Human Resting Muscle Tone (HRMT): Narrative Introduction and Modern Concepts
Alfonse T. Masi, MD, DR.P.H. *
Professor of Medicine and Epidemiology
University of Illinois College of Medicine at Peoria
One Illini Drive, Peoria, IL 61656, USA
Tel: +1 309 671 8428
Fax: +1 309 671 8513
John Charles Hannon, DC
Certified Feldenkrais Practitioner
1141 Pacific Suite B
San Luis Obispo, CA 93401, USA
Tel: +1 805 542 9925
Fax: +1 805 541 2391
Key Words: passive tone or tonus; viscoelastic; skeletal muscle; fascia; myofascial, biotensegrity
*Correspondence to: Dr. AT Masi
Abstract Human resting muscle
(myofascial) tone (HRMT) is the passive
tonus or tension of skeletal muscle that
derives from its intrinsic (EMG-silent)
molecular viscoelastic properties. The word
tone has been used to convey varying
clinical and physiological features that have
led to confusion and controversy. HRMT is
the vital low-level, passive tension, and
resistance to stretch that contributes
importantly to maintaining postural stability
in balanced equilibrium positions. In
contrast, co-contraction of muscle is an
active neuromotor control that provides
greater levels of tonus for increased
stabilization. Functionally, HRMT is
integrated with other passive fascial and
ligamentous tensional networks of the body
to form a biotensegrity system. This review
aims to achieve better understandings of
HRMT and its functional roles.
Nature is frugal and Man’s adaptations to
gravitational forces and erect postures
seemingly evolved mechanisms in skeletal
muscle tissues to economically enhance
stability. Normal passive muscle tone helps
maintain relaxed standing body posture with
minimally increased energy costs (circa 7%
over supine), and often for prolonged
durations without fatigue. Available data
infer polymorphic variations in normal
myofascial tone. However, few quantitative
studies have been performed to establish
normal frequency distributions of degrees of
myofascial tone. Clinical experience
indicates that persons with certain
symptomatic musculoskeletal conditions
may have palpably increased resting muscle
firmness or hardness (EMG-silent), such as
that of the upper trapezius in tension-type
headache, and the lumbodorsal extensors
(hartspann) in degenerative lumbar disc
disease and ankylosing spondylitis.
In summary, resting skeletal muscle tone is
an intrinsic viscoelastic tension exhibited
within the body’s kinematic chains. It
functions inseparably from fascial (i.e.
myofascial) tissues and ligamentous
structures. Thus, HRMT is a passive
myofascial property which operates within
networks of tensional tissues, i.e.,
biotensegrity. This passive tension is the
CNS-independent component resulting from
intrinsic molecular interactions of the
actomyosin filaments in sarcomeric units of
skeletal muscle and myofibroblast cells.
The overarching CNS-activated muscle
contractions generate far greater tensions
transmitted by fascial elements.
Interdisciplinary research on HRMT and its
biodynamics promises greater effectiveness
of clinical practitioners and productivity of
investigators, which warrants priority
A systems level understanding of the
human body is more complex than
defining characteristics of isolated parts of
a cell or the organism. Aristotle
perceptively propounded, “the whole is
greater than the sum of its parts”
(Aristotle). Emergent concepts from
systems approach to applied research often
require integration of many fields of
thought. We review the mainly neglected
area of human resting muscle (myofascial)
tone (HRMT). The aim is to update
current concepts and to stimulate critical
discussion for better understandings in the
Life is movement and muscle has been
studied almost entirely in its activated
Following Hippocrates, Claudius Galen, a
second century physiologist, empiricist
philosopher and writer, is often considered
the most important contributor to medicine.
He had particular interest in types of body
movements. Galen considered muscle tone
as belonging to the fourth type of movement
in which static resistance is generated; an
example being a shield held against a
striking sword (Galen). Such description of
muscle tone generated in static resistance is
more accurately described as an action,
produced by muscle co-contraction and
controlled by the nervous system
Tone and tonus [G. tonos, tone, or a tone]
are general terms which have been used for
multiple meanings since antiquity, and often
interchangeably. For instance, 100 years
ago, Fraenkel and Collins (1903) outlined
two uses. The first was a histological
application describing the general state of
the tissues, such as vascular tone, nerve
tone, skin tone, general tone etc. Their
second use exclusively applied to muscle
tonus. They described it, ‘to represent the
result of a purely neural phenomena.’ This
neural focus of muscle tone was intensified
by the extensive experimental work of
Sherrington’s group (1906, 1915, 1919, &
1947; Denny-Brown, 1929a,b).
Muscle tone has received considerable
neurophysiological attention over the years,
but it has mainly been viewed as a
manifestation of stretch reflex neuromotor
control (Denny-Brown, 1929a,b; Walsh,
1992; Simons & Mense, 1998). Relatively
little research has been done on resting
muscle tone. In the early 20th century, Sir
Charles Sherrington (1852 – 1952)
investigated decorticated and spinal-
transected experimental specimens, rather
than intact animals or humans. In his early
work, Sherrington (1906) suggested a role
for skeletal muscle reflex tonus in
maintaining postural attitude. Later (1915),
he wrote ‘a fairly literal meaning attaching
to the term 'tonus' is, of course, mechanical
tension. In this sense it fits well the slight,
steady, enduring tension so characteristic of
muscles in their state of reflex tonicity.’
Sherrington concluded that muscle tone
resulted from reflex neurogenic mechanisms
(Sherrington, 1919 & 1947), based upon his
models which interrupted central inhibitory
pathways of muscle contraction. Post-
surgical recovery, the animals displayed
generally exaggerated neurogenic reflexes.
Stretch reflex mechanisms were overly-
generalized as the cause of all muscle tonus
(Walsh, 1992; Simons & Mense, 1998).
Diligent review of Sherrington's writings did
not reveal a statement referencing the role of
passive (non-reflex), mechanical,
viscoelastic tonicity of skeletal muscle. Even today, Sherrington’s experiments have
promulgated the common belief that neurogenic reflex mechanisms are responsible for all forms
of muscle tone, including resistance to slow passive stretch in fully relaxed normal persons.
Many modern textbooks still consider muscle tone as entirely reflex in origin and resulting from
a myotatic (a stretching) reflex in the muscle spindles.
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