Heart rate and its changes during exercise

Heart rate is the number of times the heart beats per minute, measured in beats per minute (bpm). It provides a key indicator of how the body responds to physical activity. During exercise, the heart rate rises to meet the increased demand for blood and oxygen in the muscles, allowing them to work more effectively.

Key features of heart rate response

• Resting state - At rest, heart rate is typically lower as the body requires less oxygen and energy.
• Exercise impact - As exercise intensity increases, heart rate rises proportionally to deliver more oxygenated blood to working muscles.
• Measurement - Heart rate can be monitored using devices like heart rate monitors or by manually checking the pulse at the wrist or neck.

Calculating maximum heart rate

Maximum heart rate (MHR) is the highest number of beats per minute the heart can achieve during intense exercise. It serves as a benchmark for determining safe and effective training intensities. MHR decreases with age, reflecting changes in cardiovascular capacity over time.

Formula for maximum heart rate

$\text{MHR}=220-\text{age}$

Where:

• MHR = Maximum heart rate (bpm)
• Age = Person's age in years

This formula provides a theoretical estimate, which can vary slightly between individuals due to factors like genetics and fitness level. It forms the basis for calculating training zones.

Aerobic and anaerobic target zones

Target zones are specific heart rate ranges that guide training intensity to improve either aerobic or anaerobic fitness. Aerobic activity involves sustained exercise using oxygen to break down glucose for energy, while anaerobic activity relies on energy production without oxygen, often for short, high-intensity bursts.

Key target zones

• Aerobic target zone - 60%-80% of MHR; focuses on building endurance and cardiovascular efficiency.
• Anaerobic target zone - 80%-90% of MHR; develops tolerance to lactic acid and improves power for explosive movements.

Training thresholds

Training thresholds are the boundaries that define the lower and upper limits of each target zone. They help tailor training to individual needs, preventing overexertion or undertraining. Beginners should aim closer to the lower threshold to build fitness safely, while experienced athletes can push towards the upper threshold for greater gains.

Calculating target zones with examples

To find a target zone, first calculate the MHR, then determine the percentages for the lower and upper thresholds. This process allows athletes to set personalised heart rate goals for their workouts.

Steps for calculating a target zone

1. Calculate MHR using the formula: MHR = 220 - age.
2. Multiply MHR by the lower percentage (e.g., 0.6 for aerobic lower threshold).
3. Multiply MHR by the upper percentage (e.g., 0.8 for aerobic upper threshold).
4. The target zone is the range between these two values in bpm.

For anaerobic zones, use 0.8 and 0.9 as the multipliers.

Worked example - Calculating aerobic target zone

Calculate the aerobic target zone for a 25-year-old person.

Step 1: Calculate maximum heart rate

$\text{MHR}=220-25=195\text{ bpm}$

Step 2: Calculate lower threshold

Lower threshold (60% of MHR) = $195\times 0.6=117$ bpm

Step 3: Calculate upper threshold

Upper threshold (80% of MHR) = $195\times 0.8=156$ bpm

Step 4: State the target zone

The aerobic target zone is between 117 and 156 bpm.

Worked example - Calculating anaerobic target zone

Calculate the anaerobic target zone for a 30-year-old person.

Step 1: Calculate maximum heart rate

$\text{MHR}=220-30=190\text{ bpm}$

Step 2: Calculate lower threshold

Lower threshold (80% of MHR) = $190\times 0.8=152$ bpm

Step 3: Calculate upper threshold

Upper threshold (90% of MHR) = $190\times 0.9=171$ bpm

Step 4: State the target zone

The anaerobic target zone is between 152 and 171 bpm.

Matching training intensity to different activities

Training should align with the demands of the specific activity to optimise performance. Aerobic training enhances the cardiovascular system for endurance, while anaerobic training builds muscle tolerance to lactic acid, a byproduct of high-intensity efforts that can cause fatigue.

Training recommendations by activity type

• Aerobic activities (e.g., long-distance running or cycling) - Focus on aerobic target zones to improve oxygen delivery and stamina.
• Anaerobic activities (e.g., sprinting or weightlifting) - Emphasise anaerobic target zones to enhance power and lactic acid management.
• Mixed activities (e.g., team sports like lacrosse or football) - Combine both zones, as they require sustained movement with bursts of speed.