biology

Kohnstamm's phenomenon

Kohnstamm's phenomenon is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Kohnstamm's phenomenon rather than just read about it. In short: First described by German neurologist Oskar Kohnstamm (1871–1917) in 1915, Kohnstamm's phenomenon is a sustained involuntary contraction of a muscle after a prolonged voluntary contraction. The simplest demonstration, sometimes called "the floating arms experiment", is to have a subject press the arms against a door frame or wall for about thirty seconds, and then step away.

Key takeaways

Kohnstamm's phenomenon belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Kohnstamm's phenomenon to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Kohnstamm's phenomenon from memory before moving on to harder problems.

Reference excerpt

First described by German neurologist Oskar Kohnstamm (1871–1917) in 1915, Kohnstamm's phenomenon is a sustained involuntary contraction of a muscle after a prolonged voluntary contraction. The simplest demonstration, sometimes called "the floating arms experiment", is to have a subject press the arms against a door frame or wall for about thirty seconds, and then step away. The arms will involuntarily rise. Russian scientists Victor Gurfinkel, Mikhail Lebedev and Yuri Levick used Kohnstamm's phenomenon to activate tonogenic structures in humans and thereby demonstrate postural automatisms, such as neck reflexes.

See also Motor control

References Kohnstamm, O. Demonstration einer Katatonieartigen Erscheimung beim Gesunden (Katatonusversuch). Neurologisches Centralblatt B1 34S: 290–291, 1915. Gurfinkel, V.S.; Lebedev, M.A.; Levick, Yu.S. (1992). "What about the so-called neck reflexes in humans?". In Vidal, Pierre Paul; Alain Berthoz; Werner Graf (eds.). The Head-neck sensory motor system. Oxford [Oxfordshire]: Oxford University Press. pp. 543–7. ISBN 0-19-506820-3. Gurfinkel, VS; Levik, IuS; Lebedev, MA (1989). "[Immediate and remote postactivation effects in the human motor system]". Neurofiziologiia (in Russian). 21 (3): 343–51. doi:10.1007/bf01058224. PMID 2770916. S2CID 9327823. Translation into English: Neurophysiology 21: 247–253. Gurfinkel, V. S.; Levik, Yu. S. & Lebedev, M. A. (1989). "Postural automatisms revealed by enhancement of the tonic background" [Postural automatisms revealed by enhancement of the tonic background]. Doklady Akademii Nauk SSSR (in Russian). 305 (5): 1266–9. PMID 2752900. Duclos, C.; Roll, R.; Kavounoudiasa, A.; Roll, JP (January 2007). "Cerebral correlates of the 'Kohnstamm phenomenon': An fMRI study". NeuroImage. 34 (2): 774–783. doi:10.1016/j.neuroimage.2006.06.050. PMID 17095251. S2CID 26427706. Ivanenko YP, Wright WG, Gurfinkel VS, Horak F, Cordo P (February 2006). "Interaction of involuntary post-contraction activity with locomotor movements". Experimental Brain Research. 169 (2): 255–60. doi:10.1007/s00221-005-0324-3. PMC 1363359. PMID 16369781. Mathis J, Gurfinkel VS, Struppler A (August 1996). "Facilitation of motor evoked potentials by postcontraction response (Kohnstamm phenomenon)". Electroencephalography and Clinical Neurophysiology. 101 (4): 289–97. doi:10.1016/0924-980X(96)95599-X. PMID 8761038.

Worked examples

Example 1 — a first encounter with Kohnstamm's phenomenon

Start with the simplest possible case. Write down what Kohnstamm's phenomenon claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Kohnstamm's phenomenon before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Kohnstamm's phenomenon ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Kohnstamm's phenomenon

In research: Kohnstamm's phenomenon appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Kohnstamm's phenomenon in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Kohnstamm's phenomenon is common in secondary-school and first-year university syllabi. It links to neighbouring topics Neurophysiology, so understanding it makes those chapters shorter.
In everyday life: Look for Kohnstamm's phenomenon outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Kohnstamm's phenomenon in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Kohnstamm's phenomenon means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Kohnstamm's phenomenon out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Kohnstamm's phenomenon in simple terms?

Why does Kohnstamm's phenomenon matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Kohnstamm's phenomenon?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Kohnstamm's phenomenon.