There are many myths and misconceptions about exercise and weight loss, and this article sheds a bright light on the biggest fallacies in the fitness industry.
#1: Resting metabolic rate increases with exercise.
An often (over)used argument among fitness professionals is that strength training adds muscle, which will increase resting metabolic rate and, over time, will help clients lose weight because muscles are “fat-burning machines.” Contrary to what most people believe, research has shown that resting metabolic rate does not differ much between people — regardless of whether they are fat or lean — averaging about 200 to 250 milliliters of oxygen per minute, or about 3.5 milliliters of oxygen per kilogram of body mass per minute. In terms of calories, resting metabolic rate ranges from about 1,200 to 2,000 kcals per day (1,400-1,600 kcal per day in most people). Thus, heavier people actually have slightly higher resting metabolic rates because they have more mass to support all day. Research using imaging techniques to determine the surface area of internal organs has shown that each pound of muscle burns 6 to 7 calories per day.
People lose weight only when caloric expenditure is greater than caloric intake. This is referred to as being in negative energy or negative caloric balance. When people are in negative energy balance and losing weight, resting metabolic rate actually decreases. Resting metabolic rate is never elevated when people are losing weight. Since no research shows that resting metabolic rate increases when people are in negative caloric balance, how can exercise increase resting metabolic rate, resulting in weight loss?
While there is a positive relationship between fat-free weight (i.e., muscle mass) and resting metabolic rate among animals and humans with large differences in body weight, whether an individual can significantly increase his or her resting metabolic rate, is questionable. While some research has shown a significant increase in resting metabolic rate following training (Byrne & Wilmore, 2001; Dolezal & Potteiger, 1998; Lemmer et al., 2001; Poehlman & Danforth, 1991; Potteiger et al., 2008; Pratley et al., 1994), the magnitude of change is relatively small (30-142 kcal/day) compared to what is needed for weight loss. Furthermore, there are just as many studies showing that resting metabolic rate does not change in response to training (Broeder et al., 1992; Frey-Hewitt et al., 1990; Kraemer et al., 1997; Poehlman et al., 2002; Taafe et al., 1995; Wilmore et al., 1998). A few of the studies reporting an increase in resting metabolic rate with exercise have been conducted on older adults who are more likely to show increases in resting metabolic rate due to the attenuating effect of strength training on age-associated losses in muscle mass (Lemmer et al., 2001; Poehlman & Danforth, 1991; Pratley et al., 1994). In other words, resting metabolic rate can increase in response to strength training in an older population likely because strength training has a greater impact on older people since they have lost a significant amount of muscle mass over the years. Thus, strength training may have the greatest chance to increase resting metabolic rate in elderly clients or in middle-aged clients who are out of shape with little muscle mass. In either case, however, the magnitude of change in metabolic rate is still small compared to the large caloric expenditure needed for significant weight loss.
The majority of research shows that, while post-exercise metabolic rate (referred to as excess post-exercise oxygen consumption, or EPOC) is acutely elevated, resting metabolic rate does not increase following an exercise program (i.e., an increased resting metabolic rate is not a chronic adaptation to exercise training).
#2: Lactic acid causes fatigue, muscle burning, and muscle soreness.
First discovered in 1780 in sour milk, lactic acid — or lactate, as it exists at physiological pH — is produced in a metabolic pathway called glycolysis. The final product of glycolysis, pyruvate, is converted into lactate when oxygen is not supplied fast enough to meet the needs of the cell. This happens a lot during intense exercise because the muscle cell’s need for energy (ATP) is too immediate to wait on oxygen. Therefore, there is an accumulation of lactate in the muscles and blood during intense exercise.
