Application of Ergonomics to the Legs - Fundamentals and Assessment Tools for Occupational Ergonomics - page 589

polymer insole and a standard mesh insole that were issued by platoon to over 3000 marine recruits.
While the polymer insole had good shock absorbing properties, the incidence rate of lower extremity
stress injuries over the 12 week basic training program were unaffected by the insole used. Schwellnus
et al. (1990) found that the mean weekly incidence of total overuse injuries and tibial stress syndrome
decreased significantly in the 237 military recruits provided with neoprene insoles as compared to
1151 controls. These authors also found a trend ( p 0.10) suggesting that the incidence of stress fractures

was reduced with the insoles. However, Jones et al. (2002), in their review of the military intervention
studies investigating insoles, do not find convincing evidence that shock absorbent insoles prevent stress
fractures, thus suggesting they are of questionable value if the intended purpose is solely stress fracture
prevention. Rome et al. (2005), in their review of the research examining the potential for shock
absorbing shoe insoles to prevent injuries in military recruits, conclude that there is evidence to
support their use; however, the strongest supporting trial included in their review had some methodo-
logical issues.
Several studies have been conducted to evaluate variations in insole materials. Leber and Evanski
(1986) describe the characteristics of the following seven insole materials: Plastazote, Latex foam,
Dynafoam, Ortho felt, Spenco, Molo, and PPT. These authors measured the plantar pressures in 26
patients with forefoot pain. All insole materials reduced the plantar pressure by between 28 and 53%
relative to a control condition; however, PPT, Plastazote, and Spenco were the superior products. Viscolas
and Poron were found to have the best shock absorbency of the five insole materials tested by Pratt et al.
(1986). Maximum plantar pressures were found to be significantly reduced in the forefoot region with
PPT, Spenco, and Viscolas, although the three materials were not significantly different (McPoil and
Cornwall, 1992). In the rear foot region, however, McPoil and Cornwall (1992) report that only the
PPT and the Spenco insoles reduced the maximum plantar pressure relative to the barefoot condition.
The plantar pressure in the rearfoot region was not significantly reduced with the Viscolas. Interestingly,
based on the shock absorbency data from Pratt's (1988) 30-day durability test, the resilience of Viscolas,
PPT, and Plastazote could be described as excellent, good, and poor, respectively. Sanfilippo et al. (1992)
also reported the change in foot to ground contact area as a function of insole material. Plastazote,
Spenco, and PPT led to a significantly greater contact area than the other materials tested.
In summary, insoles appear to be effective at modifying the lower extremity kinematics and reducing
the peak plantar pressures, although their effectiveness is dependent upon the material used. Additional
research is needed to clarify the effectiveness of insoles in controlling lower extremity stress injuries.
Based on the previous discussion it should be clear that the effectiveness of this control strategy will
be dependent upon shock absorbing capacity, the pressure dispersion, and the durability properties of
the insole materials selected.

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29.3.3 Help for Those in Kneeling Postures
Sharrard (1963) reported that there was no relationship between the type of knee pads used and the inci-
dence of beat knee in miners. This author recorded peak pressures on the order 35.7 kg

cm 2 as simulated
mining tasks were performed. These compression forces were shown to vary widely throughout the
2.5-sec cycle time for a shoveling task. Unfortunately, the author had no instrumentation capable of
determining the shear forces and the torsional moments placed on the knee during the simulated
tasks. At the time of Sharrard's paper a “bursa pad” had been designed that allowed perspiration to
escape, pushed coal particles away from the skin, and provided satisfactory cushioning. Although no
control group was used, the author reported that of the 24 previously affected men selected to test the
pad under working conditions only two reported a recurrence of beat knee after a 12-month period.
In general, while many types of knee pads are currently commercially available, and frequently
recommended, there has been little research published on knee pad design. Clearly, there are issues
with the construction of knee pads and the resulting subjective comfort

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discomfort while performing
kneeling tasks, how the comfort compares with the the actual force distribution within the pad, and
how the pad construction interacts with ground conditions to affect a worker's postural stability. Some

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