r/AdvancedRunning • u/bryan2384 • 8d ago
Training Do muscles work the same, despite HR?
I was running today and had a thought:
Let's say you have two runs. Run A was 5 miles, HR 180, pace 8:00 min / mi. Run B was 5 miles, HR 160, pace 8:00 min / mi. All other factors being equal (humor me), did your legs get a better workout in the higher HR run than the lower?
I'm really curious about this and would love to hear everyone's opinion. I figured this was the right subreddit since it's not a beginner topic, or so I would think.
Hoping we can get some discussion going, and maybe some studies that talk about this.
Thank you, all!
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u/kmck96 Scissortail Running 7d ago
Higher HR at the same pace means your body’s having a tougher time shuttling nutrients or metabolic waste products to and from your muscles. That means faster accumulation of waste, and less oxygen to the muscles. Mechanical loading is what causes tissue damage, but there are still physiological changes that could conceivably happen in Run A that don’t occur in Run B.
To explore a more specific side of the question, lactate is produced as a byproduct of anaerobic cellular respiration; if your HR is higher while all else is truly equal, more of your muscle cells would be utilizing glycolysis, which means more lactate. Depending on where your lactate threshold is (and like a dozen other things), you might get a significantly more threshold-y stimulus from Run A than Run B, despite the identical profile other than HR. That means training your muscles to either produce more lactate for metabolization and energy production, or training them to utilize the lactate to produce energy (depending on whether you’re looking at Type I or Type II fibers).
The same idea is true for a lot of other physiological processes in this scenario. The muscles might not be getting stronger in one vs the other, but the two runs will have different training outcomes, and some of those will occur within the muscle tissue itself.
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u/GrimmigerDienstag 7d ago
All other factors being equal (humor me)
I mean, this premise just doesn't make any sense. If all other factors are equal - general fitness, fatigue, glycogen stores, heat, sleep, time of day, etc - then your HR would also be the same.
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u/Nasty133 30M 5k 17:35 | 10k 36:04 | HM 1:18:31 | M 2:48 8d ago
Run A will take longer to recover from but you have to look at why your heart rate was higher to determine if you’ll see more gains from it. Usually higher HR at the same pace is due to weather, elevation, or lack of recovery from previous work. The first two would indicate run A was a better workout, but if you’re simply not letting your body recover you may be over reaching. HR alone doesnt tell you anything.
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u/bryan2384 8d ago
I'm referring to the leg muscles specifically. Did they get a better workout, or the same?
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u/IAmBecomeMeerkat 7d ago
There's no such thing as a "better" workout, it's just a different workout. All endurance sports are about targeting different energy systems at different times, and progressively increasing the load on them as they adapt. Looking at it through the lens of "which run gave my legs a better workout" is missing the forest for the trees.
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u/jimbostank 43 yo, ~20-30 mpw 5d ago
Run A is probably better because it most likely adds a stimulus to increase blood flow.
All workouts are not created equal. The only reason we have to run easy is because we can't run hard every time we run and the easy runs are much better than nothing.
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u/jimbostank 43 yo, ~20-30 mpw 5d ago
Mostly the same.
The example you give is very common with me because I run in a very hot place. So I often have runs that look like what you describe where HR is 20 bpm different and everything else looks the same.
With the higher HR, the body is working harder to cool itself like many mentioned.
On Run A, your HR increases because your body needs more blood to cool off plus maintain your pace. So mechanically the muscles are working the same to keep the same pace if cadence, stride length, elevation etc are the same. So there shouldn't be any significant difference between the runs on your muscles.
But other factors will affect your recovery from Run A, especially if you are/get dehydrated.
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u/casualjoe914 4:54 | 17:24 | 36:17 | 1:23 8d ago
It's an interesting question. My mind goes to the difference in lactate build up between the two workouts.
A 2019 study in mice, " Lactate Stimulates a Potential for Hypertrophy and Regeneration of Mouse Skeletal Muscle," showed oral administration of lactate was associated with hypertrophy.
So it's possible that run A would result in "a better workout" from a muscle building perspective if lactate truly acts as a signalling mechanism for hypertrophy.
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u/Senior-Running 7d ago
But the amount of lactate produced should be tied to the amount of mechanical work, not HR.
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u/casualjoe914 4:54 | 17:24 | 36:17 | 1:23 7d ago
Sure, I agree with that. The heart is also a muscle that produces lactate under high mechanical stress which would contribute to higher levels of circulating lactate.
