Working harder, heart rate and calorie burn lower?

amandarunning

So today is Insanity Day 44 Max Interval Circuit. An hour of madness and almost managed the whole session without any (and I mean any apart from the 30 secs water breaks) breathers. Last set of burpees had me on my knees though! I know I worked harder than ever and yet my heart rate refused to go above 160 (seldom got there) and overall my calorie burn was down in the region of 10%.

I hope this is a good sign and one of improved fitness. Or is it just my body has adapted?? Sure feels like hard work and pushing my limits but not sure what to make of it?

JoRocka

those types of work outs you never get 'good at'... you just suck less.

sounds about right.

AllanMisner

Are you sure the HRM was on and recording properly? Remember that calorie burn is just an estimate. If your monitor stopped picking up for part of the workout (like when you were doing burpees), it would also stop recording the HR to calculate burn.

amandarunning

Monitor was recording throughout - or at least when I checked! Certainly noticed my recovery was quicker and generally hr lower on the "easier" exercises so hoping it does indeed mean I suck less :-)

jonnythan

So today is Insanity Day 44 Max Interval Circuit. An hour of madness and almost managed the whole session without any (and I mean any apart from the 30 secs water breaks) breathers. Last set of burpees had me on my knees though! I know I worked harder than ever and yet my heart rate refused to go above 160 (seldom got there) and overall my calorie burn was down in the region of 10%.

I hope this is a good sign and one of improved fitness. Or is it just my body has adapted?? Sure feels like hard work and pushing my limits but not sure what to make of it?

The ability of your cardiopulmonary system to deliver oxygen to your tissues has improved, meaning your heart has to work less (beat fewer times) to deliver the same quantity of oxygen. Doesn't mean you're burning fewer calories.

Calorie burn and oxygen consumption in aerobic activity are directly linked. You can be consuming the same amount of oxygen as a month ago, but with fewer heart beats.

bwogilvie

A couple things:

1. As you get fitter, your heart rate for the same level of exertion will go down, because your cardiovascular system gets better at delivering oxygen to your muscles (enlarged heart, more red blood cells). Your nervous system also gets better at recruiting muscle fibers.

That does not mean that you burn fewer calories, provided that you're exercising at the same intensity. Remember that the HRM gives you an estimate of calories burned, based on a formula derived from a population study. You can get slightly more efficient at performing an activity, but there are limits. A professional cyclist doesn't burn less energy than I do when we're both cycling 18 mph, provided we are on the same kind of bike in the same conditions. It's just that 18 mph is near the upper limit of the energy I can put out for a sustained period, while a pro isn't using his or her full capacity at that speed. World-class male cyclists can sustain more than 30 mph, but they're using a lot more energy at that speed. The pro will also have a lower heart rate than I would at 18 mph, because his or her CV system is more effective at delivering oxygen. But, other things being equal, we're burning the same number of calories.

Some HRMs take these factors into consideration, with settings for your maximum HR (use this only if you have had it tested; the formulas like 220-age are largely worthless), your resting HR, and sometimes your lactate threshold. My Garmin Edge 800 asks for maximum HR, and for how often and how intensely I exercise, which helps make it more accurate. Since it knows my weight, my bike's weight, how fast I'm riding, and what the terrain is like, it can do a pretty good job estimating calories on the bike (though it doesn't know about the wind speed). On the other hand, my ForeRunner 410 only asks for age and maximum HR, and is less accurate.

2. Beyond that consideration, heart rate monitors aren't very good at measuring calories burned in discontinuous activity. The formulas they use were developed for continuous, steady-state cardiovascular exercise. Your heart rate always lags effort: it takes a while to catch up to demands, and then it takes a while to slow down (though the fitter you are, the faster it slows when you stop an exertion). HRM estimates don't work well in that case, because your heart is still chugging along after you've stopped exerting yourself.

ETA a couple more sentences on HRMs.

amandarunning

Ok, so I **think** I understand and perhaps what I need to focus on more is my heart rate "maximum" achieved during the session and recovery/average? I'm quite in tune to how hard I'm working and knew today was a good day and one to push really hard so was surprised at the calorie count. Oh...Polar FT4 moitor so kind of basic I guess.

Whilst calories burned is kinda nice to see in terms of high numbers, I embarked upon this Insanity to improve my fitness in areas I lack (agility, balance and specifically explosive "power"). High volume, low intensity is my norm.