When high force levels are required, wheel turning is
very similar to exerting force against a lever or a large
wrench. Ferguson and Mason (1988) report human
strength capabilities for wrench turning for a limited
subject population (12 male ergonomists). They note
that wrench turning strength is highly dependent on the
height of the fastener, the direction of force application
and the bracing used by the subject. In interpreting
their data, they estimate maximum isometric torques
corresponding to the 5th and 95th percentiles of the
population (presumbly male) of 54 N m and 590 N m
respectively. These values are for the largest wrenches
studied at the highest height condition (1.45 m), and
decrease substantially as the height is lowered and the
wrench size is decreased. Torques for small crescent,
spanner, socket and pipe wrenches have also been
studied by Mital and colleagues (Mital, 1986; Mital and
Sanghavi, 1986). The highest torques were observed
when subjects used socket wrenches, with maximum
average torque values of 40.06 N m for males and
24.33 N m for females. They also noted substantial
differences in strength as a result of subject posture.