The Torque: “Torque is a measure of

The
elbow joint is a formed at the upper and lower arm of the body.

It
connects the humerus to radius and ulna. Elbow joint is classified as hinge
joint.

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There
are three joints made at the elbow.

·      Humeroulnar joint:
movements allowed at this joint is elbow flexion and extension.

·      Humeroradial
joint: it is involved in elbow flexion and extension but also in supination and
pronation of forearm.

·      Proximal
radioulnar joint: it also allows supination and pronation at forearm.

The elbow joint allows flexion, extension,
supination and pronation of forearm.

 

Flexion: The muscle involved in flexion are
biceps brachii, brachialis and brachioradialis.

Extension: the muscles
responsible for elbow extensions are triceps brachii and anconeus.

Supination: The supinator muscle
and biceps brachii are involved in supination.

Pronation: pronator teres
and pronator quadratus are involved in pronation of forearm.

During
the biceps curl exercise the elbow flexors muscles are contracted isometrically
while the elbow extensors i.e. triceps muscles are working eccentrically. The
joint ROM ranges from 0-180 degrees.

Torque:

“Torque is a measure of how much a force acting on an object causes that
object to rotate”.

It is a vector quantity and its direction depends on force axes.

                              (n.m)

The sum of all torque is net torque
and its unit is newton-meter.

It
is dependent upon how much force is applied, angle of force application and
moment arm length. The
moment arm length alters with the change in joint angle but they are also
dependent upon the length of the muscle.(Vigotsky, Contreras, & Beardsley, 2015)

 

                                            

Torque in human body:

Torque
is the basic principle in human body movements. Skeletal muscles generate
forces to control the movements of body parts which in turn produce torque. In
human body a single joint is crossed over by multiple muscles which in turn
allows movements at that joint.

It is
important to know the contribution of each single muscle across joint where
several muscles are acting. This means how much the individual muscle is
engaging in producing that particular movement. The contribution of each muscle
for producing a torque depends on some other factors like the muscle fiber
length, mechanical advantage of muscle(van Zuylen, van Velzen, & Denier van der Gon, 1988).

 

Joint torques:

In
orthopedics, the joint torques are of primary importance for clinicians to
determine the surgical effects on symmetry and comfort and to get signs of
functional ability for movements. Joint torques are mostly examined in patients
with osteoarthritis or scoliosis.

For example,
the insertion of brachioradialis muscle producing torques at elbow joint are
particularly significant for surgeons performing surgical procedures like IF,
OR of radial fractures.

In
stroke patients, the torque produced is a sign of functional capacity to do
elbow movements and in rehabilitation setting strength is being analyzed with
the help of maximal torque obtained at a joint. (Ballaz, Raison, Detrembleur, Gaudet, & Lemay, 2016).

 

 

Biomechanical model:

 

A
biomechanical model was developed by Zuylen et al to calculate the flexion
torques at the elbow joint from the mechanical advantage and length of muscle,
and how much force is required by all three muscles to produce torque.

The
moment arm of a flexor muscle is typically lengthiest at middle positions of
the elbow ROM, and shorter at the ends of the ROM.(Hasan
& Enoka, 1985)

 

 

 

 

 

Fig.2.

(a) mechanical advantage (b) Length of contractile part of muscles.

For bicep muscle:

The
maximum moment arm or mechanical advantage for bicep was obtained at 80-90
degrees and mechanical advantage is minimum when the joint is in full
extension. The bicep muscle has a longer moment arm than the brachialis, so it
gives a better mechanical advantage.

 

Brachialis muscle:

The
precise evaluation of mechanical advantage of brachialis muscle is little
complicated as the muscle fibers of this muscle are different in length. The
data presented in a graph is given for fiber length of 100mm.

The
maximum mechanical advantage obtained at an elbow angle of 60 – 80 degrees
where the brachialis has a small moment arm, so it gives the lowest mechanical
advantage for the three muscles. Like the biceps, the length of the contractile
part of muscle is smallest at when the elbow is in full flexion.

 

Brachioradialis Muscle:

Brachioradialis
gives the largest mechanical advantage in elbow flexor muscle with in
75-90-degree elbow angle because of its longest moment arm and when the joint
is in full extension the length of contractile part of the muscle is maximum.

Length Tension Relationship.

The
length tension relationship shows how much force is exerted by the muscles
depends upon the fiber length of the muscles. The length tension relationship
is described with the help of two mechanisms.

1.    Active length tension
relationship shows the amount of overlapping of actin myosin filaments of
sarcomere during contraction.

2.    Passive length tension
relationship.

This refers to all elastic elements in a sarcomere that
stretch and generate tension with the increase length.

 

Muscles force:

In
order to calculate how much torque is produced by muscles it is important to
find out the force generated by these muscle at elbow angles.

 

 

This
graph shows how the force changes at different elbow angles.

The
maximum force produced by elbow flexion is about 1000-1100 N.

The
brachial generated the max force at a120-140 degrees, the bicep and
brachioradialis also contributed in elbow flexion but to lower extent.

 

Angle of peak torque:

The
joint angle where the maximum force is generated is called angle of peak
torque. In angle torque relationship, the maximum torque is always generated
when the force is applied at 90-degree angle.

The
torque is dependent upon various factors.

·      Length of moment arm

·      Muscle fiber length

·      Muscle cross sectional area

·      Tendon and muscle stiffness.

·      Neural drive.       

·      Fig 4 shows how
the torque is changing at different angles in all three elbow flexors.

·      When the joint is
in full extension the torque of all three muscles were 0 and it started to
decline also when the joint was fully flexed minimum torque was obtained. The
maximum torque produced by the muscles at 90-100 degree of elbow angle. The
brachialis muscle generated the maximum torque in bicep curl exercise at
90-degree angle and bicep muscle also contributed in producing torque at the
same angle.

·      In fact, they are
responsible for 66% of the total torque produced at an angle of 90 degree.(van Zuylen et al., 1988). The brachioradialis produced a
lower torque because of its insertion is away from elbow joint.

·     
                                   

·      Conclusion:

·      Torques are
generated to allow biomechanical movements of the body. In order to get the
maximal strength of the muscle, it is important to get maximum torque a muscle
can produce. The greater the torque produced by a muscle the increase movement will
be obtained at a joint. From the above biomechanical model, it is seen that the
greatest torque is generated by elbow flexors when the angle is 90 degrees also
moment arm was longest at 90-degree angle.

·      These both factors
in turn generated a large amount of force at 90 degrees.

·      To improve the
strength in bicep muscle, a weight must be lifted at 90-degree angle because
greater force will be generated along with the longest moment arm achieved.

·     
Moment
arm is the perpendicular distance between the rotational axis and the line of
action of force”.

·     
The
equation used to calculate moment arm in model is

·       

·       

·     
Length tension
relationship:

·     
The
length tension relationship shows that muscles have an ideal optimal length at
which maximum force is produced. When the joint is in full extension the length
of sarcomere is long due to which the actin myosin is unable to form bridge and
no muscle tension is generated.

·     
When
the joint in full flexion the actin myosin overlaps each other and unable to
generate maximum force

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