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What's happening to my heart rate?

(40 posts)
  • Started 5 years ago by Greenroofer
  • Latest reply from wingpig
  • This topic is not resolved

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  1. Greenroofer
    Member

    A question for the audaxers, sports scientists and physiologists out there...

    So here's the thing. On rides of up to about 80 miles, my heart rate is relatively high: it bumps along at around 120bpm when I'm cruising,and I feel as if I have lots of power available in my legs so long as I keep the carbs flowing in. However I gradually start to feel tired, and if I don't keep the carbs flowing in then my heart rate goes through the roof with the slightest effort. I can recover this by eating some carbs. For this discussion I'm going to call this 'Type A performance'.

    After about 80 miles, my heart rate starts to drop. I feel I've got less power, but I don't notice a marked decline in speed on the flat. I stop feeling hungry, and feel like I could go on all day in a steady way. By about mile 100 my heart rate is way down (sub-100bpm) although my speed hasn't dropped hugely. I'm calling this 'Type B performance'.

    I assume that in Type A performance my muscles are firstly then burning through their stored glycogen and then using some metabolic pathway to generate energy where the rate of energy generation is limited by the rate at which my circulatory system can supply something to them (carbs, in some form, presumably). At some point, something runs out and they move to the Type B performance, where my circulatory system can supply whatever it is they need faster than they can use it, so my heart rate drops.

    Does anyone know what's going on? It's obviously 'fatigue', but what's happening?

    [It's something I've been pondering on for some time, but noticed it really clearly on a ride I did yesterday, and also saw the same effect in the Strava record of @Hankchief's weekend epic in the Cairngorms]

    Posted 5 years ago #

  2. wingpig
    Member

    Repeat the experiments making a careful note of your thirst levels and water intake/output during the two phases.

    Also, try and weigh your liver at the start, changeover and end.

    Your heart isn't just there to pump nutrients around - as far as it's concerned it's getting oxygen to your brain first, then your other tissues next, insofar as your brain might conceivably need them to stay alive. Irrespective of what your liver's doing with your fat stores, spare muscle or glycogen, your brain needs glucose. Irrespective of whatever else needs a ride around the body in the blood, your heart also has to obey secondhand instructions from the various hormones responsible for fluid balance; nutrients only hijack the circulatory system as they don't have their own system of transport-pipes to flit around through, so they tend to more influence the distribution of blood flow rather than the rate.

    Posted 5 years ago #

  3. Klaxon
    Member

    What do you mean by ‘weigh your liver’ ?

    Posted 5 years ago #

  4. wingpig
    Member

    Work out its mass. Ideally, its density too, but it's a bit difficult to get at.

    Posted 5 years ago #

  5. gembo
    Member

    Goes well with a fine Chianti and some Fava beans though.

    Greenroofer this sounds a bit like the opposite of the Quickening when your legs are struggling with hills but ok on the flat.

    Posted 5 years ago #

  6. I were right about that saddle
    Member

    Q: What do you mean by ‘weigh your liver’ ?
    A: Work out its mass.

    It won't be easy determining who has won CCE this year. This is high-grade stuff.

    To return to @Greenroofer's question: I have no idea as biochemistry is witchcraft, but it does show the perils of recording data. Where do you stop once you've started?

    Posted 5 years ago #

  7. toomanybikes
    Member

    A quick google confirms that heart rate drops when you hit the wall (run out of carbs) whether that is because of a drop in performance or because fat metabolism needs less O2 and or produces less CO2 I've no idea as I've completely forgotten the pathways.

    Common phenomenon for marathon runners apparently.

    Posted 5 years ago #

  8. Frenchy
    Member

    I only had a quick look at your heart rate data on Strava, but I'd like to play De'il's advocate and suggest that your heart rate decrease can be explained by turning round and going downhill.

    Rising @IWRATH, a power meter might help answer these questions. Or it might not.

    Posted 5 years ago #

  9. fimm
    Member

    You've stopped burning carbs and started burning fat. Or something along those lines. Err. I suppose I better Google now...

    Posted 5 years ago #

  10. crowriver
    Member

    "I'd like to play De'il's advocate and suggest that your heart rate decrease can be explained by turning round and going downhill."

    Frenchy's explanation seems the most plausible.

    What I've read about the wall / bonk etc. (i.e. running out of glycogen and glucose) is that your heart rate increases, not the other way round.

