Flexibility: components, proprioceptive mechanisms and methods

Abstract

Flexibility: components, proprioceptive mechanisms and methods
A literature review on physical flexibility was presented and discussed. This included definitions and components that influence the performance of movements requiring large joint motion ranges and muscle elasticity. Flexibility was discussed with reference to specific age groups, e.g. children and the elderly. Proprioceptive mechanisms and components directly related to flexibility were overviewed, as well as suitable approaches towards flexibilisation, i.e. maintaining and/or enhancing flexibility.

Full text

Invited Paper.. Biomedical Human Kinetics, 3, 39 – 43, 2011
DOI: 10.2478/v10101-011-0009-2
Flexibility: components, proprioceptive mechanisms and methods
Estélio H.M. Dantas 1, Rejane Daoud 1, Alexis Trott 2, Rudy J. Nodari Jr. 3, Mario C.S.C. Conceição 1
1 Human Motricity Biosciences Laboratory (LABIMH), Federal University of the State of Rio de Janeiro (UNIRIO),
RJ; 2 Laboratory of Molecular Aspects Associated to Genetic Diseases, University of Western Santa Catarina
(UNOESC), SC; 3 Laboratory of Prognostic Aspects of Intervention and Care in Health and Human Perform-
ance, UNOESC, SC, Brazil
Summary
A literature review on physical flexibility was presented and discussed. This included definitions and components
that influence the performance of movements requiring large joint motion ranges and muscle elasticity. Flexibility
was discussed with reference to specific age groups, e.g. children and the elderly. Proprioceptive mechanisms an
d
components directly related to flexibility were overviewed, as well as suitable approaches towards flexibilisation,
i.e. maintaining and/or enhancing flexibility.
Key words: Flexibility – Stretching – Flexibilising
Introduction
Flexibility is an important component of physical ap-
titude. According to the American College of Sports Medi-
cine [16], it is one of the essential qualities for acquiring
and developing human physical conditioning. An im-
proved flexibility brings certain benefits, e.g. reduced
risk of injuries and enhanced athletic performance [15].
For these and other reasons, flexibility becomes increas-
ingly incorporated into physical activity prescription
programmes. This prompted us to review the available
literature on flexibility and to dispel common miscon-
ceptions frequently associated with this physical quality.
Definition and Limits of Flexibility
Flexibility was defined by Dantas [8] as ‘physical
feature responsible for the voluntary execution of maxi-
mum joint range of motion, by a single or multiple joints,
within morphological limits, without a risk of injury’.
Thus, good flexibility may result in significant benefits
for both athletes and non-athletes. However, unlike other
physical features, it is better not to strive for maximum
flexibility, but rather to attain the “optimal limit”, i.e.
only that needed for good performance of given move-
ment. An excessive flexibility may fail to protect the
joints, thus causing injuries like permanent sprains, lig-
ament laxity, etc. [9]. In extreme cases, joints may be
damaged to the point where tendons become torn, with
serious consequences for the organism [19]. Thus, it is
just as much of a problem having an excessive flexibil-
ity which increases the risk of diminished joint stability
and leading to sprains, as it is to have insufficient flexi-
bility which may lead to muscle strains [9]. Flexibility
cannot be considered a general characteristic, since it
may be joint-specific. For example, individuals might
exhibit good flexibility in the shoulder complex, but not
be as flexible in the hip joint. For this reason, improving
overall flexibility could result in important benefits for
the organism [19].
Stretching promotes muscle relaxation, defined as
suspension of muscle tension. Muscle tension may also
increase blood pressure and hinder muscle irrigation,
leading to diminished oxygenation and nutrient supply.
This compromises the removal of elements resulting
from muscle work, which increases the amount of toxic
residues accumulated in cells and predisposes muscles
to fatigue and pain [18].
A contracted muscle also spends energy needlessly.
If constantly contracted, it becomes shortened, less flexi-
ble and more vulnerable to injuries caused by sudden
movements requiring greater range of motion [2]. Muscle
contraction can be voluntary or involuntary and painful, as
in cramps. These are generally of neural, not muscular
Author’s address Prof. Estélio H.M. Dantas, Human Motricity Biosciences Laboratory (LABIMH), Federal University of the
State of Rio de Janeiro (UNIRIO) – RJ, Brazil estelio@cobrase.org.br
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40 E.H.M. Dantas et al.
origin, initiating when a muscle is in a shortened posi-
tion and contracts even more. Cramps disappear when
the affected muscle is passively stretched or when its
antagonist is contracted. This technique is used in pro-
prioceptive neuromuscular facilitation methods, due to
stimulation of the Golgi tendon organ [11].
