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Description
Key Concepts
My Notes
Discussion

Lesson Overview

The human body's movement system is divided into a passive component (bones, joints, cartilage, ligaments) and an active component (muscles, tendons, motor units). Understanding both is essential for safe, effective AURUM coaching — from adjusting seat positions to explaining why eccentric loading builds more strength than concentric alone.

Learning Objectives

  • Name the major divisions of the skeleton and the five joint types
  • Explain the difference between concentric, eccentric, and static (isometric) muscle contractions
  • Describe the structure of a motor unit and how motor unit recruitment drives force output
  • Explain the role of tendons in transmitting muscle force to the skeleton
  • Connect musculoskeletal anatomy to AURUM's isokinetic resistance model

The Passive Movement Apparatus

The skeleton provides the framework for all movement. Its 206 bones are organised into the axial skeleton (skull, vertebral column, thorax — ~17% of body weight) and the appendicular skeleton (arms, legs, pelvis). Bones serve four functions: structural support, organ protection, mineral storage (calcium, phosphate), and blood cell production in the marrow.

Joints determine how bones move relative to each other. The five primary joint types are:

Ball & Socket (Kugelgelenk)
Example: hip — 3-axis movement
Hinge (Scharniergelenk)
Example: knee — 1-axis flex/extend
Pivot (Drehgelenk)
Example: radioulnar — rotation only
Saddle (Sattelgelenk)
Example: thumb — 2-axis movement

The Active Movement Apparatus

Over 600 skeletal muscles provide movement, stability, and force. Muscle fibres are bundled into fascicles which form the muscle belly. Within each fibre, the contractile units — sarcomeres — shorten when activated, producing force.

Muscles work in three modes: concentric (shortening under load — the push/pull phase in AURUM, 4 seconds), eccentric (lengthening under load — the return phase, 8 seconds), and isometric (holding position without length change). Eccentric loading produces the greatest structural stimulus for strength adaptation — exactly why AURUM's 8-second eccentric is the core of the protocol.

A motor unit is a single motor neuron and all the muscle fibres it innervates. Larger forces require more motor units to be recruited simultaneously — this is the nervous system's primary mechanism for controlling strength output, and it adapts with consistent training.