Age-Related Differences in Segment-Specific Center-of-Mass Acceleration During One-Leg Standing: Associations With Pelvic–Spinal Alignment
This study reveals that older adults exhibit greater mediolateral center-of-mass acceleration during one-leg standing compared to younger adults, with these balance deficits in older adults significantly associated with specific sagittal pelvic–spinal alignment characteristics such as posterior pelvic tilt and thoracic kyphosis.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Falls are a leading cause of injury and loss of independence for older adults, and the ability to maintain balance is a critical factor in preventing them. To understand why balance fails, scientists often look at how the body keeps its center of mass—the point where the body's weight is evenly distributed—steady over the feet. One common way to test this is the one-leg stand, a simple task where a person stands on one foot for as long as possible. While this test tells us how long someone can hold the pose, it does not reveal how they are actually controlling their body to stay upright. Two people might stand for the exact same amount of time, yet one could be making tiny, precise adjustments while the other sways wildly, using a different strategy to stay safe. To see these hidden differences, researchers can measure the actual movement of different body parts, such as the head, chest, and hips, to see how much they accelerate or shake in specific directions. This approach moves beyond simply timing a task to understanding the mechanics of how the body manages stability.
A recent study by researchers in Japan investigated these mechanics by asking older and younger adults to stand on one leg while their movements were tracked with high-speed cameras. The goal was to see if the way older adults control their balance differs from younger adults, and whether these differences are linked to how their spine and pelvis are aligned. The team focused on the side-to-side motion, known as the mediolateral direction, because standing on one leg narrows the base of support significantly in that direction, making it the hardest part of the task to control. They measured the acceleration of the center of mass for the whole body, as well as for the head, the chest, and the pelvis separately. They also measured the curvature of the spine and the tilt of the pelvis in the older group to see if the shape of the back and hips influenced how much the body swayed.
The results showed a clear difference between the two age groups, but only in the side-to-side direction. Older adults showed significantly more acceleration in the head, chest, pelvis, and whole body when moving side to side compared to the younger adults. In contrast, there was no significant difference in the front-to-back direction. This suggests that as people age, the challenge of maintaining balance on one leg is primarily about controlling lateral sway rather than forward or backward stability. The study found that this increased side-to-side movement was not just a general sign of aging but was distributed across the entire body system, indicating that the head, torso, and hips were all moving more vigorously to maintain equilibrium.
In the older participants, the researchers also found that the way the spine and pelvis were positioned was linked to how much the body swayed. Specifically, older adults who had a more backward tilt of the pelvis tended to have greater side-to-side acceleration in their heads, pelvis, and whole bodies. Similarly, those with a more pronounced curve in the upper back, known as thoracic kyphosis, showed greater side-to-side movement in their pelvis. These connections suggest that the mechanical alignment of the spine and pelvis may influence how the body manages balance, though the study does not prove that changing the alignment would fix the balance issue. The researchers noted that the older group also had different body compositions and sex distributions than the younger group, so the results reflect a combination of factors rather than age alone.
The study concludes that looking at how different parts of the body accelerate during a one-leg stand provides a more detailed picture of balance than simply timing how long someone can stand. It reveals that older adults rely on a broader, more active system of movement to stay upright, particularly in the side-to-side direction, and that their spinal alignment is part of this picture. While these findings offer a new way to characterize balance, the researchers caution that more studies are needed to confirm these links and determine if they can be used to predict falls or guide rehabilitation. For now, the work highlights that balance is a complex, whole-body effort where the position of the spine and the movement of the hips are deeply interconnected.
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