The tightened hamstring connecting the tibia to the pelvis provides more posterior pelvic tilting and consequent backward curvature of the sacral and lumbar vertebrae. Therefore, the study goal was to quantitatively investigate the effect of hamstring and low back stretching on the trunk biomechanics in a system-level perspective. Twelve healthy subjects performed two stretching interventions (hamstring only (HS); hamstring + low back (HLS)) for 40 s on two separate days. They sat on a stool before and after the intervention while capturing trunk kinematics and EMG. In addition, the lumbar flexion angle at which the L4 paraspinals deactivate (i.e., flexion-relaxation phenomenon; FRP) was monitored while trunk flexion-extension trials, performed before and after the protocol. The FRP onset angle was captured to verify the biomechanical changes in the lower extremity and trunk systems. In the results, the stretching intervention significantly increased the reaching distance by 6.3 cm in the sit-and-reach test performed immediately before and after the intervention. The flexible hamstring improved the lumbar flexion angle and head postures in both the HS and HLS. However, the HLS induced laxity in lumbar passive tissues, as confirmed by changes in the FRP, and significantly increased co-activation in the low back. The stress-relaxation of the hamstring and surrounding passive tissues could help to maintain better lumbar flexion angle (i.e., lumbar lordosis) while sitting. Periodic HS for 40 s without any significant lumbar flexion may be recommendable for office workers who sit for long periods.

将胫骨连接到骨盆的收紧的腘绳肌提供了更多的骨盆后倾和随之而来的骶椎和腰椎的向后弯曲。因此，研究目标是从系统层面定量研究腘绳肌和腰背拉伸对躯干生物力学的影响。12 名健康受试者在不同的两天内进行了两次拉伸干预（仅腘绳肌 (HS)；腘绳肌 + 腰背 (HLS)） 40 秒。他们在干预前后坐在凳子上，同时捕捉躯干运动学和肌电图。此外，在方案前后进行躯干屈曲-伸展试验时，监测 L4 椎旁肌停用的腰椎屈曲角度（即屈曲-松弛现象；FRP）。捕获 FRP 起始角以验证下肢和躯干系统的生物力学变化。结果显示，拉伸干预在干预前后立即进行的坐下伸展测试中显着增加了 6.3 厘米的伸展距离。灵活的腘绳肌改善了 HS 和 HLS 的腰椎屈曲角度和头部姿势。然而，正如 FRP 的变化所证实的那样，HLS 会导致腰部被动组织松弛，并显着增加下背部的共激活。腘绳肌和周围被动组织的应力松弛有助于在坐着时保持更好的腰椎屈曲角度（即腰椎前凸）。对于长时间坐着的办公室工作人员，可能建议在没有任何明显腰椎弯曲的情况下进行 40 秒的定期 HS。