Tonic in physiology refers to a muscle which is predominantly toned. The opposite of tonic is phasic (physiology).

Human tonic muscles

It can specifically refer to a muscle which is composed mainly of type II muscle fibers. As these types of muscles (trapezius, calves, jaw (muscle)) tend to be toned, they tend to shorten and be relatively inflexible and therefore tend to be short in humans.^[1] Trapezius In human anatomy, the trapezius is a large superficial muscle on a persons back. ... The calf or gastosoleus is a pair of muscles—the gastrocnemius and soleus—at the back of the lower human leg. ... For other uses, see Flexibility (disambiguation). ...

Typical tonic muscles include muscles which are used to protect and prepare the body under fight or flight situations, a reaction to the hormones epinephrine (adrenaline) and cortisol and other innate autonomic nervous system reactions^[2]. This article or section should include material from Fight-or-flight The flight or fight response, also called the acute stress response, was first described by Walter Cannon in the 1920s as a theory that animals react to threats with a general discharge of the sympathetic nervous system. ... Adrenaline redirects here. ... Cortisol is a corticosteroid hormone produced by the adrenal cortex that is involved in the response to stress; it increases blood pressure, blood sugar levels, may cause infertility in women, and suppresses the immune system. ... This article or section is in need of attention from an expert on the subject. ...

See also

• Phasic (physiology)

References

1. ^ "Back to the Basics for the New Year", by Paul Chek
2. ^ "Posture: Alternatives to The Prevailing Paradigm, Part One. Traditional Approaches to Postural And Musculoskeletal Dysfunction" by Steven Goldstein.