How the iliotibial band makes us human

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No one ever talks about the iliotibial band, except when it’s broken. It’s a band of fascial tissue running from the hip to the outside of the knee (fascia is a tendon-like type of connective tissue), and it’s the site of a common and famously difficult-to-shake injury that’s usually felt as pain on the outside of the knee.

But a pair of recent studies from Dan Lieberman’s lab at Harvard, led by former student Carolyn Eng, puts the IT band in a more positive light. Eng used five human cadavers to investigate exactly how the IT band moves and stretches when going through the range of motion used in walking and running, and built a computer model to calculate the forces and strains involved (publishing the results in the Journal of Biomechanics). She then did the same for the equivalent structure in chimpanzees, the fascia lata (publishing the comparison in the Journal of Experimental Biology).

The findings, which are described in a nice piece in the Harvard Gazette, point to a couple of interesting conclusions:

1. The IT band isn’t just a big connector that keeps the hip stable; it actually functions like a spring, storing energy when you swing your leg back and releasing it as the leg swings forward.

2. This energy storage capability is highly developed in humans, enabling it to store 15 to 20 times more energy than the comparable structure in the chimp.

The chimp comparison fits into the bigger picture of humans having evolved specific structures to enable efficient two-legged locomotion, which Lieberman and others have been developing over the past decade. How important is this energy storage? The researchers estimate that it stores about seven joules during fast running compared to the standard estimate of about 50 joules stored in the Achilles (though not everyone agrees with the estimates of energy storage in the Achilles.)

Could this improved understanding of how the IT band works contribute to fighting IT band syndrome, whose causes are still poorly understood? That’s what the researchers hope, according to the Gazette article: “One of our next steps, using the computer models that Carolyn has developed, is to estimate how much force the IT band transmits in runners with and without IT band pain,” [says study coauthor Allison Arnold-Rife]. “These studies could help us establish a scientific basis for treating athletes with IT band injury.”