Can Stretching Your Hamstrings Unlock Your Jaw? Investigating the Surprising Connection Between Hamstring Flexibility and Jaw Function.

Background: The hamstring muscles play a crucial role in posture and movement, with interventions such as stretching and myofascial release commonly used to improve flexibility and muscle function. Emerging evidence suggests that targeting the hamstrings may influence distant structures like the masseter muscle through myofascial connections, highlighting the need for studies investigating these systemic interactions.

Aim: To assess the immediate effects of hamstring stretching alone or combined with myofascial release of the hamstring muscle on masseter muscle activity, pressure pain threshold, active mouth opening, hamstring flexibility, and forward head flexed posture in recreationally active participants.

Methods: Thirty healthy young adults aged 18-25 years participated in this study. They were randomly assigned to two groups: one receiving static hamstring stretching and the other receiving stretching plus myofascial release. Masseter muscle activity was measured using surface electromyography. Pressure pain threshold (PPT), hamstring flexibility (maximum hip flexion and active knee extension), maximum mouth opening (MMO), and forward head posture [tragus-to-wall distance (TWD)] were assessed before and after the interventions.

Results: Treatment led to significant improvements in masseter muscle electromyography (EMG) activity (Group I: Right P = 0.001, Left P = 0.002; Group II: Right P < 0.001, Left P = 0.003) and active knee extension in both groups (Groups I and II: Right P < 0.001, Left P < 0.001), reflecting significant enhancements in muscle activity and flexibility. Mild improvements were also noted in masseter PPT (Group I: Right P = 0.037, Left P = 0.042; Group II: Right P = 0.035, Left P = 0.041), although MMO and TWD remained stable, indicating no significant changes posttreatment. Comparative analysis revealed no significant differences between the groups in response to interventions across all measured parameters, demonstrating that both groups experienced similar improvements and confirming the efficacy of the treatments administered.

Conclusion: The study found that the treatments significantly improved masseter muscle activity and knee extension flexibility, with mild enhancements in pain thresholds. However, there were no significant effects on jaw opening (MMO) or posture (TWD). The lack of significant differences between the groups suggests that both treatment protocolsare equally effective. These findings indicate the potential for incorporating the interventions into clinical practice to improve musculoskeletal function in both the jaw and lower limbs.