If I'm at 5% MHR I'm probably bleeding out and about to die...
I'm not sure if its possible to have 5% MHR to be honest, which is why it makes absolutely no sense for me to use % of MHR. Isn't Heart rate reserves (HRR), where its actually possible to have 0% HRR more accurate to use? Where did this 70% of MHR come from? Because its definitely not 70% of my heart's capacity, if we assume that my HR can't be lower than my resting heart rate unless I'm dead?
Looking at my easy pace, I average 72% of MHR which is equivalent of 64% of HRR. Not that it matters as my view on easy is as slow are required to recover and be ready for the rest of the week. But I am not sure I like the 65 of 70% of MHR being prescribed for easy runs in this thread.
Looking at the Reddit thread, many are using 60% to 65%.
HRR % will give a higher HR if resting hr is high. High resting hr usually means poor metabolic fitness, so probably better to use % of max hr.
I think with CP is that it’s close enough to rely on, despite many different standards. You can still use rpe and heart rate, but those sometimes lie. Power for me is the most consistent.
What do you think about the quality workouts on treadmill? I have a Horizon T7.1 Elite that goes up to 20 km/h. Today I tried a session of 5 × 5’30’’ at 3’20’’/km pace (18 km/h) (half marathon pace), with 1’30’’ recovery at 6’40’’/km. It actually felt like a pretty solid workout. My heart rate was more stable, probably because the pace is constant and you’re less affected by road and environmental conditions (wind, heat, cold, rain, etc.). I know that many pros use the treadmill a lot, and I’m starting to get interested in trying some of Sirpoc’s workouts on treadmill.
It’s really interesting to notice how, little by little, the 3:20/km pace is starting to feel easier. Over time, I’d like to be able to run 5 or 6 × 2 km at 3:15/km. If I can also bring the paces of my other workouts down—from 3:15 to around 3:10–3:05 for the 3-minute reps, and from 3:30 to 3:25 for the 10–12-minute intervals—I’m confident I could take a couple of minutes off my half marathon time. It just takes patience and consistency.
If I'm at 5% MHR I'm probably bleeding out and about to die...
I'm not sure if its possible to have 5% MHR to be honest, which is why it makes absolutely no sense for me to use % of MHR. Isn't Heart rate reserves (HRR), where its actually possible to have 0% HRR more accurate to use? Where did this 70% of MHR come from? Because its definitely not 70% of my heart's capacity, if we assume that my HR can't be lower than my resting heart rate unless I'm dead?
Looking at my easy pace, I average 72% of MHR which is equivalent of 64% of HRR. Not that it matters as my view on easy is as slow are required to recover and be ready for the rest of the week. But I am not sure I like the 65 of 70% of MHR being prescribed for easy runs in this thread.
Above roughly 70–75% HRmax, your body starts to cross the line from primarily aerobic metabolism (fat oxidation) into a zone where lactate production rises and you start burning more carbohydrate for fuel. That’s fine in small doses, but if most of your training time is spent there, you never fully develop the low-intensity adaptations that make you efficient and durable over time.
Running below 70% HRmax targets your Type I muscle fibers, builds mitochondria, expands capillary networks, and teaches your body to burn fat efficiently, all without creating significant fatigue or hormonal stress. It’s the only way you can safely accumulate the volume of running needed to improve long term.
That’s the secret: the intensity itself isn’t “magic”, it’s that by keeping the effort low enough, you can run more often and recover faster, which compounds into massive aerobic gains.
When you creep up into 75–80% HRmax, you’re in what many call the “gray zone.” It feels productive, but it’s too hard to fully recover from and too easy to drive a real adaptation. Elite and recreational runners alike fall into this trap - training moderately hard every day, never fresh enough to go truly hard or easy enough to build their aerobic base.
The best evidence and coaching experience from Lydiard, Maffetone, Seiler, Daniels, and the OG double threshold Norwegians all converge on the same point:
“Most of your running should feel gentle. If you think you’re going too slow, you’re probably doing it right.”
So it’s not that 72% or 80% are “bad.” They’re just not as efficient for building the aerobic foundation that supports all the faster running you want to do later. Below 70% HRmax is where your body quietly gets stronger every day.
What do you think about the quality workouts on treadmill? I have a Horizon T7.1 Elite that goes up to 20 km/h. Today I tried a session of 5 × 5’30’’ at 3’20’’/km pace (18 km/h) (half marathon pace), with 1’30’’ recovery at 6’40’’/km. It actually felt like a pretty solid workout. My heart rate was more stable, probably because the pace is constant and you’re less affected by road and environmental conditions (wind, heat, cold, rain, etc.). I know that many pros use the treadmill a lot, and I’m starting to get interested in trying some of Sirpoc’s workouts on treadmill.