    Posted 5 years ago #

  11. Greenroofer
    Member

    For me the drop in heart rate with fatigue is just too pronounced for it to be simply the result of going downhill. When I'm in my Type A state, it falls a bit on the downhills, but not normally to below about 90bpm. Coming down Comiston Road on Sunday with 100 miles in my legs it fell to 50bpm (normal resting rate) and my HRM kept saying I was dead.

    I agree with @crowriver that 'the bonk' causes a high heart rate for me, but I wonder if that's different from the marathon runners' 'wall', which has always sounded much more serious and irrecoverable...

    Posted 5 years ago #

  12. I were right about that saddle
    Member

    @Greenroofer

    I have hit a wall doing endurance running. It involved hallucinations, palpitations and an inability to walk and it did take a while to recover.

    Posted 5 years ago #

  13. DrAfternoon
    Member

    Very interested in this, and I work in related physiology so should know more, but I can at least offer some more data from a four day ride, shows a clear long term fall in heart rate.

    Strava West Highlands 1200

    Almost certainly related to the shift from using glucose/glycogen to fat stores, but the confusion of that is that fat burning uses more oxygen for the same energy output. Need a sports physiologist.

    Posted 5 years ago #

  14. gembo
    Member

    Strava was very insistent I allowed it to record my heart rate recently under GDPR. I declined. I only look at Strava to see what routes the strava gang have posted. Still checking strava gives you something to do at the end of a bike ride instead of talking to each other.

    Having said this, obviously interested in best food to eat to avoid The Bonk. Gels, even the pink grapefruit ones Hankchief gives me, cause heartburn if I have more than four.

    Once I get The Bonk there is no recovery. So need to keep eating every 30 mins or so

    Posted 5 years ago #

  15. crowriver
    Member

    "obviously interested in best food to eat to avoid The Bonk"

    Midget Gems. Jelly Babies. Wine Gums.

    I find fruit bars quite good too. Or a banana (but the latter do get squashed/bruised in the saddlebag/pannier).

    Posted 5 years ago #

  16. gembo
    Member

    @crowriver, yes also sports mixtures which my pal Tom claims never to have heard of, despite being a good age. He liked the ones I gave him around netherurd/elsrickle the other day. The black ones are his favourites. Not much carbs in them tho?

    Posted 5 years ago #

  17. Greenroofer
    Member

    @DrAfternoon. Exactly. While you are clearly much more of a machine than me and can last over 100 miles before it happens to you, there's a clear point where your heart rate drops off to a markedly lower steady state.

    @gembo. I've stopped eating so much on rides. I found it was making me feel sick. I've gone down from one gel every 20 minutes (suitable for racing, I fear) to a gingernut or two every 40 minutes and something more substantial every couple of hours. At the weekend it was a Ginsters pasty at mile 25, an ice cream and a bit of cake at mile 50 and a bread roll with peanut butter at mile 75. I did get through litres of electrolyte though.

    Posted 5 years ago #

  18. gembo
    Member

    @greenroofer, yes bit sick and Also I get a stitch. Trying combo of aforementioned sweets, banana bars, or date bars, Aldi do them cheap, gels and cake. I find I need a combo so afte cake will fish out old gel wrapper from pocket and squeeze the residue

    Posted 5 years ago #

  19. wingpig
    Member

    "...obviously interested in best food to eat to avoid The Bonk"

    "Midget Gems. Jelly Babies. Wine Gums."

    Just get some actual jelly (the cubes, rather than the powder). Dissolves easily in the maw and comes in a range of nice flavours.

    "I found it was making me feel sick."

    Not surprised, if you're eating gels in those quantities. Unless you stop to let your intestines steal some blood from your legs you're not going to be digesting very much very quickly.

    Oatcakes sit very lightly in the stomach.

    Posted 5 years ago #

  20. Greenroofer
    Member

    @winpig - agreed. Can't understand how anyone (other than gel manufacturers) can imagine that if you're working hard enough to need a gel every 20mins you've going to have any spare blood available to digest the things. In the depths of a long ride (when I've run out of other things to think about) I do ponder whether some of the stuff like water and simple sugars can get absorbed through the stomach wall.

    Posted 5 years ago #

  21. Greenroofer
    Member

    So I have concocted a theory, which goes like this.

    1) We have limited stores of glycogen in our muscles and liver. When that's gone, it's gone (particularly if gembo's been at the chianti again).

