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Exercise Myths and Facts

by Richard Weil, MEd, CDE

Are you confused by all the exercise advice out there? It’s no wonder: With a dozen fitness magazines on the newsstand, a wealth of health and fitness news streaming into your home over the Internet, bogus ads guaranteeing an effortless 40-pound weight loss or bigger muscles in just 10 days, not to mention the free advice from well-intentioned friends, trainers, and the guy on the bench press next to you, there’s a lot of conflicting information to sort through. Unfortunately, many popular fitness tips not only make exercise seem harder and more complicated than it really should be, but they can also lead to injury. To set the record straight and help you exercise safely, here are the facts — nothing but the facts — behind some of the most common exercise myths.

You don’t start burning fat until 20 minutes into your workout.
This is one of the most popular myths of all time. You may have heard it from a friend or even from a fitness trainer at your gym, but the fact is, muscle burns a combination of fat and carbohydrate (glucose) simultaneously almost all of the time. It’s just that you may burn a higher percentage of one or the other depending on the intensity of the exercise. For example, during high-intensity activities like sprinting or strenuous weight lifting, which get you out of breath, your muscles are burning a higher percentage of carbohydrate than fat (perhaps as much as 80% to 90% carbohydrate and 10% fat). At rest and during light-intensity physical activity (such as moderate-paced walking), when breathing is easier, the percentage could change to 70% fat and 30% carbohydrate. Why does this happen?

As you start to exercise, fat and carbohydrate are released from storage sites in the body as well as from the bloodstream and enter the working muscles. (Protein is not a fuel for exercise unless your body is in a starvation crisis.) Oxygen, transported from the lungs to the muscle, burns these fuels to generate energy. Fat contains more than twice the amount of energy per gram as carbohydrate (fat contains 9 calories per gram while carbohydrate has only 4). Your muscles would prefer to burn fat, because it’s so energy-dense, but the catch is, you must provide adequate oxygen to the muscle to burn it. Since fat contains more calories than carbohydrate, it also takes more oxygen to burn. When you’re really out of breath — during a sprint, for example — there’s not enough time for oxygen to travel from the lungs to the muscles, and so your muscles, low on oxygen, have no choice but to burn the less dense fuel, carbohydrate. As a general rule, unless you are performing brief, very intense exercise, there’s always enough oxygen in the muscles to burn some fat as well as carbohydrate. Which leads us to our next myth…

The “fat-burning” option on the exercise machine at the gym is better for weight loss than the “cardio” option.
This isn’t only a myth; it’s really bad advice. Basically, you want to burn as many calories as possible when you exercise, whether you’re trying to lose weight, increase your stamina, control your diabetes, or improve your general health. Caloric expenditure during aerobic activity is directly related to the distance you travel and how hard you work. When you select the fat-burning mode on an aerobic exercise machine, you in effect minimize the number of calories you burn, because the machine — let’s say a treadmill — keeps the speed slow and the elevation low. On the “cardio” option, the speed and elevation are set higher, so that for an equivalent amount of workout time, you end up traveling farther, working harder — and burning more calories.

The reason the lower level is labeled the “fat-burning” option is that, as described above, at lower intensities you breathe more comfortably, so you deliver more oxygen to the muscles and burn a higher percentage of fat than carbohydrate. This part of the equation is accurate, but the truth is that although you may burn a higher percentage of fat at the slower speed and intensity, you end up burning less total fat. For example, if you weigh 150 pounds and walk on the treadmill for 30 minutes at 3.0 miles per hour, you will burn about 150 calories in one session. If you walk for 30 minutes at 4.0 miles per hour, you will burn 200 calories. Now let’s say that at the lower-intensity, 3-mile-per-hour pace you burn 70% of your total calories from fat. That would be .70 x 150 calories, or a total of 105 calories burned from fat. At the faster, 4-mile-per-hour pace, you burn only 60% of your calories from fat (again, because you are working harder, you can’t get as much oxygen to the muscles to burn fat). So, .60 x 200 calories equals 120 calories from fat. As you can see, at the slower speed, not only is the number of total calories burned less (150 versus 200), but the number of fat calories burned is also less than it is at the faster speed (105 versus 120).

If this confuses you, don’t sweat it. Just remember that selecting a slower speed and lower intensity to maximize fat burning is counterproductive — unless it enables you to exercise longer and burn more calories. Whenever you exercise, try to work to the point where you feel warm and slightly out of breath. If you do, then you can be sure that you’re doing the best you can to burn lots of fat and glucose, increase your level of fitness, and improve your health.

