Biomedical Engineering Reference
In-Depth Information
10 kHz
a ( t,f )
0 Hz
750 N
F ( t )
0 N
|
Heel
Strike
To e
off
t =1.2 sec
Swing
Stance
Swing
Right Foot
Left Foot
Single
Support
Double
Support
Single
Support
Double
Support
Single
Support
Fig. 12.2 Walking in real environments produces rich, step-dependent vibromechanical infor-
mation. Shown: vibration spectrogram a ( t , f ) and low-frequency normal foot-ground force F ( t )
measured at the hard sole of a men's shoe during one footstep of a walker onto rock gravel, together
with the corresponding foot contact states within the gait cycle (author's measurements). The dark
vertical stripes in the spectrogram correspond to discrete impact or dislocation events that are
characteristic of dynamic loading of a complex, granular medium
12.3.2 Touch Sensation in the Feet
The sense of touch in the human foot is highly evolved, and is physiologically highly
similar to that in the hand, with the same types of tactile receptor populations as are
present in the former, including the fast-adapting (FA) type I and II and slow-adapting
(SA) type I and II cutaneous mechanoreceptors [ 50 , 100 ], in addition to propriocep-
tive receptors including Golgi organs, muscle spindles, and joint capsule receptors
in the muscles, tendons, and joints. The sole is sensitive to vibrotactile stimuli over a
broad range of frequencies, up to nearly 1000 Hz [ 109 ], with FA receptors comprising
about 70 % of the cutaneous population. Several differences between tactile sensa-
tion in the foot and hand have been found, including an enlargement and more even
distribution of receptive fields in the foot, and higher physiological and psychophys-
ical thresholds for vibrotactile stimuli [ 50 , 114 ], possibly related to biomechanical
differences between the skin of the hands and feet [ 115 ]. Further comparisons of the
vibrotactile sensitivity of the hand and foot were performed by Morioka et al. [ 68 ].
Self motion is the key function of walking, and most of the scientific research in
this area is related to the biomechanics of human locomotion, and to the systems
and processes underlying motor behavior on foot, including the integration of multi-
sensory information. During locomotion, sensory input and muscular responses are
coordinated by reflexes in the lower appendages [ 83 , 95 , 116 ], and prior literature
has characterized the dependence of muscular responses on both stimulus properties
and gait phase. The vibrotactile sense in the foot has been less studied in this regard,
presumably because it is not a primary channel for directly acquiring information
Search WWH ::




Custom Search