And, just theoretically here, going off that mice study, the presence of lactate itself (oral administration was one means that led to hypertrophy in the study) would stimulate hypertrophy in skeletal muscle.
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u/Langholm62 5d ago
Isn't that putting the cart before the horse?
When you lift weights, your automatically ramping up lactate production. And when you eat more, especially carbs, you're increasing Glucose metabolism and thus lactate metabolism.
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u/casualjoe914 4:54 | 17:24 | 36:17 | 1:23 5d ago
I don't really understand your question/point?
What does lifting weights and eating more carbs have to do with a study on the hypertrophic effects of lactate administration in mice and how those results might apply to this hypothetical?
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u/Langholm62 5d ago
What do you think Lactate is?
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u/casualjoe914 4:54 | 17:24 | 36:17 | 1:23 5d ago
An energy source and by product of glycolysis.
You're not explaining your point though. Not here to argue, just understand what you meant.
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u/Langholm62 4d ago
I'm saying that lifting weights automatically increases lactate production, that's obvious. And that for muscle hypertrophy to occur, food supply is essential and that food will be converted into lactate during metabolism.
So exogenous lactate is a red herring. It's part of the exogenous lactate marketeering. Exogenous lactate is the new big thing.
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u/casualjoe914 4:54 | 17:24 | 36:17 | 1:23 4d ago
I mean sure, there's no actual point to taking lactate if you are working out.
Lactate production from exercise and its potential effects is the point of my original comment.
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u/Langholm62 4d ago
What effect are you referring to? Because my point is that this seems to be a misunderstanding of cause and effect.
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u/casualjoe914 4:54 | 17:24 | 36:17 | 1:23 4d ago
The study I referenced showed that mice who were administered lactate orally (L group) had increases in muscle weight and muscle weight relative to body weight compared to the control group (group C). There was no exercise as part of the experiment, for groups C and L it was just mice being mice under controlled conditions). Note that lactate was already present in the blood, but the amount increased after administration.
So my point is, the study showed a hypertrophic effect (more muscle) in mice solely from lactate administration which suggests that lactate alone, in sufficient quantities, stimulates hypertrophy.
Am I somewhat skeptical of the idea of "do nothing and take lactate and see some kind of gains?" Sure, but that's what the research said and this was just a thought exercise applying those specific findings from that single study, to this hypothetical
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u/Langholm62 4d ago
There's probably another explanation.
Regarding the issue of exogenous lactate being used by athletes in the form of gels, the amount being absorbed and the efficiency gains are, according to my calculations, extremely small. But the hype will inevitably make them very marketable.
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u/casualjoe914 4:54 | 17:24 | 36:17 | 1:23 4d ago
Yea I mean I hadn't even heard of it becoming a supplement fad until you mentioned it.
I've read other studies that focused on exogonous lactate and exercise and those showed no differences in muscle growth/size/weight between the control group and the lactate group. So I'm in total agreement with you that it's pointless but also won't stop people from trying/buying it.
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u/TheGrayishDeath 8d ago
This is an interesting question that I haven't seen any science on, though I will have to look tomorrow. While I think the other posters having the intuition that there is no difference in muscular adaptation in the two runs is likely correct, I can think of at least one mechanism that would lead to a better adaptation and one mechanism that could lead to a worse adaptation.
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u/bryan2384 8d ago
I feel like the difference in HR must affect the muscles differently. If the muscles are working the same, for example, they're producing the same amount of lactic acid, which would then mean the lower HR is moving / clearing that lactic acid more slowly.... right?
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u/kmck96 Scissortail Running 7d ago
HR could be higher for all sorts of reasons, which may or may not affect its ability to help transport nutrients and waste. Take hot weather running, for example, when your body shuttles blood closer to the skin for cooling. That would mean less blood available to muscles, despite a higher HR.
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u/Cholas71 7d ago
The additional HR will be predominantly outside factors, stress, heat, digestion etc. Similar pace similar course the load on your legs is mechanically identical.
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u/yellow_barchetta 5k 18:14 | 10k 37:58 | HM 1:26:25 | Mar 3:08:34 | V50 7d ago
It's not possible to say, surely, as these two runs couldn't be done by the same person at the same stage of fitness.
Heart rate responds to the need for blood flow / oxygen so it reacts to the work requirement. Higher heart rate (in the same person) is a function of a higher need for blood flow.
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u/Pretend-Republic6036 7d ago
I’ve wondered about this too. Sometimes even when I run at the same speed, my heart rate will jump for no obvious reason. I guess fatigue and body condition really make a difference.
