1. Mechanical Modeling of Skinfold Compression

2. Skinfold Measurement Skinfold calipers have springs Measured in mm
Skinfold measurements are a compressed thickness of a double layer of skin plus adipose tissue
Caliper pressure: e.g. 10 gm. mm-2
2 second timing
Skinfold Modeling

3. Skinfold Compressibility
Skinfold compressibility varies from site to site due to differences in skin thickness, skin tension and adipose tissue composition.
Skinfolds in females are more compressible than in males.
Skinfold compressibility decreases with age due to dehydration and changes in elastic properties of tissues
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4. Inexpensive Acquisition of Dynamic Skinfold Data
Slim Guide Skinfold Caliper
Potentiometer to provide analog signal
A/D board
Labview software
Data saved in file to bring into EXCEL
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5. Dynamic Skinfold Compression
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6. Sampling Initially a calibration run is required
Establishes gain and offset used to convert volts of signal to mm. of thickness
Record 2 seconds of data
Long enough to monitor any meaningful changes in skinfold compression
100Hz (100 data points per second)
10 trials per skinfold
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7. Calibration
How do you change voltage values into thickness?
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8. OFFSET
Volts
Offset
Time
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9. Calibration: Hold caliper in 0mm position, record voltage (offset) Hold caliper in 50mm position, record voltage
50 mm
Voltage
difference
Volts
0 mm
Offset
Time
Gain = Voltage difference / 50mm
Skinfold thickness = (Voltage - Offset) / Gain

10. Signal Averaging: 10 trials (100 Hz)

11. Can we model this phenomenon?

12. Mechanical Modeling Spring Component Viscous Component Hook’s Law
Spring Constant
Viscous Component
Dashpot
Velocity dependent
Coefficient of viscosity

13. Y = (F - bv) / a Simple Model Viscous and Elastic Components in Series
where F=force, b = viscous, a = elastic a b
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14. Two components of spring and dashpot in parallel
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15. Mechanical Model b1 & b2 are coefficients of viscosity
k1 & k2 are coefficients of elasticity
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16. Criteria of Goodness of Fit to Real Data
Sum of Squares
Shape of curve

17. Sex Differences
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