Stretching – What does it actually do?

I was always taught that stretching improved the flexibility of the muscle group. This occurred by changing the muscle structure, for example a structural change to the myofibril.

The following three studies I recently read have been enlightening regarding this:

Law et al (2009)

• A RCT investigating the effects of a 3 week stretching program on muscle extensibility and stretch tolerance in patients with chronic musculoskeletal pain.
• The hamstring muscle on 1 leg was stretched daily for 1 minute, whilst the other leg was not stretched.

Folpp et al (2006)

• A study that involved twenty healthy able-bodied individuals with limited hamstring muscle extensibility.
• A within-subjects design was used whereby one leg of each subject was randomly allocated to the experimental condition and the other leg was allocated to the control condition.
• The hamstring muscles of each subject’s experimental leg were stretched for 20 minutes each weekday for four weeks.

Ben and Harvey (2010)

• A RCT that involved sixty healthy individuals that randomly allocated to an experimental or a control group.
• The experimental group attended supervised stretch sessions where they stretched the hamstring muscles of a randomly allocated leg for 30 min five times a week for 6 weeks. The control group did not attend any stretch sessions during this period.

So what was the conclusion from all of the above studies?

Basically the extensibility of the stretched muscles did not change i.e. the torque onset was not significantly different pre-intervention vs post-intervention. There was however a notable difference in the stretch tolerance of the individuals “stretched” hamstring i.e the participants tolerance to the discomfort of stretching their “stretched” hamstring improved and this resulted in improved “flexibility/ROM” of the hamstring.

So stretching doesn’t appear to lead to changes in muscle structure, rather regular stretching improves tolerance to the discomfort of the stretch and hence improves our patients flexibility. Not a reason to stop our patients stretching, but perhaps a reason to rethink how we talk to patients, each other and colleagues about what our “stretching” programs are doing.

Maybe this “phenomenon” also applies to improving flexibility in other structures such as joint capsule and tendons.

Interested to hear thoughts.

References:

Ben M, Harvey LA. Regular stretch does not increase muscle extensibility: a randomized controlled trial. Scand J Med Sci Sports. 2010 Feb;20(1):136-44.

Folpp H, Deall S, Harvey LA, Gwinn T. Can apparent increases in muscle extensibility with regular stretch be explained by changes in tolerance to stretch? Aust J Physiother. 2006;52(1):45-50.

Law RY, Harvey LA, Nicholas MK, Tonkin L, De Sousa M, Finniss DG. Stretch exercises increase tolerance to stretch in patients with chronic musculoskeletal pain: a randomized controlled trial. Phys Ther. 2009 Oct;89(10):1016-26.