Define what you mean by stiffness? Do you mean the change in force per unit change in length? Are you trying to measure this in animal or human muscle? If the former, is the muscle still in the animal? Do you want to know the stiffness during a passive or active contraction?

Dear Mr. Warren,

Thanks for your response. I mean passive stiffness in humans.

I am interesting in the possible protective mechanism of the stiffness against muscle injuries. Authors of a recent article (see attached, Seymore, 2017) hypothesized that  increasing tissue stiffness could contribute to injury-resistance following nordic hamstring exercise. They used elastography but I wonder If ultrasound imaging could be used for the same purpose.

I am not interested in tendon tissue stiffness, just in the stiffness of the own muscle.

It seems confusing for me as other authors (see attached, Pisot et al., 2008) assessed muscle stiffness using changes in muscle belly thickness.

Regards

Saul,

I worked with a physical therapist and an osteopathic physician to investigate the change in stiffness following a muscle energy treatment (i.e. an osteopathic manual medicine treatment used for tissues and joints that are restricted in their motions).  We investigated the straight leg raising test before and after treatment and found a significant reduction in the "passive stiffness" in this motion.  The results are in "Quantification of the Passive Resistance to Motion in the Straight Leg Raising Test on Asymptomatic Subjects" (J. A. O. A., September 22, 1992).

From a personal perspective, I do not understand how increasing muscle tissue stiffness would contribute to injury -resistance.  Passive muscle stiffness reflects primarily health of the connective tissue surrounding muscle and possibly the neurological response of muscle.  In my view of passive motions, neither the connective tissue or neurological response should affect the passive response until reaching the end of the range of motion. Am I missing something in the logic of your research?

Dear Mr. Reynolds,

It is just a hypothesis. The authors of the article I mentioned (Seymore et al., 2017, above attached) postulate that: 

"Another possible adaptation that could contribute to injury-resistance following NH exercise is increasing the stiffness of the muscle. Strain, rather than force, is responsible for injury (Lieber and Friden 1993) and stiffer muscles experience less strain for a given force. Increasing muscle stiffness can be accomplished by increasing muscle crosssectional area. Given that muscle hypertrophy accompanies resistance training, gains in muscle size and, therefore, stiffness are plausible following NH training. Another mechanism for stiffness to be modifiable is to increase the stiffness of the tissue, or elastic modulus. This also seems a viable mechanism, as muscle modulus is known to be modifiable with exercise training (Kovanen et  al. 1984). However, changes in neither muscle size nor stiffness after NH interventions have been determined. Therefore, both avenues for increasing tissue stiffness could contribute to injury-resistance following NH exercise."

The authors found nothing about it due to an unfortunate effect of random assignment, i.e.,  the nordic hamstring training group’s mean stiffness was significantly lower than the control group’s mean stiffness at baseline. Nonetheless, no changes to either group were apparent post-intervention.

What do you think?

My experience comes primarily from the paper that I referenced plus the training that I received in osteopathic manual medicine as a faculty member in the College of Osteopathic Medicine at Michigan State University.  I give you that "position of mine" to emphasize that I am not a muscle physiologist nor a physician nor actually an engineer.  My research has been focused primarily on spinal postures in living as well as cadaver subjects.

I learned at the Osteopathic College that their treatment of athletes as well as you and I was focused largely on symmetry of movement in the body.  When assymmetrical movements are found in the examination, these movements are quite often associated with injuries and develop as a protective response in the body.  However, as in the ergonomic world of repetitive injury, asymmetrical motions can be trained and produce injuries. 

All of this means to me that the high performance athlete trains symmetrically to create a range of motion that is as large as possible with the capability to control these motions with coordination required to maintain either static or dynamic stability of the body.  These thoughts bring me to the conclusion that the initial assumption in your response may be misleading.  Strain and stress are both related to injury and their respective roles may be different at different points in the range of motion.  That is, if the injury occurs at the limits of motion, the effect of strain and stress may be different than they are in the path of motion.  There are also different tissues involved throughout the motion so it would seem possible that an investigation might investigate how the system functions throughout the range and is it mechanically a different system at the end of motion than during the path of motion.  I assume that like everything I have ever investigated in the human body, non-linearity emerges and tends to dominate the discussion and investigation.

These comments are coming more from my experience as I stated at the beginning of this reply rather than a thorough examination of the literature which you have obviously been doing.  Good work and I congratulate you for tackling a very difficult problem.

I find it very difficult to get an definition because which age you are searching and which group of athetes . Older people will have an higher stifness but not all. It is still amazing that older woman can reach the ground with flat hand and knee in extension because they have done the floor Always so. I have working with neurological patients and than is muscle stifness total different m now dependent of the tone but also the reactiopn of the tone visco not contractiel structures and what is the reaction on the nerve tissue

I can also give no answer , only my feeling will say this is to much but than the assessment why ?

Succes

jan van de Rakt

Dear Mr. van de Rakt,

I think we are talking about very different things. I am talking of the hypothetical protective effect of the stiffness in hamstring muscles which appears with certain types of exercises as the NH or eccentric overload.

As it is only a hypothesis, it should be tested. Anyway, my main question was about how and with which tools can I measure stiffness (i.e., passive).

Regards

Tonometer-ultrasound elastography 

Saul, check research done with the myoton.com 

https://myoton.com

Tensomiography ?

Hi Luis, 

TMG is very speculative regarding the measurement of stiffness. I have great doubts  as there is only one study in the literature (see attached file) which has shown some correlation (r = -0.70). They correlated relative changes in Dm with relative changes in muscle thickness after 35-days bed rest. I do not understad why that relation as "stiffness".

I have worked with TMG and I have several articles under review, but the measurement of muscle stiffness by TMG is very speculative as far as I know.

Regards