Immediate body responses to starting exercise

When you begin exercising, your body reacts right away to meet the increased demands for energy and oxygen. These changes help supply working muscles with what they need and continue for a short time after you stop. This immediate response involves several systems working together to support physical activity.

Key immediate changes

• Heart rate - This is the number of times the heart beats in a minute.
• Breathing rate - This measures the number of breaths taken in a minute.
• Adrenaline - A hormone produced by the body that stimulates the heart to beat faster.

These responses happen because muscles need more energy during exercise, which comes from converting glucose (a simple sugar) into usable fuel with the help of oxygen.

Cardiovascular changes during exercise

The cardiovascular system, which includes the heart and blood vessels, adapts quickly to exercise by increasing blood flow. This helps transport oxygen and remove waste products from muscles.

How heart rate increases

Heart rate rises as soon as exercise starts because the heart must pump blood faster. This delivers more oxygen to muscles, where it's used to break down glucose for energy.

Role of adrenaline

Adrenaline is released into the bloodstream during exercise. It signals the heart to contract more forcefully and frequently, boosting heart rate.

These changes ensure muscles get the oxygen they need.

Respiratory changes during exercise

The respiratory system, involving the lungs and airways, also responds immediately to exercise. It works in tandem with the cardiovascular system to supply oxygen.

Increase in breathing rate

Breathing rate goes up to allow more oxygen to enter the body through the lungs. This oxygen then passes into the bloodstream and travels to muscles for energy production.

As exercise intensity builds, deeper and faster breaths help maintain oxygen levels.

Body temperature control during exercise

Exercise generates heat as muscles contract and work harder, which can raise body temperature. The body has mechanisms to manage this and protect vital organs from overheating.

Heat generation and initial responses

Muscles produce heat through repeated contractions. If temperature rises too much, it could damage organs like the brain, so the body activates cooling processes.

Skin reddening

Blood vessels near the skin's surface dilate (widen) during exercise, causing the skin to appear redder. This allows warm blood to move closer to the surface, where it can release heat into the cooler air.

Sweating as a cooling mechanism

Sweating releases water onto the skin's surface through sweat glands. As this sweat evaporates (turns from liquid to vapour), it absorbs and carries away body heat.

These methods work together to keep your core temperature stable.

Understanding fatigue from exercise

Fatigue is extreme tiredness resulting from physical exertion, and it can occur during or shortly after exercise. It happens when muscles can't continue working effectively, often due to waste buildup or energy depletion.

Types of muscle fibres and fatigue

Muscles contain different fibre types that fatigue at varying rates:

Fast twitch fibres:

• These are used in high-intensity activities.
• They fatigue quickly due to lactic acid buildup, a waste product from energy production without enough oxygen.
• Lactic acid causes pain and blocks further energy supply to muscle cells.

Slow twitch fibres:

• Involved in low-intensity endurance activities.
• They can function for hours before fatiguing, mainly from glucose depletion rather than lactic acid.

Localised versus whole-body fatigue

• Localised fatigue - Affects specific muscles, for example, a basketball player's legs might tire after intense jumping, while their arms remain functional.
• Whole-body fatigue - In endurance activities like long-distance cycling, fatigue often affects the whole body due to widespread glucose shortage.

Recognising fatigue helps in pacing activities to avoid overexertion, and it usually resolves with rest as the body clears waste and replenishes energy.

Causes of nausea during or after exercise

Nausea is a feeling of sickness with an inclination to vomit, and it can strike during intense exercise or soon after. It's often linked to how the body prioritises resources.

Blood flow diversion

During exercise, blood is redirected from the stomach to working muscles to supply oxygen and remove waste like carbon dioxide. This slows digestion, which can upset the stomach and cause nausea, especially if food is present – it might even lead to vomiting.

Effects of hydration levels

• Dehydration - Not drinking enough water reduces blood volume, making it harder for the body to function, which can trigger nausea.
• Over-hydration - Drinking too much water dilutes electrolytes (minerals like sodium that help cells work), disrupting body functions and leading to sickness.

To minimise nausea, avoid eating heavy meals before intense activity and maintain balanced hydration.

Light-headedness after exercise

Light-headedness, or dizziness, often occurs right after stopping strenuous exercise. It's usually temporary and related to sudden changes in circulation.

Causes of light-headedness

During exercise, blood vessels enlarge to allow greater blood flow to muscles. When you stop, heart rate slows quickly, but vessels may not constrict immediately. This mismatch can cause a drop in blood pressure, reducing blood flow to the brain and leading to dizziness.

Ways to reduce light-headedness

• Take deep breaths to increase oxygen intake and stabilise blood pressure.
• Lie down with legs elevated to help blood return to the heart and brain more easily.

These steps promote recovery, and light-headedness typically fades as the body readjusts within minutes.