Although the current study provides important information on
the biomechanics of opening CRPs, it has some limitations that
need to be noted. First, maximum gripping force was not measured
and, therefore, the relationship between torque measurement and
gripping force cannot be established. In order to collect torque data,
packages content was drained so that a torquimeter was placed
inside them, which led to a slight increase in their weight, but the
Fig. 2. Opening mechanism of a squeeze-and-turn cap.
Fig. 3. Torquimeter mounted inside the package.
Fig. 4. Gripping techniques: (a) tridigital; (b) bidigital.
G.H.C. Bonfim et al. / International Journal of Industrial Ergonomics 54 (2016) 178e183 181
packaging shape, cap-hand interface and thus handling of the
bottle were not affected. Additionally, each subject performed a
single trial for measuring maximum torque for each of the six
evaluated conditions (three caps, two gripping techniques), as
performing three trials per test could be particularly exhaustive for
both the children and the elderly. Indeed, Haidar et al. (2004)
suggest that one single measurement is not enough for grip
strength tests, although they found that, in most of the cases (76%),
subjects performed the maximum force in the first trial.
Our study focused exclusively on biomechanics interaction,
however the successful design of this type of packaging must
consider not only the biomechanical, but also the cognitive aspects
Fig. 5. Summary of average maximum torque of all groups, packagings and prehension techniques. Torque values are presented in N.m.
G.H.C. Bonfim 182 et al. / International Journal of Industrial Ergonomics 54 (2016) 178e183
related to opening process. Preventing children from accessing the
content of potentially harmful products and, at the same time,
ensuring product usability by all other users must be the target of
designers and manufacturers, in order to ensure that products can
be used with efficiency and satisfaction. Future studies should
correlate biomechanical data of CRPs opening with usability evaluation.
This might clarify the relationship between objective variables
in a functional context in terms of effectiveness, efficiency and
user satisfaction.