DISCUSSION
The results of this study demonstrate that the contraction
of TrA occurs as part of a feed-forward response when a
voluntary movement that is hypothesized to perturb the
pelvic ring is performed. However, when the same ASLR
movement is performed in individuals with long-standing
groin pain, the onset of TrA is delayed when compared with
the normal situation. It is hypothesized that this change in
coordination of TrA muscle activity may leave the pelvic
ring unprotected from reactive forces, resulting from
movement.
Feed-forward contraction of the abdominal muscles
in asymptomatic individuals. Based on biomechanics
(26 –28), anatomy (22), and previous studies (8), the
finding that TrA contracted in a feed-forward manner in
association with a perturbation of the pelvic ring was not
surprising. Hodges and Richardson (8) demonstrated feedforward
activation of the abdominal muscles in association
with lower-limb movement in a similar task with the participants
standing. It is well established that the CNS deals
with perturbations to the spine by contraction of the muscles
of the trunk either before or shortly after the onset of EMG
activity of the muscle responsible for movement of the limb
(1,8). It follows that the CNS would deal with similar
perturbations to the pelvic ring in the same feed-forward
manner.
The onset of transversus abdominus is delayed
in individuals with long-standing groin pain. The
finding that the onset of TrA was delayed in individuals with
long-standing groin pain is consistent with previous studies
of LBP populations (9). In association with upper-limb
movement in people with LBP, the onset of TrA was found
to occur more than 50 ms after the onset of EMG of the