Don’t lift weights if you’re trying to lose weight.
Some people don’t want to weight train while they’re on a weight-loss program because they know that building muscle might cause some weight gain. That’s true, because muscle tissue is heavier than fat, but muscle is exactly what you want to gain when you’re trying to lose weight. Here’s why: When you restrict calories to lose weight, you always lose some muscle. In fact, up to 25% of your body-weight loss can be from muscle. (So if you lose 10 pounds, 2.5 pounds of it could be muscle.) The problem with losing muscle during weight loss is that muscle is the engine that burns calories and helps maintain your metabolic rate. If you have less muscle, you reduce your ability to burn calories, lose more weight, and, more important, maintain your weight loss. (The plateau that many people experience during weight loss can be explained partially by loss of muscle.)

In most cases, moderate weight training will not amount to more than 3–5 pounds of weight gain anyway, but even if it did, it’s what you want, because each pound of muscle consumes about 35–50 calories a day. So next time someone drops by and offers you five pounds of muscle, go ahead and take it; it’ll help you use up an additional 175–250 calories daily.

Muscle is also the engine that burns glucose. The more muscle you have, the more glucose you can burn, and the better your diabetes control may be. So pour on the muscle. Lift weights all you want, whenever you want.

Exercise in the morning works better than exercise at night.
Some people believe that if you go to sleep right after exercise you won’t get as much benefit from the workout, because your metabolic rate slows down while you’re sleeping. If you exercise in the morning, they say, you jump-start your metabolism and burn more calories throughout the day. There’s no evidence that this is true.

Another reason some people believe morning exercise is superior to nighttime exercise is that exercising right before bed supposedly keeps you awake longer. Research shows that that may be true, but generally only for deconditioned people. For fit people, exercise before bedtime does not alter sleep patterns, probably because their bodies are used to and recover quickly from the effects of exercise. Some health experts suggest that regular exercise may even help improve sleep quality and sleep onset over time.

The bottom line is that the body responds to exercise whenever you do it. If exercising at night fits your schedule better, then by all means do it then. If getting a workout first thing in the morning makes you feel more energetic, all the better. The best time to exercise is the time you are most likely to do it.

Walking isn’t enough.
Walking may not be as arduous as training for a marathon, but when it comes to preventing diabetes, complications of diabetes, and heart disease, it’s powerful medicine. The Diabetes Prevention Program, a three-year, government-sponsored study designed to test the ability of healthy behavior changes to prevent diabetes, showed that when people under the age of 60 who had impaired glucose tolerance, or prediabetes (a condition that often precedes Type 2 diabetes), walked 150 minutes per week (that’s five 30-minute walks per week) and followed a low-fat diet (enabling them to lose 5% to 7% of their body weight), they reduced their risk of diabetes by 58%. For people over 60, the risk reduction was 71%.

In another study, close to 3,000 retired men were enrolled in the Honolulu Heart Program to study the effects of walking on heart disease. The conclusion: The more they walked, the lower their risk of heart disease. Men who walked more than 2 miles per day were half as likely to get heart disease as men who walked less than 1 mile per day.

In both of these studies, subjects walked at a moderate pace of 3.0–4.0 miles per hour.

Spot-reducing exercises can trim my trouble spots.
There’s no such thing as spot-reducing. It would be nice if you could walk on the treadmill and say, “OK, today I’ll burn fat from my thighs.” But that’s not the way it works. Whether it tends to collect on your thighs or your tummy, fat on your body belongs to your entire body, and the only way to reduce it is through regular exercise and reducing your caloric intake. Here’s some information about storing and burning fat that should help you understand how aerobic exercise, weight lifting or other resistance exercise, and attention to your diet can help you lose weight.

Fat is stored in cells called adipocytes, which are located all over the body. When you eat more fat or calories than your body needs, the fat cells gobble up much of the excess and expand in size. The larger the cells, the higher your percentage of body fat. Where on the body your fat cells are located, where you tend to store fat first, and how efficient your adipocytes are at storing fat is genetically determined; you have no control over it. As a rule, men store fat in their abdomens, and women tend to store it in their buttocks, hips, and thighs. Similarly, people generally gain and lose weight in a consistent pattern. If you’ve lost and regained weight multiple times, you probably know where you tend to lose it from first (perhaps the face), and where it tends to stick the longest (often in the hips, thighs, and buttocks).

How does exercise help you get rid of fat? During exercise, hormones like adrenaline are released that signal the adipocytes to release fat into the bloodstream. That fat is then transported to the muscles to be burned for energy. When an adipocyte releases its stored fat, it shrinks. The cells themselves never disappear, but as long as the fat is used by the muscle and does not return to fatten up the adipocyte, you will lose overall body fat. Because you have no control over which adipocytes are stimulated to release fat, however, you cannot “spot-reduce” fat from a particular body part.

Aerobic exercise (such as biking, walking, or swimming) stimulates the release of more fat than does resistance exercise like weight lifting, leg lifts, or pushups. However, resistance exercise builds muscle, and muscle is the engine that burns fat and helps maintain metabolic rate. So if you’re trying to lose weight, an exercise program that includes aerobic activity as well as some type of calisthenics or weight lifting will probably help you the most.

