THE PRINCIPLES OF RESISTANCE
An external force may be applied to the body levers to oppose the force of muscular contraction. Tension is increased within the muscles by the opposing force (or resistance) and the muscles respond by an increase in their power and hypertrophy. As the increase in muscular development occurs in response to the increase in intramuscular tension it follows that the application of the maximum resistance which is consistent with the ability of the muscles to overcome it will elicit the maximum development.
The resisting force applied to an isotonic contraction must be sufficient to increase intra-muscular tension to the maximum without interfering with the ability of the muscles to produce co-ordinated movement. A maximum increase in intra-muscular tension during an isometric contraction is elicited by a resistance which equals the muscles ability to maintain the hold.
There are five factors which contribute to the development of muscular efficiency, i.e. power, endurance, volume, speed of contraction and co-ordination. The first three are inter-related and can be built up by the use of resisted exercise.
POWER develops in response to the application of the maximum resistance which is consistent with the ability of the muscles to overcome it, therefore power can be built up when they work against a progressively increasing resistance. As the essential factor in power development is the magnitude of the resistance the method used to promote it is called PREGRESSIVE RESISTANCE-LOW REPETITION EXERCISE, the number of times the movement is repeated being relatively few to allow the resistance to be as great as possible.
ENDURANCE is a quality which develops in response to repetitive contraction, therefore as it is the number of contractions which is the essential factor, the method used in this case is called LOW RESISTANCE-HIGH REPETITION EXERCISE.
VOLUME, which can be observed or measured as an indication of hypertrophy, usually develops in proportion to power. It serves as a means of demonstrating progress to the patient although it is not invariably a reliable indication of successful treatment.
Skill is estimating the capacity of the muscles at every stage of treatment and in matching this with the correct amount of resistance is the keynote to success in the use of resisted exercise.
VARIATIONS OF THE POWER OF MUSCLES IN DIFFERENT PARTS OF THEIR RANGE
Muscles which are capable of producing a considerable range of joint movement are not equally powerful in all parts of their range.
Physiologically, muscles are capable of exerting their greatest strength when they are fully extended, i.e. in outer range, and as they shorten their force diminishes. This, however, is modifided in the case of some muscles by mechanical factors such as the angle of pull of tension of insertion, i.e. the effect of the pull on the lever is greatest when the angle of pull approaches a right angle.
For example; physiologically the flexors of the Elbow are strongest in their outer range, but mechanically stronger at about mid-range. When both these factors are taken into account, and allowance is made for overcoming the initial inertia at the beginning of the movement, it can be roughly estimated that the muscles will be most efficient in the outer part of the middle range. This, in fact, can be proved by experiment.
It seems, however, that the relative importance of these factors varies in different muscle groups but, broadly speaking, each group is found to be most powerful in the part of the range in which it is habitually used, i.e. Shoulder flexors in outer range, hip extensors in inner range. In giving manual resistance these variations in power can be felt and the resistance adjusted according, but other means of providing resistance are not so accurate from this point of view.
TECHNIQUES OF RESISTED EXERCISES
Starting position – comfort and stability for the body as a whole ensures that the patient’s whole attention can be concentrated on the pattern of movement and the effort required to overcome the resistance.
The pattern of movement – this must be well known by the patient and can be taught as passively or a free exercise. The pattern selected should, whenever possible, be one which allows contraction of the muscles in full range and it should be based on a natural pattern of purposeful movement.
Stabilization - stabilization of the bone or bones of origin of the muscles to be resisted improves their efficiency. This stabilization of the rarely static when a natural pattern of movement is used as it is constantly being adapted to the circumstances of the movement. Provided the muscles normally responsible for the stabilization have remained efficient they should be sued for this purpose, as their action is considered to provide reinforcement for the muscles producing the movement. If, however, there is a tendency for movement to be transferred to neighbouring joints so that the pattern of movement is altered, then additional means of fixation such as manual pressure or a strap must be used to ensure movement at the required joints.
Traction – preliminary stretching of the muscles to elicit the myotatic (stretch) reflex provides a powerful stimulus to contraction, and traction maintained throughout the range facilitates joint movement and maintains tension on the muscles and so augments the effect of the resisting force.
The resisting force - a variety of means may be employed to supply the force used to resist the contraction of the working muscles, e.g. manual pressure, weights, springs, etc., but in every case it should be applied in a manner which ensures that pressure is exerted on the surface of the patient’s skin which is in the direction of the movement. The advantage of manual pressure is that it can be adjusted accurately to match the power of the muscles in all circumstances and in every part of the range, but it also has the disadvantage of not being easily measurable. Mechanical resistances are usually measureable and therefore proved a useful means of recording progress.
The magnitude of the resisting force, in relation to that of the muscle power, varies according to the purpose for which it is used. Maximal resistance elicits maximal effort on the part of the muscles and it is therefore used to develop power and hypertrophy. As the quality of muscular endurance is developed by repeated contraction against resistance the latter is considerably less than maximal to allow a greater number of repetitions to make place.
