Evidence Based Physical Therapy Articles

Four Keys of Therapeutic Exercise, Part 2 by Michael Rinaldi, PT, OCS

3. Endurance.

It is well known that muscle has the ability to adapt to stimulus/stress placed on it.  Fiber types delineate whether a given muscle group has as its primary characteristic one of endurance (Type I, slow-twitch, oxidative) or are that which generate power (fast twitch, or Type II).  Type II can be sub-divided into IIA and IIB both of which have slightly different properties. Type II fibers, however can adapt between themselves to meet the needs of the musculoskeletal system. 

However, what has been historically less appreicated but is slowly gaining momentum is the role of functional muscular endurance.  For example, we know that the muscles' support of the spine can be prime movers.  However if you look at ordinary tasks such as work done a desk, you can begin to appreciate that the muscles that hold up the neck, head, and trunk are ones that require muscular endurance. 

Therefore in our rehabilitation protocols we need to critically examine our prescriptive exercises used. 

It would not be sensible to prescribe exercises with a numerical quota (three sets of 10 repetitions) to train the cervical extensors of a receptionist who sits at a desk for six hours a day.  This is not functional endurance training.  Having the patient instead perform a sustained resisted retraction for several minutes while performing upper extremity progressive resisted exercises would be more sensible in this scenario.  Or having the patient perform upper body ergometry for several minutes while using a neck-posture strengthening device (looks like an ankle weight around the head---ultra Rambo!) would also be more sensible and applicable.

The bottom line is this: if you are using a quota-based exercise prescription of repetitions, chances are you are not working endurance but merely activation of muscle and maybe strength if the intensity is high enough.  To emphasize endurance you must work the muscle consistently for a minimum of four minutes but more appropriately ten minutes would be a good target to shoot for.

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