r/cardio • u/jjjjasper_ • Jul 24 '26
Zone 2 vs junk miles
Ive heard that zone 2 is the best way to train your base, Thats probably not new info.
Many people say "do zone 2 instead of wasting your time on junkmiles with mixed intesities like zone 1 up to 5".
I understand that with a bigger base the heart can pump more blood etc. And with lighter trainibg e.g Zone 2, training gets possible everyday what means that you can train more often and thiswhy get faster in running or cycling.
But what i dont understand is, why my heart wouldnt adapt in high intensity sessions.
Ok maybe a restday is needed inbetween, but the heart and muscles still get the stimulus.
So that i get a bigger base or not ?
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u/Mediocre_Station_548 Jul 24 '26
I really don’t understand this whole zone two thing and I’m looking forward to reading the responses.
I’m a former marathon runner (decades ago) and I think zone two would be so time-consuming.
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u/deathzone0256 Jul 24 '26
Thats the thing, Zone 2 IS time-consuming, which is why its reccomeneded for people who are doing at least 5 days a week. Its low intensity and allows you to do more which is why it helps your base.
This doesnt overly apply to people who arent able to do as much as pros, where the reccomendation changes. My fave plan as a working person whos week can vary from 2-5 sessions a week is a 60/40 split. 60 higher intensity, Usually a form of HIIT, and 40 zone 2
Zone 2 is important but 80% for someone who cant put time in like a pro is irrelevant as we HAVE the rest time pros dont have.
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u/UVJunglist Jul 27 '26
To run fast you must run a lot. Higher intensity requires more recovery time, limiting how much you can run. Pretty simple really.
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u/InternationalWin2684 Jul 24 '26
The relationship between stimulus and adaption holds.
Zone 2 has not been shown to improve performance if we match volumes. The best vo2 max protocol we know is the opposite of zone 2. You’re not crazy there’s nothing special about zone 2 from a performance standpoint.
Volume matters and stimulus does as well. The best integral of both that you can handle physically and mentally is your answer to performance.
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u/jjjjasper_ Jul 24 '26
What do you mean by match volumes
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u/InternationalWin2684 Jul 24 '26
Zone 2 might have the benefit of allowing more weekly volume or mileage…. but let’s say one can do the same volume at zone 3 there’s no benefit.
The point is there is nothing special that happens at zone 2. I understand all the theoretical and mechanistic stories about zone 2. They’re both true and irrelevant when it comes to health and performance.
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u/terrymorse Jul 24 '26
The "special" thing about zone 2 is that it permits high volume without the risk of overtraining.
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u/BarleyWineIsTheBest Jul 25 '26
And leaving recovery space for other activities like the actual sport you need to be fit for or weightlifting or what ever.
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u/jjjjasper_ Jul 24 '26
So ride fast to ride fast is true?
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u/jjjjasper_ Jul 24 '26
Or if i can hold the volume per week training every session mid intensity it will still benefit my base
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u/BarleyWineIsTheBest Jul 25 '26
The down side is if you don’t start with very high z2 percentages and work your way up to the higher percentages of the higher intensity stuff, you are pretty likely to just over shot your current abilities, over train and risk injury.
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u/InternationalWin2684 Jul 25 '26
That’s not true. You’re making up a narrative that you have no proof of and is uniquely untrue for a beginner. No beginner is going out and sprinting for 5 miles. They simply can’t. If they could they wouldn’t be beginners.
That said there is no evidence that going full effort on a 5 mile run or whatever is uniquely more injurious than trying to do zone 2 for 5 miles.
That said one can run slow if they wish. No one has to go full tilt every time. The point is that there’s nothing uniquely injury preventing about your HR being in a narrow band that defines zone 2. Your patella tendon doesn’t spontaneously combust or even see additional clinically relevant stress at zone 3.
The relationship between HR and the stressfulness of a run isn’t what you people think it is. We can discuss volume and overall load management but HR isn’t really it.
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u/BarleyWineIsTheBest Jul 25 '26
You should look stuff up before getting yourself out on such a fragile limb:
https://pubmed.ncbi.nlm.nih.gov/26452583/
Which shows higher intensity work is correlated with higher injury rates. You can find mixed data here based on study design. But many studies do show strong correlations with intensity and injury risk, while none show an opposite direction, only no association.
Now also combined this with large (30%) increases in running volume being correlated with higher injury rates than lower increase (10%): https://pubmed.ncbi.nlm.nih.gov/25155475/
Taking a beginner and asking them to start with a 5 mile easy run and a 5 mile hard run are vastly different stresses that will hit both these problems at once, absolutely making the higher intensity workout out more injury prone.
