The Sliding Filament Theory How does a muscle contract

The Sliding Filament Theory: How does a muscle contract?

This blog will teach you all about sliding filament theory and muscle contractions in preparation for your Level 3 Anatomy exam.

You’ll discover:

  • Why FitPros find the sliding filament theory hard to revise
  • 6min Video Tutorial to all about muscle contractions
  • What is a sarcomere?
  • How does a muscle contract?
  • What is the sliding filament theory?
  • How to learn with simplicity for the rest of the modules
  • Three Example Mock Question about the sliding filament theory and muscle contractions

Why FitPros find the sliding filament theory so hard to revise

The sliding filament theory and muscle contractions are notoriously claimed to be one of the hardest modules within the Level 3 Anatomy and Physiology syllabus, so you are not alone if you find this area difficult to understand.

Although we can see and feel our muscles move, it is hard to picture that this is not just a solid lump of muscle, but in fact, is made up of tiny striations and microscopic protein filaments.

Although you might not be quoting the sliding filament to your clients, the knowledge of this is foundational and absolutely crucial.

It allows us to understand the demand and stress we place on the muscles during exercise and to understand what is happening on every contraction.

What is the sliding filament theory: Six mins Video Tutorial

Anatomy and Physiology Level 3 - Understanding muscle contractions

What is a Sarcomere?

To understand muscle structure and contraction, we first need to step away from muscles in order to understand it a little better.

Picture an Accordion Musical Instrument. It expands and contracts, folding onto itself. This is like a sarcomere.

A sarcomere expands and contracts as the myofilaments cross over each other.

Now imagine lots of these accordions all end on end… And they all contract and expand at the same time, like a band in unison.

One line of these accordions is like our muscle fibres, sometimes called myofibrils… which is made up of sarcomeres stacked end upon end.

When the muscle fibre is told to contract, all of the sarcomeres start to shorten in length, making a significant difference in length of the muscle.

This is our muscle contracting.

How does a muscle contract?

The Sarcomere contains myofilaments, which are small contractile proteins.

Actin is the Thin myofilament and

Myosin is the Fat myofilament with the golf club heads.

These two myofilaments connect at cross bridges and pull together. This is a concentric contraction, with the muscle getting shorter.

They can also lengthen under contraction which is an eccentric contraction.

What is the sliding filament theory?

The Actin and Myosin are the smallest parts, they interact to change the length of the muscle.

The Sarcomere is made up of the actin and the myosin.

A muscle fibre, or myofibril, is made up of multiple sarcomeres end on end

A Fascicle is a bundle of muscle fibres

A Muscle belly is a bundle of fascicles.

Essentially it is a Russian dolls approach… they all stack inside of each other, which is a smart way to get as many sarcomeres as possible in each muscle. This maximizes our ability to contract and change the length of the muscles,

This pulls on the tendon which joins muscle to bone

The tendon pulls on the bone.

The bone moves, creating an angle change in the joint = joint action.

In summary

  • The sliding filament theory explains how a muscle contracts
  • You need to know about sarcomeres, myofilaments, myofibrils, fascicles and all of the connective tissue for your exam
  • That you can learn simply and easily with our video tutorials
  • Here’s what Lydia had to say about the A&P Revision Mastery Bootcamp 👇 👇 👇

I can’t recommend Parallel Coaching enough their learning material is fantastic and definitely was a huge factor in me passing my A&P level 3.


Test your knowledge with today’s mock questions:

[NOTE: The answers are below the 3rd questions]

1.What is the name given to the thin myofilament?
A – Sarcomere
B – Actin
C – Myosin
D – Myofibril

2. What is another name given to a muscle fibre?
A. Myofibril
B. Myofilament
C. Fascicle
D. Actin

3. A sarcomere is made up of which two myofilaments?
A. Two myofibrils
B. Epimysium and Endomysium
C. Actin and Endomysium
D. Actin and Myosin

What’s the CORRECT answer?

Answers to the mock questions are :

Question 1= B, Question 2 = A, Question 3 = D

If you want more mock questions like this, then you can download more Free Mock Questions: DOWNLOAD NOW

Need More Help with your Level 3 Anatomy Revision?

For Trainee FITPROS Taking Their L3 Anatomy & Physiology Exam.

Learn, Revise & Pass Your Level 3 Anatomy & Physiology Exam In Under 10-hours

(Without Having To Spend Hours Revising Or Feeling Overwhelmed)

If you want to get your revision structured, learn everything you need to know, and feel confident on exam day, then click the link below:

Dedicated to More

Hayley “The Sliding Filament Theory” Bergman

Parallel Coaching

P.S. You can also find us on the following platforms:

Instagram: Follow Now
Facebook: Like Our Page
Twitter: Tweet Us
YouTube: Subscribe Here
More Revision Blogs: HERE