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Beyond bare bones

“This thigh bone,” says Pat Fehling, grasping a gleaming human femur she keeps on her desk, “is both a weight-bearing column that can withstand impact and a lever that moves freely with us.” A dedicated runner and Skidmore exercise scientist, she knows how bones work structurally to keep us upright and ambulatory, but she’s also interested in their physiology—especially how their interactions with other tissues play a crucial role in fitness and well-being. “Nowadays we’re engineering so much inactivity into our lives, but from an evolutionary standpoint we were designed to be active.”

In fact, research shows that exercise helps keep bones strong, but why? And how? These questions have intrigued Fehling ever since her doctoral-study days at the University of Illinois in Urbana-Champaign, where she learned to operate an early bone densitometer. Since then, Fehling has done thousands of bone scans, many on the DXA scanner in Skidmore’s Human Performance Lab. Widely used to diagnose osteoporosis, DXA (for dual-energy X-ray absorptiometry) measures a cross-section of bone, including the mineral materials like calcium and phosphorus that are stored in it, plus nearby muscle and fat. Skidmore’s DXA has been used in faculty and student research into the effects of smoking on dancers’ hip-bone density, stepping exercises for female runners, and total-body bone density in jockeys at Saratoga Race Course.

Two years ago, Fehling spent a sabbatical semester mastering a new scanning technology called pQCT—peripheral quantitative computed tomography. CT scans have been medically useful tools for decades, but applying CT imaging to study bone quality is new, and pQCT machines are so new they’re currently used only in research. The pQCT takes precise body-composition measurements in three dimensions instead of DXA’s two, and it can pick up bone-tissue changes in several weeks rather than DXA’s eighteen months. Adds Fehling, “DXA can measure the amount of bone and muscle in a given area, but pQCT can also measure the distribution of bone and muscle mass and how it works together.”

As a visiting professor in a large Canadian training study in 2004, she worked with bone specialists and physical therapists to investigate the benefits of balance training (such as tai chi and agility exercises) in reducing the falls and fractures that may follow strokes. Because strokes usually affect just one side of the body, the patients’ stroke-impaired sides could be directly compared with their own healthy opposites, which served as built-in “controls.” Says Fehling, “We expected to see that stroke-related weaknesses would be balanced by normal or possibly increased strength on the healthy sides.” But surprisingly, scans of the study’s forty-two subjects turned up no significant differences. New hypothesis: “Because stroke patients become so much less active overall, their bones lose density and strength on both sides”—a finding that seems to underscore the benefits of post-stroke exercise.

Combining DXA and pQCT data is expanding the scope of research on populations at risk for osteoporosis and fracture, as the new tools reveal more about the physiology of the muscle-bone unit. “There’s an obvious anatomical link because muscles attach to bone,” explains Fehling, “but there’s also a synergy: in order to contract, muscles need to use the calcium stored in bones.” The exact nature of that physiological and functional relationship is still something of a mystery. For Fehling, “What’s so exciting about the new pQCT technology is the glimpse it offers into how bones and muscles work together to build strength.”

Message to baby boomers: “All kinds of good things happen when we’re strong and active,” Fehling says, setting the femur back in its place of honor on her desk. “We’re meant to move.” —BAM