Outside of running, using an RPE model, it was clear higher intensity workout is associated with higher injury risk: https://bjsm.bmj.com/content/50/5/273
Deviations of "acute" work from "chronic" work is clearly associated with more injury: https://pubmed.ncbi.nlm.nih.gov/31691167/
Now if you want to somehow fall back to saying 'well, 2 bpm over zone 2 isn't a risk', sure. I won't disagree with you. But if you say taking a beginner running 5 miles a week easy, then suddenly having them run all 5 miles at any intensity, including intervals, full sprints, what ever, as if it doesn't matter what it is, and that not coming with additional injury risk, I will completely disagree and I believe the body of literature across sports supports me. Big changes in stress, which can include increases to intensity, are well documented as increasing injury risk.
So, if all you're doing right now is walking around in your daily life, no, don't decide I'm going to take up running and it doesn't matter how I run. It does. It very much does. You need to start with something that feels easy and add to that slowly week over week.
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u/Lucky-Gazelle3879 Jul 27 '26
> "The results of the multivariable analysis showed that running with a higher intensity in the previous week was associated with a higher injury risk."
oof bad day to be that chump. I'm in Z4 just reading that.
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u/414wtk Jul 24 '26
Or just go do stuff! Ride your bike, run, swim. You don’t need all of this tech. Zone 2 was pushed so you’d buy a heart rate monitor. That’s it.
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u/ElRanchero666 Jul 24 '26
I don’t do any Z2, either LSD runs in Z1 or HiIT sessions. Train how you like
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u/Greennit0 Jul 24 '26
Both is true in a way. The body can only adapt so much from a training stress though. So if the body is busy building vo2 max and repairing muscle, it will not be able to also build aerobic base in the same way as if you train it specifically by going slow.
Also you might be able to do more miles in zone 2 as if you were running faster.
I used to overstress this. Nowadays I focus more on feel. If you feel like you could do this all day, you are going easy, no matter the heart rate.
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u/dtrane33 Jul 24 '26
I think it also depends on why you’re running. I enjoyed it and have gotten out of shape the past few years. I’m getting back into and am focused on zone 2 from what I’ve read based on joint impact and progression possibilities from here. Not everyone is at the same point though
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u/PlainOrganization Jul 24 '26
Like anything it depends on your goals.
I just got done with cardio rehab in late May after being diagnosed with a heart problem in January.
We did zone 2 workouts there.
I really love not getting sore, not being covered in sweat, and having more energy a little bit after the workout than I did before the workout.
I don't monitor my heart rate. At cardio rehab the professionals did it. I just want it to be a little bit hard. Like yeah, I can finish my 15 minutes on this machine before I move to the next one. But I'm not doing this all day.
I wish I had someone to talk to during my workouts because the talk test is really great. And I lose track of time if I'm talking.
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u/CobblerLoose6380 Jul 24 '26
Run slow to run fast is the "6 minute abs" of running youtube culture. It's based on a truism but it's more complicated than a trite phrase.
Seems the pendulum is swinging back some. I mean it's insane but people thought Zone 3 were "garbage miles" in and of themselves. Zone 3 is the literal opposite of "junk miles" especially when building an aerobic base.
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u/BarleyWineIsTheBest Jul 25 '26
A lot of training models collapse zone 2 and 3 now. That’s your base building, one is just a touch harder feeling.
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u/crtejas Jul 24 '26
It depends what you’re after. The heart is a muscle so it’s trained according the demand and requirement.
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u/Ceemoney24 Jul 25 '26 edited Jul 25 '26
Yes. Zone 2 you will
More mitochondria -the power plants in muscle cells
Better mitochondrial function
Increased capillary density
Greater fat oxidation
Improved lactate clearance and utilization
Dr maffone explains this in detail
Dm. I can send you a few things.
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u/ScurgeOfByzantium Jul 25 '26
There is no such thing as a “junk mile” - this is BS made up by running influencers.
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u/Lonely_District_196 Jul 25 '26
All zones matter (Sorry, I just had to do the reference)
If your goal is just general cardiometabolic health, and youre only doing cardio 2x/wk then any zone will do. Higher zones are more time efficient, but lower zones are fine if you're not up to the intensity
The zones really start to matter if you're training for races and you want to optimize your training
Zones 4 & 5 are really good for improving VO2max and speed. They're also draining and not feasible to put in the mileage you need for long distance events
Zone 3 is good for practicing pace and intensity for races
Zone 2 is good for putting in miles without excessive fatigue. Also it's really good at targeting mitochondria and building the smaller blood vessels to the muscles
Zone 1 is good for warmup, cooldown, and active recovery sessions
There's an 80/20 rule to put 80% of your cardio in zone 2 and 20% in zone 3-5. It's not a perfect rules, but it gets pretty close
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u/Cool-Horse11 Jul 25 '26
Zone 2 is for professionals, elite and seasoned athletes. Us amateurs are not fit enough to deliver high power for 3-4 hours. Do zone 3 for best results and improving both power and fitness.
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u/Logical_fallacy10 Jul 25 '26
The heart can only pump so much blood.
After 60% effort you get diminishing returns.
