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Anatomy

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Anatomy99 topics

Exercises Calisthenics Safety Balance Flexibility

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On this page:Muscle Muscle Group Movement Term Concept Rom Reference

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◆ Muscle

42 topics

Anterior DeltoidThe front deltoid head; produces forward flexion, horizontal adduction, and internal rotation — primarily a pressing muscle.

Biceps BrachiiThe strongest flexor of the elbow joint (long and short heads); flexes the elbow, supinates the forearm, and weakly flexes the shoulder; a 2-joint muscle (ROM 135°).

BrachialisThe only pure flexor of the elbow joint; pulls on the ulna, which does not rotate.

BrachioradialisA forearm flexor that flexes the elbow and both supinates and pronates the forearm.

External ObliqueThe largest, most superficial flat abdominal; flexes the trunk and rotates it toward the opposite side.

Fibularis Longus (Peroneus Longus)The lateral lower-leg muscle that everts the foot and helps support the arch — the antagonist to the tibialis posterior.

GastrocnemiusA 2-joint calf muscle that plantar-flexes the ankle and flexes the knee; origin at the femoral condyles, insertion at the calcaneus.

Gluteus MaximusThe strongest, largest muscle in the body; the primary hip extensor and a lateral rotator of the femur.

Gluteus MediusA fan-shaped hip abductor under the gluteus maximus, important for balance in walking.

Gluteus MinimusThe smallest gluteal muscle; functions similarly to the gluteus medius as a hip abductor.

GracilisThe only 2-joint hip adductor; a weak adductor and knee flexor that the body can do without.

IliopsoasThe major hip flexor, made of the iliacus and psoas major; shortening it increases lumbar lordosis.

InfraspinatusThe "I" of SITS; an external rotator of the shoulder also involved in horizontal abduction and extension.

Internal ObliqueA flat abdominal sandwiched between the external obliques and transversus; its fibers run at right angles to the external oblique and it twists the trunk to the same side.

Latissimus DorsiA 2-joint back muscle; its strongest action is adduction (drawing the arm to the side from side-horizontal, rotating inward), with extension second.

Levator ScapulaeA neck-to-scapula strap muscle that elevates the scapula alongside the upper trapezius — the muscle most often blamed for a stiff, tight neck-shoulder junction.

Medial DeltoidThe middle deltoid head; the primary muscle of true shoulder abduction (90°), involving all three heads plus the supraspinatus.

MultifidusA deep, segment-by-segment spinal stabilizer running from the sacrum to C2 — not a prime mover for big spinal ROM, but a key part of the local stability system that's commonly found inhibited or smaller in people with chronic low-back pain.

Pectoralis MajorThe chest muscle (clavicular and sternal portions); its primary action is horizontal adduction (flexion) of the arm — a powerful action.

Pectoralis MinorA thin triangular muscle deep to the pec major that pulls the scapula forward and down — the muscle most implicated in a rounded-shoulder posture when it's chronically tight.

Posterior DeltoidThe rear deltoid head; produces horizontal abduction, backward extension, and external rotation — the most under-emphasized deltoid head.

Quadratus LumborumA deep lower-back muscle important in lateral trunk flexion; trained with side bends and lateral pelvic tilts.

Rectus AbdominisThe "abs"; a long strap-like trunk flexor split into left/right halves by the linea alba.

Rectus FemorisA 2-joint quadriceps muscle that flexes the hip and extends the knee.

Rhomboids (Major and Minor)Two muscles between the spine and the inner edge of the scapula that retract (draw together) and downwardly rotate the shoulder blades — key to upright posture and rowing movements.

SartoriusThe longest muscle in the body; a 2-joint hip flexor and adductor that also flexes and laterally rotates the knee.

Serratus AnteriorThe muscle along the rib cage that pulls the scapula forward and around the chest wall (protraction) and helps rotate it upward, acting as a stabilizer in most pressing movements.

SoleusA single-joint calf muscle that plantar-flexes the ankle; trained with seated calf raises.

SternocleidomastoidA neck muscle and the first of the atrophic-weakening muscle groups; trained with neck machines / neck strap with weight plate.

SubscapularisThe "S" of SITS; the internal rotator of the shoulder, also involved in extension and adduction.

SupraspinatusThe "S" of SITS; it abducts the humerus and does not rotate it.

Tensor Fascia LataA hip flexor that also abducts and medially rotates the femur, inserting via the iliotibial (IT) band.

