So here you are, caught in the weight loss abyss somewhere between the the culinary onslaught that was Thanksgiving, and the approaching diet-destroying duo of the Christmas and New Year’s celebrations.

Time for exercise is in short supply. You figure that your best bet is to workout even harder than ever for the little time you have in order to maximize your calorie-burning hours.

Losing weight is all about burning more calories than you take in, right?

Well, no. It’s not quite that simple.

That idea leaves a lot unsaid about the overall effects of exercise on our bodies. There are lots of technical details involving fats, carbohydrates, and number crunching to illustrate why this doesn’t completely add up.

For now, though, I’ll spare you the mumbo-jumbo so we can get right down to understanding how different exercise intensities can impact our ability to get rid of those unwanted pounds. We can also use this knowledge to exercise in a way that helps you become more fit and stay healthy in the process.

Got energy?

We exercise because it takes more energy than just sitting on the couch. The energy comes from calories we burn, and the calories themselves are burned off from stores of fat and sugar in our bodies. (We burn protein, too, but since consuming protein for energy typically happens far less than the amount of fat and sugar we burn, we’re going to leave it out for the purposes of simplifying this explanation.)

Generally speaking, our bodies have two ways of producing energy — one with oxygen, and one without. Given that we’re oxygen breathing mammals you can probably guess which one is more common, and which one our bodies prefer.

Physiologists refer to energy production in the presence of oxygen as aerobic energy, and energy production without oxygen as anaerobic energy. Anaerobic energy is the kind we rely on when we’re running hard and gasping for air. That need to breathe hard is our body’s not-so-subtle way of catching us up on the oxygen “debt” we put ourselves into by pushing ourselves harder than we’re able to go for a long period of time.

At lower levels of exertion we rely primarily on aerobic energy, and at higher levels we rely more and more on anaerobic energy.

The aerobic system is a fat burning machine. With plenty of oxygen and stored fat, you can exert yourself for hours at a time.

Without enough oxygen for higher intensity efforts, the body’s chemistry changes to burning more stored sugars. The available energy in the form of sugar is far, far less than what’s available in our fat stores, so the amount of time you can exercise at a higher, anaerobic intensity level is typically measured in minutes.

As you might guess, our bodies like oxygen, so anaerobic energy production is significantly more stressful than aerobic energy production.

Like all other forms of stress, this means that we have to treat anaerobic energy production — and the level of exertion that it requires — with some reverence. Guyton’s Textbook of Medical Physiology — the bible of the physiological field if ever there were one — refers to exercise as the biggest stressor of our bodies, bar none.

This means that when we choose to exercise, and in particular, when we choose to exercise anaerobically, we should do so carefully, with planning, and a healthy amount of respect.

Burn The Right Stuff

From a weight loss perspective, exercising at high intensities burns proportionally more sugar than it does fat. So to burn fat, you have to slow down and work at a more moderate intensity.

Yes, you will burn more total calories with that advanced “aerobics” class (you now know why they should really be called anaerobics classes!), but you’ll pay the price in many ways.

Bodies get better at tasks with repetition, and energy production is no exception. This means that the more time you spend with sugar-burning high intensity exercise, the more efficient you’ll become at it, and the more likely your body will be to rely on this source for future energy needs.

Conversely, if you spend your time in a fat-burning zone of intensity, you’ll be more likely to engage that particular energy system for other tasks as well.

Now which would you rather have, a body that leaves all that extra weight you’ve packed on untouched while you’re kicking back after the Christmas feast, or one that gets to work right away on burning off the excess fuel? Consistently exercising at a lower intensity, aerobic effort will prime your body to use fats instead of sugars as its energy source.

Additionally, with anaerobic work being more stressful, the chances of you surviving constant high intensity work without getting sick or injured are far, far less. All that excess stress induces our bodies to produce high amounts of the stress hormone cortisol, too. Cortisol is the prime culprit when it comes to feelings of being burnt out and fatigued.

If you’re a high-intensity exercise addict, ask yourself how many times you’ve been sick or injured over the last year. If your answer is more than two or three, you’re probably exercising too hard, too much, or some combination thereof.

This is why most New Year’s Resolution exercise plans don’t last much beyond February or March. Most people work out too hard, too much, too soon. After 6 or 8 weeks they’re typically sick, injured, burnt out, or all of the above.

The Remedy

The fix is to take it down a notch. Run slower. Cycle slower. Swim slower. Don’t push quite as much in the weight room.

Exercise at that oft-heard “conversational pace”. Even better, wear a heart rate monitor. Get a knowledgeable coach or doctor to prescribe an exercise test so you can figure out your personal exercise intensity that keeps your workouts in that aerobic range.

I do this frequently with patients and it does wonders to help people get more from their workouts. More weight loss. More fitness. More health and exercise longevity.

If you can’t get someone to help you figure out your personal exercise zone, take an educated guess. The best kind is the 180-formula advocated by Phil Maffetone.

Here’s how it works. Subtract your age from 180. Next, choose one of the following categories:
-If you’re on regular medication or are recovering from a serious illness, subtract 10.
-If you’re new to exercise, you’ve been injured, or you’re frequently sick, subtract 5.
-If you’ve been exercising without problems for 2 years and you don’t get sick more than a couple of time a year, make no adjustments.
-If you’ve been exercising without problems for 2 years and are making regular progress, add 5.

So, if you’re 40 years old and you get a cold a few times a year, your number is 135. This is your maximum aerobic heart rate. That is, any efforts at a heart rate above this number are considered anaerobic, and are above the intensity at which you should be exercising.

Using this formula obviously requires a heart rate monitor, but it is a minor investment when it comes to being able to workout in a way that not only helps you lose weight, but also keeps you healthy in the process.

In short, feel free not to have to work so hard all the time. It’ll help you lose weight, feel better, and enjoy the holiday season that much more!