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If you've ever started a workout plan only to find the scale doesn’t budge (or actually goes up), you're not alone. Both cardio exercise and resistance training can build muscle and reduce fat, so just because the number on the scale stays the same, it doesn’t mean all that exercise is going to wasteAmerican College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Garber CE, Blissmer B, Deschenes MR, et al. Medicine and Science in Sports and Exercise, 2011, Oct.;43(7):1530-0315.. Muscle has a much greater density than fat, meaning it takes up less volume than an equal mass of fat. This explains why it’s possible to get visibly slimmer without a significant drop in weightThe paradox of low body mass index and high body fat percentage among Chinese, Malays and Indians in Singapore. Deurenberg-Yap M, Schmidt G, van Staveren WA. International Journal of Obesity and Related Metabolic Disorders: Journal of the International Association for the Study of Obesity, 2000, Nov.;24(8):..

The Truth Behind the Myth

Ever heard the claim that a pound of muscle weighs more than a pound of fat? False! A pound is a pound (of feathers, glass, Jell-O—you name it). But because a pound of fat takes up about four times the space of muscle tissue, it’s possible to look and feel trimmer even if body weight remains the same. Of course, it’s also possible to weigh the same, but look and feel fatterSensitivity and specificity of the body mass index for the diagnosis of overweight/obesity in elderly. Vasconcelos Fde A, Cordeiro BA, Rech CR. Cadernos de Saúde Pública, 2011, Jun.;26(8):1678-4464. . This is especially evident among the elderly, as muscles tend to shrink with age because damaged muscle cells are repaired at a much slower rate than when they were young. (Your mind's not playing tricks on you—Grandma may actually be shorter these days). Plus, with reduced physical activity during the golden years, the ratio of muscle to fat tends to decrease as we get olderStrength and muscle mass loss with aging process. Age and strength loss. Keller K, Engelhardt M. Muscles, Ligaments and Tendons Journal, 2014, Feb.;3(4):2240-4554..

So while it’s a myth that muscle “weighs” more than fat, too much body fat can be a contributing factor to serious health conditions like stroke, coronary disease, and diabetesMeasures of abdominal adiposity and the risk of stroke: the MOnica Risk, Genetics, Archiving and Monograph (MORGAM) study. Bodenant M, Kuulasmaa K, Wagner A. Stroke; a journal of cerebral circulation, 2011, Aug.;42(10):1524-4628. Microvascular responsiveness in obesity: implications for therapeutic intervention. Bagi Z, Feher A, Cassuto J. British Journal of Pharmacology, 2012, May.;165(3):1476-5381. . Although it’s difficult to determine the ideal amount of body fat for each individual, too little fat can also have unhealthy consequences, including reproductive dysfunction in women. Accepting the body’s need for both muscle and fat is important in maintaining overall health and fueling an active lifestyleFat mass is inversely associated with serum carboxymethyl-lysine, an advanced glycation end product, in adults. Semba RD, Arab L, Sun K. The Journal of Nutrition, 2011, Jul.;141(9):1541-6100. .

Scaling Down the Scale

While the actual number of pounds might not waver after starting an exercise routine, the ratio of muscle to fat may be increasing, contributing to better health and improved overall fitnessAmerican College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Garber CE, Blissmer B, Deschenes MR. Medicine and Science in Sports and Exercise, 2011, Oct.;43(7):1530-0315. . . So after spending quality time bonding with the treadmill or the weight rack, don’t break off the relationship just because the scale isn’t moving in the “right” direction. It might be time to put the scale aside and instead measure results with a glance in the mirror or a new personal best in the gym.

Originally published on August 2011. Updated June 2015.