Perelman School of Medicine at the University of Pennsylvania

Human Motion Lab

Research in the Human Motion Lab

Our lab is interested in the effects of tendon injury on muscle structure and patient function. We study muscle structure using ultrasound imaging and patient function using instrumented strength machines and clinically relevant tasks such as heel raises. Our on-going work is focused on changes in muscle structure following Achilles tendon ruptures, which we have found to change the configuration of the calf muscles that ultimately explain ankle strength and power. We also use computational modeling to predict the effects of small changes in muscle and tendon structure on patient function. These models provide a platform to test possible effects of structure or interventions before performing a physical experiment.

Simulating the effects of muscle-tendon structure on patient function

The link between muscle structure and function were defined by A.V. Hill in the mid 20th century. However, structure-function relationships are much more complicated in functionally relevant contexts. For example, our lab has found that Achilles tendon ruptures stimulate changes in the shape of the calf muscles. However, these structural changes are multi-factorial, which makes it difficult for us to isolate the key structural parameters that truly govern function. To better understand how the structure of our calf muscles and Achilles tendon governs clinically relevant function, we developed a simple musculoskeletal model and simulated these complex interactions on function. Our findings suggest that longer muscles with shorter tendons are the strongest predictor of function. More interestingly, our simulations suggest that muscle strength has little to do with the ability to perform a heel raise. These simulation results highlight the importance of muscle structure on function and support the need to improve treatments that target muscle factors other than muscle strength.


Characterizing muscle changes following tendon injuries

Skeletal muscle generates human motion by pulling on tendons — which in turn rotations our joints. Unlike our tendons and bones, which are slow to respond to loading stimuli, skeletal muscle rapidly changes its structure (within weeks) in response to the loading demands of daily living. Our preliminary data suggest that people who have suffered tendon injuries undergo changes to their muscles that explain reduced function — even after the tendon is fully healed. Our group is investigating the timeline of how muscle changes following injury with the long-term goal of improving rehabilitation programs to better preserve healthy muscle structure and function. This study is possible thanks to the generous support of the Thomas B. McCabe and Jeannette E. Laws McCabe Fund


Linking tendon structure with function

The Achilles tendon is the largest tendon in the body and undergoes loads several times greater than one's body weight during each step. While the Achilles tendon usually transfers this load efficiently and pain-free, many people experience chronic pain — called tendinopathy — that decreases the tendon's mechanical integrity. Because the Achilles tendon does not respond well to conservative treatments due to its poor blood supply, it is critical to improve early detection techniques to identify patients that are at risk or are early in the progression of tendinopathy. The Human Motion Lab is studying the link between tendon structure and mechanical properties and how these intrinsic tendon properties dictate patient strength and function. After defining these links, we plan on developing low-cost tools that can be implemented in the clinic and training room to help clinicians and training staff detect tendinopathy before it becomes painful and difficult to treat. This study is possible thanks to the generous support of the Thomas B. McCabe and Jeannette E. Laws McCabe Fund and the American Orthopaedic Foot & Ankle Society.


Quantifying patient function with low-cost sensors

small motion sensor
These tiny sensors (the small black square on the red chip, about 1/8" along its edges) efficiently measure motion, cost around $5 each, and can be used in concert with other sensors to describe how multiple joints move during tasks like stair climbing or opening a jar.

Accurately tracking patient function throughout the treatment process is essential for optimizing outcomes and minimizing costs. Gold standard measurement techniques — like motion capture — accurately quantify patient function but are not practical to implement on a large scale. Thankfully, recent advances in low-cost sensors (the type that make your smartphone know its orientation) are providing new opportunities to quantify patient function in much larger populations. Our current work is focused on identifying measures of patient function that are linked with long-term outcomes and developing low-cost sensors that can be used in the clinic and home to closely monitor patient progress.