Question

Define isometric, concentric, and eccentric muscle contraction using the torque equation.

Answer 1

Muscle contraction is described as the activation within a muscle fibers in a tension generating sites. It can be described based on length and tension. Here, the force or torque can be differentiated as tension or load.

There are mainly 3 types of contraction:-

1. Isometric muscle contraction:-

In this type, muscle actively held at a fixed length. That is, muscle tension changes but the muscle length remains the same.
   Eg:- Carrying an object in front of you. Here the weight of the object will be pulling downwards because of gravitational force, but your arms and hands will be opposing this motion upwards with equal force. Your biceps will be isometrically contracting until you rises or lowers your arm.

The length of the muscle while contracting is fully responsible for the force generated during an isometric contraction. At muscles optimum length, maximal isometric tension (Po) is produced.

2. Concentric Muscle contraction:-

In this type, muscle actively shortens. That is the muscle length shortens.

Eg:- If you want to lift a load which is less than the tetanic tension it can generate, the muscle begins to shorten.

Here the force generated by the muscle is always less than the muscle's Maximum (Po). The contraction velocity increases as the load the muscle is required to lift decreases. This happens until the Maximum contraction velocity ( Vmax) of the muscle reaches.

3.Eccentric muscle contraction:-

In this type the muscle actively lengthens. That is the muscle length lengthens.

Eg:- setting an object down gently( the arm flexors controls the fall of the object).

As load on the muscle increases, the external force on the muscle become greater than the force that the muscle can generate. So it is forced to lengthen the muscle's due to high external load.

Here, we have to note two things:-

a) Relative to the muscle's maximum tetanic tension generating capacity, the absolute tension achieved are very high.( eg:- You will be able to setting down a heavy object than you can lift it )

b) The absolute tension is relatively not dependent on lengthening velocity.