According to an assessment of ergonomic risk using the RULA
method, one-fourth of the rubber tappers were found to have an
extreme posture (action level 4) that required a need for an
immediate investigation and work habit changes, while nearly half
of them, at action level 3, needed an investigation and a change in
work habits soon. In addition to the high RULA scores, the pattern of
trunk movement in high frequency repetitive trunk flexionextension
combined with twisting during rubber tapping work
may affect the lower back of rubber tappers especially when
tapping rubber trees at a low level from the ground. The effects of
trunk movement on the lower back were described by Wolfe et al.
(1996) and Guo (2002) which indicated that repetitive trunk
motion affected the pattern of trunk muscle coactivity that
appeared to be the driving force behind diminished strength and
functional capability as well as increased spine structural loading
that included both compression and shear force. Moreover, the high
frequency of weight lifting (lifting any object more than 8 kg per
time) was a co-factor affecting low back pain for rubber tappers,
which increased intradiscal pressure that can induce annular tears
and internal disk disruption resulting in lumbar disc injury (Zautra
et al., 2007).