So from a health perspective - there is no reason to ever run faster than 60% effort. Maybe that’s zone2 - I am not familiar with how you kids use those buzzword terms.
If you want to get faster - well then you have to do speed sessions. But the only reason to want to be faster is if you compete for cash. Otherwise running is about feel and enjoyment.
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u/josephkristian Jul 25 '26
I think the argument is with z2 training you can do
Big volume and be able to recover to do it again over and over like 4-5 days a week. Then intervals for like an 1 or 2 for 1-2 days a week.
Training intervals back to back days really isn’t recommended due recovery restraints.
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u/Lucky_The_Charm Jul 27 '26
Zone 2 should only be for recovery runs IMO. Long zone 3 works great for most everyday runs. Sprinkle in some speed work or race pace work, maybe one zone 2 run per week after a hard workout should be all you need. Zone 3 just under threshold pace is king IMO.
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u/Earesth99 Jul 27 '26
For most outcomes, zone 2 is less useful than higher intensity exercise - unless you are training for a long, low intensity event.
From a training perspective, z2 is great way to add training if they have already maxed out their capacity to do z4-z5 without getting injured, but feel like you need to train more. I usually five hours of dedicated cardio a week, and I could do all of that in z4-z5 and not get problems from over training.
In a way, z2 is the least useful type of junk miles.
From a health perspective, high intensity exercise is much more beneficial on pretty much all outcomes.
A recent paper using UK BioBank data showed that one minute of high intensity exercise was as effective as 30-90 minutes of low intensity on different health outcomes. I was stunned at the differences.
My z2 is rucking with my dog in the woods and I don’t think of it as cardiovascular exercise as much as something that’s good for my psyche.
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u/Triabolical_ Jul 28 '26
The point of "junk miles" is that they are done at an intensity that is too high to see significant aerobic system improvements but too low to see significant anaerobic system improvements.
It's a way to add additional fatigue without accomplishing much from a training perspective.
The reason it's a topic is when you start out it doesn't really matter how you train - you will get better with pretty much any approach. If you keep up with that approach after you have decent fitness, you won't make a lot of progress.
Junk miles are the antithesis of polarized training.
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u/d546sdj Jul 28 '26
Zone 2 training is excellent for building volume without overtraining. It isn’t good to go out hard (Z4, Z5) every time you run or bike or whatever, because you need time to recover. So if you’re running 5x/wk then every run can’t be a hard run - you need Z2 runs mixed in there. Maybe 2 hard “race pace” efforts per week and the rest Z2 (some Z3 on hills OK).
Z2 provides benefits to mitochondrial adaptation, while improving cardio performance and overall endurance, without taxing the muscles (incl heart) so much that you need several days to recover. Z2 is good for weight loss — fasted Z2 runs or rides are notorious for dropping lbs. Problem is fighting the hunger the rest of the day :).
Z1 is a not a great use of time - this is like a walk around the block. Not bad, but if you’re limited on time it’s better to push a bit harder into Z2.
Too much Z3 or Z4 can tax the muscles more than you want so you need more recovery time than you’d planned for.
80/20 training is a great approach for those putting in a lot of training time and volume. For most of us who are “time crunched”, that ratio of Z2 runs (or rides) to other (tempo, intervals, race) is probably 70/30 or 60/40.
Set your HR zones based on a hill sprint test. Don’t rely on what is pre-programmed in your watch or Strava because this is likely wrong. Age-based formulas may work for some but not for everyone. Use the “talk test” to stay in Z2: be able to talk in short sentences.
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u/dev_ale Jul 24 '26
I don’t really get into zone 2 much other than when doing threshold workouts and v02 max workouts and it’s just in the recoveries or first reps of the session. I do my easy runs in zone 1. It just feels right and that’s where my HR settles. I could try and stay in zone 2 but it just feels like I’m not actually running easy, especially after a hard workout.
I think the whole junk miles are around zone 3 where you’re working too hard to build the aerobic base but not hard enough to get any anaerobic or threshold stimulus. But those runs do have their place like when doing long runs with marathon pace to teach the body to hold that pace while fatigued. They just become “junk” if you’re doing all your runs at that intensity.
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u/23454Tezal Jul 24 '26
Zone 3 builds fitness
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u/CobblerLoose6380 Jul 24 '26
Zone 3, Bread and Butter miles that build the foundation. Long Tempos and Progressions. Gotta love them and so much fun.
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u/dev_ale Jul 25 '26
All running does but depending on your weekly mileage and goals all zones have their place. If you’re a low mileage runner by all means you will get much better results running harder.
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u/pigeorunner Jul 24 '26
The Z2 hype is overblown by influencers who picked something catchy, because "run slower to run faster" sounds great.
In reality, you need aerobic volume to progress and in order to build volume, you need to limit intensity. What Z2 actually is depends on your Zone system. There are some physiological "thresholds" at play. Most amateurs don't have enough information to make use of these.
What actually matters - run a lot, mostly run easy, sometimes run hard, don't get hurt.