Is there anything written on what the maximum amount of cardio that it is safe to do while fasted?

Spadesheart

So. I will be going on a foodie adventure downtown with a friend to try a bunch of restaurants and goodies. I just started up again with the cut last week, and will be going next week, so it is too early for a refeed/cheat day.

Regularly on Wednesday, and often the weekend I do a cardio day where I routinely use an elliptical style machine called an AMT at max resistance for 65-85 minutes. While doing this, I keep my heart rate between 150-180, averaging somewhere close to 160 I'm sure. This puts my calorie burn at about 1000-1070 calories for 65 minutes, when calculated using my size and heart rate. The machine would put me in the mid to high 1200s, I would think that would be wrong unless the resistance perhaps has an effect on muscle synthesis.

I know I could easily do many hours at 140 bpm, which puts me at 882 calories for 65 minutes. I don't usually do cardio fasted however, usually having a small meal about an hour before.

If I were to do this i might have nothing, or a very small meal (eggwhite omlette? 150 calorie-ish) and go for a couple hours before heading downtown to eat, which would likely be a couple hours later.

Is there anything written on what the maximum amount of cardio it is safe for one to do fasted? I just don't want to push to fainting or something. I want to see if I could still have a deficit so I could... have my cake and eat it too. Let me know!

dewd2

Everyone is different. If you have a condition that would push your blood sugar to drop too low (or other medical issue) then you really need to discuss it with your doctor. If your healthy then I can't see how 60-90 minutes of cardio would be a problem. I often run 2+ hours fasted with the intention of helping my body learn how to burn fat for fuel more efficiently (useful for long distance running). Other than feeling like a little depleted as my body switches from glycogen to fat, there's no issues.

sijomial

The "danger point" is when you you fully deplete your glycogen levels and bonk / hit the wall.
Crushing fatigue, mental confusion, loss of coordination are some of the symptoms. The onset can be very sudden from feeling slightly fatigued to feeling dreadful. In my confused state I though my bike's tyres must have punctured, or a strong headwind had blown up suddenly - or the world had tilted upwards!

Unfortunately getting to that point is very varied, size, how topped up your glycogen levels are, how intense your exercise is, the duration of your exercise, how accustomed you are to fasted exercise......
Two hours of very strenuous cardio is sometimes given as a rough guide to start getting concerned but that could be for someone who is an athlete and eating at maintenance calories not a prolonged deficit.

BTW - calorie estimates from HR often aren't at all accurate, the numbers you give would indicate a very high level of fitness. But they could also be a result of someone who simply has a high exercise HR.

If you are seriously concerned bonking/hitting the wall might be an issue then carbs before exercise would be far more appropriate than a high protein snack. You can recover quickly from bonking/hitting the wall (glucose gets in your bloodstream very quickly) but it's a horrible experience to be avoided not flirted with.

Spadesheart

sijomial wrote: »

The "danger point" is when you you fully deplete your glycogen levels and bonk / hit the wall.
Crushing fatigue, mental confusion, loss of coordination are some of the symptoms. The onset can be very sudden from feeling slightly fatigued to feeling dreadful. In my confused state I though my bike's tyres must have punctured, or a strong headwind had blown up suddenly - or the world had tilted upwards!

Unfortunately getting to that point is very varied, size, how topped up your glycogen levels are, how intense your exercise is, the duration of your exercise, how accustomed you are to fasted exercise......
Two hours of very strenuous cardio is sometimes given as a rough guide to start getting concerned but that could be for someone who is an athlete and eating at maintenance calories not a prolonged deficit.

BTW - calorie estimates from HR often aren't at all accurate, the numbers you give would indicate a very high level of fitness. But they could also be a result of someone who simply has a high exercise HR.

If you are seriously concerned bonking/hitting the wall might be an issue then carbs before exercise would be far more appropriate than a high protein snack. You can recover quickly from bonking/hitting the wall (glucose gets in your bloodstream very quickly) but it's a horrible experience to be avoided not flirted with.

The worst I've gotten is being depleted in a way that when I finally do sit to eat, digestion takes up so much blood flow that if I get up too quickly, I'll be faint. I actually fainted once like this years ago and didn't realize this was the cause. What you're describing sounds worse.

When I log the AMT, I still actually log somewhat conservatively on MFP and just use the default entry for the elliptical, which is about 15% less I think. Even so, I'm inclined to believe the heart rate numbers are probably the only semi accurate way for me to judge unfortunately. My resting heart rate has gone from mid 90s to 70 flat over the last year, distances, resistance, endurance have all handily increased, so I could very well be considered athletic, though I haven't really an athletic body composition yet. I didn't even log exercise calories until I started a new fat loss protocol which requires a bit of accuracy. I'm finding it to be a lot of guess work.

I guess a bowl of oatmeal is probably my best bet for safety haha.

AnnPT77

Spadesheart wrote: »

sijomial wrote: »

The "danger point" is when you you fully deplete your glycogen levels and bonk / hit the wall.
Crushing fatigue, mental confusion, loss of coordination are some of the symptoms. The onset can be very sudden from feeling slightly fatigued to feeling dreadful. In my confused state I though my bike's tyres must have punctured, or a strong headwind had blown up suddenly - or the world had tilted upwards!

Unfortunately getting to that point is very varied, size, how topped up your glycogen levels are, how intense your exercise is, the duration of your exercise, how accustomed you are to fasted exercise......
Two hours of very strenuous cardio is sometimes given as a rough guide to start getting concerned but that could be for someone who is an athlete and eating at maintenance calories not a prolonged deficit.

BTW - calorie estimates from HR often aren't at all accurate, the numbers you give would indicate a very high level of fitness. But they could also be a result of someone who simply has a high exercise HR.

If you are seriously concerned bonking/hitting the wall might be an issue then carbs before exercise would be far more appropriate than a high protein snack. You can recover quickly from bonking/hitting the wall (glucose gets in your bloodstream very quickly) but it's a horrible experience to be avoided not flirted with.

The worst I've gotten is being depleted in a way that when I finally do sit to eat, digestion takes up so much blood flow that if I get up too quickly, I'll be faint. I actually fainted once like this years ago and didn't realize this was the cause. What you're describing sounds worse.

When I log the AMT, I still actually log somewhat conservatively on MFP and just use the default entry for the elliptical, which is about 15% less I think. Even so, I'm inclined to believe the heart rate numbers are probably the only semi accurate way for me to judge unfortunately. My resting heart rate has gone from mid 90s to 70 flat over the last year, distances, resistance, endurance have all handily increased, so I could very well be considered athletic, though I haven't really an athletic body composition yet. I didn't even log exercise calories until I started a new fat loss protocol which requires a bit of accuracy. I'm finding it to be a lot of guess work.

I guess a bowl of oatmeal is probably my best bet for safety haha.

And sadly that's probably only reliable (semi-!) if you know your actual tested max heart rate vs. age-estimated, and are doing moderate steady state, not intervals or high intensity.

Congrats on the progress on resting heart rate, and other improvements, BTW!