July 2006, Issue 6

Refining the Exercise Prescription to Maintain Muscle Power as We Age

Roger Fielding, PhD, became director of the Nutrition, Exercise Physiology, and Sarcopenia Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) at Tufts University in October 2004. He was appointed a professor in the Gerald J. and Dorothy R. Friedman School of Nutrition Science and Policy in 2005. Fielding came to Tufts from the Sargent College of Health and Rehabilitation Sciences at Boston University. He received his MA in human bioenergetics from Ball State University and his PhD in human nutrition from Tufts University.

“It is well known that as people get older they lose muscle mass,” says Fielding. “My interest has been to understand what consequences sarcopenia holds for people in terms of how it may affect their ability to perform daily activities and how much risk it places on them for becoming disabled when they get older. And more importantly, what kinds of strategies and interventions, both exercise interventions and nutritional interventions, might be able to reverse this age-related loss in muscle mass.”

Fielding studies muscle at the clinical level by developing interventions to counteract sarcopenia and its consequences and at the molecular level by examining how skeletal muscle responds to exercise and how aging alters that response. He is excited to be at the HNRCA because it presents opportunities to collaborate and conduct clinical as well as laboratory research.

Although muscle mass and strength both decline with age, the declines do not correlate directly. Strength is maintained fairly well until the age of 50, but muscle mass begins to decline by about one percent a year from the age of 30. Does that mean that our declining muscle mass becomes more efficient between the ages of 30 and 50? If so, how? What adaptations occur as we lose muscle mass? And what can we do to maintain muscle mass as well as strength as we age? Fielding hopes his research will contribute answers to these and other questions.

Because neither muscle mass nor strength is a good predictor of declines in function as people age, Fielding’s research group began examining muscle “power” as a more descriptive way of assessing performance. Power is the work a muscle can perform in a given period of time. “So unlike strength, which is the maximum amount of force, power has a velocity component to it,” says Fielding. “Often, functional performance is dictated by how fast something can be done.” Fielding gives the example of a person who trips over something. That person has to make immediate, rapid movements to realign his balance to keep from falling. While strength is important in preventing injuries from falls, the velocity of muscle movement is also critical. Early results from measurements of muscle strength and power indicate that, in some situations, power is a better predictor of muscle performance than either strength or muscle mass.

Fielding’s research group is testing an exercise intervention they developed to improve muscle power. The protocol involves rapid weight lifting as opposed to the slow weight lifting of traditional resistance strength training. In preliminary studies, muscle power output appears to increase more dramatically in older individuals on the power training intervention than in those on a traditional resistance training intervention, even though in both groups gains in muscle strength appear similar. Fielding is planning additional studies on how measures of strength and power are influenced by age and by training interventions. The hope is to fine-tune an exercise prescription for maintaining muscle power with age.
To understand the biological and physiological bases for age-related declines in muscle power, Fielding’s group has been studying the Akt/protein kinase B–dependent signaling pathway that is involved in activation of protein synthesis. Using models of muscle contraction and relaxation in skeletal muscle, the group has found that older muscle tissue does not display as robust an increase in these signaling kinases as does younger muscle tissue. “I’m really excited about translating the work that we’re doing on the control of skeletal muscle growth and hypertrophy in our basic studies to some of our clinical projects,” says Fielding. “We’re trying to understand how the activation of protein synthesis is altered with age and how it’s affected by exercise and muscle contraction in humans.”

Fielding’s research group is also looking at how muscle may be influenced by changes in gene expression with age. “Technology is available that allows you to look at the expression of 30,000 genes in human tissue using gene chips,” says Fielding. “We’ve preliminarily compared young and old individuals to see what happens in muscle with aging. What we’d like to do now is look at how exercise and potentially even nutritional interventions may alter the molecular signature of aging that we’ve identified in skeletal muscle.” By “molecular signature of aging” Fielding means which genes are turned on and which are turned off in the skeletal muscle of old as compared with young people. He is investigating how changes in the molecular signature relate to muscular adaptations that take place in older people.

Professor Fielding is maintaining his collaboration with Walter Frontera at Harvard Medical School and is initiating collaborations with Andrew Greenberg, Susan Roberts, and Jose Ordovas at the HNRCA. Fielding looks forward to collaborating with other colleagues at Tufts and Tufts–New England Medical Center.

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