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origin-destination state (motor equivalence), as it is known that similar motor patterns can be
achieved by different muscle activation patterns, unconcernedly task’s complexity (Bernstein, 1967;
Levin et al., 2003; Mattos et al., 2013). Therefore, the biomechanical rationalization of lifting
objects at work has to take into account the abundance of the DOF at the neuromotor level, and
lifting tasks have to be treated as a motor control problem, where the neural controller is trying to
identify a physiologically feasible motor complex solution (neural constraint) in order to achieve a
goal with minimal physical effort and discomfort on the part of the worker (Aruin and Bernstein,
2002; Bernstein, 1930, 1967, 1996; Delleman, 2004).
Nowadays, work-technique for lifting or lowering tasks is generally perceived as an implementation
of good practices that are focused to reduce the risk of LBD within the lumbar disks from tasks
where the same load is handled repetitively in similar manner throughout the work. Therefore, it
is mainly regarded under an “educational” framework, where workers are learning stereotyped
behaviours of how to avoid or minimize the biomechanical risk factors during the lifting tasks
(NIOSH, 1981). Accordingly, a classical and simultaneously oversimplified approach to characterize
the work-technique in manual material lifting tasks is in terms of the method that the worker uses
to carry it out (liftstyle), which is deduced to the elemental concept of identifying the posture
adopted by the worker just prior to the lift. Thus, three methods have been considered widely for
accomplishing lifting tasks, namely: the stoop, the squat, and the semi-squat methods.
However, controversy persists in the scientific literature as to which of the aforementioned methods
come to the fore as the most efficient in terms of optimization of the mechanical workload on the
spine (Burgess-Limerick, 2003; Sedgwick and Gormley, 1998; Straker, 2003). In general, squat
lifting is recognized widely as the “correct” method, however it seems that is superior to stoop only
when is limited to lift loads from positions between the knees (Straker, 2003). It was postulated
that there is not biomechanical evidence in support of advocating the squat lifting technique
over the stoop one to prevent low back pain, mainly because of the unavoidable variability on
the work-task, workplace, workers’ morphology, and of the undesired adaptation of the method
to workers’ habits (Burgess-Limerick, Abernethy, and Neal, 1995; Van Dieën, Hoozemans, and
Toussaint, 1999). However, the U.S. National Health Service Centre for Reviews and Dissemination
(2001) cautioned that the review by van Dieen and coworkers (1999) contained methodological
flaws that affected the authors’ conclusions, and supports the use of the squat lift. On the other
hand, Gagnon (2005) questioned the effectiveness of these liftstyles to reduce LBD in long-term.
Likewise, the EU-OSHA underlines that there are scientific evidence that focusing only on the
position of the back during lifting is not sufficient, and furthermore, modifying the liftstyle is
not eliminate the inherent risk when the job requirements are physically stressful (Op de Beek
and Hermans, 2000). In accordance with the aforementioned, work-technique training during
manual material lifting and lowering tasks is limited to learn the workers how to adopt a posture
or execute a movement that minimize the mechanical load on the spine structure based on an
educational model approach.
However, the performance of lifting or lowering tasks requires the resolution of potentially motor
control conflicts where any misleading may results to a high risk of tissue injury (Ebenbichler
et al., 2001). Therefore, in order to reduce the incidences of LBD during lifting or lowering tasks