The Science of Stretching (part 1): muscle length vs. extensibility

Did you be assured of that longer muscles do not outcome in a more functional range of motion? New evidence has been challenging our rational faculty of flexibility. As a result, our rehabilitation and recreation practices must evolve. These posts pleasure attempt to unpack the current investigation, and demonstrate why the mechanical stretching prototype is changing in light of recent discoveries.

What is Muscle “Lengthening” Anyway?

We bear all noticed the range of suggestion (ROM) improvements that result from tedious-term stretching programs. However controversy compose exists regarding the exact cause of affability gains. Many of us take concerning granted the theory that, if we continually give a ~ the muscles, the tissue itself self-reliance “lengthen”. But which measurement carry into practice we imagine is changing here? The description of a muscle’s length is the distance between its insertion points on the bones. A vary in this measurement would require altering the locations of bones (one and the other by moving or growing). In adults, the placement of bones is determined by genetics (can be altered with surgery) and in this wise, is very unlikely to change.

In verity, there are two mechanical components of muscle “lengthening”, in the same manner with it is generally understood. These are known being of the cl~s who viscoelastic accommodation and plastic deformation, and make allusion to passive tissue properties. Viscoelastic provision of conveniences. is similar to what happens which time you pull apart a rubber cord. The elastic yields or gives, it accommodates the sprain. Plastic is a different type of important, and when you tug on it, the soft simply breaks. Connective tissue (ie. muscle) displays both these properties [1].

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The unfortunate matter about muscle’s viscoelastic properties is that they are absolutely an acute adaptation to stress. Tension is reduced without any intervention in response to load, however great number 3-8 week studies have reported a return to original shape within 1 sixty minutes after stretching [1]. In other language, accommodation is not leading to any chronic changes in muscle tissue beneath the current paradigm. In addition, a muscle can only give a certain amount (about 4-8% of length), before its weakest links commence to break apart. This is referred to because the popping sarcomere hypothesis [4]. Stretch-induced muscle loss takes time to heal and does so by adding sarcomeres in series [3], ~ the agency of adding links to the chain. The addition of sarcomeres also results in a trick in the appropriate joint angle as far as concerns optimum muscle advantage. In a clinical setting, this lineament helps patients recover from fractures or surgeries. In habitual circumstances however, the addition of sarcomeres have power to result in achieving extreme flexibility at the cost of stability in more common movements. Adding links leads to loose in the chain.

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Muscle Length vs. Extensibility

The vigor for the muscle to be extended is to what we are really trying to improve. Extensibility is to what degree much the muscle yields under emphasis (stiffness) and how easily it returns to its oddity shape (elasticity/energy). While most stretching protocols claim to request stiffness, it is just as of influence to maintain (and develop) the resiliency of the tissue, the energy released ~ dint of. return. A muscle that lacks tendency to recover results in a joint low in permanence.

In order to evaluate this, we graph the continuance (joint angle) against the tension (torque produced ~ dint of. passive resistance) to get a curve [see figure 3.]. A greater dis~ angle results in a greater aggregate of passive torque. The “stiffness” of a muscle is to what degree quickly the tension increases, the direction downward. The area under the curve represents the spiritedness of return, the passive elasticity. A “longer” muscle is any where the curve is shifted to the right. An “extensible” muscle has a smaller quantity steep curve. In Figure 3 in time, the hypothetical graph on the left demonstrates the deviation in the length/tension relationship that we imagine at what time stretching.

Screen Shot 2016-06-08 at 9.50.39 PM In reality, flexibility studies often report graphs that look more like the any on the right[1]. Following a 3-8 week stretching protocol, a larger divide angle can be attained. However, the increased amplification also corresponds with an increase in tension. Meaning, the study participants had a make different in their perceived maximum point of stretching. They felt safer putting the muscle below higher amounts of torque [1].

These tools and materials have two very important implications. First, they be the sign of that our current methods of static, automatic stretching accomplish neither the decreased rigidity nor increased length that we are ~times promised. Secondly, the change in impression reported at a given amount of stiffness suggests a nervous system component. This is called direction tolerance, and we will be diving into this in what is yet to be posts.

The point is, stretching programs are arising to favor extensibility, and muscle “length” is in reality more complex than we previously assumed. Due to feat reductions and injury risks often associated with extreme flexibility [2], it is animate to develop the stability of the joints at the identical time. Enter mobility, training for a again functional range of motion.

Joint fickleness involves a variety of factors. The nearest post will discuss the role of modifying feeling and the importance of nervous classification involvement.


Weppler, C., & Magnusson, S. (2010). Increasing muscle extensibility: a good sense of increasing length or modifying feeling . Physical Therapy, 90(3), 438-449.

Behm, D., Blazevich, J., Kay, A. & McHugh, M. (2016) Acute goods of muscle stretching on physical work, range of motion, and injury incidents in wholesome, active individuals: a systemic review. Appl Physiol Nutr and Metab, 41: 1-11.

Zöllner, A. M., Abilez, O. J., Böl, M., & Kuhl, E. (2012). Stretching skeletal muscle: inveterate muscle lengthening through sarcomerogenesis. Plos One, 7(10), e45661. doi:10.1371/newspaper.pone.0045661

Morgan, D. L., & Proske, U. (2004). Popping sarcomere supposition explains stretch-induced muscle damage. Clinical & Experimental Pharmacology & Physiology, 31(8), 541-545. doi:10.1111/j.1440-1681.2004.04029.x

A comprehensive portion of the inspiration for this intelligencer came from the work of other blogs:

Jules Mitchell has completed a lot o original research kindred to this topic in the department of exercise science. Check out her act here.

Some of the groundwork has been effected by Matthew Remski, with his What are We Actually Doing in Asana (WAWADIA) manner of moving. Take a read here.

The intelligence for this post was gathered against a conference in exercise science 380, Motor Control, University of Victoria. To derive a pdf copy of the untranslated academic poster, or to stay tuned beneficial to the next installment, click here.

Thanks y’total!


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