FSHP Academy
Human Anatomy — all lessons

Foundations of Anatomy

Anatomical terminology, planes, axes and movement directions

The Skeletal System

Skeletal system: structure and functionsBone structure, remodelling and adaptation to loading

Joints and the Muscular System

Joint types and classificationJoint mechanics: arthrokinematics and stabilityThe muscular system: organisation and major muscle groupsMuscle architecture: pennation, length and cross-sectional areaMuscle fibre types

Regional Functional Anatomy

Spine and postureThe shoulder complexThe hip complexThe knee complexThe ankle and foot complexCore and pelvic stabilityElbow and wrist functional anatomyCervical and thoracic spine functional anatomy

The muscular system: organisation and major muscle groups

The three muscle tissue types, how skeletal muscles are named and attached, the roles muscles play in a movement, and the major muscle groups used in training.

Beginner Evidence: Established consensus 3 min read Reviewed 2026-10-31 Status: draft

Learning objectives

  • Compare skeletal, cardiac and smooth muscle
  • Use attachments (origin/insertion) and muscle names to predict action
  • Define agonist, antagonist, synergist and stabiliser roles
  • Identify the major muscle groups and their primary actions

Before this lesson

Why this matters

Programme design, exercise selection and coaching cues all depend on knowing which muscles drive a movement and which control it.

Fundamental concepts: three muscle tissues

TissueControlStriatedLocation
SkeletalVoluntaryYesAttached to bones
CardiacInvoluntary (autonomic)YesHeart
SmoothInvoluntaryNoBlood vessels, gut, airways

Humans have more than 600 skeletal muscles [openstax2022musc].

Attachments and action

Muscles attach to bone via tendons (or broad sheets called aponeuroses). Traditionally the more stable attachment is the origin and the more mobile the insertion; many modern texts prefer proximal and distal attachments, since which end moves depends on the task (in a pull-up the arm is fixed and the trunk moves).

A muscle’s action follows from: (1) which joints it crosses, (2) which side of each joint axis its line of pull passes. A muscle crossing the front of the hip flexes it; one crossing behind extends it [neumann2017].

Names give clues: location (tibialis anterior), shape (deltoid, triangle), size (gluteus maximus), direction of fibres (rectus, straight; obliquus), number of heads (biceps, quadriceps), attachments (sternocleidomastoid), action (adductor longus).

Roles in a movement

  • Agonist (prime mover) — main muscle producing the action.
  • Antagonist — opposes it; relaxes or co-contracts to control and protect the joint.
  • Synergist — assists the agonist or neutralises unwanted actions.
  • Stabiliser (fixator) — holds a proximal segment steady (e.g., scapular muscles during a press).

Roles are task-specific: the hamstrings are agonists in a leg curl but act eccentrically to decelerate the shank during sprinting.

Two-joint muscles (rectus femoris, hamstrings, gastrocnemius, biceps brachii) can become actively insufficient (too short to produce much force when shortened over both joints) or passively insufficient (too stretched to allow full motion at both joints).

Major muscle groups

GroupMain musclesPrimary actionsExample exercises
ChestPectoralis major/minorShoulder horizontal adduction, flexionBench press, push-up
Upper backLatissimus dorsi, trapezius, rhomboidsShoulder extension/adduction; scapular retractionRow, pull-up
ShouldersDeltoids, rotator cuffAbduction, flexion, rotation; humeral head controlOverhead press, external rotation
ArmsBiceps, brachialis, tricepsElbow flexion/extensionCurl, dip
TrunkRectus abdominis, obliques, transversus abdominis, erector spinae, multifidusFlexion, rotation, extension, stiffeningPlank, carries, back extension
HipGluteus maximus/medius, iliopsoas, adductorsExtension, abduction, flexion, adductionHip thrust, lunge
ThighQuadriceps, hamstringsKnee extension; hip extension + knee flexionSquat, RDL, Nordic
Lower legGastrocnemius, soleus, tibialis anteriorPlantarflexion, dorsiflexionCalf raise

Practical application

Common mistakes and misconceptions

Case study

A client’s squat shows limited depth and strong quadriceps fatigue but little glute soreness. The trainer explains muscle roles, adds hip-dominant exercises (hip thrust, RDL), and cues “sit back and push the floor away” to share load between hip and knee extensors — linking to movement patterns.

Further learning: video lessons

Video links are only marked “verified” after a human has watched them. Unverified entries open a YouTube search for that channel and topic rather than a guessed link.

Introductory needs verification — opens a YouTube search

The muscular system overview

Crash Course

You will understand: muscle types and organisation

Why: Accessible starting point.
Technical needs verification — opens a YouTube search

Muscles of the lower limb — actions and attachments

Kenhub

You will understand: attachments and actions of the major training muscles

Why: Anatomy educator with clear 3D visuals.

Knowledge check

Knowledge check · 0/5

1. In the lifting phase of a biceps curl, the triceps brachii acts as the…

Answer B. The triceps opposes elbow flexion; it relaxes or co-contracts to control the movement.

2. Why is grip weaker with the wrist fully flexed?

Answer B. The finger flexors cross the wrist; with the wrist flexed they are too short to generate much force (active insufficiency).

3. The hamstrings cross which joints?

Answer C. Most hamstrings are two-joint muscles (hip extension, knee flexion); the short head of biceps femoris crosses only the knee.

4. Which tissue is involuntary and striated?

Answer C. Cardiac muscle is striated but under autonomic control.

5. During a squat, the gluteus maximus is mainly a…

Answer A. It extends the hip, working concentrically on ascent and eccentrically on descent.

Short-answer & application questions

  1. For a push-up, list the agonists, synergists, antagonists and stabilisers.
  2. Explain why rectus femoris contributes less to knee extension when the hip is flexed in a deep squat.
  3. Use the name “extensor carpi radialis longus” to predict location and action.

Key takeaways

  • Skeletal muscle is voluntary and striated; cardiac is involuntary and striated; smooth is involuntary and non-striated.
  • A muscle’s action follows from the joints it crosses and the line between its attachments.
  • In any movement, muscles act as agonists, antagonists, synergists or stabilisers — roles change with the task.
  • Two-joint muscles can become actively or passively insufficient at extreme combined positions.

Connected topics

physiology

Muscle physiology: excitation–contraction and the sliding filament model

anatomy

Muscle architecture: pennation, length and cross-sectional area

anatomy

Muscle fibre types

functional training

Fundamental movement patterns: push, pull, squat, hinge

References

  1. Betts JG, Young KA, Wise JA, et al. (2022). Anatomy and Physiology 2e — Chapter 11: The Muscular System. OpenStax, Rice University. · Link Textbook check pending
  2. Neumann DA (2017). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation (3rd ed.). Elsevier. Textbook check pending

Educational content only — not medical advice. Consult a qualified clinician for diagnosis or treatment.