From the time Nobel Prize winners A.V. Hill and Otto Meyerhof discovered in the 1920s that lactic acid is produced during fatiguing muscle contractions in the absence of oxygen, lactic acid has been the exercising community’s scapegoat for fatigue. But there has never been any experimental evidence proving a cause-and-effect relationship between lactate and fatigue. Hill & Meyerhof’s observations falsely led to associations between oxygen insufficiency, lactic acid, acidosis, and fatigue, which continue to be proliferated. While lactate increases during intense exercise, so do other metabolites, including potassium ions, hydrogen ions, and the two constituents of ATP — ADP and Pi — each of which disrupt or inhibit specific cellular functions that ultimately lead to a decrease in muscle force production (i.e., fatigue). Because of lactate’s concomitant increase with these other metabolites and the simple method of measuring its concentration, blood lactate is used by scientists only as an indirect measure of acidosis and fatigue.
Lactate also does not cause muscle burning. No physiologist has ever burned himself when taking a blood sample containing a high blood lactate concentration. The exact cause of the sensation of muscle burning is unknown, but it may be nothing more than the increase in muscle temperature that accompanies intense exercise.
Lactate also does not cause muscle soreness. Muscle and blood lactate return to pre-exercise levels within 30 to 60 minutes after exercise, so lactate is long gone by the time soreness develops. Muscle soreness is the result of microscopic tears in the muscle fibers, causing an initial mechanical injury (related to the contractile proteins — actin and myosin — pulling apart), and a consequent inflammatory response, which brings about the perception of soreness.
Not only does lactate not cause fatigue, muscle burning, or muscle soreness, its production in muscle is vital during intense exercise, as it serves a number of roles. Lactate production maintains the ratio of certain biochemical molecules, supporting the continued ability of glycolysis to keep working. Lactate is also used as a fuel by the heart, is used by the liver to make new glucose via gluconeogenesis, and is converted back into glycogen (the stored form of carbohydrates) by a reversal of the chemical reactions of glycolysis. Both the new glucose and glycogen are then themselves used as fuels by muscles so exercise can continue at the desired intensity. Research on biopsied muscle fibers bathed in lactic acid has shown that muscle force production actually increases (Nielsen et al., 1991). So much for lactate being a waste product!
#3: Your clients have to exercise in their fat burning zone.
People often assume that low-intensity exercise is best for burning fat. During exercise at a very low intensity (e.g., walking), fat does account for most of the energy expenditure, while at a moderate intensity (e.g., 80% maximum heart rate), fat accounts for only about half of the energy used. While your clients use both fat and carbohydrates for energy during exercise, these two fuels provide that energy on a sliding scale — as clients increase their intensity up to their lactate threshold (the exercise intensity that demarcates the transition between exercise that is almost purely aerobic and exercise that includes a significant anaerobic contribution; also considered the highest sustainable aerobic intensity), the contribution from fat decreases while the contribution from carbohydrates increases. When your clients exercise at an intensity above their lactate threshold, they use only carbohydrates. While there is only a minimal amount of fat used when exercising just below the lactate threshold, the number of calories used per minute and the total number of calories expended are much greater than when exercising at a lower intensity, so the amount of fat used is also greater. Research has shown that the highest rate of fat use occurs when exercising at or slightly below the lactate threshold (Achten et al., 2002). What matters is the rate of energy expenditure, rather than simply the percentage of energy expenditure derived from fat. Since your clients use only carbohydrates when exercising at a high intensity, does that mean that if they run fast or take a high-intensity spinning class, they won’t get rid of that flabby belly? Of course not.
Despite what most people think, clients don’t have to use fat during exercise to lose fat from their waistlines. After all, have you ever seen a fat sprinter? Sprinters primarily train anaerobically, never using fat during their workouts. Carbohydrates are actually the muscles’ preferred fuel during exercise. The little amount of fat that is used in combination with carbohydrates during exercise below the lactate threshold is in the form of intramuscular triglycerides — tiny droplets of fat within muscles. Adipose fat (the fat on your clients’ waistlines and thighs) is burned during the hours before and after their workouts while they’re sitting at their desks. Since fat is oxidized inside the muscles’ mitochondria — microscopic aerobic factories that contain the enzymes involved in aerobic metabolism—it is more efficient to use fat that is physically closer to the mitochondria during exercise when your clients need to regenerate energy quickly for muscle contraction. For fat and weight loss, what matters most is the difference between the number of calories your clients expend and the number of calories they consume. Weight loss is really all about burning lots of calories.
