Civil Engineering Reference
In-Depth Information
30.2.3 Running
Walking changes to running, for normal size adults, at about 2.5 m
h), since it uses less
energy (for the same speed). Running differs from walking in that both feet are off the ground for
part of the stride. In addition, the heel strike should be renamed the “foot strike,” since the initial
contact probably will be forward of the heel. After foot strike (usually on the outside edge of the
foot), the foot rolls inward and flattens out (pronation). Then the foot rolls through the ball and
rotates outward (supination).
Peak force is about three times body weight at about 0.1 sec after contact. For running, the average
contact duration is 0.29 sec. In contrast, it is 0.48 sec for walking (Scanton and McMaster, 1976).
sec (6 miles
/
/
30.2.4 Stepping
Descending stairs demands a gait quite different from ascent (Templer, 1992).
For descent, the leading foot swings forward over the nosing edge and stops its forward motion when it
is directly over the tread below; the toe is pointed downward. Meanwhile, the heel of the rear foot begins
to rise, starting a controlled fall downward toward the tread. The heel of the forward foot then is lowered
and the weight is transferred to the forward foot. The rear foot then begins to swing forward.
We tend to hold our center of gravity as far back as possible by leaning backward. Problems are over-
stepping the nosing with the forward foot, catching the toe of the forward foot, and snagging the heel of
the rear foot on the nosing as it swings past. Falls tend to be down the stairs.
For ascent, the leading foot has a toe-off, swing, and first contact with the upper step. The foot is
approximately horizontal. The ball of the foot is well forward of the tread; the heel may or may not
be on the tread. The rear foot then rises on tiptoes, pushing down and back. The rear foot then
begins the swing phase. The primary problem is catching the toe, foot or heel of either foot on the
stair nosing. Another problem is the rear foot slipping when it pushes backward. Falls tend to be upward.
30.3 Accidents
30.3.1 Problem of Falls
Courtney et al. (2001) provide the following statistics to indicate the magnitude of the slip, trip and fall
problem.
Slips and falls are second largest source of unintentional injury deaths
.
Slips and falls are the leading reason for unintentional emergency department visits (21% of visits
or about 550,000
.
year)
/
Slips and falls have an annual direct cost
/
capita of occupational injuries of $50-400 (depending on
.
the industry)
In industrial fatalities, falls account for about 12%, which is greater than the total for electrical current,
fires, burns, drowning, and poisons.
Falls that occur when a person is carrying something are especially dangerous. The object carried
decreases stability as a function of the torque above the ankle (weight times object height above
ankle). Other problems are that the arms cannot be used for balance (to prevent a fall), to grab a
railing, or to break the fall.
Not all underfoot accidents result in falls, and not all falls result in a lost-time injury. Some falls result
in no lost time, some result in strains and sprains, some in broken bones, and some in death. In addition,
falls often are not recorded by accident-reporting procedures. Thus, the accident reports tend to drasti-
cally underestimate the number of falls.
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