Hamstring tightness is a common complaint and is implicated in tissue loading in the lumbar spine, SIJ and lower limb.

It is important to have an understanding of the functional causes of this to address this in the clinic.

We should ask “Why is the central and / or peripheral nervous system increasing tone or stiffness in the hamstrings”? The purpose of this blog is to highlight a few functional causes.

Primitive Reflexes

Numerous primitive reflexes have the potential to increase tone in the hamstrings. All of the reflexes that produce trunk extension (e.g., Landau) and knee flexion (e.g., Symmetrical Tonic Neck Reflex) have the potential to be involved. It is not the purpose here to fully explain the causes or rehab of primitive reflexes. All of these reflexes should be explored. They are very common in neurodevelopmental disorders.

Neurodynamics

Also from the 90’s it was recognized that the hamstrings will respond to increased activity to neurodynamic reactivity. It is recommended to always check neurodynamics. It is quite possible the hamstring stiffness is reacting or “protecting” an aspect of the nervous system. Note: the mechanism and cause of the neurodynamic reactivity should then be explored.

Translation Control

It is well established now that there is a highly variable response to increased shear forces. Some people have too much stiffness and some people have too little stiffness. The bulk of this research is based on low back pain. It is logical to consider that there could be increased stiffness in the hamstring due to shear forces in the SIJ, hip or knee. All these should be explored.

Muscle Imbalance

Many years ago, the concept of “muscle imbalance” would be a first choice. This construct is not well defined and does not have the evidence base it is assumed to have. There are many interpretations of “muscle imbalance”. In this instance it refers to an “imbalance” between synergistic muscles of hip extension (i.e., gluteus maximus and hamtrings). Despite the limited evidence (rather than evidence refuting it) for this, it is my opinion that it exists in a subgroup of people (Note: I measure muscle stiffness in the clinic and if you don’t please do not comment). The mechanisms and causes of this imbalance should be explored. Non-specific gluteus maximus rehabilitation may not be sufficient.

Injury

If someone has had a true hamstring strain, the resulting swelling, +/- bleeding and healing can result in intrinsic stiffness.

Overtraining

Repeated hamstring strengthening in shorted range could lead to increased intrinsic stiffness. A simplistic approach could reverse this (e.g., alter training order, encourage extension based exercises).

Other Influences

There are a variety of biomechanical influences that have been reported to increase load on the hamstrings, but it is unknown if they influence resting tone. These include (but not limited to): foot posture (pronation), standing posture, functional hallux limitus, running / sprint biomechanics, load acrriage, footwear type and surface.  It is likely biomechanics is involved and likely interact with other functional causes.

Perceived Stiffness

There are people that report “stiffness”, but do not have reduced range of motion (Note: hypermobility syndromes are common in neurodevelopmental disorders so a large range of motion does not rule out increased tone or stiffness). There are also people who have “unexplained” stiffness (e.g. complain of stiffness, but stiffness is not observed with objective measures).  There are always unknowns in clinical practice. There may be a role for the autonomic nervous system, endocrine dysregulation of low grade systemic inflammation.

Summary

Stretching is not always the answer to muscle tightness. The mechanisms and causes should be explored. Strong beliefs on this prevail!

Primitive reflexes are common and should be considered. Increased tone is a neurological problem and requires a neurological solution!