For many people, it’s the source of a nagging — and painful — injury, but for Carolyn Eng, the IT band is an intriguing mystery, one she may be close to solving.
A former Ph.D. student in Harvard’s Graduate School of Arts and Sciences, Eng is the first author of two studies that examine how the iliotibial band stores and releases elastic energy to make walking and running more efficient. The studies — co-authored by Daniel Lieberman, the Edwin M. Lerner II Professor of Biological Sciences and chair of the Department of Human Evolutionary Biology; Andrew Biewener, the Charles P. Lyman Professor of Biology; and Allison Arnold-Rife, a research associate in Biewener’s lab — are described in new papers in the Journal of Experimental Biology and the Journal of Biomechanics.
“We found that the human IT band has the capacity to store 15 to 20 times more elastic energy per body mass than its much-less-developed precursor structure in a chimp,” Eng said. “We looked at the IT band’s capacity to store energy during running, and we found its energy-storage capacity is substantially greater during running than walking, and that’s partly because running is a much springier gait. We don’t know whether the IT band evolved for running or walking; it could have evolved for walking and later evolved to play a larger role in running.”
The IT band runs along the outside of the thigh, from just above the hip to just below the knee, and is made up of fascia, an elastic connective tissue found throughout the body. Though often compared to tendons — the two can serve similar functions — fascia is composed of large sheets, while tendons are more rope-like.
Fascia is “a sheath that encloses muscles, connects muscles to bone and … compartmentalizes muscles that serve a similar function, and the IT band is the largest piece of fascia in the human body,” Eng said.
The notion that the IT band acts as a spring to aid in locomotion runs counter to the decades-old belief that its primary function is to stabilize the hip during walking.
“Unlike many clinicians and anatomists, we use the lens of evolution to think about how humans are adapted not just for walking, but also for running, so we look at the IT band from a totally different perspective,” Lieberman said. “When we looked at the difference between a chimp and a human, we saw this big elastic band, and the immediate idea that leapt out at us was that the IT band looked like another elastic structure, like the Achilles tendon, that might be important in saving energy during locomotion, especially running.”
The findings, Biewener said, “will have key importance for basic science and clinical studies that seek to integrate the role of this key fascial structure into programs of sports-exercise training and gait rehabilitation.”
To understand what role the IT band plays in locomotion, the researchers developed a computer model to estimate how much it stretched ― and by extension, how much energy it stored — during walking and running.
