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.