Anatomy and Physiology for the NASM CPT: Body Systems Tied to Training

The body systems in NASM's Domain 1

Two knowledge statements frame this topic. K1 covers the anatomy of the nervous, muscular, skeletal, cardiorespiratory and endocrine systems. K2 covers exercise physiology for the same five, plus the digestive system and bioenergetics and exercise metabolism. Bioenergetics has its own guide, energy systems and metabolism. This page takes the systems one at a time and ends each with the training decision it informs.

Nervous system: control, feedback, and motor units

The autonomic nervous system has two branches. StatPearls calls the sympathetic branch "fight or flight" and the parasympathetic branch "rest and digest." At rest, parasympathetic tone keeps heart rate and breathing lower. During exercise, sympathetic activation helps raise both to meet demand.

Muscles are controlled through motor units. A motor unit is one motor neuron plus all the muscle fibers it supplies. StatPearls explains that the force of a contraction depends on how many motor units are recruited and how often they fire.

Feedback comes from proprioceptors. Muscle spindles respond to changes in muscle length, and Golgi tendon organs respond to tension.

Training decision: balance and proprioceptive progressions work this feedback system. The blueprint's own examples are closing the eyes, moving to a single-leg stance, or sitting for a regression.

Muscular system: fiber types and contraction

Muscle shortens when actin and myosin filaments slide past each other inside each sarcomere. StatPearls' exercise physiology chapter describes three main fiber types:

Some exercise texts label the fastest human fibers IIb. A 1995 single-fiber study of human thigh muscle found that fibers classified that way express the human equivalent of the IIx myosin found in rats, so IIx is the more accurate human label. Do not treat IIb and IIx as interchangeable names. Training also shifts fiber characteristics. Heavy resistance training, for example, tends to shift IIx fibers toward IIa.

Training decision: match the training stimulus to the goal. Postural endurance and sprint power draw on different fiber types.

Skeletal system: Wolff's law

StatPearls summarizes Wolff's law: bone adapts to the mechanical load placed on it. More loading strengthens the internal spongy bone and then the outer cortical layer. Less loading weakens both. The exercise physiology chapter adds that loading in childhood and adolescence builds bone, with similar effects in adults.

Training decision: include weight-bearing and resistance work as tolerated. The WHO's 2020 guidelines recommend muscle-strengthening activity on two or more days a week for adults. For older adults, they add varied multicomponent activity emphasizing balance and strength on three or more days a week, to improve function and prevent falls.

Cardiorespiratory system: cardiac output and VO2

Cardiac output is the amount of blood the heart pumps per minute: heart rate times stroke volume. When oxygen demand rises during exercise, both rise. StatPearls lists the adaptations to aerobic training as a larger heart, stronger contractions, more total blood volume and greater capillary density, which together raise stroke volume and oxygen delivery. Pulmonary ventilation can climb from about 10 liters per minute at rest to more than 100 liters per minute at high intensity.

Oxygen consumption (VO2) equals cardiac output times the difference in oxygen content between arterial and venous blood. VO2 max is the highest rate of oxygen uptake a person can reach during maximal effort. StatPearls notes it falls by about 10% per decade after age 30 in healthy adults.

Training decision: progress cardio gradually and track intensity. The WHO describes moderate intensity as about 5 or 6 on a 0–10 effort scale and vigorous as 7 or 8.

Endocrine system: hormones that respond to training

StatPearls lists the main hormonal responses to exercise:

• Insulin sensitivity improves with regular exercise. During exercise, contracting muscle takes up glucose through a pathway that does not depend on insulin, and the effect can last several hours.
• Cortisol rises during exercise. It follows a daily rhythm, highest in the morning and lowest around midnight.
• Anabolic hormones such as testosterone, growth hormone and insulin-like growth factors support muscle growth and repair.
• Catecholamines such as epinephrine and norepinephrine raise heart rate and cardiac output during hard effort.

Training decision: a client with diabetes needs their clinician's guidance on exercise, food and medication. NASM's handbook states that trainers do not diagnose or treat disease and refer such needs to health care professionals.

Digestive system: from food to fuel

StatPearls describes digestion as mechanical breakdown plus chemical breakdown by enzymes. Carbohydrates, proteins and fats are digested mainly in the small intestine, then absorbed into the blood or lymph. During exercise, blood flow is shunted away from the digestive and renal systems toward working muscles.

Training decision: meal timing questions stay general. Anything individualized goes to a dietitian, as the NASM nutrition and scope guide explains.

Recall-to-application drills for NASM CPT anatomy

The clients below are fictional. Cover the right column and answer.

When the answers come quickly, see how the sciences domain shows up in 20 mixed NASM CPT questions →, from a plane-of-motion choice to an energy-system call. For how these systems produce movement, continue with human movement science.