One of the strongest arguments in favor of free weights over weight machines for strength training has to do with symmetry. The problem is that humans aren’t symmetrical. People with minimal asymmetry often can power through weight machine workouts without problems, but people with significant structural and muscular asymmetry have a greater chance of injury in the form of strains or tears on their weaker or smaller side. Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and Harvard’s Wyss Institute for Biologically Inspired Engineering developed a wearable robotic exosuit that adjusts to a wearer’s muscle force asymmetry among other aspects of muscle dynamics.

Conventional wearable robotics to help people walk require hours of manual adjustments and tuning, according to Wyss researchers. Individuals who are already compromised physically often have a difficult time customizing the wearables and some cannot complete the process. The SEAS and Wyss engineers devised a method using ultrasound to measure an individual’s muscle dynamics quickly. The researchers published a study in Science Robotics that explains how the ultrasound measurements calibrate to a wearer’s muscle dynamics. The process takes just seconds to adapt to provide personalized activity-specific assistance.

The SEAS/Wyss wearable measures the individual’s muscle and tendon movement under the skin, instead of the leg’s movement. According to Richard Nuckols, a Postdoctoral Research Associate at both institutions, “There is not necessarily a direct mapping between the movement of the limbs and that of the underlying muscles driving their motion.” When the team strapped an ultrasound reader to exosuit wearers’ calves, they were able to determine the assistive force needed to help the wearer in the “push-off” phase of walking. A few seconds walking with the ultrasound machine is enough to capture the information needed. When the researchers measured the metabolic energy used in walking, they found a significant reduction in the metabolic energy required to walk using the wearable compared to walking without assistance. Users also expended less energy walking with the ultrasound-based wearable than with exosuits that rely on leg movement measurements to determine assistive energy requirements.

Next steps for the Wyss and SEAS researchers include testing the wearable system’s ability to adjust assistive force requirements in real-time based on individual and environmental changes such as muscle fatigue, walking speed, and incline. It’s exhilarating to read about a fine tuning process that improves user efficiency and lessens the difficulty and energy consumption for walking. We can see significant benefits for otherwise healthy people who would be able to continue living independently if moving around their homes and community was no longer exhausting.