Students should develop knowledge and understanding of the changes within…

The idea

This section builds a three-phase model of how the body responds to physical activity. Before exercise, anticipatory responses raise heart rate, stroke volume, ventilation and muscle blood flow through sympathetic stimulation and adrenaline release. During exercise, intensity determines the scale of change: at low intensity, cardiac output rises mainly through stroke volume, while at high intensity heart rate contributes more; ventilation increases through greater tidal volume and frequency; and the musculo-skeletal, cardio-respiratory and neuro-muscular systems adjust together. During recovery, heart rate, ventilation and blood lactate fall at different rates, with excess post-exercise oxygen consumption restoring oxygen stores and removing by-products. Learn each variable, its direction of change and the mechanism causing it.

What earns the marks

• Identifies that anticipatory (pre-exercise) changes include increased heart rate, stroke volume, ventilation and redirected blood flow, driven by sympathetic activity and adrenaline.
• Explains that during exercise of differing intensities, cardiac output increases, with stroke volume dominating at lower intensities and heart rate contributing more as intensity rises.
• Describes respiratory changes during exercise: increased tidal volume and breathing frequency raise pulmonary ventilation and oxygen uptake.
• States that during recovery, heart rate and ventilation decline gradually, oxygen debt or excess post-exercise oxygen consumption repays oxygen deficit and lactate is removed.
• Distinguishes the roles of the musculo-skeletal, cardio-respiratory and neuro-muscular systems in producing and supporting movement at each phase.

Common mistakes and how to put them right

• Thinking heart rate returns to resting level immediately exercise stops.

  Put it right: In fact it declines gradually, and the rate of decline depends on fitness and exercise intensity.

• Confusing cardiac output with stroke volume.

  Put it right: Cardiac output is the product of heart rate and stroke volume, so it is always the larger quantity.

• Assuming ventilation increases only by breathing faster.

  Put it right: Tidal volume also rises substantially, especially at moderate intensity.

• Believing lactate is the sole cause of fatigue.

  Put it right: Hydrogen ion accumulation and other metabolic factors also contribute.

Exam tips

• For multiple-choice items, eliminate options that reverse the direction of change, such as claiming stroke volume falls during exercise.
• Check whether the question specifies pre-exercise, during exercise or recovery, because the correct response differs by phase.
• Use the relationship cardiac output = heart rate × stroke volume to test whether a numerical option is plausible.
• Read the intensity qualifier carefully: low, moderate and maximal exercise produce different dominant mechanisms.