Instead, they make use of tridigital
grip to exert a level of force that is enough to open the packaging.
The evaluation of maximum torque transmission may provide
objective data supporting the design of squeeze-and-turn caps,
preventing them from being opened by children as well as keeping
the locking mechanism undamaged and, consequently, optimizing
packaging safety.
Age is a factor that influences manual force. We found reduced
torque measurements for the two extreme age groups: young
children and the elderly. Furthermore, the decline in the ability to
exert force started at around sixty years. Our results corroborate
with the study of Yoxall et al. (2006), which showed that maximum
applicable torque in lid opening begins to decrease around the age
of sixty for both males and females. Indeed, previous studies (Shim
et al., 2004; Kapur et al., 2010) have already shown that the
decrease in force due to aging mostly affect distal muscles. This is
an important finding that, ultimately, affects the openability of
everyday products and therefore must be taken into account by
designers and manufacturers in the design of packaging.
The cap diameter is directly related to maximum torque transmission:
for both gripping techniques and all the groups, maximum
torque was obtained with the cap of largest diameter (packaging
with inverted conical cap). This is consistent with previous studies
reporting greater torque transmission with a larger diameter in
manually-operated devices (Kong et al., 2007; Kong and Lowe,
2005a, b). Crawford et al. (2002) found higher torque exertion
measures when the cap diameter increased from 20 mm to 50 mm.
However, it is important to highlight that the findings of the present
study are restricted for the three evaluated packages and,
therefore, are not representative of other packages that use the
squeeze-and-turn opening system.