Poster Presentation 51st International Society for the Study of the Lumbar Spine Annual Meeting 2025

Introduction: Chronic and sub-chronic low back pain (LBP) can disrupt neuromuscular coordination, leading to altered motor responses in trunk and limb muscles. These changes impact reaction times and muscle activation patterns, which are essential for maintaining balance and avoiding injuries, especially when responding to unexpected external perturbations. The purpose of this study was to investigate differences in reaction times and the symmetry index (SI) of bilateral trunk and limb muscles between individuals with and without sub-chronic LBP. Reaction time provides insight into how quickly muscles respond to destabilizing forces, while the symmetry index measures the balance between the left and right sides of the body, particularly in the core and limb muscles that contribute to stability.

Methods: Fifty-seven right limb dominant subjects (31 healthy control subjects and 26 subjects with LBP) participated in this study. The subjects were exposed to a slip perturbation (0.24 m/sec velocity for 1.20 cm), which caused them to move forward for 0.10 seconds in standing while holding a tray (Figure 1). The electromyography (EMG) electrodes were placed on the bilateral erector spinae (ES), rectus abdominis (RA), rectus femoris, hamstring, tibialis anterior, gastrocnemius, biceps brachii (BB), and triceps brachii. The reaction times were analyzed, and the SI was used to compare the bilateral trunk and limb muscles for the degree of asymmetry between groups (Figure 2).

Results: The ES reaction time was significantly delayed in the control group (0.33 ± 0.22 for the control group vs. 0.22 ± 0.17 for the LBP group; t = 2.25, p = 0.03). The SI of reaction times was significantly different on the RA (t = -2.28, p = 0.03), ES (t = -2.36, p = 0.04), and BB (t = -2.15, p = 0.04) muscles between groups (Figure 13.

Discussion: The delayed non-dominant ES reaction time might indicate a freedom of pain recurrence in the control group. Although the asymmetry increased on the RA and BB muscles in the LBP group, it decreased on the ES muscle. The findings are anticipated to inform rehabilitation strategies by highlighting specific muscle asymmetries and delayed responses that could contribute to persistent pain or recurrent injury, guiding targeted interventions for restoring balanced and efficient postural control. The asymmetrical reactions in the arm-trunk muscles need to be considered for rehabilitation strategies, although not all asymmetry causes LBP. These findings have significant implications for rehabilitation. Targeted interventions should focus on addressing specific muscle asymmetries and enhancing bilateral symmetry in core and limb muscles to optimize postural control and mitigate the risk of future pain episodes. Restoring symmetrical activation in the RA and BB muscles may be crucial for preventing over-reliance on one side of the body, reducing compensatory strain, and improving overall neuromuscular efficiency. In addition, the delayed reaction in the ES muscle of the control group, which may indicate a lower need for compensatory mechanisms, suggests that training for neuromuscular flexibility and control could be beneficial in the LBP group.