Person skillfully navigating crowded marketplace by rotating shoulders and carrying a baguette

Mastering the Art of the Sidestep: How Your Brain Navigates Tight Spaces

Soraya Malik in Mind & Education August 2025 • 4 min read.

"Uncover the hidden rules your brain uses to calculate shoulder rotation when squeezing through narrow openings, especially with extra baggage."

Navigating through crowded streets, narrow doorways, or bustling hallways is a daily challenge. We effortlessly twist and turn, avoiding collisions with a grace that seems almost instinctive. But what if there was a hidden algorithm driving these movements, a set of rules our brains follow to ensure we slip through even the tightest squeezes?

Previous research has highlighted the importance of the "critical ratio value" – the brain's perception of the relationship between aperture width and body width – in determining body rotation. The central nervous system (CNS) seemingly relies on this ratio to adjust our movements, initiating shoulder rotations to minimize spatial demands. However, this model may not fully explain how we manage when carrying objects that extend our overall width.

Now, a new study sheds light on how the brain adapts these strategies when spatial requirements increase, suggesting that our brains might not simply rely on a fixed ratio. Instead, the CNS appears to prioritize maintaining a minimum spatial margin, cleverly adjusting shoulder rotations based on the combined width of the body and any carried objects. Let's explore this fascinating new perspective on our subconscious navigation skills.

The Minimal Margin Rule: A Smarter Way to Squeeze Through?

Person skillfully navigating crowded marketplace by rotating shoulders and carrying a baguette

The study, conducted by researchers at Tokyo Metropolitan University and Ritsumeikan University, challenged the conventional understanding of how we navigate narrow spaces. Instead of just reacting to the critical ratio value, the researchers proposed that the CNS follows a 'minimal spatial margin' rule. This means the brain calculates the necessary shoulder rotations to maintain a consistent buffer of space on either side of the body, regardless of whether we are carrying an object.

To test this hypothesis, participants were asked to walk through narrow apertures while holding bars of varying lengths. If the brain only considered the critical ratio, the shoulder rotation angles should remain constant for a given ratio, irrespective of the bar length. However, the results revealed a different story. As the bar length increased, the amplitude of shoulder rotation decreased, suggesting the brain was adapting to maintain a consistent spatial margin.

Constant Ratio Prediction: If shoulder rotation depended solely on the critical ratio (aperture width relative to body width), the rotation angle would remain the same regardless of the bar length.
Observed Result: The rotation angle decreased as the bar length increased, indicating the brain was doing more than just reacting to the simple ratio.
Minimal Margin Theory: Participants aimed to maintain a consistent minimum space between themselves (plus the bar) and the aperture edges.

This suggests the brain is actively accounting for the total width – body plus object – and adjusting movements to ensure a safe and efficient passage. It's not just about the relative size of the opening; it's about preserving a comfortable safety zone.

The Visuomotor Symphony: A New Understanding of Spatial Control

These findings reveal a more nuanced understanding of how we interact with our environment. Our brains don't just react to simple ratios; they actively calculate and adjust movements to ensure a consistent safety margin, especially when navigating complex situations. This insight offers a new perspective on the visuomotor control of locomotion, highlighting the brain's remarkable ability to adapt and optimize our movements for seamless passage through the world around us. This ability highlights human capability for error handling and adaptation.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1371/journal.pone.0048123, Alternate LINK

Title: Rule For Scaling Shoulder Rotation Angles While Walking Through Apertures

Subject: Multidisciplinary

Journal: PLoS ONE

Publisher: Public Library of Science (PLoS)

Authors: Takahiro Higuchi, Yasuhiro Seya, Kuniyasu Imanaka

Published: 2012-10-29

Everything You Need To Know

How does the brain figure out how much to rotate the shoulders when squeezing through a narrow space?

The central nervous system (CNS) uses a concept called the 'critical ratio value' to determine body rotation. This ratio reflects the relationship between the aperture width and the body width. The CNS employs this ratio to initiate shoulder rotations, which helps to minimize the spatial demands needed to pass through narrow openings. This method, however, doesn't fully explain how people navigate with added items.

What is the 'minimal spatial margin' rule, and how does it work?

The 'minimal spatial margin' rule suggests that the central nervous system (CNS) calculates the necessary shoulder rotations to keep a consistent buffer of space on each side of the body, no matter whether an individual is carrying an object. This is different from relying on a fixed 'critical ratio value'. The brain adjusts movements based on the combined width of the body and any items being carried, ensuring safe and efficient passage. This strategy is especially crucial when spatial requirements increase, such as when carrying a bar through a narrow aperture.

What role does shoulder rotation play in navigating tight spaces, and how is it adjusted?

Shoulder rotation is the primary mechanism the brain uses to navigate tight spaces. The brain adjusts the amplitude of these rotations to minimize the spatial demands, as influenced by the 'critical ratio value' and the 'minimal spatial margin'. The amount of shoulder rotation changes according to the aperture width and the total width of the body and any objects being carried. When carrying objects, shoulder rotation is decreased to maintain a consistent spatial margin. These movements showcase the brain's capacity to handle errors and adjust.

What is the 'critical ratio value', and how does it relate to navigating narrow spaces?

The 'critical ratio value' is the brain's assessment of the relationship between the aperture width and the body width. Previous research suggested the central nervous system (CNS) utilized this ratio to determine body rotation. However, this model falls short in explaining how humans handle objects. The study revealed that the brain does more than just react to this ratio. It actively calculates and adjusts movements to maintain a consistent safety margin, particularly when faced with complex situations.

What is the 'visuomotor control of locomotion', and how does the research provide a new understanding of this?

The visuomotor control of locomotion refers to the brain's process of using visual information to guide and control movement. The study's findings provide a deeper understanding of this, highlighting the brain's adaptability in how it navigates through space. Rather than simply reacting to ratios, the brain actively calculates and adjusts movements to ensure a consistent safety margin. This is crucial when handling objects and passing through tight spaces. This process showcases human error handling and adaptive capabilities.