What is the scientifically correct way to measure calories burned when exercising ?

Really the type of exercise determines the best way to estimate calories - there isn't one way that works for everything.

Heart rate can be useful (for cardio) but it is subject to a lot of variables both for an individual but even greater between individuals. Individually: stress, caffeine, heat, cardiac drift, hydration etc .

If you start to throw in the HR variation between individuals, even similarly fit individuals, then you can see the chances of using a basic HRM and getting an "accurate" number are slim. I've seen variations of up to 40% in HR between experienced and fit cyclists producing the same power who would be burning calories at a very similar rate.
Caveat is that few people actually need precision, consistency and "reasonableness" works fine.

I use power measurement when doing indoor cycle training (you can convert power to energy) but even that has an assumed efficiency ratio, but for experienced cyclists it's a well known and fairly narrow estimated efficiency ratio.
It's certainly accurate enough but probably not precise.
At a rate of 3.6 cals per watt/hour gives me 720 net calories for a hard one hour 200 watt workout.

If you want to see the formula and assumptions to convert watts to calories.....
http://mccraw.co.uk/powertap-meter-convert-watts-calories-burned/

totaldetermination wrote: »

Thanks for the reply.
Another question, then.
In the same person is calories burned at a given heart rate consistent (even if you don't know exactly how many calories) ?

eg
I run on a treadmill and keep my heart rate at a certain number for 30 mins
compared to me swimming with my heart rate at the same number for 30 mins.

Would they burn the same calories (without necessarily knowing accurately how many) ?

No. As others observed, HR is a proxy for calorie burn, not a measurement. Each exercise places different 'work' demands on the body. Also, it's likely that we're more efficient at doing one exercise vs. another. In particular, the amount of strain in the exercise can raise HR significantly, for the same reasons that HR can go way up during weight training even though the calorie burn is modest.

Personally. I suspect my HR is disproportionately elevated during freestyle swimming because I'm terrible at the breathing part, so my heart's pounding like crazy trying to distribute the inadequate oxygen. Backstroke at my highest intensity doesn't have that effect.

For me, I will even get a somewhat different calorie estimate from my HRM for the same exercise at the same intensity at pretty much the same fitness level. It's not like 3x bigger, but maybe 10% or more at times, from memory. It's usually explainable by something like significantly different air temperature or dehydration, which affect HR but don't materially affect actual calorie burn.

(Some ways I know it's the same exercise time/intensity is from other measurements compared to HRM calorie estimates, such as when I do a rowing machine piece of the same distance at the same pace on different days, or row the same distance on water in the same time period, but HRM calories are very different).

A person who is more fit will burn fewer calories when running the same distance at the same weight because they use calories more efficiently. A fit person will usually have a lower heart rate when doing so, but this isn't always the case. It is quite possible for the less fit person to have the lower heart rate and still burn more calories. But the person who burns the most calories will always use more air than the other person.

Over the course of a long bike ride, I get slightly dehydrated and my blood thickens as it loses water content. Then my heart rate must go up for the same workload, because the blood is more viscous and harder to pump. This happens to everybody. You can see it with a heart rate monitor and a power meter or by looking at split times running on flat ground. Same output, different heart rate.

RavenLibra wrote: »

It’s about mass and muscle recruitment... if one weighs 220 lbs , moving that mass a mile in say... 15 minutes is going to burn more calories than moving 140 lbs the same distance in the same time limit. Just as in your example of swimming v running. to move (swim) requires more muscle recruitment than running, therefore swimming will burn more calories than running. Calories are a unit of energy. So... once again the higher the mass the more energy it takes to move that mass. Heart rate doesn’t play a part in the equation

Actually, swimming tends to burn fewer calories than running at any given heart rate. It’s mainly due to the body position — the heart doesn’t have to work as hard because of the lessened effect of gravity.

One of the biggest false assumptions is that “increased muscle mass involved equals more calories burned”. It’s just not true. For some people, an arm and leg movement might make it easier for them to reach a certain cardiac output, but it’s the cardiac output (VO2) that determines calorie burn, not the movement itself.

TimothyFish wrote: »

jgnatca wrote: »

Hot yoga people think they are burning awesome calories because the heart rate rises. But in hot yoga it’s an attempt to shed heat, not calorie burn.

Similarly people who are excited or anxious will have an accelerated heart rate even if they are still.

Keep in mind that the bulk of the calories we burn go into BMR which includes what our bodies do to regulate temperature.

It’s still not a significant effect.