The character of the movement – the movement is essentially smooth and controlled throughout, the effort involved commanding the patient’s full attention. The speed of movement is consistent with the optimum rate of contraction for the particular group of muscles in relation to the resistance which constitutes the load. The range movement is full whenever possible, but resistance cab be applied in any part of the range which is convenient or desirable and the muscles can also be resisted so that they work statically at any particular point in their range.
Repetitions – the number of times the muscles are thrown into action against a resistance varies according to the condition and the individual patient, and it is inadvisable to accept any rule of thumb procedure.
Low resistance-high repetition exercises appear to be more suitable for weak or elderly patients whose muscles are less resilient than those of the young and strong, and they have proved to be effective in such conditions as Osteo-arthritis. High resistance-low repetitions exercises on the other hand undoubtedly build up power and hypertrophy muscles suffering from disuse as the result of traumatic injury or in connection with orthopaedic surgery, e.g. menisectormy, when there is effusion or joint changes are present, as in Rheumatoid arthritis, static resisted contraction of the muscles passing over the joint with a high repetition figure are valuable for retaining muscular efficiency and they can be performed In any part of the range which is pain-free. The number of repetitions may also be determined by the desirability of, or the contraindication to, fatiguing the neuromuscular mechanism in the treatment of a specific condition.
The co-operation of the patient – the effort exerted by the patient and his interest in the treatment undoubtedly play and important part in the development of his muscles by means of resisted exercise. Interest is stimulated by precision in applying the resistance, regular measurement and recording of progress, verbal encouragement and, in suitable cases, by competition.
RESISTANCE
A resistance force other that provided by gravity and friction may be provided by:
- The physiotherapist
- The patient
- Weights
- Weight and pulley circuits
- Springs and other elastic structures
- Substances which are malleable
- water
RESISTANCE BY THE PHYSIOTHERAPIST
This is usually applied manually in the line of the movement, and the physiotherapist’s hand is placed on the surface of the skin which is in the direction of the movement. To prevent waste of effort and to ensure smooth controlled pressure the physiotherapist’s stance must be in the line of the movement, so that the thrusting action of the legs and the body weight are utilized. Traction or approximation may be maintained throughout the movement and the resistance varied according to the variation in power in different parts of the muscles’s range.
RESISTANCE BY THE PATIENT
The patient can resist his own movements with the sound limb, or by using his own body weight. The latter method is probably more accurately classified as a free exercise, but is included here as the quantity of resistance is obviously much greater when, as in this case, the muscles work with reversed origin and insertion to move the trunk on the limbs. This type of resistance is convenient, but tends to be unreliable as it cannot be measured or felt by the physiotherapist and it requires careful instruction and the co-operation and understanding of the patient.
EXAMPLES – from high sitting the extensors of one knee can be resisted by the weight and pressure of the other leg when the ankles are crossed. The body can be pressed up from the floor by the arms, if their strength is sufficient.
RESISTANCE BY WEIGHT
The direct application of weights to the body forms a simple and effective method of resisting active exercise. The apparatus required is commonly sandbags, metal weights or a medicine ball, which can be applied by being held in the hand, by attachment to a shoe, or to any other part, by suitable straps. When sandbags or metal weights are used, a canvas bag may be strapped to the part and any number of units of weight can be inserted top provide the required resistance. It is essential that the means of attachment should be comfortable and efficient, but it need not be elaborate.
By this method, resistance must, of necessity, be given in the direcxtion of gravity; its effect increases progressively if the weight is moved away from the central axis of the body. It is a convenient method and suitable for home practice after adequate instruction has been giver.
EXAMPLES – Lifting a weight held in the hand or attached to the foot or throwing a medicine ball are common examples.
Resistance by weights is also used for the technique known as “progressive resistance exercise”.
RESISTANCE BY WEIGHT AND PULLEY CIRCUIT
The use of a rope and pulley allows the force exerted by a weight to act in any direction. Therefore the muscles need not be required to work against the resistance of both gravity and the weight. The effect of gravity cab be counterbalanced if the movement takes place in a horizontal plane. This provides a useful method of arranging resistance for weak muscles when the limb is heavy.
EXAMPLE – in sitting the resistance of gravity to the knee extensors is approximately 5kg. if these muscles are unable to straighten the knee against this resistance, they may still be able to perform the exercise adequately when, in side lying, the leg is supported horizontally and resistance of, perhaps, 4kg is appled.
As the angle of pull of the rope by which it is applied. And therefore the resistance itself, must vary during the course of a movement, a resistance can be offered to the muscles which matches the variation of their power in different parts of the range more accurately than that supplied by means of a weight applied directly to the part or by a spring.
Assuming that a particular muscle group is most powerful in midrange it is there that the resistance is applied at right angles. Both the power of the muscles and the force of the resistance will diminish on either side of this point.
To ensure relaxation and lack of strain on the joints between movements a relaxation stop is incorporated on the circuit by means of a clip or knot which prevents the rope from passing the pulley, or by arranging for the weight to be supported at the end of the movement. Psychologically, it is of the greatest importance for the patient to be able to see the weight moving as the result of his work and to know and record the poundage lifted.