It’s really interesting to notice how, little by little, the 3:20/km pace is starting to feel easier. Over time, I’d like to be able to run 5 or 6 × 2 km at 3:15/km. If I can also bring the paces of my other workouts down—from 3:15 to around 3:10–3:05 for the 3-minute reps, and from 3:30 to 3:25 for the 10–12-minute intervals—I’m confident I could take a couple of minutes off my half marathon time. It just takes patience and consistency.
My view on the use of treadmills by the Norwegians specifically is that, as you point out, it is a controlled environment and you don't have to worry about pacing, wind, hills etc. The only caveat is that they will be Lactate testing to ensure they're getting the perfect intensity. Pace doesn't really matter, it is the intensity and particular lactate levels they want.
If you mess around with the paces and have an understanding of the HR that is roughly in line with LT2 then I see this as a good way of running your quality work
Above roughly 70–75% HRmax, your body starts to cross the line from primarily aerobic metabolism (fat oxidation) into a zone where lactate production rises and you start burning more carbohydrate for fuel. That’s fine in small doses, but if most of your training time is spent there, you never fully develop the low-intensity adaptations that make you efficient and durable over time.
Running below 70% HRmax targets your Type I muscle fibers, builds mitochondria, expands capillary networks, and teaches your body to burn fat efficiently, all without creating significant fatigue or hormonal stress. It’s the only way you can safely accumulate the volume of running needed to improve long term.
That’s the secret: the intensity itself isn’t “magic”, it’s that by keeping the effort low enough, you can run more often and recover faster, which compounds into massive aerobic gains.
When you creep up into 75–80% HRmax, you’re in what many call the “gray zone.” It feels productive, but it’s too hard to fully recover from and too easy to drive a real adaptation. Elite and recreational runners alike fall into this trap - training moderately hard every day, never fresh enough to go truly hard or easy enough to build their aerobic base.
The best evidence and coaching experience from Lydiard, Maffetone, Seiler, Daniels, and the OG double threshold Norwegians all converge on the same point:
“Most of your running should feel gentle. If you think you’re going too slow, you’re probably doing it right.”
So it’s not that 72% or 80% are “bad.” They’re just not as efficient for building the aerobic foundation that supports all the faster running you want to do later. Below 70% HRmax is where your body quietly gets stronger every day.
Some people will just not listen. There's people on Strava and Reddit who claim they can't run below 70% MHR. That is not possible, but they can run an hour at 90%+ LTHR and it still feels easy. People can't be trusted to make their own judgements, that's what this thread has taught me. Me included.
I see sirpoc jogging around at 4:35/km probably with a beer in one hand and wondered why I couldn't do the same. My ego was so focused on pace, it forget about that fact he's doing these runs at mid 60s of max HR %. When I slowed down, the whole thing worked. The puzzle here in this thread is absolutely huge, not as easy as some folks think. But once the pieces start fitting, starts working great and things have massively turned around for me since the new year and I'm glad I stuck with it. But before, I was in the mid 70s for MHR and it just wasn't sustainable.
You have to remember, I've seen and heard sirpoc speak about this. If he is going up a hill, incline and it's long enough to raise HR too much, he said he walks. I've started to adopt this philosophy myself.
My view on the use of treadmills by the Norwegians specifically is that, as you point out, it is a controlled environment and you don't have to worry about pacing, wind, hills etc. The only caveat is that they will be Lactate testing to ensure they're getting the perfect intensity. Pace doesn't really matter, it is the intensity and particular lactate levels they want.
If you mess around with the paces and have an understanding of the HR that is roughly in line with LT2 then I see this as a good way of running your quality work
The treadmill was great for me until the weather broke. But, I just can't raise lactate enough for some reason. I know others have said similarly. Maybe it's a biomechanics thing. It feels easier, than running outside, even when outside is a still, calm and perfect running day.
I actually have seemed to improve more, by running outside where when I've measured lactate, it's always higher for the equivalent session. Maybe there's nothing to it, maybe there is. Maybe it's placebo. Maybe it's some real world specificity. It's still better for me than doing nothing, but I do think outside for me has proven more fruitfull, even if inside is more controlled.
Sirpoc always points out that 70 % is an arbitrary value he used, because he felt it makes sure you are under LT1. Running Writings has an article on LT1 variation between athletes, where he says being below 70 % MHR will put 95 % of runners below LT1. So it's a safe number to use and a nice round number that is easy to remember.
I'm not sure if its possible to have 5% MHR to be honest, which is why it makes absolutely no sense for me to use % of MHR. Isn't Heart rate reserves (HRR), where its actually possible to have 0% HRR more accurate to use? Where did this 70% of MHR come from? Because its definitely not 70% of my heart's capacity, if we assume that my HR can't be lower than my resting heart rate unless I'm dead?
Looking at my easy pace, I average 72% of MHR which is equivalent of 64% of HRR. Not that it matters as my view on easy is as slow are required to recover and be ready for the rest of the week. But I am not sure I like the 65 of 70% of MHR being prescribed for easy runs in this thread.
