During heel-toe running, the vertical ground reaction force (VGRF)
profile has both impact and active peaks. Although the mass-spring model (a
single mass and a linear spring) is simple and useful to predict running
characteristics, its simulation of VGRF profiles produces only a single peak rather
than the double peak typically observed in running. In contrast, the mass-spring-damper
model (two masses, two springs and a damper) produces a simulated force
profile with two separate peak values.
Running barefoot versus with shoes of varying stiffness produces VGRF
profiles with quite different characteristics. The purpose of this study was to use
the mass-spring and mass-spring-damper models to investigate the stiffness
characteristics of human running in barefoot, hard-shoe and soft-shoe conditions.
Ten recreational runners ran overground at 3.83 m/s and completed five trials of
each footwear condition. Force data and two-dimensional kinematic data were
recorded simultaneously at 1000 and 250 Hz respectively. Using the mass-spring
model, vertical stiffnesses with the barefoot, hard-shoe and soft-shoe conditions
were 27.6, 25.3 and 24.6 kN/m, respectively. Hard-shoe and soft-shoe material
stiffnesses were about 150 and 100 kNm�����. Considering the leg and shoe as two
springs in series, the leg's actual vertical stiffness could be estimated as 30 and 33
kNm����� for hard and soft-shoe conditions. The result suggested that runners
increased their actual vertical stiffness with the sequence of barefoot, hard-shoe,
and soft-shoe conditions.
Using the mass-spring-damper model, the upper spring stiffness was
relatively constant while the lower spring stiffness changed with footwear
condition: 274, 136 and 126 kN/m, respectively. While it is mathematically
convenient to model the leg and body with constant spring characteristics over
time, physiologically it is likely that muscle-tendon stiffness does change during
stance as muscle activity changes. This suggests that mass-spring models of
running would be improved by time varying spring characteristics. Variable
stiffness of the simple mass-spring model was tested using a smoothly varying
stiffness function. This provided a significantly better force profile simulation for
each of the footwear conditions than did the constant stiffness model. Further
mass-spring-damper modeling may also be improved through incorporation of such
time varying characteristics. / Graduation date: 2002
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32474 |
| Date | 16 July 2001 |
| Creators | Watanatada, Pasakorn |
| Contributors | Smith, Gerald A. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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