Does anyone track their heart beats per kilometer?

No but I've added a column to my spreadsheet for road rides - various surfaces, gradients, intensities. 

Min 336, Max 515, Ave 395. Picking out the same hard route through the year there is definitely a downward trend.

Interesting idea. As I understand it, your heart rate is governed mainly by the amount of CO2 you need to expel, rather than the oxygen you need. Of course if you need oxygen it will increase but usually there's a bit of headroom available for oxygen - this is why CPR works (ish), because there's still plenty of oxygen in the air you breathe out. If you're less fit, you are probably burning more glycogen when riding at a given pace, which I think maybe is less efficient than burning fat in terms of the amount needed for a certain amount of energy, which means more CO2. As you get fitter, riding at the same pace you'd burn more fat and hence produce less CO2 meaning your heart would need to beat slower - maybe..? Hopefully an actual physiologist will be along to correct me.

It may not be as useful a stat outside though, since if you ride twice as fast you do (more or less) four times as much work, so beats/km versus speed would not be linear. However indoors, it probably would be. Except that you get much hotter indoors and some of your beats are needed to keep you cool.

No but Veloviewer has it. Also just like HR it's specific to the person and not really comparable. BUT

Zwift best is around 230 yearly averages about 275 everything from recovery to racing.

Commutes - so flat steady miles about 275-300

Rides - MTB/Road - Average about 400

XC Racing at Glentress 600+

Long group road ride 330-350

Actual highest for an actual ride 1165. It was for a 7km "gravel" ride

It may not be as useful a stat outside though, since if you ride twice as fast you do (more or less) four times as much work, so beats/km versus speed would not be linear. 

Like I said, I've been using it both on the rollers and outside but only for Z2 rides.  I expected there to be a large difference but the numbers are surprisingly similar.  It could be the rollers and no fans means it's compensating for the more irregular outdoor riding.  If I had a decent set of fans and a turbo then the numbers might be lower.

Haven't tried it on the mtb yet but I'd be very surprised if tracking beats per km would be any use at all.  Might still be interesting though.

I try not to get too into tracking things on the mountain bike though.  That's supposed to be the fun carefree thing and the entire reason for doing the sessions on the rollers 🙂

Anyone else tracking this and if so what kind of numbers are you seeing?

Going to be highly dependent on the stroke depth of your heart, mine is shallow (don't fully fill the chamber), so I have very high heart rate exercising eg 200 max. If your heart fully fills the chamber, you will have a lower HR when exercising.

Going to be highly dependent on the stroke depth of your heart, mine is shallow

Stroke depth when talking about heart beats is something I've not heard before.  I know people have different heart rates when training (mine has always been high but I just assumed it was because I wasn't fit).

My beats per km is definitely trending downwards with more regular Z2 training though (gone from 400 down to 300 in the last few months), so there is definitely something changing in my body but stroke depth sounds like it's something that doesn't change with more exercise.

Stroke depth when talking about heart beats is something I’ve not heard before.

We have four cadiologists from Papworth in our Saturday club run, you learn a lot about hearts....

but stroke depth sounds like it’s something that doesn’t change with more exercise.

My understanding is not, but I'm not a cardiologist. They did say there is a lot of variation person to person in the stroke.

We have four cadiologists from Papworth in our Saturday club run, you learn a lot about hearts….

I tried googling 'shallow heart stroke' to which google decided meant, 'Am I having a heart attack or a stroke?'

It is quite interesting to me as I generally have a much higher heart rate than I should when exercising (but I can also sustain a high heart rate for much longer than I should be able to).

I'd like to find out more about it, I just need to find the right combination of search terms that doesn't make google think I'm trying to diagnose which particular emergency medical condition I am in the process of dying from.

What does 'BPKM' actually tell you?

I can't see it being a useful metric for performance or health purposes. Is it just a nice to know ride to ride comparator without any real context?

What does ‘BPKM’ actually tell you?

I don't do any 'training' unless there's a single number that I can put in a spreadsheet and see on a chart.  Up until this year I didn't really need to worry about any specific Z2 training because I was commuting 20km per day and that seemed to take care of my low intensity riding needs.

I switched job last year and my commute became 6km and I really noticed that when I tried to go mountain biking for more than an hour.

BPKM is a single number that can be applied to any Z2 ride (possibly other types of ride but I suspect it wouldn't be as much use) regardless of time or whether it's at upper Z2 speed or lower Z2 speed.

Actually having replicated your calculation in my spreadsheet it occurs to me that for repeats of the same ride it's not really any different to comparing average heart rate.