Your clients become better fat-burning machines by enhancing the metabolic profile of their muscles. For example, endurance training enhances fat oxidation by increasing skeletal muscle mitochondrial content and cellular respiratory capacity, allowing for the sparing of muscle glycogen. This steering in fuel use to a greater reliance on fat at the same exercise intensity is one of the hallmark adaptations of endurance training.
People are also led to believe that exercising first thing in the morning burns more fat. While muscles are forced to rely on fat when blood glucose and muscle glycogen are low, as they often are first thing in the morning, exercising when blood glucose is low will decrease exercise intensity, resulting in a lower-quality workout and less calories burned.
So tell your clients not to worry about exercising in their fat burning zone, because there’s no such thing.
#4: People get fat because they eat too much.
We eat three things — carbohydrates, protein, and fat. The carbs that we eat are used to replace muscle and liver glycogen and maintain blood glucose levels. Protein is used to repair muscle tissue and build structures, like actin and myosin and enzymes and mitochondria. Fat is an important component of cell membranes, is the largest store of energy, and is used for insulation and organ protection.
A metabolic priority of muscle recovering from a workout is replenishment of glycogen stores and the reparation of damaged tissue. With no exercise, there is never a drain on muscle glycogen nor any tissue to repair or build, so any calories consumed that are not used to meet these metabolic needs or repair and build tissue are stored as fat. Thus, while caloric intake certainly influences body weight, creating a very large metabolic demand by exercising a lot will limit how much fat is stored because the calories that are consumed will serve to meet the metabolic needs first.
#5: Strength training before cardio increases the amount of fat used during cardio, helping to burn more fat.
Your clients have enough glycogen to last about two hours of sustained moderate-intensity activity. Any strength training workout is not likely to deplete muscle glycogen because it’s not long enough and most of the workout time is spent resting between sets and exercises. Even if the workout were long and intense enough to cause glycogen depletion, exercising in a glycogen-depleted state has many negative consequences, including ketosis, low blood insulin, hypoglycemia, increased amino acid (protein) metabolism, and increased blood and muscle ammonia. There is no research showing that strength training immediately before doing a cardio workout increases the amount of fat used during the cardio workout. Exercise intensity determines which substrate is used, with high-intensity exercise using more carbohydrates. Furthermore, it’s possible that the muscle fatigue incurred from strength training may cause clients to decrease their subsequent cardio intensity, thus causing them to expend fewer calories over the whole workout. If your client’s primary goal is to increase aerobic endurance or lose weight, then cardiovascular exercise should be performed first. Conversely, if your client’s primary goal is to increase muscular strength, local muscular endurance, or sculpt his or her body, then strength training should be performed first. The most important type of exercise should be performed when the client is not fatigued, so that he or she can get the most out of the workout.
#6: Eating right before going to bed will make you fat.
Enzymes don’t wear watches. It makes no difference what time your clients eat; weight loss and weight gain is about how many calories they consume vs. how many calories they expend. If your clients create a large metabolic demand during the day by exercising a lot, the calories they consume will go to fulfill the metabolic needs, regardless of the time they eat.
#7: Low-carb diets are good for weight loss.
While some research shows that low-carb diets can result in initial weight loss, they are not good for the long-term. Low-carb diets are not sustainable. Exercise, which is dependent on carbohydrates, leads to sustained weight loss. Fat burns in the flame of carbohydrate!
#8: Doing crunches will shrink your clients’ waistlines.
Despite what those late-night compelling infomercials claim, crunches will not shrink your clients’ waistlines. It would take a billion crunches to add up to enough calories to make a difference in your clients’ waistlines. Crunches can strengthen and hypertrophy the abdominal muscles, but not make your clients lose fat.
- Achten, J., Gleeson, M., and Jeukendrup, A.E. (2002). Determination of the exercise intensity that elicits maximal fat oxidation. Medicine and Science in Sports and Exercise 34 (1):92-97.
