Tuesday, 06 January, 2004

Exercise and weight loss

Using exercise as a component of weight loss is tricky.  If you do a mild amount of daily exercise, say burning 200 to 300 calories, you'll probably do okay without increasing your food consumption.  Your body can make up maybe 500 calories difference every day by metabolizing stored fat without you feeling hungry or suffering any ill effects.  But if you step up your exercise beyond that point, you will have to start eating more unless you're on one of those 1,000 calorie per day, doctor-supervised crash diets.  When you start exercising more than about 500 calories per day, controlling diet becomes very difficult because the tendency is to satisfy hunger by eating until you're full, which often results in you eating more than you burned during exercise.

For example, I burn approximately 500 calories per hour when I'm cycling at my 100-mile pace.  I burn more when I'm riding hard and less when I'm taking it easy, but if I average out a week it's always right around 500 calories per hour.  Starting this month, I'll be spending 15 to 20 hours a week on the bike.  That's 1-1/2 to 2 hours a day 5 days a week, and a long ride of 7 or 8 hours each weekend.  (I schedule one day off each week.)  It works out to an average of 1,100 to 1,400 calories per day.  Subtract the 500 or so that I want gone to lose an average of a pound per week and I'm still left with a 600 to 900 calorie deficit.  Is it any wonder that I'm always hungry?  The really hard part, though, is limiting myself to those extra 600 to 900 calories rather than stuffing my face until I can't eat any more.

It gets worse.  Feeding is a very important part of long-distance cycling.  The problem is that you can burn energy a whole heck of a lot faster than your body can absorb it.  A fit, well-trained athlete (we're talking a Tour de France rider here) can assimilate 400 or 500 calories per hour.  At my current level of training, I'd be lucky to get half of that.  I could eat that much, certainly, but my body wouldn't process it.  Anything over 200 or 250 calories an hour just sits in my gut and makes me sick.  This is a problem with sports drinks like Gatorade that contain 250 calories or more per liter (see below).  So at my 500 calories per hour pace, I'm running at a 50 or 60 percent deficit.  This is why it's very important to know your anaerobic threshold and to maintain a pace that's below that point.  At aerobic levels, your body can metabolize fat for energy.  Once you go anaerobic, you rely solely on muscle glycogen and blood glucose stores, which at best are about 1,500 calories, or a little under 2 hours worth of energy for me at anaerobic levels.  If you stay aerobic for the most part, going anaerobic for quick sprints or climbing hills, you can go a very long time on your body's fat stores (about 70,000 calories for that mythical 160 pound man) even if you're running a 50% deficit.  Provided, that is, that you maintain the proper levels of hydration and important electrolytes like sodium and potassium.

It gets even worse.  It's very easy to get dehydrated, especially when the temperature is over 80 degrees.  If I train my body, I might get it to assimilate up to two liters of water an hour.  If I drink any more than that, I end up feeling bloated and having to stop every 10 or 15 minutes to release the excess.  The problem is that on a hot day I can lose twice that amount in perspiration and respiration.  This is why it's very important to be well hydrated before an event, and to keep drinking throughout the ride.  "Carbo loading" (building up carbohydrate stores in the days before a major event) helps because your body stores a molecule of water with every molecule of carbohydrate.  Even so, on a hot day it's very important to be cognizant of how much you're sweating, and to back off on your effort if you feel you're going too far into hydration deficit.  Sports drinks can cause a problem here because they're too calorie rich.  People who rely on sports drinks for food and hydration will consume 500 or more calories each hour with their two liters of sports drink and become nauseated after a couple of hours because their bodies can't process all the food.  They correctly deduce that it's the sports drink causing the problem, but then they stop drinking it and become dehydrated.

There's a whole lot to learn when stepping up from 50 to 100 or more miles.  Training your body to digest food and assimilate water while you're exercising is just as important as getting your legs used to pushing the bike and your butt used to sitting in the saddle for hours on end.  I highly recommend The Complete Book of Long-Distance Cycling if you're contemplating such a training program.