Incidentally, although they don’t change your weight-loss pattern, exercises that work your abdomen, thighs, hips, and buttocks will indeed strengthen and tone the underlying muscles, so even if there is still that pesky layer of fat on top, your physique will be tighter and your clothes may even feel looser.

Exercise will make me hungry.
There is no compelling evidence that moderate exercise affects a person’s overall appetite; it neither makes you hungry nor suppresses your appetite. Some people report that they make better food choices if they exercise regularly, but this has not been studied carefully. The only time exercise is likely to make you hungry is if it’s been 3–4 hours since your last meal or snack, and you exercise on an empty stomach.

If I don’t sweat during exercise I’m not getting any benefit.
Sweating is important because it’s a way of cooling off muscles that heat up during exercise, but it is not necessarily an indicator of how hard you are working. Temperature, humidity, wind conditions, and even how you are dressed all affect how much you sweat on a given day. Moreover, not everyone sweats at the same rate.

Do you ever turn beet-red during exercise? That happens because blood vessels below the skin in the face are dilating; as they widen, they transport heat from the muscles to the skin to cool off the body. Chances are, if you’re a person who turns bright red in the face during exercise, you may not sweat as much as a person who does not turn red; it usually has nothing to do with the amount of exercise you do or how much effort you’re putting into it. Which brings us to a related myth…

The fitter I get, the less I will sweat.
There’s no relationship between how fit you are and how much you sweat. Some people sweat buckets, while others don’t sweat much at all, regardless of their fitness level or degree of exertion. Heavy sweating during exercise may not be pleasant, but it means that the body is cooling itself efficiently, which may enhance your performance.

The only possible physiological downside of heavy sweating is that if you don’t replace the lost fluid by drinking water, you run the risk of dehydration. Dehydration is unhealthy for all people, but it can be even more of a concern for people with diabetes, because it is more likely to occur when blood glucose levels aren’t under control.

It’s relatively easy to dehydrate if you sweat a lot; on a hot, humid day, you can lose more than 5% of your body weight from sweat during a workout. Athletic performance can be adversely affected by as little as a 1% drop in body weight, and when fluid loss exceeds 3% of body weight, endurance can diminish by as much as 20% to 30%. Weight loss from sweat should never exceed 2% of body weight. (For a 150-pound person, 2% of body weight is 3 pounds.)

Thirst is not a good indicator of hydration status, because by the time you feel thirsty, you may already be dehydrated. Proper hydration, or fluid replacement, should begin before you exercise and continue during and after the activity. The amount of water you drink should approximately equal the amount of fluid lost in sweat and urine. To get a sense of how much fluid you need, weigh yourself nude before and after exercise and drink 2 cups of water for every pound lost. Some people can lose 1/2 to 2 liters of fluid per hour (1 liter of water weighs 2.25 pounds). A more general guideline for maintaining proper hydration is as follows:

  • Drink 17 to 20 ounces of water (about 2–2 1/2 cups) 2 to 3 hours before exercise.
  • Drink 7 to 10 ounces of water (about 1–1 1/2 cups) 10 to 20 minutes before exercise.
  • Drink 7 to 10 ounces of water every 10 to 20 minutes during activity.

If you sweat heavily, you may need to drink more.

If I’m not sore after my workout, I’m not getting any benefit.
This myth may hail back to that old “no pain, no gain” adage that’s simply not true. Muscle soreness is not a prerequisite for muscle growth. When just starting an exercise program or a new activity, it’s common to feel stiff or sore for a day or more afterward. Once the body adapts to a particular exercise, however, you won’t feel as sore every time you work out, though clearly you are getting stronger. You can minimize muscle pain by beginning with small amounts of activity and only gradually increasing the intensity and duration of your workout.

If you’re already used to exercise, you know that you are capable of various degrees of intensity when working out. You don’t need to push to the limit at each workout to realize gains in performance (in fact, overdoing it can cause burnout or injury), but if you feel you’ve hit a plateau in your routine, and you consider a little soreness to be “good pain,” kicking your effort up a notch or two can help you reach your next fitness goal. Try lifting weights more slowly, particularly on the lowering portion of the lift, which tends to cause more soreness. You could also ask a spotter to help you with the final few repetitions once you’re fatigued and cannot complete a full repetition. You begin the lift on your own, and when you cannot lift any further, the spotter helps you finish the lift; you then lower the weight on your own. This is called assisted negative training, and it will help you build muscle.

To increase the intensity of aerobic workouts, try interval training once or twice a week. Interval training involves setting up a work-to-active-recovery ratio, in which you alternate more intense periods of activity with less intense, “active recovery” periods. For example, if you usually walk on the treadmill for 30 minutes at a steady, 3.5-mile-per-hour pace, here’s what a 30-minute interval training session might look like: Walk for 10 minutes at your usual pace (so you’re good and warmed up), then increase the speed to, say, 3.8 mph (which will get your heart thumping) for one minute. Return to your 3.5-mph pace for another 3 minutes, then pick up the pace to 3.8 mph again for one minute.

