SingaporeSports ScienceSyllabus dot point

How is training intensity measured, and where do the aerobic and anaerobic training thresholds lie?

Explain training intensity using heart-rate thresholds and determine which training zone a measured heart rate falls into

A focused answer to the O-Level ESS outcome on training intensity. Measuring intensity, the aerobic and anaerobic heart-rate thresholds, and deciding which training zone a heart rate falls into.

Generated by Claude Opus 4.88 min answerUpdated 2026-06-06

Reviewed by: AI editorial process; not yet individually human-reviewed

Have a quick question? Jump to the Q&A page

Jump to a section

What this dot point is asking
The answer
Examples in context
Try this

What this dot point is asking

SEAB wants you to explain how training intensity is measured and where the aerobic and anaerobic thresholds lie, then to decide which training zone a measured heart rate falls into. The central idea is that intensity can be set precisely using heart-rate zones, and that training in the right zone develops the fitness you are aiming for.

The answer

Measuring training intensity

Intensity is how hard you train, and the simplest measure in the field is heart rate. Because heart rate rises with effort, a given percentage of maximum heart rate corresponds to a given intensity. The maximum heart rate is estimated as:

\text{HR}_{\max} = 220 - \text{age}

Training zones and thresholds

A training threshold is a heart-rate boundary that marks where a type of fitness is developed.

The aerobic threshold is around 60 percent of maximum heart rate. Below it, training is too easy to improve fitness much.
The aerobic training zone runs from about 60 percent to 80 percent of maximum. Training here develops cardiovascular (aerobic) fitness.
The anaerobic threshold is around 80 percent of maximum. Above it the body relies heavily on anaerobic energy and lactic acid builds up quickly.
The anaerobic training zone runs from about 80 percent to 90 percent of maximum. Training here develops anaerobic fitness and speed but cannot be sustained for long.

Choosing the right zone

The zone you train in depends on the goal. A distance runner trains mostly in the aerobic zone to build endurance; a sprinter or games player spends time in the anaerobic zone to build speed and tolerance of lactic acid. Knowing your zones lets you set intensity deliberately rather than by guesswork.

Deciding which zone a heart rate falls into

A 20-year-old trains at a measured heart rate of $160\ \text{bpm}$ . The aerobic zone is 60 to 80 percent and the anaerobic zone 80 to 90 percent of maximum. Find the zone. Work through it.

Step 1: Find the maximum heart rate

\text{HR}_{\max} = 220 - 20 = 200\ \text{bpm}

Step 2: Calculate the aerobic zone

Lower edge: $0.60 \times 200 = 120\ \text{bpm}$ . Upper edge: $0.80 \times 200 = 160\ \text{bpm}$ . So the aerobic zone is $120$ to $160\ \text{bpm}$ .

Step 3: Calculate the anaerobic zone

Lower edge: $0.80 \times 200 = 160\ \text{bpm}$ . Upper edge: $0.90 \times 200 = 180\ \text{bpm}$ . So the anaerobic zone is $160$ to $180\ \text{bpm}$ .

Step 4: Place the measured heart rate

A heart rate of $160\ \text{bpm}$ sits right at the boundary: the top of the aerobic zone and the bottom of the anaerobic zone, which is the anaerobic threshold. So the athlete is training at the very top of the aerobic zone, on the edge of anaerobic work. Show the maximum, both zones and the placement to earn full marks.

Examples in context

Example 1. A marathon runner on a long run. The runner keeps their heart rate in the aerobic zone, around 65 to 75 percent of maximum, so they build endurance without accumulating lactic acid. Drifting above the anaerobic threshold would force them to slow, which is why pacing by heart rate matters in endurance events.

Example 2. A boxer doing high-intensity rounds. During hard rounds the boxer's heart rate climbs into the anaerobic zone above 80 percent of maximum, building the anaerobic fitness and lactic-acid tolerance a bout demands. The recovery between rounds lets the heart rate fall before the next effort.

Try this

Cue. Calculate the aerobic training zone (60 to 80 percent) for a 30-year-old. (Maximum $220 - 30 = 190$ ; zone is $0.60 \times 190 = 114$ to $0.80 \times 190 = 152\ \text{bpm}$ .)
Cue. State roughly where the aerobic and anaerobic thresholds sit as percentages of maximum heart rate. (Aerobic threshold around 60 percent; anaerobic threshold around 80 percent.)
Cue. Explain which zone a distance runner should train in for most sessions and why. (The aerobic zone, about 60 to 80 percent, to build cardiovascular endurance without excessive lactic acid build-up.)

Exam-style practice questions

Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Original5 marksA 20-year-old trains with a measured heart rate of

160\ \text{bpm}

. The aerobic training zone is 60 to 80 percent of maximum and the anaerobic zone is 80 to 90 percent. Determine which zone they are training in.

Show worked answer →

Maximum heart rate: $220 - 20 = 200\ \text{bpm}$ .

Aerobic zone: $0.60 \times 200 = 120\ \text{bpm}$ up to $0.80 \times 200 = 160\ \text{bpm}$ , so $120$ to $160\ \text{bpm}$ .

Anaerobic zone: $0.80 \times 200 = 160\ \text{bpm}$ up to $0.90 \times 200 = 180\ \text{bpm}$ , so $160$ to $180\ \text{bpm}$ .

A heart rate of $160\ \text{bpm}$ sits exactly at the top of the aerobic zone and the bottom of the anaerobic zone (the aerobic threshold), so the athlete is training at the upper limit of the aerobic zone, on the edge of anaerobic work.

What markers reward: the correct maximum heart rate, both zones calculated as ranges, and the conclusion that 160 bpm sits at the boundary between the two zones.

Original4 marksExplain what is meant by a training threshold, and state why training above the aerobic threshold but below the anaerobic threshold develops aerobic fitness.

Show worked answer →

A training threshold is a heart-rate boundary that marks where a particular type of fitness is developed. The aerobic threshold is the lower boundary (around 60 percent of maximum) above which aerobic fitness improves; the anaerobic threshold (around 80 percent) is where the body starts to rely heavily on anaerobic energy and lactic acid builds up.

Training between the two thresholds keeps the athlete working hard enough to stress the aerobic system (above 60 percent) but not so hard that they tip into heavy anaerobic work, so the heart, lungs and aerobic system are developed without rapid fatigue.

What markers reward: defining a threshold as a heart-rate boundary for a type of training, and explaining that the aerobic zone lies above 60 percent and below the anaerobic threshold so aerobic fitness improves without excessive lactic acid.