Perelman School of Medicine at the University of Pennsylvania

Human Motion Lab

Research equipment and techniques

The Human Motion Lab is equipped with high-speed motion capture cameras, ultrasound imaging, and other devices used to precisely measure human motion and calculate how the tissues in the body are functioning to move the body during activities of daily living and athletics. We utilize a nail-first, hammer-second approach: first identifying the problem and then selecting the right tool for the job. Because of this philosophy, lab equipment may change to support clinically relevant research by making the right measurements with the right equipment.

Motion Analysis

The motion capture system measures the locations of reflective markers attached to the body while force platforms quantify the interaction forces between the person and the ground.

The Human Motion Lab is equipped with a 12-camera motion analysis system that accurately track 3-dimensional locations of reflective markers to sub-millimeter accuracy at up to 500 samples per second. Although cameras only see in 2-dimensions (photo graphs lack depth), 2-dimensional images of the same object can be combined to create a 3-dimensional approximation of where the object actually is located. Motion capture uses this concept to achieve incredible feats and is the corner stone of labs studying human motion. While everything from movies and video games to cable news now use motion capture, labs studying human motion used these techniques before it was cool! 

In addition to a high-speed 3-dimensional camera system, the Human Motion Lab utilizes three force platforms that are embedded in the lab floor to measure the interaction between study participants and the ground. Essentially, very expensive bathroom scales, these force platforms measure the interaction between the ground and the foot — called ground reaction forces — which are essential for calculating the loads generated by each joint in order for motion to occur.

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Ultrasound Imaging

Ultrasound imaging allows us to see inside the body to quantify both the structure as well as function of musculoskeletal tissues. For example, the region that the Achilles tendon inserts into the calf muscle can be tracked during activities like running and jumping to understand why some people develop tendon pain.

Ultrasound imaging is a cost-effective and non-invasive tool that helps researchers study the interaction between soft tissue structure and function. Unlike other medical imaging techniques, portable ultrasound systems can be used in just about any setting to study tissue biomechanics. To this end, we can study larger patient populations to develop a better understanding of how certain musculoskeletal disorders affect tissue structure and function. 

Instead of quantifying just the structure of specific parts of the body, we incorporate other research tools (like motion capture and dynamometry) to accurately measure how muscles and tendons work together to generate healthy motion and how injuries limit this normal function. 

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Isokinetic Dynamometry

An isokinetic dynamometer (Biodex System 4) measures joint strength and power while holding the joint stationary or letting it move through prescribe motions.

The Human Motion Lab has an isokinetic dynamometer — historically used for measuring the power generated by engines, the technology has been implemented in assessing joint strength and function in humans. This device can go through prescribed motions while measuring how hard patients press against the device to assess functional deficits brought on by injuries or improved function following an intervention. 

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Computational Modeling

Measurements of limb motion and ground reaction forces are used to approximate how the muscles, joints, and ligaments are loaded during motion.

The Human Motion Lab uses computational modeling to predict what is going on inside the body that cannot be directly measured. These models use tried-and-true techniques (established by Sir Isaac Newton) to approximate the loads that are being exerted by each joint to produce the measured motion. Some assumptions are then made to estimate how each muscle contributes to generate motion. These results can identify strategies used to compensate for pain during activities of daily living or determine if patients are safely loading their total joint replacement. More sophisticated computational models are at our disposal to investigate the effects of joint replacements on motion and loading. 

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Electromyography

Small sensors — about the size of a matchbox — measure electrical signals that describe how the nervous system and skeletal muscles work together to generate motion.
Human motion is the result of a complex series of events — starting with brain signals that excite our muscles. Electromyography (EMG) sensors measure tiny electrical signals generated by the body during muscle contractions. The Human Motion Lab utilizes EMG sensors to help researchers understand how the nervous system may compensate for changes in mobility and function caused by orthopaedic conditions. Our small-wireless sensors allow patients to move unencumbered so we can identifying possible neuromuscular problems and improve treatment strategies.

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Wearable Sensors

small wearable device
Small and low-cost devices allow for rapid prototyping to quickly test new ideas and measure clinically important motions outside of the lab.

Recent advances in low-cost sensors and electronics have opened new doors to expanding the analysis of human motion past the lab setting into the clinic and home. We are developing low-cost sensors to measure everything from knee motion when climbing stairs to thumb motion when opening a jar. These little devices may help change the landscape of clinical care by providing patients and clinicians with objective feedback regarding functional improvements during treatment and raise warning flags when certain benchmarks aren't been met. 

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