It’s through the study of sarcopenia that a greater appreciation of muscle mass is evolving.Two seminal works, “Starvation in Man,” an article published in the
New England Journal of Medicine in 1970, and
Hunger Disease: Studies by the Jewish Physicians in the Warsaw Ghetto, a book published in 1979, show that the depletion of muscle mass is the cause of death in human starvation. This is because essential organs and tissues such as the brain, heart, and liver rely on a steady supply of amino acids to synthesize new proteins and maintain function. Normally, dietary protein supplies these amino acids. Under duress, however, these organs maintain homeostasis by drawing protein from the muscles. Our skeletal muscle mass, besides powering all of our movements, also serves as a reservoir for our vital organs. And like all reservoirs, this one can run low—or, in the case of starvation, run dry.
Less dramatic maladies also demonstrate a deep relationship with sarcopenia. “Not surprisingly,” observes Wolfe, “individuals with limited reserves of muscle mass respond poorly to stress.” A 2000 study in the
Annals of the New York Academy of Science examining lung-cancer patients undergoing chemotherapy, for instance, showed that the recurrence of cancer was predicted by levels of body protein. In 2004, a study in the
Annals of Medicine demonstrated a clear link between diminished muscle mass and cardiac failure. And a 2006 study in the
Journal of the American College of Surgeons found that survival from severe burns was lowest among individuals with reduced muscle mass.
In 2005, results from the Mediterranean Intensive Oxidant Study, which examined the causes of osteoporosis in men, found that bone density and mineral content had a direct correlation to skeletal muscle mass. “The stronger and thicker your muscle tissue, the more force that tissue exerts on the bone,” explains Maddalozzo. “And increased force, both during exercise and normal daily functioning, results in the bones growing stronger and denser. That significantly retards osteoporosis and, as a man ages, the rate of hip fractures.” A man with a full reservoir of muscle mass enjoys dual protection: stronger bones combined with enhanced strength and agility.
Muscle mass has also proved to play a key role in more common, but no less deadly, conditions such as cardiovascular disease and diabetes. A study of scientific literature published in
Circulation in 2006 cites articles showing that sarcopenia has been linked to insulin resistance (the main factor in adult-onset, or type 2, diabetes), elevated lipid levels in the blood, and increased body fat, especially “visceral adipose tissue,” which gathers around the heart and other vital organs and is a primary risk factor of heart disease. In fact, researchers concluded that long-term adaptation to resistance training lowers cortical response to acute stress; increases total energy expenditure; relieves anxiety, depression, and insomnia; and demonstrates beneficial effects on bone density, arthritis, hypertension, lipid profiles, and exercise tolerance in coronary artery disease. “As the dates on these studies indicate, we are just seeing the tip of the research iceberg,” says Wolfe. “In the years ahead, we are likely to see the proof of even closer relationships between muscle mass and disease states.”
The case against overreliance on cardiovascular fitness—a case striking close to my heart—was made best in a study conducted at East Tennessee State University more than a decade ago. Researchers studied 43 healthy individuals who were 55 or older. Twenty-three of the subjects worked out three times a week for 30 minutes per session, confining their exercise to the treadmill, stair machine, and stationary bike. The other 20 subjects performed 15 minutes of aerobic exercise and devoted the rest of their sessions to training their major muscle groups on weight machines. After four months, bone density and lean muscle mass increased significantly in the group combining aerobic and strength training, but it did not improve for the group confined to aerobic activity.
Maddalozzo and I leave the Bone Lab and stroll across campus. He nods hello to students, whose endocrine systems sluice with testosterone and growth hormone, the juices goosing youthful muscle development. From a modest distance, Maddalozzo, at age 52, might pass as one of them. He carries a well-toned 150 pounds on a 5-foot-9-inch frame, with just 10 percent body fat.
Despite the sunshine, the professor’s hospitality, and the presence of so many attractive young people, my mood continues to darken. I experience a moment of classic middle-aged angst, as if I were approaching a sigmoidoscopy or a periodontal exam. I worry, in short, that I’ve seen the light too late. My “muscle intervention” threatens to be as penitential as it sounds. According to Wolfe, Kraemer, Chodzko-Zajko, and other experts, resistance training must be conducted at a high intensity, at 70 percent or more of the maximum perceived effort, in order to produce the cellular and metabolic changes that yield stronger, thicker muscles and the resultant health benefits. “A little bit of training—swinging a five-pound dumbbell around—just won’t cut it,” says Kraemer. “That’s not enough to catalyze growth and engage the systems.”
