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IB Sports, Exercise & Health Science: A.3 · Response

Energy systems, cardiorespiratory response, training adaptations. 3 subtopics, 15 key terms.

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In this topic: A.3.1 · A.3.2 · A.3.3

A.3.1Energy systems

ATP: Adenosine triphosphate: the only direct energy source for muscle contraction.
ATP–PC system: Anaerobic; resynthesizes ATP from phosphocreatine for about 10 seconds of maximal work.
Anaerobic glycolysis: Breaks glucose down without oxygen, producing lactate; dominant for about 10 s to 2 min.
Aerobic system: Uses oxygen in mitochondria to break down carbohydrate and fat; dominant beyond about 2 min.
EPOC: Excess post-exercise oxygen consumption: extra oxygen used during recovery.

All three systems work at once; the energy continuum describes which dominates for a given intensity and duration.

The full notes, worked example, interactive diagram and check questions for this subtopic are in the app.

Exam tip: Always justify the dominant system with both intensity and duration.

Cardiac output (Q): Volume of blood pumped by one ventricle per minute: Q = HR × SV.
Stroke volume (SV): Volume of blood ejected by the left ventricle per beat.
Minute ventilation (VE): Volume of air breathed per minute: VE = tidal volume × breathing frequency.
VO₂ max: Maximum rate of oxygen uptake and use during exhaustive exercise.
a–vO₂ difference: Difference in oxygen content between arterial and venous blood: how much oxygen the muscles extract.

During exercise heart rate, stroke volume, cardiac output, breathing rate, tidal volume and a–vO₂ difference all increase.

The full notes, worked example, interactive diagram and check questions for this subtopic are in the app.

Exam tip: Give units for cardiac output (L min⁻¹) and convert ml to litres.

Progressive overload: Gradually increasing training demand so the body keeps adapting.
Specificity: Training should match the demands of the sport.
Reversibility: Adaptations are lost when training stops.
Periodization: Dividing training into cycles (macro-, meso-, microcycles) to peak at the right time.
Overtraining: Too much training with too little recovery, causing a drop in performance.

FITT: frequency, intensity, time, type. Intensity can be set using heart rate zones (Karvonen) or RPE.

The full notes, worked example and check questions for this subtopic are in the app.

Exam tip: State the adaptation, then its effect on performance: e.g. more capillaries → more oxygen delivered → delays fatigue.