Civil Engineering Reference
In-Depth Information
107 mm. The distance between foot centerlines is about 107
þ
90
197 mm (200 mm in round numbers).
¼
The distance between outside edges is 107
286 mm (300 mm in round numbers). Yet mean
height for males is 1756 mm! Thus there is only a base of 200-300 mm for a structure of 1756 mm.
There is no significant average difference between the left and right feet. However, for specific individ-
uals, that there often is considerable difference between the left and right foot.
The technical name for differences in leg length in the same person is leg length discrepancy (LLD).
Contreras et al. (1993), summarizing studies with N
þ
90
þ
89
¼
2377, reported that 40% of people had LLD
¼
14 mm.
Weight of leg segments, as a percent of body weight, are 1.47 for foot, 4.35 for calf, and 10.27 for thigh; a
total leg is 16.1 and both legs are 32.2. Thus the leg weight of a 70 kg person would be 0.322 (70)
5 mm, 30% had LLD
11 mm, and 10% had LLD
22.5 kg.
When people stand at a work surface, there needs to be an indentation (150 mm deep, 150 mm high,
and 500 mm wide) so they can stand close to the work surface.
¼
30.2 Activities of the Foot
30.2.1 Standing
During standing, the legs will generally move occasionally. Figure 30.3 shows how to support the stand-
ing body. The changed height of the foot rotates the thigh bone forward, enabling the hip on that side to
be fixed; it also flattens the lumbar curve and relaxes the iliopsoas muscle. When a leg is on the rail
foot-
rest, the large back muscles on that side of the body are relaxed and receive a flow of blood (bringing
nutrients and removing waste products).
/
30.2.2 Walking
When walking, the activity of one leg has a shorter swing phase (when the foot is being passed forward)
and the longer support (stepping, contact) phase (when the foot is on the ground). The support phase
starts at heel strike and ends at toe-off; it has an early, passive section and a later active (propulsion)
section.
At heel strike, the forward-moving heel hits the
ground (causing deceleration). Continued forward
motion of the body results in the forefoot contact-
ing the ground; propulsion (acceleration) begins.
The heel rises and the foot is pushed backward
under the body. This tendency is resisted by fric-
tion under the sole; the body is propelled
forward. The foot is everted, increasing forefoot
contact area on the inner side, until only the skin
around the big toe is in ground contact. Finally,
contact ceases and the cycle repeats.
Because the swing phase is shorter than the
support phase, heel strike on the opposite limb
occurs during the propulsion part of the support
phase. At heel strike, horizontal velocity decreases
from about 450 to 20 cm
FIGURE 30.3 Bar footrests along a work station or
conveyor can reduce standing stress. (From Rodgers,
S. 1984. Working with Backache. Perinton Press, Fairport,
NY. With permission.) A small platform is another
alternative. (From Konz, S. and Johnson, S. 2004. Work
Design: Occupational Ergonomics, 6th ed. Holcomb-
Hathaway, Scottsdale, AZ. With permission.)
sec; heel angle to the
/
floor changes
from about 20
8
prior
to heel
contact to 0
sec after contact (Redfern
and Rhoades, 1996). During a slip, instead of stop-
ping, the heel continues to move and the leading
foot moves out in front of the body.
8
at 100m
/
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