The work-to-active-recovery ratio in this workout is 1:3: The minute at 3.8 mph is the “work,” and the three minutes at 3.5 mph is the “active recovery.” Over time, as you get fitter, you’ll be able to extend the “work” time to 1.5 minutes and spend only 2.5 minutes at the slower pace. Eventually, your regular, steady pace will be 3.8 mph, and when you interval train, your “work” pace will be even faster.

You can’t build muscle after age 50.
This myth was shattered by a landmark study published in 1990, in which 10 frail nursing home residents, ages 90 to 96, lifted weights for eight weeks. After the study was completed, their strength gain averaged 174%, thigh muscle area increased 9.0%, and walking speed increased by 48%.

Other studies have shown similar results, so it seems clear that muscle loss is caused not by aging itself but by lack of activity. Not only is muscle gain possible, but it’s also very beneficial for older adults: Strength training helps increase bone mass, reduce the risk of falling, and preserve greater independence. It’s fair to say that it’s never too late to start lifting.

Exercise always leads to weight loss.
Disappointing as it may seem, exercise is much more important for weight maintenance than it is for weight loss. In fact, in virtually all studies that compare people who exercise to lose weight with people who diet to lose weight, the dieters always lose lots of weight, and the exercisers lose very little, if any.

That’s no reason to give up on exercise, though. For one thing, you gain important health benefits from exercise even if you don’t lose a pound. For another, when you lose weight by restricting calories, it’s very difficult to keep the weight off permanently unless you exercise to raise your metabolic rate and prevent muscle loss. Many weight-loss researchers believe that including regular exercise in a weight-loss program is the single best predictor of long-term weight-loss success. (If you cut calories but remain sedentary, there’s a high likelihood that you will regain all of the weight you lose.)

This may not sound like great news, but it is. It means that you do not have to do Herculean amounts of exercise to lose weight. If you get started on weight loss by reducing your caloric intake, then gradually increase your level of physical activity while continuing to watch your calories, you will steadily lose weight. As you lose pounds, you should find it easier to move, and by the time you reach your target weight, you should be physically active enough to keep the weight off.

If you find you have gained weight after starting to exercise, there are two probable explanations:

  • You may be gaining muscle. Muscle is heavier than fat, and it’s possible to gain 3–5 pounds of muscle mass in 4–8 weeks, particularly during a weight-lifting program. (You’re likely to gain more muscle from lifting weights than from doing aerobic exercise.) This is not a bad thing.
  • You may have started to eat more. Some people eat more when they first begin to exercise because they feel hungrier (although it’s not all that common, as mentioned before), and some people eat more because they think they are “allowed to” since they’re exercising. The problem is that exercise may not burn as many calories as you think it does. If you weigh 150 pounds and run for 30 minutes at 6.0 mph, you’ll burn about 300 calories. That may seem like a lot, but if you also eat an extra 500 calories throughout the day, you’re going to gain weight.

If you exercise on an empty stomach, you may eat more than usual after exercise. For instance, if you exercise after work but before dinner, and you haven’t eaten since lunch, by the time you finish exercising, you may not have eaten for 5 or 6 hours. When you’re famished after a workout, it’s very easy to eat more than you intend to at dinner, which can cause the calories to add up. To help control hunger, try having a snack 4&–60 minutes before exercise if it’s been more than 3–4 hours since you last ate. Half a bagel, 8 ounces of sugar-free yogurt, an energy bar, or a banana are some suggestions for a light pre-exercise snack.

For people who take insulin or oral medicines that lower blood glucose level, exercising without a pre-exercise snack can cause hypoglycemia, or low blood glucose. Developing low blood sugar during a workout can make exercise very frustrating, and if it happens on a regular basis, the extra calories you need to treat the hypoglycemia can add up. If you’re unhappy about always having to eat before or during exercise to prevent or treat low blood sugar, speak to your doctor or diabetes educator about lowering your insulin doses on days you exercise. After all, if you’re trying to maintain weight loss, what’s the point of exercising if you have to eat every time you work out? To read more about managing blood glucose during exercise, see the article “The Great Blood Glucose Balancing Act” on the Diabetes Self-Management Web site.

The truth about exercise
So there you have some crucial facts about exercise. In today’s world, where information is the name of the game, it’s easy to lose track of the simplicity of movement. Exercise doesn’t have to be complicated: Pick an activity that you like and that gets your heart thumping a little (remember, the key is to feel warm and slightly out of breath), then do it daily or on most days, and ignore all the hype. If you do this, you have a great shot at good health and physical fitness.

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