Elastography Study of Hamstring Behaviors during Passive Stretching

<div><p>Introduction</p><p>The mechanical properties of hamstring muscles are usually inferred from global passive torque/angle relationships, in combination with adjoining tissues crossing the joint investigated. Shear modulus measurement provides an estimate of changes in muscle-tendon stiffness and passive tension. This study aimed to assess the passive individual behavior of each hamstring muscle in different stretching positions using shear wave elastography.</p><p>Methods/Results</p><p>The muscle shear modulus of each hamstring muscle was measured during a standardized slow passive knee extension (PKE, 80% of maximal range of motion) on eighteen healthy male volunteers. Firstly, we assessed the reliability of the measurements. Results were good for <i>semitendinosus</i> (<i>ST</i>, CV: 8.9%-13.4%), <i>semimembranosus</i> (<i>SM</i>, CV: 10.3%-11.2%) and <i>biceps femoris long-head</i> (<i>BF-lh</i>, CV: 8.6%-13.3%), but not for <i>biceps femoris short-head</i> (<i>BF-sh</i>, CV: 20.3%-44.9%). Secondly, we investigated each reliable muscle in three stretch positions: 70°, 90° and 110° of hip flexion. The results showed different values of shear modulus for the same amount of perceived stretch, with the highest measurements in the high-flexed hip situation. Moreover, individual muscles displayed different values, with values increasing or <i>BF-lh</i>, <i>SM</i> and <i>ST</i>, respectively. The inter-subject variability was 35.3% for <i>ST</i>, 27.4% for <i>SM</i> and 30.2% for <i>BF-lh</i>.</p><p>Conclusion</p><p>This study showed that the hip needs to be high-flexed to efficiently tension the hamstrings, and reports a higher muscle-tendon stress tolerance at 110° of hip angle. In addition muscles have different passive behaviors, and future works will clarify if it can be linked with rate of injury.</p>