Biomechanics
Picture A Muscle's Route From One Bone To Another, And It Gets Easy To Predict When It Is Working
From the FASTER syllabus: this article is taught in full in Movement Coach, where muscle function is taught in full →
In short: A muscle starts on one bone, called its origin, and finishes on another, called its insertion. Movement Coach teaches that picturing that route is a great visual that makes it possible to predict when a muscle is in action. Major muscles then take one of four roles: the agonist drives the movement, the antagonist opposes it, synergists assist and fixators steady the other muscles. In a biceps curl the biceps is the agonist, the triceps the antagonist, and muscles around the shoulder and forearm assist and steady. The muscle also contracts three ways in the same curl: concentric on the way up, eccentric on the way down and isometric when held.
The question this answers
A trainer can know which muscle is working in a movement without a textbook open. Movement Coach gives a short route to that. Know the route each muscle takes, then watch the joints.
One muscle, two bones
Every muscle starts on one bone and finishes on another. The start is the origin and the finish is the insertion. The course puts the payoff plainly: being able to picture the muscle and its route from one place to another is a great visual that results in the ability to predict when a muscle is in action.
Take the biceps brachii. One head starts on the shoulder blade, the other head on a point just above the shoulder joint, and it finishes on the radius in the forearm. Picture that line and the job is obvious. When the elbow bends, that line gets shorter.
Four roles a muscle can play
Major muscles take one of four roles in a movement:
- Agonist (prime mover): provides the main force driving the action.
- Antagonist: opposes the agonist. If the agonist produces flexion, the antagonist produces extension.
- Synergist: assists the agonist.
- Fixator: steadies the prime mover and the synergists while the movement happens.
In the course's example of a biceps curl, the biceps is the agonist and lifts the weight. The triceps is the antagonist and lets the movement happen. Muscles around the shoulder and forearm assist and steady.
Three ways the same muscle works
The curl also shows the three contractions:
- Concentric: the muscle shortens. That is the lift.
- Eccentric: the muscle lengthens under control. That is the lowering, and it governs the speed.
- Isometric: the muscle holds without changing length. That is the pause at the top.
One muscle, one exercise, three different jobs. A trainer who sees the movement phase can name what the muscle is doing in it.
Why it works on anything
The curl is one example. The same questions fit a press, a row or a throw: where does the force act, which muscles run against it, which assist, which steady. FASTER teaches this as seeing and predicting what is happening, described as normal movement, so the trainer can say it aloud to a client without any drama.
How Movement Coach teaches it
Movement Coach is visual and interactive. The lesson can be read, listened to, answered in writing or dictated. Origin and insertion are pictured, not memorised from a list. PT Manager opens the moment you sign up with FASTER, and today's third post shows the tool that lets a client turn the body around and look.
Where to go next
Movement Coach covers muscle function in full. Today's PT Manager post shows how to put it in front of a client.
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You just read one answer. The course is all of them.
Movement Coach, where muscle function is taught in full — taught by the people who wrote it, with free return access for life. The price is on the page, payment plans at checkout, no sales calls.
Also worth a look: PT Manager's movement demonstrator, free with any FASTER course.
See what the course covers →Frequently asked
What are origin and insertion?
The origin is the bone a muscle starts from and the insertion is the bone it finishes at. Picturing that route helps a trainer predict when the muscle is working.
What are the four muscle roles?
Agonist (prime mover), antagonist (opposes the movement), synergist (assists) and fixator (steadies the other muscles).
What is the difference between concentric, eccentric and isometric?
Concentric means the muscle shortens, eccentric means it lengthens under control, and isometric means it holds without changing length.
Where is this taught?
In FASTER's Movement Coach course, in the section on the function of muscles.
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