NASM-CPT

The body has more than 600 muscles that produce movement, maintain posture, and generate heat. Skeletal muscle is voluntary and striated, cardiac muscle is involuntary and striated, and smooth muscle is involuntary and non-striated. Personal trainers work primarily with skeletal muscle.

Skeletal muscle is organized in layers: the whole muscle is wrapped in epimysium, bundles of fibers (fascicles) in perimysium, and each fiber in endomysium. Each fiber contains myofibrils made of the contractile proteins actin (thin filaments) and myosin (thick filaments), arranged in sarcomeres.

The Sliding Filament Theory

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Signal reaches the fiber

From the sarcoplasmic

Myosin heads attach to

ATP powers the pull;

reticulum

Ca²⁺ binds troponin;

actin

cycle repeats

tropomyosin shifts

The cycle continues as long as calcium and ATP are available, sliding the filaments toward the center of the sarcomere.

Muscle Fiber Types

FiberType	Characteristics	BestSuitedFor
TypeI(slowtwitch)	Red(highmyoglobin) many ,	Enduranceactivitiesandposturalstabilization
	capillariesandmitochondria ,
	fatigueresistant lowerforce ,
Type IIa (fast oxidative-	Intermediate;moderatelyfatigue	Sustained moderate-to-high intensity work
glycolytic)	resistant
TypeIIx(fast	White(lowmyoglobin) fewer ,	Short explosive maximalefforts , ,
glycolytic)	capillaries fatiguequickly high , ,
	force

Muscle Actions and Force Relationships

Muscle shortens while producing force

Muscle lengthens while producing

Muscle produces force without

(lifting a dumbbell in a curl).

force (lowering the dumbbell).

changing length (holding a plank).

Acceleration of movement.

Produces the greatest force and is

Stabilization.

most associated with delayed-onset muscle soreness (DOMS). Deceleration.

Force-velocity relationship: force is greatest during slow or isometric contractions and decreases as shortening velocity increases. Heavy loads move slowly; explosive movements require lighter loads.

Length-tension relationship: a muscle produces the most force near its resting length, where actin-myosin overlap is optimal. Force decreases when the muscle is too shortened or too lengthened.

Force-couple relationship: muscles work together to produce movement around a joint, such as the upper and lower trapezius and serratus anterior rotating the scapula upward.

Muscle Roles in Movement

Role	Function	Example:BicepsCurl
Agonist	Primemoverprimarilyresponsibleforthe	Bicepsbrachii
	movement
Synergist	Assiststheagonist	Brachialis brachioradialis ,
Stabilizer	Supportsbodysegmentswhilethemovement	Rotatorcuffandcoremuscles
	occurs
Antagonist	Opposestheagonistandmustrelaxorcontrolthe	Tricepsbrachii
	movementeccentrically

Core: rectus abdominis, transverse abdominis, internal and external obliques, erector spinae, multifidus. Hip complex: gluteus maximus, medius, and minimus; psoas and iliacus; adductors; piriformis. Lower extremity: quadriceps, hamstrings, gastrocnemius, soleus, anterior tibialis, peroneals. Upper body: pectoralis major and minor, latissimus dorsi, trapezius, rhomboids, deltoids, rotator cuff, biceps, triceps, serratus anterior, levator scapulae.

The cardiovascular system (heart, blood vessels, and blood) and the respiratory system work together to deliver oxygen and remove carbon dioxide. The heart is a four-chambered muscular pump.

Cardiac cycle: systole is ventricular contraction; diastole is ventricular relaxation and filling. Blood pressure is recorded as systolic over diastolic. Normal resting blood pressure is below 120/80 mmHg, and hypertension begins at 130/80 mmHg.

Heart rate is set by the sinoatrial (SA) node, the heart's natural pacemaker. Sympathetic stimulation raises heart rate; parasympathetic stimulation lowers it. Maximal heart rate is commonly estimated as 220 − age, although individuals vary.

Blood vessels: arteries carry blood away from the heart under high pressure; arterioles regulate flow to tissues; capillaries are the site of gas and nutrient exchange; venules and veins return blood to the heart, with valves that prevent backflow.

Blood redistribution: during exercise, vasodilation in active muscles and vasoconstriction in inactive areas shift muscle blood flow from about 15–20% of cardiac output at rest to about 80–85% during maximal exercise.

Cardiac output (Q) = Heart rate × Stroke volume

Minute ventilation = Tidal volume × Breathing rate

Resting cardiac output is about 5 L/min and can reach 20–25 L/min during maximal exercise in trained individuals. Tidal volume in a normal breath is about 500 mL.

Air travels through the nose or mouth, pharynx, larynx, trachea, bronchi, and bronchioles to the alveoli, where oxygen diffuses into the blood and carbon dioxide diffuses out along partial pressure gradients. VO2max, the maximal rate of oxygen consumption, reflects cardiorespiratory fitness; it depends on cardiac output and the arteriovenous oxygen difference and can improve by about 15–20% with training.