels, this might be similar to the second wind described by marathon runners: https://en.wikipedia.org/wiki/Second_wind

I've always put it down to the metabolic switching hypothesis.
Title: Re: Heart Rate on Audax
Post by: riddon on March 25, 2019, 01:20:41 pm
Thats really interesting info. Thanks Guys.  Sounds like I am in good company.
Title: Re: Heart Rate on Audax
Post by: phil w on March 25, 2019, 05:15:45 pm
You could be getting dehydrated in the first 50km, that would lead to increased heart rate, and things getting harder. By 150km you have managed to get back to a hydrated state , and so the heart rate drops and things get much easier and you feel stronger for the finish.  That certainly a pattern I sometimes see when I don't drink enough early on.
Title: Re: Heart Rate on Audax
Post by: hellymedic on March 25, 2019, 05:34:51 pm
I hit ridiculously high rates commuting to work. I was young and (too) well-fed.

Tried commuting fasted; got The Slows and couldn't push up HR until I'd eaten.

I don't think I ever bothered with my monitor on Audax.
Title: Re: Heart Rate on Audax
Post by: mattc on March 25, 2019, 07:07:40 pm
I asked my cardiologist about it and he said "adaptation".  Apparently you start using oxygen more efficiently (mitochondrion population hike?) so your heart doesn't need to pump as hard.
If that's the case, isn't it amazing??

If you think about most fitness adaptations (e.g. reaction to weight-lifting) it takes days to get any benefit, often weeks. And this is happening while we're still riding 18hour days!??


I have looked into this in the past, and there seems to be verrrrry little hard research. I think sports science is focused on elite sport and durations upto Ironman - multi-day stuff probably just doesn't pay!
Title: Re: Heart Rate on Audax
Post by: Ian H on March 25, 2019, 08:05:59 pm
I certainly noticed this when I wore a heart-monitor. 

I stopped wearing a heart-monitor and no longer notice it.
Title: Re: Heart Rate on Audax
Post by: T42 on March 26, 2019, 08:50:17 am
I asked my cardiologist about it and he said "adaptation".  Apparently you start using oxygen more efficiently (mitochondrion population hike?) so your heart doesn't need to pump as hard.
If that's the case, isn't it amazing??

If you think about most fitness adaptations (e.g. reaction to weight-lifting) it takes days to get any benefit, often weeks. And this is happening while we're still riding 18hour days!??


I have looked into this in the past, and there seems to be verrrrry little hard research. I think sports science is focused on elite sport and durations upto Ironman - multi-day stuff probably just doesn't pay!

I had a gander at the mitochondrial life cycle and learnt very little other that they arise from existing mitochondria.
(https://www.researchgate.net/profile/Joseph_McInnes/publication/257985338/figure/fig1/AS:203153619329032@1425447005543/The-mitochondrial-life-cycle-Since-mitochondria-cannot-be-synthesized-de-novo-they-must.png) (https://www.researchgate.net/figure/The-mitochondrial-life-cycle-Since-mitochondria-cannot-be-synthesized-de-novo-they-must_fig1_257985338).

That ^^^ is a bit like coming into the film halfway through, since a lot of the characters are proteins we haven't met yet, and to be quite honest I'm not that curious. (I note that parkin is involved, which might suggest that Northerners make good Audaxers.)

Anyway, all the abstracts I glanced at involved studies over 10 weeks or so and none about short-term evolution.

Upon reflection, I'm now thinking that decreased heart rate mostly results from fat metabolism kicking in, which might also be what the cardio called adaptation. Might also explain why I used to fly on the third day and zonk on the fourth - inadequate fat reserves. Unfortunately, that is no longer the case.
Title: Re: Heart Rate on Audax
Post by: phil w on March 26, 2019, 12:12:10 pm
Even a skinny 65kg person has about 47,000 calories worth of fat so I would doubt you'd burn through it in a day. Like Matt I would doubt you would see much adaption mid exercise. The literature does talk about adaption when you rest. Exercise creates the potential for fitness and adaption, rest realises it.
Title: Re: Heart Rate on Audax
Post by: mattc on March 26, 2019, 12:24:18 pm
It's definitely something getting more efficient, I just think the mechanism is uncertain. Anecdata seems to show similar power generated at much lower HR later in multi-day rides. I don't think it's as simple as fatigue.

(Pretty sure that Greenbank posted some massive graphs of speed* & HR logs, possibly from PBP 2011? Or an LEL?

*I think it was speed - the problem was converting this into power of course!)
Title: Re: Heart Rate on Audax
Post by: T42 on March 26, 2019, 03:06:26 pm
Even a skinny 65kg person has about 47,000 calories worth of fat so I would doubt you'd burn through it in a day. Like Matt I would doubt you would see much adaption mid exercise. The literature does talk about adaption when you rest. Exercise creates the potential for fitness and adaption, rest realises it.

The report of an experiment I saw around 10 years ago said that a five-minute pause after an hour's exercise appeared to start fat metabolism at a low level. And a diagram I saw years before that depicted a gradual change from glucose-based to fat-based over about 5 hours.
Title: Re: Heart Rate on Audax
Post by: CrazyEnglishTriathlete on March 26, 2019, 08:01:23 pm
I haven't wore a heart rate monitor for long enough to get data, but if I look at my average speed on Audax events (when fit) it drops after about 8 hours.  On multiday events it picks up for the first session of the day (2 - 3hours) and then drops back again.  I've always correlated this with my body's fuel supplies - that the body is happy to burn a relatively high carb mix until it runs out.  Once it has run out of carbs once, it tends to conserve them, even when carbs are provided.  That correlates to feeling nauseous if I reach the higher heart rate zones.  I normally go through a rough patch around about (or before if I'm not fit) the 8 hour mark.  It may be a coincidence but the 8 hour mark is what I'd get round a flat 200 (when I'm fit) - so I'm probably never quite exhausting my carb supply (or if I am getting close its near to the finish so my body will let me continue on fumes).

An alternative explanation is that its a natural function of the heart protecting itself from overexertion, but that would require proper medical knowledge to digest rather than practical experience.
Title: Re: Heart Rate on Audax
Post by: CrazyEnglishTriathlete on March 31, 2019, 09:53:12 am
Real data from Le Tour de Neuf Chevaux Blancs - with ride to and from the start - total distance was 373km over 18.5 hours.  Average heart rate was 132.  However, up to 7.5 hours the heart rate was higher with peaks in the low 160s (even though I wasn't trying to go super-hard given the distance).  From 7.5 hours to 12.5 hours the peaks gradually dropped.  After 12.5 hours the heart rate never topped 135 and would have been averaging a little under 120.

However, I wouldn't argue that I was getting more efficient during the ride.  I just slowed down, which I would argue is adaptation arising from fatigue.