Effect of Hamstring Stretching on Pain at Masseter Muscle and Mouth Opening: A Systematic Review.

TL;DR

A new systematic review found that hamstring stretching may temporarily improve jaw opening and reduce pressure pain in the masseter muscle, but the evidence is sparse and heterogeneous. The studies reviewed were small and varied in design, so these findings should be interpreted cautiously.

What the Study Found

Researchers conducting a systematic review of studies from 2006-2025 identified a potential mechanistic link between hamstring flexibility and temporomandibular joint (TMJ) function. The core hypothesis: tightness in the hamstrings, part of the posterior kinetic chain, could create tension that propagates upward through interconnected fascial and neural pathways, ultimately affecting the jaw and chewing muscles. This aligns with the broader concept of myofascial chains, where restrictions in one body region theoretically influence distant sites through continuous connective tissue networks.

The review's preliminary findings are modest but suggestive. Studies examining acute or short-term hamstring stretching interventions showed temporary improvements in two measurable outcomes: pressure pain threshold at the masseter muscle (the primary jaw-closing muscle) and maximum mouth opening. In practical terms, participants reported slightly less tenderness and could open their mouths a bit wider after hamstring stretching. However, the authors explicitly caution that these results require careful interpretation. The number of randomized controlled trials meeting inclusion criteria was small, and heterogeneity in study design, intervention protocols, and outcome measurement makes it difficult to draw firm conclusions about the consistency or magnitude of these effects.

The mechanistic explanation offered centers on neuro-myofascial connectivity: the idea that the nervous system and fascia form integrated networks where local restrictions can affect distant regions through neural pathways, mechanical continuity, or both. Hamstring tightness might increase tension along the posterior chain extending to the cervical spine, which then influences TMJ mechanics and masseter muscle function. This is biologically plausible given the known anatomical connections between the cervical spine and masticatory system, but the review found insufficient evidence to establish this mechanism definitively.

Importantly, the authors note that while the possibility of myofascial and neural interconnections is supported conceptually, the current evidence base cannot confirm whether observed improvements in jaw opening and pain were due to these proposed mechanisms or other factors. Improvement could reflect general relaxation, placebo effects, or unknown confounders. The temporary nature of the effects also raises questions about whether hamstring stretching produces meaningful, durable benefit for TMJ disorders.

What This Means for You

If you experience jaw pain or limited mouth opening, this finding does not yet justify hamstring stretching as a primary treatment. The evidence is too preliminary. However, it does suggest that if you're working with a physical therapist on TMJ issues, discussing your posterior chain flexibility (particularly hamstrings) may be worthwhile as part of a comprehensive assessment. Limited hamstring flexibility might contribute to postural and movement patterns that indirectly affect jaw mechanics, even if the direct myofascial link remains unproven.

For general musculoskeletal health, regular stretching of major muscle groups including the hamstrings remains sensible practice independent of TMJ concerns. The evidence here simply doesn't yet support a specific claim that hamstring stretching treats jaw pain.

Practitioners managing TMJ dysfunction should be cautious about overinterpreting these findings. Standard evidence-based approaches for TMJ disorders (physical therapy focused on the jaw and cervical spine, posture correction, stress management) remain the foundation. Hamstring work may complement these strategies, but the evidence for it as a focused intervention for jaw pain is currently weak.

Study Details

Sources

Hamstring Stretching Effect on TMJ Pain and Mouth Opening (Systematic Review). *Physiotherapy Research International*. PubMed: 42574083