Huxley's Sliding Filament Theory: how muscles contract

The sliding filament theory by Andrew Huxley was first postulated around the early 1950's to describe how muscles contract. This will be a very brief introduction to muscle contractions and what happens when muscle fibers are innervated.

Sliding Filament Theory
It all starts with an action potential that signals the muscle to fire coming from the brain. The action potential signals the release of acetylcholine (a neurotransmitter) to be released at the synaptic cleft along with calcium ions opening up the channel of neurotransmitters to stimulate muscle contraction.

The synaptic cleft is the terminal region where a neuron meets a muscle fiber. From there, calcium ions attach to actin causing what is called cross bridging between actin and myosin. ATP is the compound that powers this cross bridging to happen. From there, actin and myosin overlap eachother causing the muscle to contract.

The sarcomere which is the unit that contains the actin and myosin filaments shortens. There is much more details that go into the science behind muscle contractions. Wanted to give you guys a very brief and quick introduction to the science of muscle contractions which is also known as Huxley's Sliding Filament Theory which was found by Andrew Huxley a biophysicist who won a Nobel Peace prize in 1963.

Coach Cano

3 types of muscle contractions and their application

There are 3 types of muscular contractions. The muscle contractions are Concentric, Eccentric, and Isometric. This article will in brief discuss those contractions and their application to sports performance. Applying practical use of these contractions will help the athlete achieve optimum performance.

Eccentric Muscle Contraction
This type of muscle contraction is also known as the negative contraction. The forces go with the force of gravity in a downward momentum. By moving with the force of gravity potential energy is stored within the movement and then released in the final phase assuming a short amortization phase. Think of the downward movement of a depth jump or the downward movement of a bicep curl. Eccentric contractions are associated with a lengthening of the muscle fibers which causes them to stretch or become longer in length.

Concentric Muscle Contraction
This type of muscle contraction is also known as the positive contraction. The forces produced by the muscles for the most part move against the force of gravity usually in an upward movement. Think about a vertical jump or the upward movement of the bicep curl. Concentric muscle contractions usually cause a shortening of the muscles. The muscle cross bridging come together which causes the muscle to shorten in length.

Isometric Muscle Contraction
This type of muscle contraction is unique in that there is no movement associated with the contraction. There is no velocity associated with this movement thus in physics terms it's a scalar because it still has magnitude. There is still force production within the contraction. An example is a wall squat where you contract using your muscles and push against a wall.

Sports Performance and muscle contractions
Concentric and eccentric muscle contractions are usually employed during sports performance since most sports require movement. Take for example plyometric training. In order to fully utilize the stored elastic energy coming from the eccentric downward movement of the jump the amortization phase of the movement must be as short as possible. If not, dynamic energy will be lost as heat. Another example is the stretch reflex of a squat. The eccentric movement has potential energy that when coming off the bottom of the squat with an extremely short amortization phase will transfer to kinetic energy getting a dynamic boost from the bottom of the squat.

All the best and see you on the platform.

Coach Cap