One for clever science bods!
(please note this is not guaranteed to be accurate) i think it depends on how your run is, if your HR is low then you generally will burn fat, as it increases then you will start to burn glycogen which come from carbohydrades.
i think i generally burn them from my upper body as my thighs are still the same size as when i started running...
Thanks ShleyBey, that's taken me back to my A level biology revision from 20-odd years ago!
But MD6 is correct that at lower levels of energy output fat is predominantly burnt. According to the diagram in Noakes the crossover point when carbohydrate usage overtakes fat is about 35% VO2max. That is of course until you have depleted all the available glycogen stores when you have to revert to fat anyway. The scientific reference quoted is Brooks, one of the papers he wrote is this one:
although this paper seems to say 45% VO2 max is the turning point.
Well there are two ways of looking at it, a slower run burns more fat calories but at the same time it burns fewer calories. I read that someone walking in the fat burning zone still burns fewer fat calories than someone running and fewer calories overall.
Also when you run faster you take longer to recover and burn calories after you finish running. ]
Fat burning zones are used a lot by gyms as a way of making scientific the fact that you shouldn't be out of breath or sweating so people feel like they are doing well.
The main thing I take from the science is that people are right when they say that if you want to get rid of excess fat you are better off going for a long walk than a run, as fat is what you will mainly burn at walking speeds. You would have to be running very slowly indeed to get down to this threshold pace. But you've raised a good point, and to quote from 'Better training for distance runners' by Peter Coe and David Martin
1. carbohydrate is a less efficient form of stored energy than fat as fat has a higher proportion of C and H.
2. as intensity increases the lower proportion of stored O in fat becomes a liability thus favouring carbs
3. fats are higher in energy per unit mass than carbs
There is also some stuff about how much CO2 is produced by burning different fuels.
These seem to be the main factors for starting with fat then crossing to carbs, according to this book anyway.
Joe Volcano wrote (see)
The main thing I take from the science is that people are right when they say that if you want to get rid of excess fat you are better off going for a long walk than a run, as fat is what you will mainly burn at walking speeds.
If that is true then you should just stay in bed because then an even higher percentage of your calories burned will come from fat!
Part of the problem is the limited supplies of available carbohydrate, so once this has run out, you have to switch to fat, whatever the intensity- naturally, you are likely to be able to maintain continuous excercise for long enough to get into this zone, if you're going slowly!!!!- Someone else posted a different thread about a strange smell they give off post long- run- and I reckon this is due to fat metabolism kicking in, and Ketones being excreted as a by product.
I think I read somewhere that on average this is after about 90minutes, but must vary from person to person
Good luck with the exams SB- just be aware that there's quite a bit of "pseudo science" in running (and other sport) literature, so something presented as "gospel" in the running world may be deemed downright WRONG by conventional science (ie your exam marker!!!)
Yes there is a lot of pseudo-science on here but I certainly wouldn't put Noakes who is one of the world's foremost experts on the science of running in that category, especially as every statement he gives is backed up with a reference to the latest scientific journals, one of which I cited. He is professor of exercise and sports science at Cape Town University and former president of the South African Sports Medicine Association.
Martin, the other author I cited, is professor of health sciences at George State University.
One thing about Noakes in particular though is that he quotes a lot of leading edge science, some of which is contradictory. So in that respect you could argue that despite his knowledge his book is not necessarily conventional science.
Personally I am not an expert on human biology and I don't want to put SB off his exam revision by misquoting something.I skipped the CO2 bit as I didn't fully understand its significance. Stick to the recommended texts for your course and get a good result in the exams.
I have an interesting conundrum - whenever I do my long runs I seem to put ON weight, only to see it generally come off a day or so later....is there a biological theory for this, or is it just that I probably overeat afterwards!!!!
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