Limitations. There are a number of limitations that require
consideration. First, a nonfunctional task was used to
perturb the pelvic ring, limiting the generalization of the
motor-control deficit found in this study to more functional
activities. However, the task was specifically chosen because
it had been demonstrated to perturb the pelvic ring
(16); by performing the task in a supine position, the supporting
the role of the abdominals in single-leg balance was
removed. Thus, further study could include functional tasks
such as kicking.
Second, although the ASLR task used was chosen because
it perturbs the pelvic ring, this task also perturbs the
lumbar spine (17). Thus, we can not be certain that the
finding of a delay in the activation of TrA was associated
with the perturbation of the pelvic ring, as the finding might
have been due to a perturbation of the lumbar spine produced
by the ASLR task (indeed, as both the lumbar spine
and pelvic ring are perturbed, it is likely that the observed
response occurs to control both segments). This is a difficult
problem, as the anatomy/biomechanics of the lumbo-pelvic
region dictate that a task that specifically perturbs an isolated
segment, such as the pubic symphysis, would be virtually
impossible to design.
Additional limitations include the fact that only the symptomatic
side was measured. Further study should include
assessment of muscle activation on the asymptomatic (or
less symptomatic side for participants with bilateral groin
pain), as it is possible/likely that the delay in TrA activation
occurs bilaterally. Also of importance would be to establish
whether physiotherapy treatment commonly used for longstanding
groin pain (see above) is able to alter neuromotor
control of TrA in these individuals.
Lastly, also of note is the variable temporal response of
the abdominal muscles accompanying limb movement in
seemingly constant conditions. There are a number of possible
explanations for this variation, including variability
between subjects, and variations in placement of fine-wire
electrodes. However, the degree of variability for the majority
of the muscles investigated is comparable to previous
studies investigating abdominal activity in LBP (9,10).