Affiliations: [a] Human Performance Group, Biosurgery & Surgical
Technology, Imperial College London, London, UK
Note: [] Address for correspondence: Alison H. McGregor, Human
Performance Group, Biosurgery & Surgical Technology, Imperial College
London, Charing Cross Hospital Campus, London W6 8RP, UK. Tel.: +44 20 8383
8831; Fax: +44 20 8383 8835; E-mail: a.mcgregor@imperial.ac.uk
Abstract: Background: Trunk flexor-extensor asymmetry has been attributed a
role in spinal function. However, left-right asymmetry within muscle groups
(extensors or flexors) has received little attention. Objective: To examine left-right symmetry within trunk
extensors and flexors and the influence of different sporting tasks on this
symmetry. Method: Thirty-five subjects (21 males) were recruited and
written informed consent obtained; 12 subjects participated in unilateral (UL)
sports e.g. tennis, 13 in bilateral (BL) activities e.g. running and 10
controls (C) who were not involved in sport. Isokinetic and isometric trunk
flexions and extensions including a fatiguing isometric hold were performed
using a Cybex isokinetic dynamometer synchronised with bilateral
electromyographic (EMG) recordings from the erector spinae at L4 and rectus
abdominis at T10. A ratio of left-right EMG activity was calculated for each
set of muscles, to examine asymmetry. Results: No differences were seen in left:right extensor EMG
ratios across any of the test protocols. However, the UL group had higher
(P < 0.05) left:right flexor EMG ratios than the BL group during
pre-fatigue (UL: 1.32 ± 0.15 vs BL: 0.84 ± 0.07) and post-fatigue (UL:
1.30 ± 0.18 vs BL: 0.84 ± 0.07) isometric flexion. Torque data showed
that the trunk extensor-flexor ratio was larger (P < 0.05) in the BL group
compared to the C in the isokinetic exercises at the 30°/s (BL: 1.27
± 0.05; C: 1.00 ± 0.06) and at the 90°/s (BL: 1.28 ±
0.05; C: 0.95 ± 0.08), but no differences were seen during isometric
testing. Conclusion: This study suggests that participation in
different activities such as sports may generate asymmetry in the trunk
flexors, the importance of which requires further research.