RESISTANCE BY SPRINGS AND OTHER ELASTIC SUBSTANCES
The resisting force of a spring increases progressively as it is stretched or compressed according to the type of spring used.
Although convenient to arrange, the use of springs for resisting muscular contraction must be regarded as a somewhat crude method as it is virtually impossible to match their resistance to the capacity of the muscles with regard to both power and range of movement.
When springs are used the speed of movement must be carefully controlled by the muscles both in contraction and during controlled relaxation as the accumulated energy in an extended spring makes its natural speed of recoil very great.
Other sensible materials such as rubber elastic of various widths and thickness behave in a manner similar to that of springs, but they are not so durable. The elastic properties of SORBO RUBBER are apparent on pressure, and rubber sponges, Dunlopillo and rubber balls afford varying resistances which are particularly useful in developing the gripping muscles of the hand.
RESISTANCE BY SUBSTANCES WHICH ARE MALLEABLE
Substances such as putty, clay, some kinds of wax, plasticine and wet sand can be moulded into different shapes. The resistance they offer to this change in form is variable and can be used both for strengthening and for mobilizing the hands.
RESISTANCE BY WATER
As the power of the muscle increases, the resistance must be increased proportionately.
There are four main methods of increasing resistance to muscle action. Each method may be used singly or in combination with any other method:
- Increase in poundage or weight of the resisting force
- Increase in leverage of the resistance force
- Alteration in the speed of movement
- Increases in the duration of the exercise
INCREASE
IN POUNDAGE OR WEIGHT – for example: it is found that a muscle group, able to
achieve full-range contraction against a weight of 2 kg. when it is applied at
a specific point, can contract at a specific speed and for a specific duration.
As the muscle power increases, the weight is increased proportionately to 2.3
kg, 3 kg, or 4 kg., while the other conditions remain constant. The actual
amount of the increase is variable according to the particular muscle group, its
rate of progress to recovery and the frequency at which an increase is made
INCREASE
IN LEVERAGE – the total resistance offered by a given weight depends on the
position of its point of application in relation to the fulcrum. ( moment of
force = weight × perpendicular distance from the fulcrum) the greater the
perpendicular distance of the point of application from the fulcrum, i.e. the
joint at which movement takes place, the greater the resistance offered by the
weight.
EXAMPLE – the effect of a
resistance, which constant, given to the shoulder abductors with the arm
straight, is much greater when applied at the wrist than at the elbow.
ALTERATION
IN THE SPEED OF MOVEMENT –muscular contraction is most efficient when it takes
place at an optimum or natural speed. This speed varies according to the form
and structure of the muscles concerned, the resistance, and the individual.
Increase or decrease in this natural speed of contraction increases the effect of
the resistance the slower the movement the greater the effect of the
resistance, i.e. concentric work is easiest at natural speed, eccentric work at
high speeds.
EXAMPLE – It is easier to climb a
steep hill at your own speed than at one dictated by a companion who may prefer
to go faster or slower than you do, but it is easier to come down rapidly.
INCREASE
IN THE DURATION – As muscles warm up to their task of overcoming a resistance,
they become more efficient and therefore the effect of the resistance decreases
and the exercise seems easier. If, however, it is continued a sufficient number
of times, fatigue reduces the efficiency of the muscles and the resistance
therefore appears greater.
EXAMPLE – Sawing a log of wood
may seem to become easier as you warm up to it, but it becomes hard work by the
end of an hour.
EFFECTS
AND USES OF RESISTED EXERCISES
1.Muscle
power can only be maintained or increased by contraction, and in these
exercises the working muscles are strengthened and hypertrophied in response to
the tension created in them by the resistance. Their power and endurance is
increased.
Resisted exercises are used to
build up weak muscles and so to restore the balance of muscle power which is
essential for stability and co-ordinated movement.
2.The
blood flow to the working muscles is increased in proportion to the amount of
work they are called upon to don thus providing the materials for repair and
hypertrophy.
Although the flow is impeded
during the actual contraction, the amount of blood contained in the muscles
immediately after contraction may be as much as ten times as great during
strenuous exercise as the amount contained during rest.
This increase in the blood flow
to the muscles continues for sometime after exercise, bringing oxygen and
nutrition to the part and assisting the removal of metabolic products.
3.A
general rise in blood pressure frequently anticipates exercise and may be
increased by the mental effort required to perform these exercises correctly
4.Heat,
which is produced as the result of strenuous muscular activity, stimulates the
heat-regulating centre causing vaso-dilatation in the skin. This follows a
constriction of these vessels which occurs in the first place to compensate for
the increase in the blood flow to the muscles. If there has been sufficient
exercise, the skin feels warm and possible moist and appears pink, indicating
that heat is being lost from the surface to balance the gain from muscle
activity and so keep the body temperature within normal limits. The degree of
moisture depends largely on the temperature, humidity and movement of the
atmosphere.
THOSE ABOVE ARE COLLECTED FROM SOME BOOKS AND
WEBSITES..
(The
Principles of Exercise therapy - M. Dena Gardiner)
THANK YOU,
SRIKUMARAN
PHYSIOTHERAPY CLINIC & FITNESS CENTER
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