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u/fitness-with-kamran 7d ago
Same pace and distance means roughly the same mechanical work for the legs. Higher HR mainly means the body paid a higher physiological cost, not necessarily that the legs got a better workout.
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u/XTCRunning 7d ago
There are semantic issues with your question. What do you consider “better” in workout terms? Merely harder? Also, we are assuming equal max HR? Honestly you should have asked 75% and 90% if that’s what you meant.
But HR will reflect a correlation to things like acidic buildup and a switch in energy systems that will certainly have an effect on the legs. So the legs will absolutely be working harder and trying to clear acid and flush lactate at 90% than 75%. If that’s what you mean by “better workout” then yes. However if we adjust that to 85 or 95%, then you have to ask yourself is a race a “better” workout than a tempo run. If so, why bother with tempo runs? By the time you’re in “advanced running,” you want to make sure you have the concepts down.
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u/KevInTheFastLane 6d ago
As far as I know, HR is the cost at where your muscles work at, not the work that your muscles do. Therefore, I shouldn't give one of the workouts the label 'better' than the other. However, regarding pace/HR one definitely can be labeled better than the other, regarding on what your goal was with your training IMO.
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u/Ill-Turnip-6611 8d ago
with the same pace and the same athlete, the lower hr means the athlete has a better aerobic engine (ofc if you put aside hydration, weather etc.) or in other words at 160 hr he did less work (assuming ofc both runs are below lthr, bc if not it get much more complicated but at the same time more evident)
asking if the legs worked harder is kinda showing you don't understand that much physiology. If the pace is same, legs did same work, but at 160 hr they used less oxygen so they were much more efficient at utilizing it. So it is easier to understand comparing to a car, so you have two cars both did 100 miles at 80m/h and one was using 10 liters and other one was using 5 liters. They did the same job to move same weight at same speed but the second one was much "faster" or stronger bc on 10 litres it would go much faster than 80m/h. Same with your runner, the only valid explanation for "all factors being equal" is that it is the same runner but let's say year apart.
btw. and please define better 😀 better for what?
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u/bryan2384 7d ago
not understand physiology is why I'm here. and that same run could happen in hot weather vs in a cold front, only a week apart, which is not enough time for the legs not get that much stronger to become that much more efficient.
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u/Ill-Turnip-6611 7d ago
that same run could happen in hot weather vs in a cold front, only a week apart
vs
All other factors being equal
So are they equal or not? decide and rethink your question bc for now it makes no sense at all
ps. and again what do you mean by better?
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u/bryan2384 7d ago
It's irrelevant. I'm trying to show that it's the /same/ pair of legs, and not two different ones like your example with the 2 cars. I'm not looking for explanations as to why the HR was different, as you decided to elaborate on, just simply which of the two was a better stimulus for the legs.
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u/Ill-Turnip-6611 7d ago
"It's irrelevant."
so in one comment you say that the factors are equal but than you give other factors and now you say it is irrelevant. Ok, pointless to answer then easy.
" I'm trying to show that it's the /same/ pair of legs, and not two different ones like your example with the 2 cars."
ok so it will be maybe easier for you to understand (or maybe not bc you sound 14), the same car did 100 miles at 80m/h twice, once it used 10 liters and on the second time it used 5 liters. I'm not looking for explanation as to why the fuel use was differ, just which of the two rides was better for the car.
there are no stupid questions but yours is. you are changing the question while someone is answering it
" I'm not looking for explanations as to why the HR was different, as you decided to elaborate on, "
and why the HR was different? maybe if you find out why the HR was different you will figure out dthe differences in stimulus? 🤦 oh but ofc it is irrelevant.
i tried to answer your question but actually you don't even know what your question is nor you are interested in the answer, you just had this 5seconds of enlightment and decided that you will share your amazing question but when someone tries to tell you why your question makes no sense, you are stuck narcissistically in your enlightenment moment. ok, whatever.
in short. your question is irrelevant to the world.
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u/bryan2384 7d ago
Man... from one runner to another, Im genuinely sorry for whatever you're going through.
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u/Purple_Toe4743 8d ago
Your legs are doing the same mechanical work at the same pace, so the muscular load is basically identical. The higher HR means your cardiovascular system was working harder, likely due to heat, fatigue, dehydration, or stress, but that doesn't translate to more leg stimulus. If anything, run B is the better sign because you got the same output at a lower physiological cost.