Muscle Contractions

Isotonic Contractions

Isotonic contractions are those which cause the muscle to change length as it contracts causing movement.

There are two types of isotonic contraction: -

Concentric
A concentric contraction is a type of muscle contraction in which the muscles shorten while generating force.

During a concentric contraction, a muscle is stimulated to contract according to the sliding filament mechanism.

This occurs throughout the length of the muscle, generating force at the musculo-tendinous junction, causing the muscle to shorten and changing the angle of the joint.

An example is bending the arm, at the elbow from straight to fully flexed, as when performing a “Biceps Curl” movement, taking the hands from your hips to your shoulder, causing a concentric contraction of the Biceps Brachii muscle – the muscle attachments draw closer together.

Concentric contractions are the most common type of muscle contraction within the body and occur with general movement.

Eccentric
In Eccentric contractions, the muscle develops tension whilst lengthening, to overcome a resistance, i.e. the attachments move further apart. This movement is the opposite of concentric and occurs when the muscle lengthens as it contracts.

Eccentric contractions normally occur as a braking force in opposition to a concentric contraction to protect joints and muscles from injury. Eccentric contractions assist in keeping motions smooth, but can also slow rapid movements such as the hamstring muscles acting eccentrically to the quadriceps muscles when kicking a football.

When eccentric contractions are performed in strength training exercises, they are normally referred to as "negatives", as generally it involves a slow lowering of the resistance / weight – suggested example would be lowering the bar slowly to the chest during a bench press movement.

During a concentric contraction exercise, muscle fibers slide across each other pulling the Z-lines together. During an eccentric exercise contraction, the filaments slide past each other the opposite way.

During eccentric contraction, greater muscle soreness will be caused, increasing the risk of injury, so any such movements such as lowering the weight down slowly in a biceps curl, will increase the muscles strength in an eccentric contraction.

This type of movement should be performed only when the muscles being worked, are both fully warmed up and not exhausted. Never train sore muscles in this manner as they are greater risk of injury. Muscles are approximately 10% stronger during eccentric contractions movements than during concentric contractions)

Recent research is suggesting that less muscle’s fibres be recruited during a maximal eccentric contraction, with fast twitch fibres recruited in preference to slow twitch ones. This is useful information for those requiring fast twitch explosive power.

The advantages of an Isotonic contraction, is that it enables you to train a muscle to your specific sporting / strength requirements, throughout the complete range of movement. The disadvantages are that most strength gains are at the weakest point of the movement.

Isometric Contractions
Isometric contractions occur when the muscle develops tension to overcome a resistance but without any change in length, i.e. the muscle attachments remain the same distance apart.

A number of gymnastic movements, such as the Iron Cross, where the bodies muscles are under considerable strain, yet are fully static in movement, are good examples of isometric contractions.

A more common, everyday example is grip strength, such as holding a bag of shopping. There will be no movement in muscles of the joint of the hand, but yet the static contraction keeps the bag within your hand.

A forth muscle contraction is Isokinetic contractions. This is similar to isotonic in that the muscle changes length during the contraction, however where they differ is that Isokinetic contractions produce movement at a constant speed.