## 4 Discussion and Conclusions  
The purpose of this review was to evaluate the acute and chronic effects of static stretching on neuromuscular properties by summarizing the selected joint behaviors and neuromuscular responses based on data from the recent literature. The results of our meta-analyses based on the reviewed studies suggested that (1) acute static stretching may change joint behaviors (e.g., increased ROM, decreased PRT, increased PRT\({}_{\text{max}}\), decreased MVIT, decreased MTU stiffness) and muscular responses (e.g., decreased muscle stiffness, decreased tendon stiffness, decreased shear elastic modulus), and that (2) chronic static stretching may change joint behaviors (e.g., increased ROM, increased PRT\({}_{\text{max}}\)) and muscular responses (e.g., decreased muscle stiffness, decreased shear elastic modulus or shear wave speed). It has been suggested that a stretching-induced increase in ROM may be a result of an increase in stretch tolerance (i.e., the ability to tolerate the discomfort at the end of ROM) [87] and/or changes in MTU mechanical properties (e.g., reduced stiffness of muscle and connective tissues) [88]. The results from our meta-analyses support the findings that both acute and chronic static stretching appear to be effective in increasing ROM and PRT\({}_{\text{max}}\) (a measure of an increase in stretch tolerance), suggesting that the increased ROM may be explained, in part, by an increase in stretch tolerance, as reflected in the increased PRT\({}_{\text{max}}\). Moreover, considering the significant overall effect for the MTU stiffness and muscle/tendon stiffness after acute static stretching, increased ROM in response to acute static stretching may also be associated with reduced MTU mechanical properties. However, as the results of our meta-analyses showed no significant overall effect for the MTU stiffness and tendon stiffness after chronic static stretching, the potential associations between the increased ROM and changes in MTU mechanical properties in response to chronic static stretching are unclear. Interestingly, despite no significant changes in MTU stiffness and tendon stiffness, muscle stiffness and shear elastic modulus or shear wave speed (i.e., muscle-specific variables) were significantly reduced in response to chronic static stretching. These results may imply that in the reviewed studies, changes in the mechanical properties of muscle tissue did not lead to changes in mechanical behavior at joint levels, especially for chronic static stretching. Indeed, based on the presumption that non-muscular structures (e.g., fasciae, nerves, vessels, skin) sitting in/around/across muscles can also contribute to the mechanical properties measured at joint levels, the non-muscular structures have been considered a possible contributor to changes in joint behavior in response to static stretching. For example, it has been evidenced that ankle joint ROM is substantially influenced by different hip and knee joint positions [89], and such notable hip joint position-dependent ankle ROM was observed even without significant changes in ankle joint torque and MG shear elastic modulus for a given ankle angle [90]. These findings have emphasized the possible role of fasciae which connect inter-muscles from ankle to hip/spine joints, also referred to myofasical tissue connectivity (for review see [91]). Acute static stretching protocols aiming to load the sciatic nerve also led to a significant increase in ankle ROM and a significant decrease in the sciatic nerve shear wave velocity (an index of stiffness) without significant changes in MG and BF shear wave velocity, indicating that changes in the mechanical properties of nerves only can directly affect a joint's ROM without changes in the mechanical properties of the muscles across the joint [92].