Aerobic base training metric: meters-per-beat

[MudSweatAndYears]

Recently I started to evaluate the meters covered per heartbeat in my zone 2 (aerobic base / steady state) trainings. The maths is straightforward: first derive the average speed (in meters per minute) by dividing the distance covered during training by the duration in minutes. The average speed is then divided by the average heart rate (in beats per minute). The result is the distance in meter covered on average per heartbeat.

For instance if in a 30 minutes session you cover 6900 meters, the average speed is 6900/30 = 230 meter/minute. If your average heart rate during the 30 minutes was 115 beats/minute, you obtain a meter-per-beat result of 230/115 = 2.00 meter/beat.

It should be obvious that the meter-per-beat metric is influenced by your stroke efficiency as well as by the development of your aerobic base. Also the precise meter-per-beat result will depend on how well you tune your effort level towards an optimal result. And a whole range of external factors (air temperature, air humidity, etc.) will also influence the result.

What this new metric did for me is to make my steady state training more interesting. I keep watching both my heart rate and the Wattage on the PM5, and keep trying to tune my effort level to keep the first low without dropping the second too much. I discovered that for optimum results I shouldn't let my heart rate exceed twice my resting heart rate. Thus I now do my aerobic base training at a really low effort level (comfortably in zone 2 and well below my ventilatory threshold). Arguably, this constitutes an improvement in my training approach, as in the past I often fell victim of training too hard during zone 2 trainings.

Currently, due to a knee injury, I do all my erg training on a SkiErg. I observe that in the summer heat a good fan is essential. With a fan I can reach SkiErg values North of 2 m/beat. Without a fan this is hopeless.

If the above piques your interest and you decide to try this out for yourself, I would be keen to hear your experience. Is your optimum meter-per-beat result also obtained at an effort slightly below twice your resting heart rate? Does tracking of the meter-per-beat metric make you change your steady state workouts?

[twcronin]

That's an interesting metric. I suspect that it favors being really low in Z2 or even in Z1, because speed goes as the cube root of power and power output is typically something like linear in HR-HR_resting. In fact, if you do the calculus for: speed ~ (P)^(1/3) ~ (HR-HR_resting)^(1/3) then you get an optimal heart rate (maximizing speed/HR) that is equal to 1.5 times HR_resting. HR_resting might not be your zero-power heart rate while sitting on the erg, though... I'd suspect that just the static position of sitting in a rowing position will elevate your heart rate quite a bit relative to a watch-based RHR.

[MudSweatAndYears]

Ah yes, that makes a lot of sense. Your result is also in line with my experience that HR should be kept below 2 HRrest.

If I add a small friction term linear in speed: HR - HRrest = a v^3 + b v
and redo the math, then it appears that the HR for which HR/v reaches a minimum will be slightly larger than 1.5 HRrest.

[gvcormac]

I think watts/HR would be a better measure. The trouble with pace is that the effort to go faster is super-linear with speed.

An even better measure would, I think, be watts/HRR. HRR (heart rate reserve) is (HR - rest HR)/(Max HR - rest HR).

Stephen Seiler (Mr. Polarized Training) suggests HRR is approximately proportional to effort, which rowing pace is not. (Running pace is close to proportional.)

Note that if you're just tracking yourself, you can drop the division by (Max HR - Rest HR).

[MudSweatAndYears]

I think watts/HR would be a better measure. The trouble with pace is that the effort to go faster is super-linear with speed.

An even better measure would, I think, be watts/HRR. HRR (heart rate reserve) is (HR - rest HR)/(Max HR - rest HR).

Stephen Seiler (Mr. Polarized Training) suggests HRR is approximately proportional to effort, which rowing pace is not. (Running pace is close to proportional.)

Note that if you're just tracking yourself, you can drop the division by (Max HR - Rest HR).

That's right. The relationship HR = restHR + P/E (with P = power in Watts, and E = energy (in Watt.minute) dissipated per heartbeat into the flywheel) provides an excellent model for HR versus power. So you are right, P/(HR - restHR), which according to the model equals E, provides us with a sound measure for how well-trained the athlete is. However, as you rightly remark, this does not provide us with a uniform metric as it involves a parameter (the resting heart rate) that needs to be selected per individual.

