Biomedical Engineering Reference
In-Depth Information
6.2.2 Overground Versus Treadmill Walking
While treadmills allow for the observation of walking behavior over extended peri-
ods of time, it is still a matter of debate as to whether gait during treadmill walking
is different than overground walking [
3
]. There is evidence that treadmill walking
can significantly alter the temporal [
3
,
30
,
100
,
114
], kinematic [
3
], and energetic
[
78
] characteristics of walking. One apparently robust finding is that walking on
a (motorized) treadmill increases step frequency (cadence) by approximately 6%
[
3
,
30
,
100
,
114
]. It has, therefore, been concluded by many researchers that motor-
ized treadmills may produce misleading or erroneous results and that care should
be taken in their interpretation. At the same time there are also studies that do not
find any significant differences between overground and treadmill walking [
75
,
84
].
Two possible sources for this discrepancy that we have addressed in our research are
differences between walking surfaces and the availability of relevant visual feedback
about self-motion during treadmill versus overground walking.
Treadmills are typically more compliant than the regular laboratory walking sur-
faces used in past studies, and it has been speculated that it is this difference in surface
stiffness that affects locomotion patterns when directly comparing treadmill walking
with overground walking (e.g., [
30
,
31
]). Such speculations are warranted by other
research showing significant effects of walking surface compliance on basic gait
parameters such as step frequency and step length [
72
]. Interestingly, the one study
that compared overground with treadmill walking using similar walking surfaces
found no differences in gait parameters [
84
].
Another potential factor to consider is that participants typically have visual
information available during walking. During natural, overground walking, dynamic
visual information (i.e. optic flow), is consistent with the non-visual information spec-
ifying movement through space. However, during treadmill walking, a considerable
sensory conflict is created between the proprioceptive information and the visual (and
vestibular) information (see also Sect.
6.3.2
) such that the former informs participants
that they are moving, yet the latter informs them they are in fact stationary. Although
it is not obvious how such a conflict might specifically alter gait parameters, there is
evidence that walking parameters are affected by whether visual feedback is available
or not. For instance, Sheik-Nainar and Kaber [
91
] evaluated different aspects of gait,
such as speed, cadence, and joint angles when walking on a treadmill. They evaluated
the effects of presenting participants with congruent and updated visuals (via a HMD
projecting a simulated version of the lab space), compared to stationary visuals (real
world lab space with reduced FOV to approximate HMD). These two conditions
were compared to natural, overground walking. Results indicated that while both the
treadmill conditions caused participants to walk slower and take smaller steps, when
optic flow was consistent with the walking speed, gait characteristics more closely
approximated that of overground walking. Further, Hallemans et al. [
50
] compared
gait patterns in people with and without a visual impairment and compared the gait
patterns of normally sighted participants under full vision and no vision conditions.
Results demonstrated that participants with a visual impairment walkedwith a shorter
