Anatomy and Physiology
Movement and support
Skeletal muscle is organized from whole muscle down to the sarcomere, where actin and myosin filaments slide past one another in a calcium-dependent, ATP-driven cycle. Fiber type matters: Type I fibers are oxidative and fatigue-resistant; Type IIa are fast and moderately fatigue-resistant; Type IIx are fast, powerful, and fatigue quickly. Connective tissue - endomysium, perimysium, epimysium, tendon - transmits force, and bone remodels along lines of stress (Wolff's law).
Control
A motor unit is one motor neuron plus the fibers it innervates; recruitment follows the size principle, with small units firing first. Proprioceptors are a classic testing target: muscle spindles detect stretch and trigger a reflexive contraction, while Golgi tendon organs detect tension and inhibit it.
Cardiorespiratory
Cardiac output equals heart rate times stroke volume and rises from roughly 5 L/min at rest to more than 20 L/min at maximal effort, driven mostly by stroke volume in trained individuals. The right heart sends blood to the lungs, the left to the body; arteries carry blood away from the heart.
Energy systems
The phosphagen (ATP-PC) system fuels all-out efforts up to about 10 seconds; glycolysis dominates from roughly 10 seconds to 2 minutes; oxidative metabolism takes over beyond that. The endocrine response to training includes catecholamines, cortisol, growth hormone, testosterone, and insulin.
Traps
Questions love to swap spindle and GTO roles, ask which energy system dominates a given bout, or offer 'cardiac output = heart rate divided by stroke volume' as a distractor.
Rule of thumb: match the energy system to bout duration, not to the athlete's reputation - a 100 m sprint is phosphagen-fueled even though the sprinter trains aerobically all week.