Teres MajorThe "lat's little helper" — a scapula-to-humerus synergist that extends, adducts, and internally rotates the shoulder alongside the latissimus dorsi.

Teres MinorThe "T" of SITS; an external rotator of the shoulder also involved in horizontal abduction and extension.

Tibialis AnteriorThe shin muscle that dorsiflexes the foot (lifts the top of the foot toward the shin) — the antagonist to the calf muscles.

Tibialis PosteriorThe deep calf muscle that inverts the foot and is the primary dynamic support of the medial arch — the antagonist to the fibularis (peroneal) muscles.

Transverse AbdominisThe deepest abdominal muscle; compresses the abdomen, supports the abdominal contents, and aids lower-back stability.

TrapeziusA muscle that functions as three different muscles — upper, middle, and lower traps — moving the scapula.

Triceps BrachiiThe three-headed elbow extensor (long, medial, lateral heads); the long head also assists shoulder extension.

Vastus IntermediusThe deepest of the four quadriceps heads, sitting directly beneath rectus femoris where it can't be seen or palpated separately — a pure knee extensor that still moves real weight even though it's functionally invisible.

Vastus LateralisThe largest and outermost of the four quadriceps heads — a pure knee extensor running down the lateral thigh, and the muscle most often biopsied in exercise-physiology research because of its size and easy access.

Vastus MedialisThe medial quadriceps head, whose distal fibers (the "VMO") angle sharply inward and fire hardest in the last 15° of knee extension — the medial counterbalance that keeps the kneecap tracking straight.

◆ Muscle Group

17 topics

Abdominals (Midsection)Four muscles — rectus abdominis, external oblique, internal oblique, transverse abdominis — that flex, rotate, and laterally flex the trunk and compress the abdomen.

Antigravity MusculatureThe large muscle groups that resist gravity to maintain erect posture — gastrocnemius/soleus, quadriceps, gluteus maximus, erector spinae, and abdominals.

Atrophic Weakening Muscle GroupsEight major muscle groups especially prone to age-related atrophic weakening that a sound strength program should target.

Calves (Gastrocnemius and Soleus)The calf comprises the gastrocnemius (crosses knee and ankle) and the soleus (crosses only the ankle); both plantar-flex the foot.

DeltoidsThe three-headed shoulder muscle — anterior, medial, and posterior deltoid — each with distinct actions.

Erector Spinae (Sacrospinalis)Three muscle-group columns (iliocostalis, longissimus, spinalis) running skull-to-sacrum that extend, laterally flex, and rotate the vertebral column.

Forearm FlexorsThe forearm flexors — flexor carpi ulnaris and flexor carpi radialis — flex the wrist; trained with wrist curls.

HamstringsThree 2-joint muscles — biceps femoris, semitendinosus, semimembranosus — that flex the knee (primary) and extend the hip (secondary); knee-flexion ROM 125°.

Hip AbductorsThe hip abductors are the gluteus medius and gluteus minimus.

Hip AdductorsThe hip adductors are the pectineus, adductor brevis, adductor longus, adductor magnus, and gracilis.

Hip ExtensorsThe primary hip extensors are the gluteus maximus and the hamstrings.

Hip FlexorsThe 4 major hip flexors — iliopsoas, rectus femoris, tensor fascia lata, sartorius — plus secondary flexors.

Hip Lateral Rotators (6 Short Muscles)Six short muscles produce lateral (outward) rotation of the hip.

The 12 Major Muscle GroupsFor balanced development and reduced injury risk, strengthen the 12 major muscle groups (plus obliques and adductors/abductors).

QuadricepsThe four knee extensors — rectus femoris, vastus medialis, vastus lateralis, vastus intermedius (rectus femoris also flexes the hip); knee ROM 90°.

Rotator Cuff (SITS)The four rotator cuff muscles — Supraspinatus, Infraspinatus, Teres minor, Subscapularis (SITS) — that rotate and stabilize the shoulder joint.

Wrist ExtensorsThe extensor carpi radialis longus/brevis and extensor carpi ulnaris — the mirror-image group to the wrist flexors, trained with reverse curls and reverse wrist curls.

◆ Movement Term

17 topics

AbductionMovement of a body part away from the midline (axis) of the trunk.

AdductionMovement of a body part toward the midline (axis) of the trunk.

DepressionDownward movement returning to the normal position from elevation.

DorsiflexionMovement of the top of the foot toward the anterior tibia bone.

