Power, Heart rate and Calories...

tomUK

I can't quite get my head around this question and so I thought I would ask for some help!

While I understand that power is a measure of work done in a specific period of time, I don't quite see how this is consistant with heart rate.

For example, when my body is laying in bed at rest in the morning my resting heart rate maybe 40bpm. If though I have consumed 2-3 pints of beer the night before my resting heart rate in the morning is say 55bpm.

In the first example I might go and climb a hill and do 130 Joules of work in 6 minutes with an average Heart rate of 150bpm. In the second example (after the beer) I may also produce 130 Joules of work in 6 minutes but with an average HR of 170.

The question is has my body burnt the same amount of calories in both cases or is it high in the second case due to an increased HR?

T.

jws

Tom,

You can't really draw conclusions about work or workrate(power) based on HR, because there are many other factors affecting HR. If you use power you are better off ignoring HR except out of curiosity!

biker-linz

HR is used as a measure of intensity because in general it scales in a linear fashion with O2 consumption.


You've done the same amount of work in both cases, and burned the same number of calories. The problem with HR is it only tells half the story (the other half being stroke volume, or in other words how much blood is pumped with each beat), and also can be affected by many factors other than exercise. For example after a 'big night out' your sympathetic nervous system might be suppressed causing your HR to be lower. However your heart will compensate by increasing stroke volume so it still pumps the same amount of blood, unfortunately there's no way of telling this from looking at your HRM.
This is why PMs are sooo cool, it is a direct measure of load rather than load inferred from a physiological response.

Hope this helps,

L.

__________________
MSc (Applied Sport and Exercise Science)
RST Associate Coach
ABCC Level 3 Coach
Doctoral Student (Physiology), University of Oxford, UK.
www.cyclecoach.com
www.science4sport.com

jws

Yes, I guess linz actually answered your question directly. Number of calories burned will be related to work; power(Watts)= Joules/second; work(J)=power(W)*time(sec); calories can be derived if you know efficiency.

Read this:

http://www.bikesafety.org/wattage/faq.htm#Q21

tomUK

Linz -

Actually, I've always noticed after a big night out my HR tend to be a lot higher for the same amount of work.

and just to throw a cat among...

Perceived Exertion is said to be a good guide to recovery. i.e. if I go out one day and am - 'cooking on gas' - producing 250W at a PE of 5 (scale 1-10) yet another day producing this same power rates PE at 8. It's hard to know - am I tired (over reaching) or just hacked off, bored with riding, had a crappy day etc...

Any good advice?!
T.

frenchyge

It can do that?? Cool.

Is that why HR tends to be higher when riding at a higher cadence, even though power output is the same?

biker-linz

Personally I've found that one of the best indicators of overreaching / incomplete recovery is simply whether you're able to complete a scheduled workout. One of the most consistent markers of overreaching is compromised performance (actually it's the definition of overreaching), which is fairly easy to pick up with a PM.

L.

__________________
MSc (Applied Sport and Exercise Science)
RST Associate Coach
ABCC Level 3 Coach
Doctoral Student (Physiology), University of Oxford, UK.
www.cyclecoach.com
www.science4sport.com

biker-linz

Actually you're not the first person the think of that (or something similar)!

http://www.ncbi.nlm.nih.gov/entrez/...st_uids=8775571

L.

__________________
MSc (Applied Sport and Exercise Science)
RST Associate Coach
ABCC Level 3 Coach
Doctoral Student (Physiology), University of Oxford, UK.
www.cyclecoach.com
www.science4sport.com

biker-linz

I've just realised that what I wrote could be a little misleading so...although the heart can actually beat on its own without any 'guidance' from outside this is a very primitive basic system and the heart's activity is heavily regulated from outside. It's output is defined by both heart rate *and* stroke volume, so that cardiac output (usually referred to as Q for some reason) in L / min = HR (bpm) X SV (L / beat). Just because heart rate changes doesn't necessarily mean that Q has changed too, or to put it another way heart rate can be lower while Q remains the same because SV might be higher. The reverse of this is what occurs during cardiac drift.

L.

__________________
MSc (Applied Sport and Exercise Science)
RST Associate Coach
ABCC Level 3 Coach
Doctoral Student (Physiology), University of Oxford, UK.
www.cyclecoach.com
www.science4sport.com

robkit

heart rate does not scale linearly with VO2 consumption, apparently

%VO2max = (%MHR - 37) * (1/.64)

and they say each litre of O2 consumed liberates circa 20,000 joules (5kcal)

hence if you know the %MHR you are working at, efficiency, and your VO2max you can do a pretty decent job of working out theoretical power outputs

__________________
I am my favorite rider.

tomUK

Would it be fair to say that Cardiac drift can be seen at the end of a workout? When I start my workout I warm up at about 100bpm and that produces and avg power of 150W. However, after my workout I cool down at 100bpm - during that time my avg power is only 100W. i.e. HR has increase and stroke volume has decreased.

When put in these terms this is what I experience after a night on the beer. HR seems to be 'through the roof' for the same wattage as a 'normal' day.

biker-linz

Actually HR does scale linearly with O2 consumption, which is why it is used as a proxy. I've attached a little chart, hopefully it's ok to read (if not let me know and I can send it to you direct). I'm not sure where you got the equation from, but it makes some pretty sweeping generalisations so I'd treat it with some caution. Also although 1L O2 will be around 5 kcal if CHO is the primary fuel being burned, you still have to take into account an individual's economy before you can try and infer power output.

L.

Attached Thumbnails

 

__________________
MSc (Applied Sport and Exercise Science)
RST Associate Coach
ABCC Level 3 Coach
Doctoral Student (Physiology), University of Oxford, UK.
www.cyclecoach.com
www.science4sport.com

biker-linz

That would be absolutely correct. For a fuller explanation see:

http://www.ncbi.nlm.nih.gov/entrez/...t_uids=11337829

It could also be due to dehydration; this would result in a reduction in plasma volume which causes a reduction in SV and might result in a higher HR?? (didn't you say your HR was suppressed though?)

L.

__________________
MSc (Applied Sport and Exercise Science)
RST Associate Coach
ABCC Level 3 Coach
Doctoral Student (Physiology), University of Oxford, UK.
www.cyclecoach.com
www.science4sport.com

tomUK

Nope. Always after a night out, the morning after my HR is higher than normal for a given wattage. Usually about 20-30 beats.

You trying to tell me I have a dodgy heart?!