TYPES OF MUSCLE CONTRACTION &

CLASSIFICATION OF EXERCISE

-USNISH ADHIKARI5TH SEMESTER

• Skeletal muscles are the principal executor of exercise.

• Human skeletal muscle can exert maximal contractile force of around 3-4 kg per square cm of cross sectional area.

• The total tension that could be developed if all the muscles in an adult man pulled together is approximately 25 tons.

• Contraction of a skeletal muscle is explained by

the sliding filament mechanism.

TYPES OF MUSCLE CONTRACTION

• Two types of muscle contraction have been observed in skeletal muscles:

A.

B.

A. ISOTONIC CONTRACTION

• Muscle contraction is said to be isotonic when the tension on the muscle remains constant throughout, though the length changes.

• ‘Iso’= same, ‘Tonic’= strength or tension

• Since Work done = Force X Distance moved

work is done in case of isotonic contraction.

• The characteristics of isotonic contraction depends

on the load against which the muscle contracts

as well as the inertia of the load.

Isotonic contraction can be : Concentric contraction:

– Here the muscle actively shortens against constant load.

– Velocity of contraction is inversely proportional to

the load.

Eccentric contraction :– Here, the muscle actively contracts while

lengthening.– Load is much greater than the force which the muscle

can generate. Also negative work is done by muscle.– Muscle is more prone to injury during this type of

contraction.

B. ISOMETRIC CONTRACTION

• Muscle contraction is said to be isometric when the length of the muscle remains constant.

• ‘Iso’=same ‘Metric’= length• Work done = 0 • Muscle is in a state of continuous tetanic contraction.

ISOTONICISOMETRIC

ISOMETRIC

ISOTONIC• Series elastic component stretched . • Elastic components

less stretched.

LOAD-VELOCITY RELATIONSHIP

•Concentric contraction (muscle shortening) occurs when the force of contraction is greater than the resistance (positive work)

•Zero velocity occurs (no change in muscle length) when force of contraction equals resistance (isometric point)

•Eccentric contraction (muscle lengthening) occurs when the force of contraction is less than the resistance (negative work)

Set-up for demonstration of isotonic and isometric contraction

EXERCISE

o What is exercise ? Any state other than rest can be designated as an

exercise.

Therapeutically, exercise is performance of physical exertion for improvement of health or correction of physical deformity.

o The type of exercise should be selected

according to the objective.

CLASSIFICATION OF EXERCISE

Exercise can be classified on the basis of type of muscle contraction and metabolic demands:

Isometric exercise does not mean that all the muscles

involved are in state of isometric contraction;

The metabolic pattern resembles though. Same

in the case of Isotonic exercise.

According to type of muscle contraction

ISOMETRIC EXERCISE

ISOTONIC EXERCISE

According to metabolism

ANAEROBIC EXERCISE

AEROBIC EXERCSE

A. ISOMETRIC EXERCISE

• In this kind of exercise, majority of the muscles are in a metabolic state similar to isometric contraction.

• High degree of tissue tension develops in the muscles, due to which the blood vessels supplying the muscles get occluded. Hence the muscle resorts to ANAEROBIC metabolism.

• These exercises cannot be performed for long

time as lactic acid production leads to ischemic

pain ( Muscle fatigue).

• Isometric exercises lead to increase in the STRENGTH of the muscles. This is achieved by both increase in muscle size and maximal contractile force per unit area.

• Target muscles are those with predominantly

Fast Twitch White fibres like Gastrocnemius.

• Isometric exercises are recommended for: Power Games like sprinting, weight-lifting, boxing,

shot-put etc.

Gain of function of atrophied muscles.

B. ISOTONIC EXERCISE

• In this kind of exercise, majority of the muscles are in a metabolic state similar to isotonic contraction.

• Energy is derived by the muscles through AEROBIC METABOLISM.

• These exercises can be performed for long time at

a stretch.

• Isotonic exercises lead to increase in the

ENDURANCE of muscles ( measured by time till

they can sustain exertion until complete exhaustion)

• Target muscles are those with predominantly

Slow Twitch Red fibers like Soleus.

• Isotonic exercises are recommended for: Endurance games like Marathon running, swimming,

cycling etc.

Cardiovascular prophylaxis.

Relative abundance of different muscle fibres in different persons:

• Hereditary differences have been observed among athletes regarding the relative proportions of Fast and Slow Twitch fibers.

• Athletic training and exercise has not been shown to change the percentage of slow and fast twitch fibers in humans. So some people are born to be sprinters, while others are born to be marathoners.

• However, experiments on mice have shown

varying results in this respect.

The selection of proper exercise should be based on long term objectives to gain the

maximum benefit.