Flexibility is applicable at every age, provided the
physiological transformations at given age are observed,
especially in children and in the elderly [7]. Since chil-
dren are in the longitudinal growth phase, their bones and
soft tissues do not grow at the same rate. Bones may grow
more rapidly than muscles and their conjunctive tissues,
thereby increasing muscle tension. At certain stages of
development, conjunctive tissue may exceed bone growth,
causing hypermobility and leaving the joint vulnerable
to sprains.
According to Weineck [27], mobility training at early
school age must be undertaken very carefully; he stated
that ‘Contradictory tendencies can be identified during
mobility development in this age group. On one hand,
flexion capacity of the hip and shoulder joint, as well as
the spine shows highest mobility at 8 – 9 years of age.
On the other, a decrease is observed in capacity to ex-
tend the legs apart at the hip joint and dorsally directed
mobility in the shoulder joint.’ ([27] p.277). He further
reported that muscles and ligaments do not accompany
accelerated bone growth at the onset of adolescence
because of rapid height growth and reduced mechanical
strength in the passive locomotor apparatus. His conclu-
sion was: ‘Care must be taken to ensure a balanced re-
lationship between load and the capacity to support them,
avoiding exercises performed with partners, unilateral
and twisting movements, as well as torso hyperflexion
and hyperextension.’
A study conducted by Farinatti et al. [10] on 487 boys
and 414 girls aged 5 – 15 years by using the flexitest,
revealed that younger children exhibited more flexibility
than the older ones due to greater articular mobility since
their ligaments and joints were not completely developed.
Advancing age causes an increase in ultimate tensile
strength in these structures and a gradual decrease in
flexibility potential. The authors report that intrinsic and
extrinsic factors act together.
With respect to ageing, the joint motion ranges de-
crease due to enriched connective tissue (tendons and
ligaments) and reduced muscle fibre elasticity. Reduced
mobility may contribute to lower range of motion and
pathologies related to the osteomuscular system, more
common in the elderly. Functional decline occurs with
the participation of various systems, leading to e.g. sen-
sory and motor control losses. Weineck ([27], p.328)
stated that during the ageing process ‘Alterations in active
and passive locomotor apparatuses, cardiocirculatory
and cardiopulmonary systems are mainly responsible
for decreased physical performance capacity.’ Many of
these disorders are irreversible, although physical activ-
ity may partially restore functional skills and psycho-
logical capacity of the elderly.
Dantas ([8], p. 204) studied the ageing-related reduc-
tion of flexibility and found that muscle elasticity and
joint mobility losses contributed to 54 and 46%, respec-
tively, of that reduction. Ueno et al. [24] applied a physi-
cal capacity development programme, including stretch-
ing sessions, to 13 men and 25 women aged 60 years or
more, with the aim of improving performance of daily
activities. At the end of the programme, the participants
experienced less pain, as well as enhanced quality and
improved performance of daily movements.
Pereira [7] compared two age groups (31 – 45 and
61 – 75 years) with respect to 10 joint movements meas-
ured by goniometry and found that cervical spine rotation
and hip flexion showed greatest losses of motion ranges.
Applying stretching adequate for the elderly might con-
tribute to preventing or minimising ageing effects, pro-
vided the exercises correctly and safely adjusted indi-
vidually.
Factors Influencing Flexibility
The major problem with the study of flexibility is its
extreme complexity, largely due to the diversity of inter-
vening components. Four factors are primarily respon-
sible for the degree of joint flexibility: mobility, elastic-
ity, plasticity and pliability [8].
Joint mobility is the degree of joint movement, ac-
counting for 47% of flexibility resistance. Elasticity re-
fers to the stretching of muscle components, contribut-
ing to 41% of flexibility resistance. Plasticity refers to
the level of plastic component deformation during flexi-
bility exercises, its residual post-exercise deformation
being called hysteresis. Pliability refers to skin changes
in the segment required for the movement. Resistance
flexibility accounts for only 2%.
Proprioception Mechanisms
The locomotor apparatus is not the only factor influ-
encing flexibility. Controlling the range of motion and
muscle tension, and limiting the arc of joint motion,
aimed at preventing injuries, is mostly due to the action
of the nervous system. Proprioception in this system may
be associated with joints or muscles [12].
Joint proprioceptors are formed by Pacinian and Ruf-
fini corpuscles. Their function is to provide joint position
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Flexibility 41
sense, velocity of movement and information on resis-
tance that opposes the movement. Several different types
of sensitive receptors are found in the joint capsules and
ligaments [11]. Muscle proprioceptors are formed by the
muscle spindle and the Golgi tendon organ (GTO). The
muscle spindle is located in muscle fibre. When a mus-
cle is stretched, the central portion of the muscle spindle
called the nuclear bag accompanies the movement and
is pulled back, activating the sensitive terminals called
annulospiral endings. These send impulses to the medulla,
where synapses are made with α-motoneurons. After
stimulation, they send commands to contract extrafusal
fibres (myotatic reflex) [13].
