Short-Term Effects of Exercise

When you begin exercising, your body responds immediately to meet the increased demand for energy. These responses are called short-term effects (or acute responses) because they happen during and shortly after exercise, and they reverse once you stop and rest. Understanding these effects is essential for the Edexcel GCSE PE specification (1PE0 — Topic 1: Applied Anatomy and Physiology). You must be able to describe each effect and explain why it happens.

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What Are Short-Term Effects?

Short-term effects of exercise are temporary physiological changes that occur in response to physical activity. They begin as soon as you start exercising and return to normal once you stop and recover. They are the body's way of ensuring that the working muscles receive enough oxygen and energy to sustain the activity.

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Key Short-Term Effects

1. Increased Heart Rate (HR)

During exercise, the heart beats faster to pump more blood — and therefore more oxygen and glucose — to the working muscles. At rest, the heart rate of an average adult is approximately 72 bpm. During vigorous exercise it can exceed 180 bpm or more.

Why does it increase?

• Working muscles demand more oxygen and glucose for energy production.
• More carbon dioxide needs to be removed as a waste product.
• The brain detects the increased demand and sends nerve impulses to the heart via the sympathetic nervous system, increasing the rate.
• Hormones such as adrenaline are released, which also increase heart rate.

Condition	Approximate Heart Rate
Rest (untrained adult)	60–80 bpm
Light exercise (walking)	90–110 bpm
Moderate exercise (jogging)	120–160 bpm
Vigorous exercise (sprinting)	170–200+ bpm

2. Increased Breathing Rate and Depth

Both the rate (number of breaths per minute) and depth (tidal volume — the amount of air per breath) increase during exercise.

Why?

• The body needs to take in more oxygen from the atmosphere to supply the working muscles.
• The body needs to expel more carbon dioxide, a waste product of energy production.
• Receptors called chemoreceptors in the brain and blood vessels detect rising CO₂ levels and trigger faster, deeper breathing.

Condition	Breathing Rate (breaths/min)	Tidal Volume (litres)
Rest	12–20	~0.5
Moderate exercise	30–40	~1.5–2.0
Vigorous exercise	40–60+	~2.5–3.0+

3. Increased Body Temperature

Muscles working harder produce more heat as a by-product of energy production. Core body temperature rises from about 37 °C at rest and can exceed 39 °C during intense exercise.

4. Sweating

As body temperature rises, the body activates its cooling mechanism: sweating. Sweat is produced by sweat glands in the skin and is released onto the surface. When sweat evaporates, it takes heat energy with it, cooling the body down. This process is called evaporative cooling.

5. Vasodilation and Skin Redness

Vasodilation is the widening (dilation) of blood vessels near the skin surface. This allows more blood to flow close to the skin, where heat can be lost to the environment by radiation. This is why the skin often appears red or flushed during exercise.

Exam Tip: Make sure you can distinguish between vasodilation (blood vessels widen to lose heat through the skin) and vasoconstriction (blood vessels narrow to conserve heat or redirect blood flow). Edexcel may test both.

6. Muscle Fatigue

During prolonged or high-intensity exercise, muscles begin to fatigue — they become less efficient and the performer feels tired and may experience a burning sensation. Fatigue during anaerobic exercise is largely caused by the build-up of lactic acid. During aerobic exercise, fatigue may result from the depletion of glycogen stores or dehydration.

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How Short-Term Effects Are Linked

The short-term effects of exercise are all interconnected. The following diagram shows how they relate to one another:

graph TD
    A[Exercise Begins] --> B["Muscles demand more<br>oxygen and glucose"]
    B --> C[Heart rate increases]
    B --> D["Breathing rate and<br>depth increase"]
    C --> E["More blood pumped<br>to working muscles"]
    D --> F["More oxygen inhaled<br>More CO₂ exhaled"]
    E --> G["Increased energy<br>production in muscles"]
    G --> H["Heat produced<br>as by-product"]
    H --> I[Body temperature rises]
    I --> J[Sweating begins]
    I --> K["Vasodilation occurs<br>Skin goes red"]
    G --> L["Lactic acid may<br>accumulate if anaerobic"]
    L --> M[Muscle fatigue]

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Short-Term Effects — Complete Summary Table

Effect	What Happens	Why It Happens
Heart rate	Increases	To pump more oxygenated blood to working muscles
Breathing rate	Increases	To take in more O₂ and remove more CO₂
Tidal volume	Increases	To increase the volume of air exchanged per breath
Body temperature	Rises	Heat is a by-product of increased energy production
Sweating	Begins / increases	To cool the body via evaporative cooling
Vasodilation	Blood vessels near skin widen	To allow heat loss through radiation from the skin
Skin colour	Becomes red / flushed	More blood flowing near the skin surface
Muscle fatigue	Muscles tire, performance drops	Lactic acid build-up (anaerobic) or glycogen depletion (aerobic)

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Reversibility of Short-Term Effects

All short-term effects are reversible. Once exercise stops:

• Heart rate gradually returns to its resting rate.
• Breathing rate and depth return to normal.
• Body temperature drops back to approximately 37 °C.
• Sweating decreases and eventually stops.
• Vasodilation reduces; skin colour returns to normal.
• Lactic acid is broken down during the recovery process (see later lesson on recovery).

The time it takes for the body to return to its resting state depends on the intensity and duration of the exercise, and the fitness level of the performer. A fitter person recovers more quickly.

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Applying Short-Term Effects to Exam Scenarios

Edexcel exam questions often present a scenario — for example, "A netball player has just completed a hard training session" — and ask you to describe or explain the short-term effects.

Sample 4-mark question: Describe two short-term effects of exercise on the body and explain why each occurs.

Model answer:

1. Heart rate increases because the working muscles require more oxygen and glucose for energy production, so the heart must pump blood faster to deliver these.
2. Breathing rate increases because the body needs to take in more oxygen to supply the working muscles and remove the increased carbon dioxide produced as a waste product of respiration.

Exam Tip: For "describe" questions, state what happens. For "explain" questions, state what happens and give the reason why. Always link back to the demand of the working muscles.

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Common Exam Mistakes