Actually having replicated your calculation in my spreadsheet it occurs to me that for repeats of the same ride it’s not really any different to comparing average heart rate.

Sure, but it's similar to tracking your progress in lifting by calculating 1 rep max from however many reps you do rather than having to track 5 rep maxes, 3 rep maxes, 1 rep max, etc individually.  It boils it down to a single number that can be applied to rides of different speeds and different distances (within reason, obviously).

Must be terrain dependent for zones. Think about a threshold hill climb vs. a threshold time trial. I could do 175 bpm for 10 miles (say 20 min - I wish) or 175 bpm for 3 miles up a decent hill. I'd have a different bpk for essentially the same effort. Of course time will play some role here too. But I am not surprised that Z2 gives consistent results everywhere. Power for HR is probably more informative and speed(power plus other variables). PowerCal calculates an estimate of power based on rate of change of HR. It's not bad at averages.

Have tried looking for this stat in veloviewer, bu can't see it, can some one point me in the right direction please

Just thinking about this... As Slowoldman says, it's effectively same as average heart rate, just a different way to slice the data salami....
if your bpkm is 360, and your average HR is 120, then that's 3 mins per km, so speed is 20kmh.

Not sure that's telling me anything different to what I get from recording a lower average HR over a regular loop or segment, or quicker time for same average HR

I can't find it in Veloviewer either so I calculated it from the columns which are in VV (I already have those downloaded into my annual spreadsheet so the calculation was trivial).

but stroke depth sounds like it’s something that doesn’t change with more exercise.

My understanding is not, but I’m not a cardiologist. They did say there is a lot of variation person to person in the stroke.

Am cardiologist - though I suspect an exercise physiologist or sports med person would know a lot more than I do. You're talking about stroke volume. Absolutely it does change with training - a combination of dilatation of the heart (accepts more blood per beat) and a mild degree of wall hypertrophy (muscle thickening). BUT this tends to be in lifelong athletes / people who train a lot and probably doesn't apply to most of us.

As you say, there is more variation person-to-person than in untrained-vs-trained individuals.

As I understand it, your heart rate is governed mainly by the amount of CO2 you need to expel, rather than the oxygen you need.

You are thinking about respiratory rate, not heart rate, I think?

Heart beats per km is an interesting metric. I guess it's a kind of marker of overall efficiency - pedalling style, aerodynamics, choosing an efficient speed to ride at etc, but if all those variables are optimised, you can probably improve it by training (improving your body's metabolic efficiency). There are a lot of confounders there, though - something like lactate threshold / FTP is much easier to accurately track. I wonder if there is an application in ultra-endurance sports where efficiency is key. Round the world rides, trans-continental, that sort of thing.

Not sure that’s telling me anything different to what I get from recording a lower average HR over a regular loop or segment, or quicker time for same average HR

If I tracked my average HR then the line on my spreadsheet would be flat because I ride to my heart rate.

I could track my average speed but then that would vary depending if I was doing an upper Z2 day or a lower Z2 day.

My thinking is that it's better to boil things down to a single number with training as much as possible and work towards improving that number.  It always feels good to get a new PB and the more chances you can give yourself to beat a PB the more likely you are to do the activity in the first place.  Z2 is not something most people associate with getting PBs in so this is one way of doing that.  But that might just be what I need for motivation.

Obviously you have to put some limitations on the rides that count.  The easiest way to get a PB would be to roll down a hill so it has to be limited to loops where you can't freewheel and where the ups aren't so steep you're forced out of Z2.

Heart beats per km is an interesting metric. I guess it’s a kind of marker of overall efficiency – pedalling style, aerodynamics, choosing an efficient speed to ride at etc, but if all those variables are optimised, you can probably improve it by training (improving your body’s metabolic efficiency). There are a lot of confounders there, though – something like lactate threshold / FTP is much easier to accurately track. I wonder if there is an application in ultra-endurance sports where efficiency is key. Round the world rides, trans-continental, that sort of thing.

Thanks for the input.  Like I said, I find I can only motivate myself to train if I'm aiming to beat a PB which Z2 doesn't really lend itself to.  Since I started this I've seen my beats per km drop from 400 to 300 (relatively flat road loops and sessions on the rollers).  I saw the expected high initial drop and now it's leveling out but still trending downwards so I'm still motivated to keep going down to the basement and sitting on the rollers for 70 minutes.

Lactate threshold would almost certainly be a better metric.  HR is just easier though and for the moment is accurate enough to keep me motivated.