    2) We can replace some of this by eating carbs, but at any appreciable work rate we can't take in carbs as fast as we're using them.The digestive system is a conveyor belt that slows down as we start working hard, and if we overload the conveyor belt we start feeling sick. So we will, at some point, run out of carbs.

    3) So, after a point, we reach steady state where the available carbs in the system are the ones we're putting in, and we can't put them in very fast. At that point we can't produce high levels of work because the carbs aren't available. We're in the 'fat burning zone' which seems to be about 60%-70% of max heart rate. In normal people, this zone is achieved by not working too hard. In the case of a long bike ride, we're in this zone because we can't actually work any harder: we've used all the other fuel.

    So this suggests two strategies to maximise performance:
    1) Get really fit, so we can ride fast at very low intensity and eke out our supplies of carbs and hope they don't run out before the end of the ride. This would gives reserves of power for hill climbs and sprints.
    2) Don't worry too much about eating lots. Let the carbs run out and accept that it will lead to unlimited plodding with no spare power. Eat gently to maintain the carbs at minimum low level. Actually a perfectly acceptable way to cover long distances, but not suitable for racing.

    I made all this up. It may be wrong. What do you think?

    Posted 5 years ago #

  22. wingpig
    Member

    What do professional bicycle racing people eat, apart from erythropoietin and salbutamol? Their lack of visible fat suggests they're doing enough work to use up any spare energy, whilst maintaining enough inter-organ fat to keep them idling if they get their food dosage wrong. Unless one of the jobs of their support team is to flush them out thoroughly prior to the racing session and keep them stoppered whilst on the bike, they can't be eating that much bulky stuff during a race.

    Posted 5 years ago #

  23. unhurt
    Member

    @crowriver @gembo re: Le Bonk - ooh, yes, first met before I even knew what it was called, in 2007, on day three of an ill-prepared for ride from Seattle to SF (on an dirt cheap Ed Bikes hybrid with way too much stuff and exactly one three day long practice tour behind me, ahem). One Kellogs Rice Crispie Square bar for breakfast after not enough sleep and two days of - in retrospect - eating nowhere NEAR enough food - and I started falling asleep on the bike mid morning. Like, head dropping, almost impossible to not just keel over and pass out on the verge. Quite scary, as I had no idea what was going on! Ended up lying on picnic table bench outside a small store forcing myself to eat a whole bag of jelly beans, conking out there for 45 minutes, then dragging myself over the road to the diner for emergency coffee and discovering that I was starving. One massive platter of fried red potatoes with bacon, sausage, mushroom & egg scramble and a pancake on the side and another hour snoozing on the bench outside before my legs finally came back online enough to proceed. Slowly, and with emergency Reese's Peanut Butter Cups on hand.

    Still dream about those amazing fried potatoes sometimes.

    Posted 5 years ago #

  24. gembo
    Member

    @greenroofer good theory

    I do not eat gels every twenty minutes. I eat something every half hour or so. Alternating sweets, date bars and gels.

    The magic gels that hankchief gives me should take about twenty minutes to even start working but I find I get a psychological boost - because they are what is called Isotonic. The Scientists at Hankchief Gels Inc. claim only their gels are isotonic and merely need a few sips of water to help whereas other inferior non scientific gels require 500mls of water to work.

    Before cares came on the radar I used to eat a wholemeal Jeely piece and drink Ribena out in the wilds of west Lothian.

    Posted 5 years ago #

  25. fimm
    Member

    @greenroofer that's what I was trying to say.
    @wingpig, according to Mr fimm even a gentleman with about 4% body fat (which is the minimum for a healthy man) has about 10,000 calories stored away there.

    I've taken to having a jelly baby every 20 minutes if I'm running a long way. I believe that one can train ones stomach to an extent - if you do in training what you are going to do in racing then your body gets more used to it.

    There's a different way to train, which is not to use carbs at all. That, as I understand it, trains your body to go for the fat reserves much more quickly and you can then run on fat.

    All this is stuff I think I remember rather than stuff I've checked. I'll try and ask Mr fimm, he knows more about this sort of thing than I do. When he runs ultramarathons, he nibbles on a mixture of stuff including jelly babies and bits of flapjack but also cheese and sausage. It is very definitely "what works for one may well not work for another" though.

