When Your Arms Stop Swinging, Your Body May Be Sending an Early Signal
Normally, when your right leg moves forward, your left arm swings forward with it. That motion helps counter the twist of your body as you step. Parkinson's disease can disrupt that coordination.
As the brain loses nerve cells that make dopamine—a chemical that helps control movement—muscles can stiffen and movements can slow. A team at the University of New South Wales in Sydney wanted to know how early those effects might show up in an ordinary walk.
Wrist Sensor Data From 73,000 People Reveals Early Differences
The researchers drew on the UK Biobank, a long-running health study that invited more than 100,000 volunteers to wear a wrist sensor for a week. The team analyzed usable recordings from 73,413 people and followed them through their medical records for up to a decade. During that time, 314 received a Parkinson's diagnosis after wearing the sensor.
A wrist sensor registers the movement of a hand reaching for a cup as readily as it registers a swinging arm. The team used software called Watch Walk to find the stretches of recordings that captured walking, estimating step counts, walking speed, and step regularity. The direction the wrist pointed and the way it moved helped the software distinguish a swinging arm from a hand held near the head or in front of the body.
Fewer Steps and Less Arm Swing Before Diagnosis
The researchers grouped people who later received a diagnosis by how much time passed between the recording and their diagnosis. Those diagnosed within 40 months of wearing the sensor averaged about 4,000 steps a day, compared with about 6,400 among people with no recorded Parkinson's diagnosis during follow-up. The gap was smaller among people whose diagnosis came later.
People who later received a diagnosis also tended to reach lower top walking speeds, and the rhythm of their steps and the share of walking done in longer stretches differed too. The wrist told part of the story that a step count alone would miss: those who went on to receive a diagnosis tended to spend less of their walking time swinging their arms naturally. The team could see a difference even in recordings made nearly seven years before diagnosis.
What This Means and What It Doesn't
- A new angle for early screening: Wrist recordings offer a view of how people move outside the exam room. If the findings hold up in other groups, the recordings could help researchers identify people to invite into trials of treatments designed to slow the disease in its early stages.
- Not an individual prediction: For now, the results describe differences between groups. They can't tell an individual whether they'll develop Parkinson's. Pain, medication, and other health conditions can also affect how someone walks.
- Limits of a single monitoring period: The team recorded each person's movements during a single monitoring period, so it couldn't tell when anyone's arm swing began to change. A follow-up study could track the same people at regular intervals to see how their walking changes over time.
The research was published in the Journal of Neural Transmission. Scientists have also looked for early signs of Parkinson's in blood proteins, and gait data from wearables is becoming a closely watched area in movement health.
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