TYPES OF MUSCLE
CONTRACTIONS
Types of Muscle Contractions

Isometric contraction: when the muscles
does not shorten during contraction
while tension is increasing.

Isotonic contraction: when the muscles
shortens or lengthens while the tension
on the muscles remains 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 Variation

The tension in the muscle may vary in its length:
Passive tension: tension developed in the muscle length is
increased while is not stimulated ( i.e. concentric
contraction).
Total Tension: tension that a muscle develops when
stimulated to contract isometrically.This tension also vary
with the change of the initial length.
Active tension: is the difference between the total tension
and the passive tension at any length( the amount of
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.
ANGLE OF PULL

A muscle is most effective when applied right angles
to the bone/lever.

◦Angle of Pull: angle between muscle insertion and
bone on which it inserts.
Components of force due to angle of pull
Components of force due to angle of pull
>90 degreesincludes stabilizing component
=90 degrees100% rotary force
<90 degreesincludes dislocating component

Mechanical efficiency of muscle:
1.Mechanically , the pull is most efficient when the muscle
is inserted at right angles to the mone.

This efficiency is decreased as the angle of pull is reduced

Example: at knee 90 degrees the muscle efficiency will be
more and At knee 0 degrees extension the efficiency will be
less .

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.
2.
3.
4.
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.
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.
Since there is no joint mov. , strength will devlop only at th
position in which the ex. is performed.
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.
2.
3.
4.
5.
Pain ( sever pain in joints e.g. arthritis);
Effusion of the knee.( static cont. of the knee).
Weakness of the m.( as 1st step in m. reeducation).
Immobilization in plaster cast or back splint.
Inflammation of the joint ( static contraction around the joint)
to avoid weakness during theacute stage.
Contraindications of Isometric contractions
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).