ElevationUpward movement, as in shrugging the shoulder girdles.

EversionTurning the sole outward, placing weight on the inner edge of the foot.

ExtensionStraightening a joint so the bones move apart.

External RotationRotation with the axis of the bone turning away from the body (e.g., the humerus turned outward).

FlexionBending a joint so the bones come closer together.

Horizontal Extension (Abduction)Returning the humerus from the front-horizontal position back to the side-horizontal position.

Horizontal Flexion (Adduction)Drawing the humerus from the side-horizontal to the front-horizontal position.

Internal RotationRotation with the axis of the bone turning toward the body (e.g., the humerus turned inward).

Inversion (Foot Movement)Turning the sole inward, placing weight on the outer edge of the foot.

Plantar FlexionMovement of the sole downward toward the floor, as in performing calf raises.

PronationRotation of the forearm that turns the palm down, rotating the radius on the ulna.

Scapular MovementThe scapula moves through elevation/depression, adduction (retraction)/abduction (protraction), and upward/downward rotation.

SupinationRotation of the forearm that turns the palm up, rotating the radius on the ulna.

◆ Concept

11 topics

Body Frame Types (T/A/O-Frame) — Dated Terminology, Modern EquivalentA 1996 magazine series classified women into T-frame, A-frame, and O-frame body shapes with muscle-emphasis advice for visual symmetry — dated terminology now superseded by the ratio-based Inverted Triangle / Pear / Apple system, but the underlying idea (train to balance proportions) still holds.

Body Shape — Somatotypes (Endomorph / Mesomorph / Ectomorph)Sheldon's (1954) three-component somatotype system rates each person on endomorphy (fat), mesomorphy (muscle), and ectomorphy (linearity) on a 1-7 scale each — most people are a combination of two, not a single dominant type.

Femur Length vs. Torso Length (Squat Mechanics)Long-femured lifters lean farther forward in the squat, shifting emphasis toward the glutes and erector spinae.

Kinesiology and Biomechanics (Introduction)Kinesiology is the science of human movement; biomechanics applies the principles of mechanics to exercise.

Knee-Toe RelationshipA squat-alignment concept balancing keeping the knees from passing the toes against keeping the spine vertical — the "happy medium."

Bones and Levers in MovementMuscles exert force on body levers (bones); the muscle's mechanical ability to exert force changes through the range of motion as lever and joint angle change.

Muscle Action Roles (Agonist, Antagonist, Synergist)A muscle can act as a primary mover, secondary mover, antagonist, synergist/neutralizer, or stabilizer; reciprocal innervation relaxes the antagonist as the agonist contracts.

Muscle Fiber Arrangements (Penniform vs. Fusiform)The two major fiber arrangements — penniform (greater cross-section, more force) and fusiform (parallel fibers, speed but less force).

The Body's Three Planes of MotionThe body moves in three planes — frontal, transverse, and sagittal.

Range of Motion (ROM)The complete movement capability of a joint; train through the full ROM a joint safely allows.

Two-Joint (2-Joint) MusclesMuscles crossing two joints generate the greatest force when not required to shorten over both joints simultaneously; stabilize one joint when training them.

◆ Rom Reference

8 topics

Elbow / Biceps Range of MotionThe biceps brachii (a 2-joint muscle) has a ROM of 135 degrees at the elbow.

Foot / Ankle Range of MotionPlantar flexion of the foot 45°, dorsiflexion of the foot 10–15°.

Hip Joint Range of MotionHip flexion 90° (knee extended) to 120° (up to 135°, knee flexed); hyperextension 10–30°; adduction 30°; abduction 45°; medial rotation 30–45°; lateral rotation 45–60°.

Joint Range of Motion ChartReference table of degree-of-motion values for the hip, knee, spine, arm/shoulder, neck, and foot (Kennedy & Legel, 1992).

Knee Joint Range of MotionThe knee is a hinge joint: extension 90°, flexion 120° (hamstring knee-flexion ROM stated as 125°).

Neck Range of MotionNeck abduction/adduction 40°, flexion 40°, hyperextension 50°, rotation 55°.

Shoulder / Arm Range of MotionArm flexion 135°, shoulder adduction 50°, shoulder hyperextension 45°, shoulder abduction 90–180°.

Spine Range of MotionSpinal lateral bending 30°, rotation 40°, flexion 70° (standing and lying), hyperextension 70°.