Acute and chronic effects of static stretching of different target muscles on shear elastic modulus: A narrative review.

We investigated the acute and chronic effects of static stretching on shear elastic modulus and assessed whether these effects could differ among various target muscles. PubMed, Scopus, and Google Scholar databases were searched for articles published up to 2023, using the terms "stretch," "stretching," "static stretching," "shear elastic modulus," "shear modulus," and "shear wave elastography." Thirty-seven original studies measured the shear elastic modulus after stretching: 32 and five evaluated acute and chronic effects, respectively. Acute stretching significantly decreased the shear elastic modulus in various muscles as follows: infraspinatus and pectoralis minor (2/2 studies, 100 %); medial gastrocnemius (15/17 studies, 88.2 %); lateral gastrocnemius (4/6 studies, 66.7 %); semimembranosus and semitendinosus (4/5 studies, 80 %); biceps femoris (3/5 studies, 60 %); and rectus femoris (3/4 studies, 75 %). No significant changes were found in the soleus, vastus lateralis, vastus medialis, teres minor, and posterior deltoid muscles, highlighting the variability in the effects of stretching on shear elastic modulus across different muscles. The difference in the effect depends on the stretching methods, including the position, duration, and intensity and position at which the shear elastic modulus is measured. Therefore, we should establish stretching methods for each muscle and investigate chronic effects on the shear elastic modulus.