Isometric Muscle Contraction

Muscle contractions carried out by the central nervous system occurs due to conscious effort spearheading in the brain. The brain sends signals to the motor neuron via the nervous system to activate the muscles. The motor neurons innervates the muscle fibers by generating tension via the cross-bridging of muscle fibers called actin and myosin. Even though the word 'contraction' implies shortening, in the case of muscle contraction, we are actually referring to the tension generated by the muscle fibers in response to the motor neurons. Muscle contractions occurring in the body can be classified in four categories: isotonic, eccentric, isometric and isokinetic.

What is Isometric Contraction?

Isometric contraction of muscle is that type of contraction in which the muscle is activated, however, instead of shortening or lengthening, the muscle is allowed to remain at constant length. Thus, in simple terms isometric contractions are contractions in which muscle activity is held at fixed length. There is no movement at the joint when isometric muscle contraction takes place. However, even if there is no muscle length change or movement at the joint, the muscle fibers still fire. The force generated during an isometric contraction is completely dependent on the length of the muscle contracting. This isometric contraction is also known as static contraction.

Example of Isometric Contractions

Carrying a Heavy Object

The best and most common example used to explain isometric contraction is carrying an object in front of you. While carrying the object and walking, the weight of the carried object will be acting downwards, while your hands will be acting in the opposite direction. The upward pressure exerted by the hands equals the downward pressure exerted by the object and you are able to carry the object to the required destination. At this stage, the biceps in your arms are isometrically contracting and prevent the arms from not rising or lowering their position.

Gripping a Tennis Racket

Another example of isometric contractions is when we grip a tennis racket. During this action, the joints of the hand do not move, however, the muscle contracts to provide enough force that enables the hand to hold on to the racket. The force produced as a result of isometric contraction, actually depends on the length of muscle involved at the point of contraction. The maximum isometric force that a muscle can produce will depend on each muscle's optimum length.

Isometric Contraction Exercises

Isometric exercises are a type of strength training, used by several bodybuilders. In these exercises, the joint angle and muscle length remain unchanged and the best part about these exercises is that they can be used for general as well as rehabilitation strengthening, without stressing out the joints of the body. Isometric exercises help us develop static strength required to pull or push heavy objects. Besides, these exercises are easy to do and can be done anywhere without the need for expensive exercise equipment.

However, the popular notion that isometric exercises increase muscular endurance is not true! Isometric exercises increase static strength, only in the angle at which the exercise is carried out. Isometric contraction and blood pressure are also related and cannot be ignored for important reasons. During the exercise, blood flow to the muscle stops, blood pressure rises and less blood flows back to the heart. This can conduce to dangerous situations for those with heart problems.

Isometric muscle contractions are part of our daily activities, though we rarely seem to recognize them. Right from holding a bag of groceries to holding a pile of books, etc. all involve isometric contractions. So, the next time you lift an object in front of you, you know what forces are acting!