The Golgi tendon organ is located near the insertion
point of muscle fibre in the tendon. On average, 10 to 15
muscle fibres are connected in a direct line to each GTO,
which responds to the tension produced by the bundle of
muscle fibres. Nerve impulses discharged by the GTO
are transmitted by fast conducting afferent axons to the
spinal medulla and cerebellum. Upon reaching the me-
dulla, those impulses excite inhibitory interneurons that
secrete an inhibitory neuromediator, γ-aminobutyric
acid (GABA). This acts on α-motoneurons, provoking
muscle relaxation.
Components of Flexibility
Flexibility performance depends directly on different
structures. Joints are formed by one or more bones, and
movable joints are the most important for flexibility. Liga-
ments are another important structure that influences
flexibility. These are strong fibrous cords of connective
tissue, flexible but inelastic, which connect two bones.
Their primary function is to sustain a joint. Ligaments
are composed of bundles of collagen fibres placed paral-
lel or intertwined around each other; they are pliable and
flexible, offering freedom of movement, but strong and
inextensible enough not to yield to the applied forces.
The joint capsule and ligaments account for 47% of the
total resistance to movement [2].
Tendons are formed by fibrous tissue responsible for
connecting a muscle to bone. They are practically inex-
tensible, offering approximately 10% of total resistance
to movement. Their main function is to transmit muscle
tension to the bones, thereby producing movement. This
structure is composed mainly of firmly compressed par-
allel collagen fascicles of varying length and width [2].
Muscles are an essential component of flexibility
owing to their elastic properties. They are active organs
composed of fibre bundles that bring about voluntary
and involuntary movement because of their contracting
capacity, thus being the principal structure in flexibility
performance [3]. Muscle fibres are covered by membrane
(sarcolemma), overlaid by conjunctive tissue (endomys-
ium). The sarcolemma contains contractile proteins, en-
zymes, food substrates, nuclei, organelles and the sarco-
plasmic reticulum, where the muscle contraction proc-
ess initiates [20]. Muscle fibre clusters form bundles
(fascicles) surrounded by perimysium. A set of fascicles
is covered by a sheath (epimysium), forming a muscle
[20]. Fibres at muscle endings become increasingly scarce
and the conjunctive tissue layers that surround the mus-
cles begin to compact, forming tendons, which insert
themselves into the bones. The functional unit of a mus-
cle is the sarcomere, composed of myofilaments of actin
(thin) and myosin (thick), bordered by the Z-line. Each
sarcomere contains approximately 450 thick filaments at
the centre and 900 thin filaments at the ends. Several
sarcomeres form the myofibril, filaments that slide over
each other causing muscle contraction [1].
The two previously described filaments are inexten-
sible and only participate in muscle contraction, without
changing their length during sarcomere extension. How-
ever, recent studies [14,20,21,23] revealed a third fila-
ment, thinner than actin, called titin, which takes part in
the extension of a smaller functional muscle unit. The
thick filament (myosin) is connected to both ends of the
Z-line via titin, responsible for increased sarcomere length.
The length of this filament is what determines the amount
of sarcomere stretching. According to Trinick and Tskhov-
rebora [23], titin molecule resembles a chain and con-
sists mainly of immunoglobulin and fibronectin. It forms
a connection between the Z-line and A-band and is the
third type of sarcomeric filament. Titin is responsible
for muscle constitution and elasticity, thus being an im-
portant component in muscle stretching due to unfold-
ing inside sarcomeres, the smaller functional units of a
muscle [20].
From a mechanical point of view, the locomotor ap-
paratus can be divided into elastic, plastic and inexten-
sible components. During stretching, elastic and plastic
muscle components are deformed, since the inextensible
ones do not undergo significant deformation. Elastic com-
ponents formed by conjunctive tissue and myofilaments
are those that return to their original form after muscle
relaxation. Conjunctive tissue, because of its disposition
both in series and parallel, provokes participation of
parallel elastic components (PEC) surrounding both the
sarcolemma/endomysium and fascicles (perimysium),
and series elastic components (SEC) [25]. Plastic com-
ponents, composed of mitochondria, reticulum, the tu-
bular system, ligaments and intervertebral discs, do not
return to their original form after stretching. Inextensible
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42 E.H.M. Dantas et al.
components are made up of the bones (totally inexten-
sible) and tendons (partially inextensible). Tendons are
not affected by training; ligaments, however adapt to
stretching, since they do not return to their original form
as elastic components do. Therefore, a ligament that is
constantly injured may become loose and not perform
its functional role.