    Posted 5 years ago #

  26. remberbuck
    Member

    You've really got two different things going on here. The first is hitting the wall, which is simply the body running out of stored glycogen and transferring to burning fat. The distance involved isn't that important - you can get it on an innocuous evening 6 mile run just as on a full endurance effort. It shouldn't impact directly on your heart rate, though the attendant anxiety plus the other things you've been doing to your body won't be helping!

    It seems more dramatic in running as there are other muscular fatigue issues going on. When Lance Armstrong missed his food stop in the 2000 TdF he didn't end up with Calum Hawkins' problems, though the cause was largely the same.

    Building your glycogen reserves beforehand is never wrong - there is method in the marathon runner's traditional pre race evening pasta, and the couple of days before as well. I'd have a big bowl of porridge a couple of hours before setting out, and a couple of porridges bar an hour or so in to give the stomach something to work on. Maybe gels after that, but I'm cautious with them as they are basically a sugar spike, and what goes up ....

    (I've only seen the no carb running suggested for first thing in the morning and 10k max, but the theory seems sound).

    Provided you're fit enough then any form of persistent exercise should bring the heart rate down. Simply, it has adjusted to the effort, and worked hard enough to bring the body down to a manageable temperature. Most runners will get there somewhere in the first hour. It will be more complex with cyclists as the effort is more variable depending on where the hills are.

    I wouldn't be too worried about the heart rate drop. Your cardio vascular system will be excellent, and a measure of that is how quickly it returns to normal. Getting straight back to your resting rate sounds quite dramatic, but provided there are no other unexpected discomforts, I'd just take it as a compliment to your fitness.

    Posted 5 years ago #

  27. crowriver
    Member

    "a Ginsters pasty at mile 25"
    Snap! Exactly what I fancied after riding out to Burntisland last week. Available from the local Co-op.

    "Just get some actual jelly (the cubes, rather than the powder). "
    I used to like eating jelly "raw" as a bairn but not since the age of 12 or so.

    "Oatcakes"
    Now you're talking. Used to always pack some in the saddlebag on audaxes as emergency rations, next to the wine gums...

    "Provided you're fit enough then any form of persistent exercise should bring the heart rate down. "
    Sounds about right. The body finds its "level" after getting accustomed to the effort over time.

    @unhurt, that sounds like an adventure! Should have had your Ready Brek in the morning... :-)

    Posted 5 years ago #

  28. Arellcat
    Moderator

    I remember The Bonk while riding from Lochgilphead to Dalmally, via the B840 that skirts Loch Awe before zigzagging up to the A819. I'd had a full Scottish Breakfast that morning, actually against my better judgement, and as I reached the A-road and stopped for a breather, I very nearly fell over.

    It took me a good hour to recover, with the help of a couple of biscuits and some water.

    While touring in the US the following year, I had one wobbly moment, during which my riding buddy ordered me to "eat this banana, and drink a ton of water". I eventually found I worked best by alternating water and Mountain Dew (which I found surprisingly palatable), and Oreos/crisps and bananas. I never really found Jelly Babies that good for touring because I'd have to stop to eat them, and then bits of them would get stuck in my teeth.

    When doing my Battle Mountain training last year, I would have some porridge for breakfast, but needed to hit the road before I started digesting, otherwise my blood flow would go to my stomach and not my leg muscles. At peak fitness I used about two-thirds of a bottle of water and one energy gel for a roughly 30 mile ride, which was really extended intervals rather than a constant pace. My resting HR went down to 42bpm.

    Posted 5 years ago #

  29. neddie
    Member

    Maybe gels after that, but I'm cautious with them as they are basically a sugar spike, and what goes up ....

    ^^^ This

    My "made up" rule is that after a pint, a Mars bar or anything sugary you've got around 20mins before you get an insulin spike and then crash again.

    Save the gels for the emergency 20 mins required to get home / get to the nearest station.

    Posted 5 years ago #

  30. Cyclingmollie
    Member

    I consulted a huge book about sports science today in the secondhand bookshop in Goldenacre. Their section on heart rate described something called cardiovascular drift. But their charts only covered two hours of exercise. During that time the observed heart rate increased. Googling that I got:
    Cardiovascular drift is mostly caused by increased body core temperature. This increases heart rate, but decreases stroke volume so that cardiac output (and oxygen uptake) remain the same. The effect can be enhanced by the decrease in plasma volume that is caused by water loss during exercise.
    That's what I used to find during one hour turbo sessions: my heart rate got higher over the hour. So we're really no further forward.

    Posted 5 years ago #

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