So I rode into the figurative wall today....

[Sue]

I was biking and "only" did 15 miles and I was TIRED! I had to push myself to get through the last 15 minutes. So I am left wondering if it was because I did eliptical yesterday (without lifting my heels), because I am getting up at 5 am to go to the gym. OR (this is what I am hoping) my body ran out of fat in the muscles for energy, now it has to get the subcutaneous fat, which takes more energy (did I ever mention I am an extremely optimistic person??? :rofl::rofl:.)

Has anyone else hit this wall when they were exercising?

[jump4joy]

Hitting the wall, or "bonking" as it is commonly known in cycling (any Brits out there can start laughing now) is typically caused by muscle glycogen depletion. Your muscles can hold enough glycogen to generate about 1500 to 2000 cal of energy. Intense cycling can burn 500 - 1500 an hour, so most cyclists won't bonk until about two hours into exercise. But if you've exercised intensely the day before and not replaced your glycogen stores afterwards, you might start an exercise in a depleted state and bonk anyways.

This kind of effect can also be caused by lack of sleep, by excess lactate acid in muscles (if you're doing sprints about lactate threshold) or more commonly by dehydration. Often we're in a slightly dehydrated state and don't know it. These can all feel like a "bonk" although technically they're not. They can also exacerbate a bonk-in-progress.

I've only hit the wall once really hard, which was in a race where I left my gel packs in the transition area and they ran out of carbo drink on the course, so I only had water for an hour at the end of a 5-hour race. At that point, I was bonking so hard I was seeing spots in front of my eyes and worrying about falling over. NOT a pleasant feeling!

To avoid the dreaded wall, make sure you eat around 200 calories of mostly carbs right after exercising, and you can eat something light before exercising or even during (like an exercise drink) if the exercise is going to be longer than an hour to an hour and a half. Unfortunately on your fat-burning theory, our bodies do not burn fat well without either glycogen or carbohydrates converted into simple sugar (the saying "fat burns in a carbohydrate flame" is usually the way this is described). So avoiding bonking is still a better (and safer) way to burn fat, by making sure you have adequate glycogen stores.

[Sue]

Wow thanks for the great info. (snickers at bonking) I was feeling pretty dehydrated this morning. So I bet that was it. I *needed* to drink about 20 ounces of water while I was working out, because I just rolled out of bed and went to the gym. I am making an effort to drink more water today. :-)

I only ride for an hour right now. But I am hoping to extend that once or twice a week eventually. So I will also make sure I have a nice snack before hand.

[bannanabette]

I was biking and "only" did 15 miles and I was TIRED! I had to push myself to get through the last 15 minutes. So I am left wondering if it was because I did eliptical yesterday (without lifting my heels), because I am getting up at 5 am to go to the gym. OR (this is what I am hoping) my body ran out of fat in the muscles for energy, now it has to get the subcutaneous fat, which takes more energy (did I ever mention I am an extremely optimistic person??? :rofl::rofl:.)

Has anyone else hit this wall when they were exercising?

That was me yesterday! I keep my runs short, only 30 minutes total and I throw in walk segments into it, but yesterday I got about 15 minutes in and just couldn't continue. I thought because I had two days rest I could push it a little, but I only got 3 hours of sleep the night before, so I was wiped.

It happens to me more frequently than I'd like - every couple of weeks or so. It's almost always lack of sleep, but sometimes it's that I didn't eat right or my period. (ha, I just realized I hit the trifecta yesterday - no wonder I stopped after 15 minutes)