Please help, trying to understand "anaerobic" exercise

[arkle]

Hi,

The general consensus on cardiovascular exercise seems to be that you should try to stick within the "aerobic zone" 70-80% of your maximum heart rate, and that excursions into the "anaerobic zone" (80-90% MHR) and "red-line zone" (90-100% MHR) are to be saved for short periods of interval training because in these zones your muscles are working "anaerobically".

I have two questions:

1 If training above 80% MHR is "anaerobic" then how is it possible to maintain a heart rate of 90% MHR for an entire hour without passing out?

2 The gym charts show that at 70-80% MHR you're using calories sourced from fat and above 80% you're using calories sourced from somewhere else. Why does it matter where the calories are coming from? If the calories at 90% are coming from somewhere else doesn't that just mean that those calories won't be available to lay down as fat, or fat will be used to later replenish those calories in your muscles, so in the end it balances out?

arkle

[Alex Simmons/RST]

Hi,

The general consensus on cardiovascular exercise seems to be that you should try to stick within the "aerobic zone" 70-80% of your maximum heart rate, and that excursions into the "anaerobic zone" (80-90% MHR) and "red-line zone" (90-100% MHR) are to be saved for short periods of interval training because in these zones your muscles are working "anaerobically".

I have two questions:

1 If training above 80% MHR is "anaerobic" then how is it possible to maintain a heart rate of 90% MHR for an entire hour without passing out?

2 The gym charts show that at 70-80% MHR you're using calories sourced from fat and above 80% you're using calories sourced from somewhere else. Why does it matter where the calories are coming from? If the calories at 90% are coming from somewhere else doesn't that just mean that those calories won't be available to lay down as fat, or fat will be used to later replenish those calories in your muscles, so in the end it balances out?

arkle

That "general consensus" is wrong to start with.
Hence:
1. because a HR level doesn't indicate whether one is "anaerobic". Any effort longer than 60-90 seconds, no matter how hard you go, will still be predominantly driven by aerobic metabolism

2. We utilise a combination of fats and carbohydrates (CHO/glycogen) as fuel at all times. The ratio varies depending on many factors (intensity of effort, variability of effort, diet, level of fitness, duration of exercise, state of glycogen stores etc etc). At rest it's about 50:50, moving to exclusively tapping into your glycogen stores when we are going very hard.

When we deplete glycogen, we are forced to go slower as the rate of energy supply from FFA is lower than for CHO.

We have enough glycogen if well fueled and reasonably fit to go hard for about 90-minutes.

From a weight management POV, it's total calorie balance that matters. The fuel substrate used is pretty irrelevant.

[arkle]

That "general consensus" is wrong to start with.
Hence:
1. because a HR level doesn't indicate whether one is "anaerobic". Any effort longer than 60-90 seconds, no matter how hard you go, will still be predominantly driven by aerobic metabolism

2. We utilise a combination of fats and carbohydrates (CHO/glycogen) as fuel at all times. The ratio varies depending on many factors (intensity of effort, variability of effort, diet, level of fitness, duration of exercise, state of glycogen stores etc etc). At rest it's about 50:50, moving to exclusively tapping into your glycogen stores when we are going very hard.

When we deplete glycogen, we are forced to go slower as the rate of energy supply from FFA is lower than for CHO.

We have enough glycogen if well fueled and reasonably fit to go hard for about 90-minutes.

From a weight management POV, it's total calorie balance that matters. The fuel substrate used is pretty irrelevant.

Thanks Alex. So those gym charts you see with anaerobic zone plastered across above 80% MHR are rather misleading. The 90 minute figure is interesting. That ties in pretty well with how long it takes me to start feeling exhausted on a long bike ride. And I think you're saying that replenishing the glycogen used during high intensity exercise is ultimately going to have to come from fats anyway, just with a time delay. Are there any advantages to doing CVT at 80% rather than 90%? 80% is just so easy.

arkle

[brendancg]

Sorry I think you are a little confused. The way I read what Alex has said is that 'individually' the level in which we operate varies. You cannot pick a magic number as those graphs show and work off that number. You can know in yourself where the areas are

See the below link which explains the energy system continuum

http://www.humankinetics.com/mediasvr/M ... p34-36.pdf

[arkle]

Sorry I think you are a little confused. The way I read what Alex has said is that 'individually' the level in which we operate varies. You cannot pick a magic number as those graphs show and work off that number. You can know in yourself where the areas are

See the below link which explains the energy system continuum

http://www.humankinetics.com/mediasvr/M ... p34-36.pdf

Good article. Let's see if I've got this right. To increase VO2 max and lactate threshold (i.e. moving the energy continuum upwards) it is best to exercise so as to overload the body's CV system so that it adapts by becoming fitter. The intensity at which a person can maintain this level of activity depends on the individual. It is most beneficial for an individual to exercise at the highest heart rate they can tolerate for the duration of the exercise, e.g. an hour.

Sorry for being a bit thick.

arkle

[brendancg]

Thats it. Simply put frequency intensity time and type (FITT Principle).

[mikesbytes]

We have enough glycogen if well fueled and reasonably fit to go hard for about 90-minutes

My observation is that how long (without refueling) tends to depend on the size of the person. There is a significantly wide range of durations.

Alex, Brendacg, are the glycogen stores used only within the muscles they are stored? This would seem logical to me, but I've not seen any documentation on it.

[brendancg]

Mike

I am not an expert on this subject. However I will endeavor to answer your question and I use "The essential guide to fitness for the fitness instructor" as my reference here.

My observation is that how long (without refueling) tends to depend on the size of the person. There is a significantly wide range of durations.

As you point out it also depends on other things such as how you prepared for what you are doing, what you ate, the continued level of effort being undertaken, the training you have previously undertaken for the event and your genetics also play a part.

Alex, Brendancg, are the glycogen stores used only within the muscles they are stored? This would seem logical to me, but I've not seen any documentation on it.

Glycogen is the stored version of glucose and is located in the muscles and liver. The liver uses glycogen to convert lactic acid into glucose. I have never found any documentation to suggest otherwise and from what I have read I would say yes. The body will use glucose which is in the blood stream first and will only resort to glycogen if it runs out of glucose or if the effort required is faster than what it can supply to the muscles.

[sogood]

When blood Glu is running low, the body will extract glycogen out of its stores ie. Liver as well as muscle. So don't expect the muscle to have the exclusive use of glycogen stored in it.

[WonkyWheels]

Just maintain a level of intensity where you can’t really speak while riding and you can only say a couple of words if you try.
Good enough to only say “good day”; “how's it going” or just "hey!" when you see other cyclist.

[Wayfarer]

Good article. Let's see if I've got this right. To increase VO2 max and lactate threshold (i.e. moving the energy continuum upwards) it is best to exercise so as to overload the body's CV system so that it adapts by becoming fitter. The intensity at which a person can maintain this level of activity depends on the individual. It is most beneficial for an individual to exercise at the highest heart rate they can tolerate for the duration of the exercise, e.g. an hour.

Sorry for being a bit thick.

arkle

Sort of.. Interval and fartlek training is used in running to increase the aerobic zone; thus it depends highly on the individual. I'd guess that keeping a constant intensity at a high maintainable heart rate will be good, but not as good as pushing over the limit (say, for 5 minutes for arguments sake) then going back to the maintainable heart rate for 5 minutes etc.