Types of flexibility: There are four types of flexibility:
static, dynamic, ballistic and controlled. Static flexibility
occurs when the individual maintains a position, moving
the segment slowly and gradually until the maximum
articular arc has been reached. This type of flexibility is
most frequently used to evaluate flexibility. It is charac-
terised by the maximum range of motion attained during
movement execution and is used extensively in physical
education practices. Ballistic flexibility forces the limb
into an extended range of motion when the muscle is not
relaxed enough to enter it. It involves fast bouncing move-
ments and is widely used by ballerinas and gymnasts.
Stretching vs. flexibilising: Specific methods are used
to improve joint mobility and increasingly extend mus-
cle fibres within physiologically feasible levels. How-
ever, if the objective is to maintain flexibility, the most
widely indicated methodology uses muscle stretching
with normal joint range of motion. This is a sub-maximal
exercise aimed at maintaining flexibility obtained and
performing normal range of motion with the least amount
of physical restriction possible [5]. On the other hand, if
the goal is an enhanced flexibility (greater joint range of
motion arc), muscle elasticity and joint range of motion
must extend to their maximum limits. This is achieved
by flexibilising exercises [6].
Since stretching involves low intensity demands on
flexibility components, it does not activate propriocep-
tion mechanisms. However, flexibilising constantly ex-
cites these mechanisms depending on the velocity of the
movement. In compensation, stretching almost totally
deforms plastic components. Quick movements stimu-
late muscle spindle, triggering the myotatic reflex and
calling for muscle contraction. Slow and gradual muscle
flexibilising activates the Golgi tendon organ, leading to
muscle relaxation. Dynamic stretching, therefore, acts
primarily on muscles, whereas static stretching has a
greater effect on joint mobility.
Because of proprioceptor mechanisms, stretching and
flexibilising must be applied according to the desired
objective. If a response is required immediately after
flexibility exercises, as in athletic competitions, stretch-
ing should be used only to prepare joint and muscle plas-
tic components for the activity to be performed immedi-
ately. When the aim is to enhance flexibility, i.e. to ac-
quire chronic deformation in plastic and muscle compo-
nents, flexibilising should be used in specific sessions.
Flexibility Training Methods
As mentioned earlier, flexibility can be shaped using
two processes: stretching and flexibilising by applying a
variety of techniques. Stretching can be applied as elon-
gation, suspension or release. Elongation aims at de-
forming the plastic components using movements with-
in the normal joint arc. The suspension technique uses
the action of gravity to stretch ligaments and muscles.
Their objective is to eliminate various catabolites fol-
lowing muscle contraction. Release consists of balanc-
ing limbs or muscles, resulting in muscle relaxation and
muscle spindle deactivation.
Flexibilising can be applied by different approaches,
like active, passive or proprioceptive neuromuscular
facilitation (PNF) [4]. The active method uses dynamic
(ballistic) speed exercises, reaching maximum range of
motion, that activates the muscle spindle and provokes a
myotactic reflex. This method emphasises muscle elas-
ticity and increases long-term flexibility levels. The pas-
sive method or static flexibilising aims at slowly, stead-
ily reaching the largest range of joint motion and main-
taining the position for 10 – 15 s, repeating the routine 3
to 6 times with a decontracting interval [6,22,26]. This
technique emphasises joint mobility and activates the
Golgi tendon organ, resulting in muscle relaxation, that
does not require excessive muscle contractions immedi-
ately after its application and risk compromising joint
components.
The Proprioceptive neuromuscular facilitation relies
on the muscle spindle and Golgi tendon organ and its
antagonist to obtain greater range of motion. Among the
most commonly used techniques are Scientific Stretch-
ing for Sports-3S processes – hold-relax, contract-relax-
antagonist and the slow-reversal one.
Concluding Remarks
This review aimed at emphasising the complexity
and multifaceted nature of flexibility. Further studies are
needed on this physical feature, so important for all those
engaged in motor activities, i.e. both athletes and non-
athletes. The steadily increasing sedentariness contrib-
utes to the inactivity-related diseases apart from decreas-
ing the joint ranges of motion.
It is reassuring for professionals involved in flexibil-
ity training to know that young athletes will not be ad-
versely affected, at least in the spine, as demonstrated
by Raty et al. [17]. Flexibility has to be included in all
training programmes, irrespectively of their objectives,
since its importance for children, adolescents, adults and
the elderly is undoubted.
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Flexibility 43
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Received 12.04.2011
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