Oxygenation and fatiguability status of the truncal muscles during endurance task execution: a comparative study between young individuals with and without idiopathic scoliosis

Background: Impaired spinal kinematics during the execution of daily functional movements has been shown in adolescents with idiopathic scoliosis (AIS). While compositional differences between concave- and convex-side paraspinal muscles have been reviewed in AIS, comprehensive studying of muscle endurance and its impacts on movement quality remains limited. This study aimed to investigate the endurance performance of the truncal muscles in adolescents with AIS and if changes in the movement kinematics during walking occur after fatiguing of the truncal muscles.
Method: Real-time muscle oxygenation and muscle activity during truncal endurance tasks (modified Sorensen test for thoracic extensors, bilateral side plank for truncal side flexors, and abdominal curl up for truncal flexors) were acquired by Near-Infrared Spectroscopy (NIRS) and electromyography (EMG) respectively in27 individuals with AIS and 32 healthy controls (HC). The fatigability during the endurance tests was verified by self-perceived exertion and spectrum analysis of EMG. The endurance times, muscle oxygenation and EMG activity during the endurance tests, were compared between two groups of participants.
Result: Participants in AIS group showed a significantly lower endurance time in bilateral side plank tasks when compared to the HC group (p<0.05). Meanwhile, a comparable level of endurance of the truncal flexors and extensors were revealed between two groups (p>0.05). The slope of the median frequency of the EMG activity showed a steeper decline in the quadratus lumborum over the concave-side of AIS as compared to HC (p = 0.003). There was no significant between-group and between-side difference in oxyhemoglobin (O2Hb) levels of corresponding prime movers during all muscle endurance tasks (p>0.05).
Conclusion: The muscle endurance of the concave-sided quadratus lumborum (QL) of AIS participants was found to be reduced when compared to those without scoliotic curve. While there is emerging evidence indicating the immediate impaired coronal movement control in AIS following the trunk muscle endurance tasks. Long-term impacts associated with deficiency of truncal muscle endurance and muscle fatigue on postural control or curve progression in AIS group are yet to be investigated, Further research that examine the specific role of QL in trunk stabilization and its effect on the scoliotic curve progression are recommended to help refine the physiotherapy specific exercise for rehabilitation of individuals with AIS.