Musculoskeletal Anatomy & Movement Terminology

Bone, Skeletal Muscle, and Connective Tissue

Bone serves four functions central to exercise physiology: structural support, protection of vital organs, mineral storage (calcium, phosphorus), and — most relevant to prescribing exercise — a rigid lever system that skeletal muscle pulls against to produce movement. Bones are classified as long (femur, humerus), short (carpals, tarsals), flat (sternum, scapula), or irregular (vertebrae). Bone is living tissue that remodels in response to mechanical loading, which is why weight-bearing and resistance exercise are prescribed to preserve bone mineral density (covered further in Chapter 10).

Skeletal muscle is organized hierarchically: the whole muscle is wrapped in epimysium, bundles of fibers (fascicles) are wrapped in perimysium, and individual fibers are wrapped in endomysium. Each skeletal muscle attaches to bone at two points. The origin is the attachment on the more fixed, typically more proximal bone; the insertion is the attachment on the bone that moves, typically more distal. When a muscle contracts concentrically, the insertion is pulled toward the origin.

Three connective-tissue structures link the musculoskeletal system together:

• Tendons connect muscle to bone and transmit contractile force to produce joint movement.
• Ligaments connect bone to bone and provide passive stability at a joint.
• Fascia envelops and organizes muscles and muscle groups, while hyaline cartilage cushions the articulating surfaces of synovial joints and reduces friction.

An EP-C who can name these structures accurately can explain assessment findings, describe injury mechanisms (e.g., a "strain" injures muscle or tendon; a "sprain" injures ligament), and communicate technique cues using correct anatomical vocabulary.

Major Muscles: Location and Primary Action

The exam expects an EP-C to identify major muscles by location and know their primary joint action(s), because interpreting strength and flexibility assessments (Chapter 5) and building targeted FITT prescriptions (Chapters 6–8) both depend on this knowledge.

Joints and Their Movements

Most exercise-relevant joints are synovial — freely movable joints enclosed in a fluid-filled capsule. Synovial joints are further classified by the movement pattern they permit:

• Hinge (elbow, knee) — uniplanar flexion/extension only
• Ball-and-socket (shoulder, hip) — multiplanar flexion/extension, abduction/adduction, rotation, and circumduction
• Pivot (proximal radioulnar, atlantoaxial) — rotation only
• Condyloid (wrist) — flexion/extension and abduction/adduction, but no independent rotation
• Saddle (thumb carpometacarpal) — flexion/extension, abduction/adduction, and opposition

Knowing a joint's structural classification predicts which movements — and therefore which assessments and exercises — are anatomically appropriate at that joint.

Directional and Movement Terminology

Precise anatomical language lets an EP-C describe assessment findings and cue exercise technique without ambiguity. Directional terms are always defined relative to the anatomical position (standing upright, palms facing forward):

• Anterior/posterior — toward the front of the body/toward the back
• Proximal/distal — closer to the trunk or point of attachment/farther away
• Medial/lateral — closer to the midline of the body/farther from the midline
• Superior/inferior — above a reference point/below it

Movement terms describe the specific joint action produced:

• Flexion/extension — decreasing a joint angle/increasing it (predominantly sagittal-plane)
• Abduction/adduction — moving a limb away from the midline/toward it (predominantly frontal-plane)
• Internal (medial) rotation/external (lateral) rotation — rotating a limb toward/away from the midline around its long axis
• Supination/pronation — rotating the forearm so the palm faces up/down
• Dorsiflexion/plantarflexion and inversion/eversion — ankle-specific sagittal- and frontal-plane movements

Functionally, muscles are also classified by the role they play during a given movement:

• Agonist (prime mover) — generates the primary force that produces the movement
• Antagonist — opposes the agonist and lengthens, or contracts eccentrically, to permit controlled movement
• Synergist — assists the agonist, often by neutralizing an unwanted secondary action of another muscle
• Stabilizer (fixator) — contracts isometrically to hold a body segment steady so the agonist can act efficiently

Planes and Axes of Movement

Human movement is described relative to three cardinal planes, each paired with a perpendicular axis of rotation:

An EP-C uses plane-of-motion language to select assessment protocols and to design programs that train movement in all three planes rather than the sagittal plane alone, which is the plane most commonly over-trained in traditional resistance programs. Recognizing which plane and axis a given exercise or assessment movement occurs in is directly testable and underlies safe, well-rounded program design.