A New Way to Look at Asymmetries

When assessing the length of a muscle, it is important to distinguish between muscle stiffness and adaptive shortening. Take the Thomas Test, for example. You will notice that the ASIS will begin to rise far earlier than when motion stops. The reason for this: stiffness, or resistance to stretch. Adaptive shortening, on the other hand, is when motion no longer occurs due to muscle restriction. Should we still prescribe stretching exercises for our patients if stiffness is the issue?

Mizuno et al found in a couple studies that, while changes in stiffness did occur after stretching, those changes disappeared in as soon as 10 minutes. It would seem that we should not address stiffness with stretching. Just because muscle length isn't an issue doesn't mean we should ignore any differences in stiffness. Increased resistance to stretch on one side of the body compared to the other can still place abnormal stresses on certain tissues. Think about increased stiffness on one hip flexor in a patient with SIJ Dysfunction. Some of our training may lead us to think that we should direct our patients to stretching of the hip flexor, but as you can see, we would have little effect on the impairments.

So how do we address these differences? Shirley Sahrmann discussed this topic in a lecture that we highly recommend listening to. Instead of focusing on the side with increased stiffness, we should address the side with decreased stiffness. Strength training has been found to increase muscle stiffness (Magnusson, 1998). By bringing both sides of the body to symmetry (equal stiffness), an equal distribution of forces prevents any abnormal stresses on the body. Stretching still has its place, of course, but we must be sure to distinguish between muscle stiffness and adaptive shortening when choosing to apply the intervention. Next time you're measuring muscle length, check for stiffness and muscle length!

References:
Magnusson SP. (1998). Passive properties of human skeletal muscle during stretch maneuvers. A review. Scand J Med Sci Sports. 1998 Apr;8(2):65-77. Web. 10 June 2013.

Mizuno T, Matsumoto M, Umemura Y. (2013). Decrements in Stiffness are Restored within 10 min. Int J Sports Med. 2013 Jun;34(6):484-90. Web. 10 June 2013.

Mizuno T, Matsumoto M, Umemura Y. (2013). Viscoelasticity of the muscle-tendon unit is returned more rapidly than range of motion after stretching. Scand J Med Sci Sports. 2013 Feb;23(1):23-30. Web. 10 June 2013.