Above roughly 70–75% HRmax, your body starts to cross the line from primarily aerobic metabolism (fat oxidation) into a zone where lactate production rises and you start burning more carbohydrate for fuel. That’s fine in small doses, but if most of your training time is spent there, you never fully develop the low-intensity adaptations that make you efficient and durable over time.
Running below 70% HRmax targets your Type I muscle fibers, builds mitochondria, expands capillary networks, and teaches your body to burn fat efficiently, all without creating significant fatigue or hormonal stress. It’s the only way you can safely accumulate the volume of running needed to improve long term.
That’s the secret: the intensity itself isn’t “magic”, it’s that by keeping the effort low enough, you can run more often and recover faster, which compounds into massive aerobic gains.
When you creep up into 75–80% HRmax, you’re in what many call the “gray zone.” It feels productive, but it’s too hard to fully recover from and too easy to drive a real adaptation. Elite and recreational runners alike fall into this trap - training moderately hard every day, never fresh enough to go truly hard or easy enough to build their aerobic base.
The best evidence and coaching experience from Lydiard, Maffetone, Seiler, Daniels, and the OG double threshold Norwegians all converge on the same point:
“Most of your running should feel gentle. If you think you’re going too slow, you’re probably doing it right.”
So it’s not that 72% or 80% are “bad.” They’re just not as efficient for building the aerobic foundation that supports all the faster running you want to do later. Below 70% HRmax is where your body quietly gets stronger every day.
I agree with everything except the use of HRmax instead of HRR. One of the earliest research on this was by Karvonen et al. (1957), where they concluded that aerobic adaptations occurred effectively around 60–70% of HRR, which corresponds roughly to 70–75% of HRmax for most people.
I'm not sure if its possible to have 5% MHR to be honest, which is why it makes absolutely no sense for me to use % of MHR. Isn't Heart rate reserves (HRR), where its actually possible to have 0% HRR more accurate to use? Where did this 70% of MHR come from? Because its definitely not 70% of my heart's capacity, if we assume that my HR can't be lower than my resting heart rate unless I'm dead?
Looking at my easy pace, I average 72% of MHR which is equivalent of 64% of HRR. Not that it matters as my view on easy is as slow are required to recover and be ready for the rest of the week. But I am not sure I like the 65 of 70% of MHR being prescribed for easy runs in this thread.
Looking at the Reddit thread, many are using 60% to 65%.
HRR % will give a higher HR if resting hr is high. High resting hr usually means poor metabolic fitness, so probably better to use % of max hr.
This is one of the benefits of HRR. It considers your fitness level, instead of prescribing the same HR for people with same MRmax, but different fitness levels.
This post was edited 3 minutes after it was posted.
I don’t own a lactate meter, but with a heart rate monitor I can compare the same workout done indoors and outdoors. If the graphs overlap, then I think I’m on the right track.
Some people will just not listen. There's people on Strava and Reddit who claim they can't run below 70% MHR. That is not possible, but they can run an hour at 90%+ LTHR and it still feels easy. People can't be trusted to make their own judgements, that's what this thread has taught me. Me included.
I see sirpoc jogging around at 4:35/km probably with a beer in one hand and wondered why I couldn't do the same. My ego was so focused on pace, it forget about that fact he's doing these runs at mid 60s of max HR %. When I slowed down, the whole thing worked. The puzzle here in this thread is absolutely huge, not as easy as some folks think. But once the pieces start fitting, starts working great and things have massively turned around for me since the new year and I'm glad I stuck with it. But before, I was in the mid 70s for MHR and it just wasn't sustainable.
You have to remember, I've seen and heard sirpoc speak about this. If he is going up a hill, incline and it's long enough to raise HR too much, he said he walks. I've started to adopt this philosophy myself.
The treadmill was great for me until the weather broke. But, I just can't raise lactate enough for some reason. I know others have said similarly. Maybe it's a biomechanics thing. It feels easier, than running outside, even when outside is a still, calm and perfect running day.
I actually have seemed to improve more, by running outside where when I've measured lactate, it's always higher for the equivalent session. Maybe there's nothing to it, maybe there is. Maybe it's placebo. Maybe it's some real world specificity. It's still better for me than doing nothing, but I do think outside for me has proven more fruitfull, even if inside is more controlled.
Similar experience to me on the mill. I've no evidence other than anecdotal to me, but honestly it's really hard to raise lactate like I can at the track or outside on the road, that to me it's akin to one step away from cross training. Absolutely, it's a means to an end. I'm in the snow for 2-3 months, it's either that or don't run. But just purely in my own feel on when I'm going good, it is always after a period of outdoor running, despite even being more consistent and potentially more controlled volume, indoors.
Of all the threads on Letsrun, this probably has the best collection of sharp minds to get to the bottom of this issue that seemingly seems to crop up, reasonably often.
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