First, define "muscle tone". It is not a scientific term. The extent of muscle activation, which I think is what you're interested in, is affected by motor unit recruitment and rate coding. Your question should be framed in these terms.

Dear Gordon L Warren, could you specifiy why you think 'muscle tone' (or 'muscle tonus') is not a scientific term? Being puzzled by your statement I checked Pubmed for "muscle tone", and received many hits in titles of recent papers. If a critique of this term(s) is available, please send us the reference.

The five "best match" articles are:

The immediate effect of PNF pattern on muscle tone and muscle stiffness in chronic stroke patient.

Wang JS, Lee SB, Moon SH.

J Phys Ther Sci. 2016 Mar;28(3):967-70. doi: 10.1589/jpts.28.967. Epub 2016 Mar 31. PMID: 27134394 Free PMC Article

Excessive anterior cervical muscle tone affects hyoid bone kinetics during swallowing in adults.

Yamazaki Y, Tohara H, Hara K, Nakane A, Wakasugi Y, Yamaguchi K, Minakuchi S.

Clin Interv Aging. 2017 Nov 8;12:1903-1910. doi: 10.2147/CIA.S143175. eCollection 2017. Erratum in: Clin Interv Aging. 2018 Mar 13;13:403.

PMID: 29184396 Free PMC Article

Effect of muscle tone on ankle kinetics during gait with ankle-foot orthoses in persons with stroke.

Mizuno S, Sonoda S, Takeda K, Maeshima S.

Top Stroke Rehabil. 2017 Dec;24(8):567-572. doi: 10.1080/10749357.2017.1373930. Epub 2017 Sep 25. PMID: 28945975

Infant muscle tone and childhood autistic traits: A longitudinal study in the general population.

Serdarevic F, Ghassabian A, van Batenburg-Eddes T, White T, Blanken LME, Jaddoe VWV, Verhulst FC, Tiemeier H.

Autism Res. 2017 May;10(5):757-768. doi: 10.1002/aur.1739. Epub 2017 Feb 9.

PMID: 28181411 Free PMC Article

The effects of functional electrical stimulation on muscle tone and stiffness of stroke patients.

Moon SH, Choi JH, Park SE.

J Phys Ther Sci. 2017 Feb;29(2):238-241. doi: 10.1589/jpts.29.238. Epub 2017 Feb 24. PMID: 28265148 Free PMC Article

I have been a muscle physiologist for 30 years. 'Muscle tone" is not a credible term. Yes, it can appear in the literature but that does not mean it is legitimate. Please explain to me the cellular and molecular bases for "muscle tone".

Dear Gordon L Warren, judging from the Pubmed searches of "muscle tone", and "muscle tonus" one would not come immediately to the impression that these terms are controversial or even that one would see an expert calling their use not "legitimate" (?). The two terms are used both in article titles and as keywords by your fellow physiologists. As to this being controversial issue or concept is news to me, I'd like to learn more about the controversy. Did you publish this your critique somewhere, and/or could you please cite literature that backs up your assertion? (I mean, if your assertion is correct, it cannot remain a trade secret, and the interested public should be informed with best knowledge.)

Dear Gordon, thanks for your answer. Could you tell me how motor unit recruitment and rate coding can be increased by affective processes? Does the limbic system target the spinal motoneurons? Or the primary somatomotor cortex? Or... ? And besides the 'target', what is the source of such limbic influence? The ACC, or the amygdala, or... ?

Otherwise, I'm in a similar situation as Rudolf, and curious to receive a detailed argument why the term muscle tone should not be used.

Best regards,

Benedek

Dear Rudolf, thanks for your answer and your question too!

I checked the mentioned papers, but it seems to me, they do not give the answer to my question, namely, how the function of the muscles can be affected by affective (e.g. emotional) processes.

This paper probably doesn't answer your question either, but they do find measurable changes in muscle activity linked to emotional states:

SAINSBURY, P, and J G GIBSON. "Symptoms of anxiety and tension and the accompanying physiological changes in the muscular system." Journal of neurology, neurosurgery, and psychiatry 17.3 (1954): 216-224.

The authors found a positive correlation between the degree of anxiety and resting EMG levels in forearm extensor muscles and the frontalis muscle. They speculate that increased activity of resting muscles may be a physiological consequence of anxiety.