- Broeder, C.E., Burrhus, K.A., Svanevik, L.S., and J.H. Wilmore. (1992). The effects of either high-intensity resistance or endurance training on resting metabolic rate. American Journal of Clinical Nutrition 55:802-810.
- Byrne, H.K. and Wilmore, J.H. (2001). The effects of a 20-week exercise training program on resting metabolic rate in previously sedentary, moderately obese women. International Journal of Sports Nutrition and Exercise Metabolism 11(1):15-31.
- Dolezal, B.A. and Potteiger, J.A. (1998). Concurrent resistance and endurance training influence basal metabolic rate in nondieting individuals. Journal of Applied Physiology 85(2):695-700.
- Faulkner, J.A., et al. (1993). Injury to skeletal muscle fibers during contractions: Conditions of occurrence and prevention. Physical Therapy 73(12):911-921.
- Frey-Hewitt, B., Vranizan, K.M., Dreon, D.M., and Wood, P.D. (1990). The effect of weight loss by dieting or exercise on resting metabolic rate in overweight men. International Journal of Obesity 14(4):327-334.
- Lemmer, J.T., Ivey, F.M., Ryan, A.S., Martel, G.F., Hurlbut, D.E., Metter, J.E., Fozard, J.L., Fleg, J.L. & Hurley, B.F. (2001). Effect of strength training on resting metabolic rate and physical activity: age and gender comparisons. Medicine and Science in Sports and Exercise 33(4):532-541.
- Kraemer, W.J., Volek, J.S., Clark, K.L., Gordon, S.E., Incledon, T., Puhl, S.M., Triplett-McBride, N.T., McBride, J.M., Putukian, M., and Sebastianelli, W.J. (1997). Physiological adaptations to a weight-loss dietary regimen and exercise programs in women. Journal of Applied Physiology. 83(1):270-279.
- Nielsen, O.B., de Paoli, F., and Overgaard, K. (1991). Protective effects of lactic acid on force production in rat skeletal muscle. Journal of Physiology 536(1):161-166.
- Poehlman, E.T. and Danforth Jr., E. (1991). Endurance training increases metabolic rate and norepinephrine appearance rate in older individuals. American Journal of Physiology, Endocrinology and Metabolism 261: E233-E239.
- Poehlman, E.T., Denino, W.F., Beckett, T., Kinaman, K.A., Dionne, I.J., Dvorak, R. & Ades, P.A. (2002). Effects of endurance and resistance training on total daily energy expenditure in young women: a controlled randomized trial. Journal of Clinical Endocrinology and Metabolism 87(3):1004-1009.
- Potteiger, J.A, Kirk, E.P., Jacobsen, D.J., and Donnelly, J.E. (2008). Changes in resting metabolic rate and substrate oxidation after 16 months of exercise training in overweight adults. International Journal of Sports Nutrition and Exercise Metabolism 18(1):79-95.
- Pratley, R., Nicklas, B., Rubin, M., Miller, J., Smith, A., Smith, M., Hurley, B., and Goldberg A. (1994). Strength training increases resting metabolic rate and norepinephrine levels in healthy 50- to 65-yr old men. Journal of Applied Physiology 76:133–137.
- Taaffe D.R., Pruitt, L., Reim, J., Butterfield, G. & Marcus, R. (1995). Effect of sustained resistance training on basal metabolic rate in older women. Journal of the American Geriatrics Society 43(5):465-471.
- Volek, J.S., VanHeest, J.L. & Forsythe, C.E. (2005). Diet and exercise for weight loss. Sports Medicine 35(1):1-9.
- Wilmore, J.H., Stanforth, P.R., Hudspeth, L.A., Gagnon, J., Daw, E.W., Leon, A.S., Rao, D.C., Skinner, J.S. & Bouchard, C. (1998). Alterations in resting metabolic rate as a consequence of 20 weeks of endurance training: The HERITAGE Family Study. American Journal of Clinical Nutrition 68: 66-71.