Load cells and Parkinson’s Disease

Load cells are used extensively in medical research and diagnostics. So, given that it’s World Parkinson’s Day today, Thursday 11 April, we loom at the role load cells have played in the investigation of this disease.

What is Parkinson’s disease?

Parkinson’s disease causes progressive brain damage which in turn affects the nervous system. Symptoms of Parkinson’s disease include:

• Tremors or shaking of various parts of the body
• Slow movement
• Stiff muscles
• Reduced mobility and impaired balance

 

Load cells and tremor

Medical researchers have used load cells to track the progress of the disease by assessing the tremors and muscle movement. One of the major studies, “Regularity of Force Tremor in Parkinson’s Disease” looked into how medics could effectively identify the early stages of Parkinson’s against the early signs of normal aging. The team’s hypothesis was that:

“Analyses of the regularity of tremor can help in discriminating normal aging from Parkinson’d Disease.”

To test this, they chose three age groups to test:

• 1 group without the disease aged 21-29 years
• 1 group without the disease aged 68-80 years
• 1 group with the disease aged 68-80 years

The test subjects were asked to squeeze two load cells together using their index finger and thumbs force at what they assessed as 5, 25 and 50% of their maximal voluntary contraction. The researchers used spectral analysis and approximate entropy (ApEn) to analyse the frequency and timing of tremor.

The study concluded that:

“Tremor analyses should not be limited to just the frequency and amplitude of the oscillation, and that the time-dependent structure of tremor is useful in differentiating tremor in healthy people from those with PD.”

In another paper by the same authors, “Visual control of isometric force in Parkinson’s disease” they analysed how the results differed if the subjects could see the load cell they were squeezing, or not. Their paper concluded that:

“There was no difference in the time between visual feedback removal and the beginning of force decay in PD. There was a larger amount and faster rate of force decay after visual feedback removal in PD subjects compared to the controls. It is proposed that the increased force decay in PD does not result from sensory reflex deficits but from higher order sensory–motor memory processes.”

 

Precision of movement measurement in the lab

An interesting thesis by Richard Bumann for ETH Zurich examined “Using Load-Cells to Unveil Limitations to the Human Movement System” . The paper suggests a new approach to a specific issue:

“Code of practice in the Brain-body dynamics lab has always been the use of six-axis load-cells for this purpose. They can accurately measure forces and torques in all spatial directions. Nevertheless, active usage changes the mechanical properties of the complex system and changes the calibration parameters of the sensor. … We developed an approach to calibrate complex load-cells in-lab with a precision that comes close to industry standards.”

 

Strength–Dexterity testing

Na-hyeon Ko and her team at the Brain-Body Dynamics Laboratory, University of Southern California Los Angeles took a slightly different approach. They measured an individual’s control of fingertip forces when compressing a:

“Compliant and slender spring prone to buckling … A maximal level of sustained compression is informative of the greatest instability the person can control, and thus is indicative of the integrity of the neuromuscular system for dexterous manipulation.”

By comparing the left and right hands of those with Parkinson’s Disease, the team were able to measure the force variability in two bands:

• Low frequency (<4 Hz, FLF)
• High frequency (4–12 Hz, FHF)

The more affected hand had lower force (F) and lower FLF than the less affected hand. Their conclusion was:

“The nature of force variability in the voluntary range during this dynamic and dexterous task may be a biomarker of greater motor capability/flexibility/adaptability in Parkinson’s Disease (PD). This approach may provide a more quantitative clinical assessment of changes of sensorimotor control in individuals with PD.”

 

Load cells for researchers and universities

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