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HMS · Planes & Axes · Joint Actions · Muscle Actions · Roles · Length-Tension · Force-Couples · Levers · Muscle Reference
Chapter 17 Theory Quiz
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—MCQ (20)
—Fill-In (5)
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Part A — Multiple Choice
20 Questions · 1 pt each
Part B — Fill in the Blank
5 Questions · 1 pt each
Part C — True / False
5 Questions · 1 pt each
Chapter 17 Case Studies
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Case Studies (Multiple Choice)
7 Cases · 35 Questions · 1 pt each
Planes of Motion, Joint Actions & Axes
| Plane | Divides body | Joint motions | Axis of rotation | Examples |
|---|---|---|---|---|
| Sagittal | Right & left halves | Flexion / extension (ankle: dorsiflexion / plantarflexion) | Frontal (coronal) axis | Biceps curls, squats, walking, stair climbing |
| Frontal | Front & back halves | Abduction / adduction, lateral flexion, eversion / inversion | Anterior-posterior axis | Lateral raises, side lunges, side shuffles |
| Transverse | Upper & lower halves | Internal / external rotation, L/R spinal rotation, pronation / supination | Longitudinal (vertical) axis | Cable rotations, throwing, swinging a bat |
The Three Muscle Actions
Concentric — isolated functionMuscle shortens and accelerates a movement (e.g., lifting phase of a curl).
Eccentric — integrated functionMuscle lengthens under load and decelerates a movement; absorbs force (e.g., lowering phase).
Isometric — integrated functionMuscle produces force with no change in length and stabilizes a joint (e.g., plank).
The Four Muscle Roles
| Role | What it does |
|---|---|
| Agonist | Prime mover — drives the motion |
| Antagonist | Directly opposes the prime mover |
| Synergist | Assists the prime mover |
| Stabilizer | Supports/holds while movers work |
Hip extension exampleAgonist: gluteus maximus · Antagonist: psoas · Synergist: hamstrings · Stabilizer: deep core (TVA, multifidus)
Pronation vs Supination
| Pronation (loading) | Supination (push-off) |
|---|---|
| Eccentric — decelerates | Concentric — produces force |
| Tibia/femur internal rotation | Tibia/femur external rotation |
| Foot/ankle: dorsiflex, evert, abduct | Foot/ankle: plantarflex, invert, adduct |
| Knee/hip: flex, adduct, IR | Knee/hip: extend, abduct, ER |
Tri-planarBoth are multiplanar, synchronized motions occurring in all three planes at once.
Mechanics — Length-Tension, Couples, Levers
Length-tensionA muscle produces its greatest force at its optimal (resting) length. Chronically lengthened or shortened muscles lose force.
Force-coupleTwo+ muscles pulling in different directions to rotate a joint. Scapular upward rotation = upper trap + lower trap + serratus anterior.
LeversBones = levers · joints = fulcrums · muscles = force · body part/weight = resistance. 3 lever classes. Torque = force × distance from fulcrum.
Muscle Reference — Quick Facts
| Muscle | Concentric action |
|---|---|
| Gluteus maximus | Hip extension & external rotation |
| Gastrocnemius / soleus | Ankle plantarflexion |
| Anterior tibialis | Dorsiflexion & inversion |
| Rectus femoris | Knee extension & hip flexion |
| Subscapularis | Shoulder internal rotation |
| Infraspinatus / teres minor | Shoulder external rotation |
Full referenceEvery muscle's origin, insertion, function & innervation lives in the Theory Guide →