In a breakthrough for fall prevention and humanoid robotics, researchers at the University of British Columbia (UBC) have shown that increasing physical stability (by boosting inertia and damping) can override the effects of delayed sensory feedback.
Their robotic "body-swap" simulator reveals a surprising neural principle: the brain interprets mechanical instability and delayed feedback in similar ways, and one can compensate for the other.
Rethinking Balance: When the Brain Meets Delay
Maintaining balance might seem automatic, but it’s a finely tuned feat of real-time neural processing. The brain constantly integrates sensory signals from the eyes, inner ear, and body to keep us upright. However, this system isn’t instant.
Even in healthy individuals, there's a natural delay as signals travel to and from the brain. These delays worsen with age or neurological conditions like diabetic neuropathy, disrupting the feedback loop and increasing fall risk, which is a major concern for older adults.
But until now, studying how the brain handles these delays has been nearly impossible. Ethically and practically, researchers can’t slow down nerve conduction in living people. That limitation has left a major gap in understanding how to design effective interventions or devices to help people maintain balance as they age.
Rewriting the Rules of Physics - With a Robot
To solve this, the researchers from UBC developed a robotic platform that lets them rewrite the physical rules governing the human body, both virtually and in real-time.
Participants stood on force plates connected to a motor-driven system that could modify key physical properties: gravity, inertia (resistance to movement), and viscosity (damping from muscles and joints).
By altering these properties, the robot made participants feel heavier (with higher inertia) or as if their limbs were moving through syrup (with more viscosity). It could also simulate negative viscosity, causing a destabilizing push that made the body lean faster than usual.
Its most innovative capability was introducing controlled neural delays. By briefly holding the body still after it detected movement - delaying feedback by about 200 milliseconds - the robot simulated the feeling of sluggish neural response. This gave researchers a safe, reversible way to mimic the real-life effects of aging or disease on balance.
The robot lets us rewrite the rules your body normally plays by...In an instant, you’re moving under a completely different set of physical laws - almost like stepping into a different body.
Dr. Jean-Sébastien Blouin, Senior Author
This unprecedented control allowed the team to conduct three targeted experiments, isolating how the brain processes and adapts to both spatial (mechanical) and temporal (delay-based) balance challenges.
A Shared Neural Code for Time and Space
The team’s experiments revealed something unexpected: the brain doesn’t treat all balance challenges separately. Instead, it seems to use a shared strategy to deal with both mechanical instability and delays in sensory feedback.
To explore this, the researchers ran three carefully designed tests. In the first, they introduced a 200-millisecond delay between a participant’s movement and the system’s response, simulating the kind of slowed feedback that can occur with aging or neurological conditions.
The result was striking: participants began to sway noticeably, sometimes far enough to simulate a real-world fall. This led to a critical follow-up question: could mechanical instability feel the same as delayed feedback?
To find out, the team reduced the participants’ virtual body inertia or applied negative viscosity, which made their movements feel looser and less controlled. The effects were nearly identical. Participants lost balance in similar ways and, just as importantly, reported that both conditions felt the same.
The brain wasn’t distinguishing much between spatial (physical) and temporal (timing) disruptions. It was reacting to both as if they were the same kind of threat to stability.
With that connection established, the researchers flipped the problem around. If mechanical instability can mimic a delay, could mechanical stability help overcome one?
In their final experiment, they added the 200-millisecond delay up front, then increased the body’s inertia and viscosity to simulate a heavier, more grounded physical state. The results were immediate: participants swayed less, regained control faster, and most avoided crossing the virtual threshold that would indicate a fall.
We were amazed that adding inertia and viscosity could partly cancel the instability caused by late feedback.
Paul Belzner, Lead Author
Simulation results supported this, showing that when inertia and viscosity were increased by median values of 3.3× and 53×, the area of stable control expanded significantly.
In short, the experiments showed a kind of trade-off at work. When the brain faces delayed feedback, adding mechanical stability helps restore balance. This suggests that our internal control systems don’t treat space and time as separate problems - they treat them as two sides of the same equation.
This finding could change how we design fall-prevention tools, rehabilitation programs, and even next-generation robots that need to stay on their feet.
Conclusion
At its core, this research gives us a deeper understanding of how we stay on our feet. It shows that the brain doesn’t treat every balance challenge as a separate problem. Instead, it relies on a shared strategy to handle both delayed feedback and changes in the body’s physical stability.
That simple but powerful idea could change how we think about fall prevention, rehabilitation, and even robot design.
The findings open the door to smarter assistive technologies like wearable exoskeletons or sensor-packed clothing that can sense when someone starts to lose balance and step in with just the right amount of support. They also suggest new ways to help people in rehab learn how to adapt to slower reflexes or disrupted feedback, using robotics in a safe, controlled way.
And for engineers building humanoid robots, this work offers something valuable: a clearer blueprint for making machines that stay upright the way people do, not by reacting instantly, but by balancing physical design with smart control.
In the end, UBC’s body-swap robot did more than simulate instability. It revealed something deeply human about how we move through the world and how, with the right tools, we can help people do it more safely for longer.
Journal Reference
Belzner, P., Forbes, P. A., Kuo, C., & Blouin, J.-S. (2025). Robotic manipulation of human bipedalism reveals overlapping internal representations of space and time. Science Robotics, 10(108). DOI:10.1126/scirobotics.adv0496. https://www.science.org/doi/10.1126/scirobotics.adv0496
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