The combination speed/HR does provide a uniform metric (no individual parameters, just the speed and the heart rate measured during the effort), albeit a non-linear one. So one should expect that this metric will in general be dependent on the effort level (i.e. dependent on the heart rate). The point is, however, that within zone 2 this metric appears to be hardly dependent on heart rate. Thus it can be useful as a zone 2 training metric.

[Sakly]

If I would train slightly below or at twice my resting HR, I would only be allowed to take a walk.
My resting HR is 50 or below, depending on my recovery state. When I take a walk at normal speed, ~11min per km, my HR average is about 85.
I typically do long sessions on the rower at HR ~135 with no drift. Pace around 2:02-2:04 depending on recovery state.
To get a metric of 2m/beat I would need to significantly reduce the speed, but that would definitely impact my stroke quality, as I am already down to r18 for these long steadies. So I would need to use weak strokes or reduce rate to r15 or something. Not practical for me.

[MudSweatAndYears]

If I would train slightly below or at twice my resting HR, I would only be allowed to take a walk.
My resting HR is 50 or below, depending on my recovery state. When I take a walk at normal speed, ~11min per km, my HR average is about 85.
I typically do long sessions on the rower at HR ~135 with no drift. Pace around 2:02-2:04 depending on recovery state.

My resting HR is similar to yours, and my ventilatory threshold is 2.4 times my resting HR. Identifying the ventilatory threshold as the upper range for zone 2, training at twice my resting HR puts me comfortably in zone 2. Your ratio between your ventilatory threshold and your resting HR is probably higher than 2.4?

To get a metric of 2m/beat I would need to significantly reduce the speed, but that would definitely impact my stroke quality, as I am already down to r18 for these long steadies. So I would need to use weak strokes or reduce rate to r15 or something. Not practical for me.

The value of 2 m/beat represents by no means a target. It's different for different individuals. It does happen to the value I can barely exceed at the SkiErg on a hot day.

[Sakly]

If I would train slightly below or at twice my resting HR, I would only be allowed to take a walk.
My resting HR is 50 or below, depending on my recovery state. When I take a walk at normal speed, ~11min per km, my HR average is about 85.
I typically do long sessions on the rower at HR ~135 with no drift. Pace around 2:02-2:04 depending on recovery state.

My resting HR is similar to yours, and my ventilatory threshold is 2.4 times my resting HR. Identifying the ventilatory threshold as the upper range for zone 2, training at twice my resting HR puts me comfortably in zone 2. Your ratio between your ventilatory threshold and your resting HR is probably higher than 2.4?

I really have no idea. I try to go for long sessions at a decent pace with no significant HR drift. That gives me paces I wrote.
On the skierg it's completely different, slower paces give me higher HR, but never did long sessions on this machine to prime my body for it.

To get a metric of 2m/beat I would need to significantly reduce the speed, but that would definitely impact my stroke quality, as I am already down to r18 for these long steadies. So I would need to use weak strokes or reduce rate to r15 or something. Not practical for me.

The value of 2 m/beat represents by no means a target. It's different for different individuals. It does happen to the value I can barely exceed at the SkiErg on a hot day.

Ok, I got it wrong then, I thought you mean this as a target.

Overall I don't know if the metric you mention gives me any advantage. For the long steady pieces I typically don't get caught by ego and go too fast. When I understand correctly, this is the main reason you did this?

[MudSweatAndYears]

Overall I don't know if the metric you mention gives me any advantage. For the long steady pieces I typically don't get caught by ego and go too fast. When I understand correctly, this is the main reason you did this?

Indeed. The metric meter/beat acts for me as an 'ego buster'...

At long steady pieces when I see my wattage decrease, I tend to get into 'catch up mode'. This happens frequently when ambient temperatures are higher. Focusing on meter/beat (instead of watts) I am much more successful in managing my pace.

[Sakly]

Overall I don't know if the metric you mention gives me any advantage. For the long steady pieces I typically don't get caught by ego and go too fast. When I understand correctly, this is the main reason you did this?

Indeed. The metric meter/beat acts for me as an 'ego buster'...

At long steady pieces when I see my wattage decrease, I tend to get into 'catch up mode'. This happens frequently when ambient temperatures are higher. Focusing on meter/beat (instead of watts) I am much more successful in managing my pace.

Great strategy, when it works for you!
I started doing steady states with covered PM5, only remaining time/distance, rate and HR visible. This way I can check how long I need to go and what my current intensity is HR - wise and align that with my RPE. Works really well for me this way.