TYPES OF MUSCLE CONTRACTIONS

PHTH 201PHTH 201

Types of Muscle ContractionsTypes of Muscle Contractions

Isometric contractionIsometric contraction: when the ms. : when the ms. does not shorten during contraction does not shorten during contraction while tension is increasing.while tension is increasing.

Isotonic contractionIsotonic contraction: when the ms. : when the ms. shortens or lengthens while the shortens or lengthens while the tension on the ms. remains tension on the ms. remains constant.constant.

Isotonic Contraction Isometric Contraction

Tension is constant Tension n the ms. Rises markedly

Length is decreased or lengthened Length of the ms. is constant

External work is done No work is done

Mechanical efficiency = 25% Mechanicl efficiency = 0

Long duration Short duration

less energy used/muscle contraction

More energy used/muscle contraction

Contraction occurs when the legs are moved in walking

Contraction occurs during standing to maintain posture against gravity

Types of Isotonic Contractions

2 Types:

Concentric: the muscle shortens, e.g. contraction of the biceps to produce elbow flexion.

Eccentric: muscle lengthen or is stretched while contracting, e.g. lowering a load on the ground.

Tension VariationTension Variation

The tension in the muscle may vary in its length:The tension in the muscle may vary in its length:

Passive tension: tension developed in the ms. length is : tension developed in the ms. length is increased while is not stimulated ( i.e. concentric increased while is not stimulated ( i.e. concentric contraction).contraction).

Total Tension: tension that a ms. develops when stimulated : tension that a ms. develops when stimulated to contract isometrically.This tension also vary with the to contract isometrically.This tension also vary with the change of the initial length.change of the initial length.

Active tension: is the difference between the total tension : is the difference between the total tension and the passive tension at any length( the amount of and the passive tension at any length( the amount of tension) actually generated by the contractile process.tension) actually generated by the contractile process.

Tension Variation (cont.)

Tension increases with an increased length, but overstretch may lead to weakness of the muscle.

Rupture of the muscle occur when it is stretched to about 3 times its equilibrium length of the relaxed muscle cut from its bony attachment.

Types of Skeletal Fibers

1. Slow Oxidative or Type 1 Fibers: In postural ms. as can maintain contractions for long

periods. Produces ATP with high efficiency. Has a large number of mitochondria & mitochondrial

enzymes. Has aerobic energy transfer. Is innervated by small motor neurons that activate

small number of fibers

2. Fast Oxidative or Type II a Fibers: Are moderately resistant to fatigue. Have mytochondrias & considerable amount of

myoglobin. Red fibers. Moderately well developed capacity for aerobic &

anaerobic energy transfer. Intermediate motor neuron, its activities are e.g;

middle distance runnng, swimming,…

Types of Skeletal Fibers (cont.)

Fast Glycolitc or Type IIb Fibers:– Rely on anaerobic glycolysis.

– Become fatigued easily.

– Few mitochondria.

– Little myoglobin → white fibers.

– Specialised in powerful, brief types of contractions.

– Large motor neurons that activate large number of fibers for heavy loads.

– Mixed with other muscle fibers as in limb muscles, eye and finger muscles.

Isometric Exercises

Isometric resistance is a static form of exercise that occur when the muscle contracts without an appreciable change in the length or the muscle or without joint motion.

No physical work is done by the force ( force x distance), but a great amount of tension and force out put are produced.

A muscle can generate greater tension with a max. isometric contraction, but not as much as with a max. eccentric contraction

Isometric Exercises (cont)

i.e.

– Eccentric cont. = max. tension– Isometric cont. = intermediate tension.– Isotonic cont. ( concentric) = minimum

tension.i.e. to start a stregthening program:

– Start by isotonic (concentric) harden by isometric then harden by eccentric .

– If no contraction start by static then follow the same progression.

Rules and Principles of Isometric Exs.

1. Strength will increase if an isometric contraction is sustained against resistance for at least 6 seconds. Isometric resistance exs. will not improve m. endurance as effectively as dynamic exs.

2. During isometric training it is suffiscient to use an exercise load ( resistance) up to 60-80% of th m. force-devloping capacity in order to gain strength.

3. Since there is no joint mov. , strength will devlop only at th position in which the ex. is performed.

4. To develop strength throughout the ROM, resistance must be applied when the jt. is in several positions.

Rules and Principles of Isometric Exs.(cont.)

4.The length of a m. at the time of a contraction directly affects the amount of tension that can be produced at a specific point in the ROM.→ the amount of resistance will vary at different points in the range.

5. Resistance can be applied either manully or mechnically by having the pt. hold against a heavy load or push against an immovble object.

Rules and Principles of Isometric Exs.(cont.)

6. Muscle setting exercises are also a form of isometric exs. but are not performed against apreciable resistance.

a. Muscle setting exercises will be used to describe gentle static muscle contractions used to maintain mobility between muscle fibers and then decrease muscle spasm & pain.

b. Quadriceps settings and gluteal settings are common examples.

c. They are not performed against resistance and will not increase appreciably muscle strength.

d. Settings may retard atrophy in the evry early stage of rehab. of muscle or joint when jt. Immobilization is necessary.

Indications of Isometric contractions

1. Pain ( sever pain in joints e.g. arthritis);

2. Effusion of the knee.( static cont. of the knee).

3. Weakness of the m.( as 1st step in m. reeducation).

4. Immobilization in plaster cast or back splint.

5. Inflammation of the joint ( static contraction around the joint) to avoid weakness during theacute stage.

Practical Points

1. Position: suitable & comfortable.2. Time of contraction equal time of relaxation( not less

than 6 sec.)3. Repetition, teach the pt. on the sound limb, then on the

affected limb to be repeated 10 min. every hour.4. Manual or mechanical ( Velcro weights or elastised

material as Theraband) could be used gradually , beginning with high repetitions and low resistance the reverse.

5. Instruct the pt. not to hold his breath.

Contraindications to Isometric Exs.

1. Hypertension

2. Haert Disease

Isometric Regimens

Brief maximal isometric exercise (Hettinger & Muller): Single isometric cont. of the muscle to be strengthened

against a fixed resistance. Hold for 5 -6 sec. , once a day, 5 – 6 days a week.

Brief Repetitive Isometric Exs. (BRIME): Refinement of the previous study. 5 – 10 brief but max. isometric contactions are performed

against max. isometric contactins are performed against resistance 5 days per week.

Isometric Regimens in Rehabilitation & Conditioning

• Early studies documented that isometric resistance exs. can be effective means of improving muscle strength.

• Minimal effects in muscle endurance→ dynamic

( isotonic& isokinetic) exs. are more effective.• Multiple angle isometric exs. are necessary to improve

strength throughout the ROM.– Resistance should be applied at least every 20°

throughout the range.– 10 sets of 10 repetitions of 10 sec contraction every

10° in the ROM ( Davies).