PURPOSE Harvest of the semitendinosus (ST) tendon for anterior cruciate ligament reconstruction (ACLR) causes persistent hypotrophy of this muscle even after a return to sport, although it is unclear if hamstring activation patterns are altered during eccentric exercise. It was hypothesised that in comparison with contralateral control limbs, limbs with previous ACLR involving ST grafts would display (i) deficits in ST activation during maximal eccentric exercise; (ii) smaller ST muscle volumes and anatomical cross-sectional areas (ACSAs); and (iii) lower eccentric knee flexor strength. METHODS Fourteen athletes who had successfully returned to sport after unilateral ACLR involving ST tendon graft were recruited. Median time since surgery was 49 months (range 12-78 months). Participants underwent functional magnetic resonance imaging (MRI) of their thighs before and after the Nordic hamstring exercise (NHE) and percentage change in transverse (T2) relaxation time was used as an index of hamstring activation. Muscle volumes and ACSAs were determined from MRI and distal ST tendons were evaluated via ultrasound. Eccentric knee flexor strength was determined during the NHE. RESULTS Exercise-induced T2 change was lower for ST muscles in surgical than control limbs (95% CI - 3.8 to - 16.0%). Both ST muscle volume (95% CI - 57.1 to - 104.7 cm3) and ACSA (95% CI - 1.9 to - 5.0 cm2) were markedly lower in surgical limbs. Semimembranosus (95% CI 5.5-14.0 cm3) and biceps femoris short head (95% CI 0.6-11.0 cm3) volumes were slightly higher in surgical limbs. No between-limb difference in eccentric knee flexor strength was observed (95% CI 33 N to - 74 N). CONCLUSION ST activation is significantly lower in surgical than control limbs during eccentric knee flexor exercise 1-6 years after ACLR with ST graft. Lower levels of ST activation may partially explain this muscle's persistent hypotrophy post ACLR and have implications for the design of more effective rehabilitation programs. LEVEL OF EVIDENCE IV.

中文翻译：

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半腱肌移植重建前十字韧带后1-6年，绳肌的激活和形态发生了显着改变。

目的收割半腱肌（S​​T）肌腱用于前十字韧带重建（ACLR）甚至在恢复运动后仍会导致该肌肉持续萎缩，尽管目前尚不清楚在离心运动过程中绳肌的激活方式是否发生改变。假设与对侧对照肢体相比，先前ACLR涉及ST移植的肢体将表现出（i）在最大的离心运动过程中ST的激活不足；（ii）较小的ST肌肉体积和解剖截面积（ACSA）；（iii）降低偏心膝屈肌力量。方法招募14名单侧ACLR累及ST肌腱移植物后成功恢复运动的运动员。自手术以来的中位时间为49个月（范围12-78个月）。参与者在进行北欧绳肌锻炼（NHE）之前和之后对其大腿进行功能磁共振成像（MRI），并将横向（T2）松弛时间的百分比变化用作绳肌激活的指标。通过MRI确定肌肉体积和ACSA，并通过超声评估远端ST肌腱。在NHE期间确定偏心屈肌力量。结果手术引起的ST肌肉运动引起的T2变化低于对照组肢体（95％CI-3.8至-16.0％）。手术肢体的ST肌肉体积（95％CI-57.1至-104.7 cm3）和ACSA（95％CI-1.9至-5.0 cm2）均显着降低。手术肢体的半膜（95％CI 5.5-14.0 cm3）和股二头肌短头（95％CI 0.6-11.0 cm3）体积略高。在偏心膝屈肌强度上未观察到两肢间差异（95％CI 33 N至-74 N）。结论ACLR联合ST移植后1-6年，在偏心膝屈肌锻炼中，手术肢体的ST激活明显低于对照组。较低水平的ST激活可能部分解释了ACLR后该肌肉的持续萎缩，并且对设计更有效的康复计划有影响。证据级别IV。