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Functional anatomy – muscle work and joints

Understand what actually happens when the body moves

Functional anatomy is not about knowing Latin names, but about understanding what happens in the body when a person moves. Once you know that, you can look at any exercise and assess what it trains, where the load lands, and why one variant is safer than another.

§Three forms of muscle work

A muscle can work three ways and it's crucial to know the difference – especially because the phase many underestimate is the one where you brake the movement.

TypeWhat's happeningExample
ConcentricMuscle contracts and shortensWeigh up in a biceps curl
EccentricMuscle works while lengthening (braking)The slow way down into the curl
IsometricMuscle works without changing lengthKeeping a plank or a static position

The eccentric phase is often where you get strong — and at the same time the one that gives the most muscle soreness. Many members throw the weight down instead of controlling it; teaching them to brake is one of the most valuable corrections you can give.

§Muscles' roles in a movement

Rarely does a muscle work alone. In every movement muscles play different roles and if you understand them you can explain why an exercise feels the way it does.

  • 01Agonist – the muscle that performs the movement (prime mover).
  • 02Antagonist – the opposing player who performs the opposite movement and controls it.
  • 03Synergist – helper muscles that support the main movement.
  • 04Stabilizer – holds a body part in place so movement can happen in a controlled way.

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Muscles create movement across joints, and joints allow different movements. You don't need to know anatomy by heart, but you should know the common movement directions so you can describe an exercise precisely.

MovementMeaningExample
Flexion / extensionFlexion / extensionBend and straighten the elbow or knee
Abduction / adductionLead away from / toward the body's centerPLACEHOLDER_63
RotationRotate about an axisRotate the upper arm inward/outward

Different joints allow different movements: some joints move only in one direction like a hinge e.g. the elbow while others can move in multiple directions like the ball joint in the shoulder. A joint's freedom of movement determines which exercises suit it — and which put pressure on it wrongly.

§From anatomy to balanced programme

Understanding agonist and antagonist has a direct consequence for programme planning: if you only train one side of a joint (e.g. the front) imbalances occur. A good programme trains the opposing players so the body is loaded evenly. Anatomy is not theory for theory's sake — it is your reason for putting together a balanced programme.