How many participants do I need for an IB SEHS IA experiment?

The IB does not prescribe one universal minimum number of participants for an SEHS scientific investigation. Your sample must be sufficient to reveal variation and support the analysis you intend to use, while remaining manageable and ethical. Human physiological data are often highly variable, so very small samples can produce unstable means and weak statistical conclusions. Use a pilot study to estimate variability, then discuss a realistic sample and statistical plan with your teacher. If recruitment is limited, a carefully controlled repeated-measures design is usually more informative than dividing a small sample into separate groups.

Does an IB SEHS IA have to involve human participants?

SEHS investigations commonly involve human participants because the subject examines human physiology, biomechanics, psychology, nutrition, exercise, and health. However, the precise permitted approaches depend on the current course requirements, your research question, and your teacher’s approval. Primary physiological experiments are often effective because they connect a controlled activity to a measurable response. Secondary-data investigations may also be possible where their methodology satisfies the scientific investigation requirements. Confirm the acceptability of your intended data source with your teacher before developing the full design.

Can I investigate caffeine or energy drinks in my SEHS IA?

You must not administer caffeine, energy drinks, dietary supplements, medicines, alcohol, or other substances to participants as part of an IB student experiment. This restriction applies even if participants regularly consume the product outside the investigation. Asking participants to consume a substance introduces ethical, medical, dosage, and consent risks that are inappropriate for a school investigation. You may discuss published research about caffeine when establishing scientific context, but it should not become an intervention you conduct. Choose a safer variable such as recovery activity, warm-up structure, cadence, posture, or rest duration.

What makes a physiological dependent variable suitable for an SEHS IA?

A suitable dependent variable is quantitative, relevant to the research question, measurable with available equipment, and sensitive enough to detect the expected effect. Examples include heart rate recovery, reaction time, respiratory rate, jump height, movement velocity, or blood pressure when appropriately supervised. Define exactly when and how the measurement is taken rather than writing only the name of the variable. Check instrument resolution, sampling rate, calibration, and likely measurement error during the pilot. The best variable is not the most advanced one, but the one you can measure consistently and interpret physiologically.

Should I use a repeated-measures or independent-groups design?

A repeated-measures design is often preferable because every participant completes each condition and therefore acts as their own control. This reduces the influence of differences in fitness, age, body size, training history, and baseline physiology. You must still address order effects by randomizing or counterbalancing conditions and providing adequate recovery. An independent-groups design may be necessary when one condition has a lasting effect or repeated testing is impractical. However, it normally requires larger, well-matched groups to distinguish the treatment effect from participant differences.

Do I need informed consent and a PAR-Q for my SEHS IA?

Written informed consent is required for planned IB experimentation involving human participants, and the study must receive approval from the supervising teacher. Participants must understand the procedure, foreseeable risks, confidentiality arrangements, and their right to withdraw. The IB experimentation guidance requires parental or guardian permission for participants under 16, although schools or local regulations may impose stricter requirements. A health declaration such as a PAR-Q is required when the investigation involves moderate-to-vigorous physical activity. Screening does not make an unsafe protocol acceptable, so you still need a risk assessment, appropriate supervision, and clear stop criteria.

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How to Design an IB SEHS IA Experiment That Works

IB Sports Exercise and Health Science Internal Assessment IB IA

• 1 Oct 2026•11

How to Design an IB SEHS IA Experiment That Works

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How to Design an IB SEHS IA Experiment That Works | RevisionDojo

Back to all posts

How to Design an IB SEHS IA Experiment That Works

IB Sports Exercise and Health Science Internal Assessment IB IA

• 1 Oct 2026•11

An effective IB SEHS IA experiment does not need to be complicated. It needs a focused question, measurable physiological data, a reproducible method, and appropriate ethical protection for participants.

For the SEHS course first assessed in 2026, the IA is officially called the scientific investigation. It is worth 24% of the final grade, is allocated approximately 10 hours, and has a maximum overall word count of 3,200 words. Your design must therefore produce analysable evidence within realistic school constraints.

Start with a testable research question

A useful structure is:

How does independent variable X affect physiological dependent variable Y in defined participants, measured using method Z?

For example:

How does seated passive recovery compared with low-intensity walking affect heart rate recovery during the first three minutes after a standardized submaximal step test in physically active students aged 16-18?

This identifies the recovery conditions, physiological response, measurement period, exercise protocol, and participant group. It also supports discussion of venous return, autonomic recovery, cardiac output, and the muscle pump.

Avoid broad questions such as “How does exercise affect heart rate?” Exercise intensity, duration, participants, and measurement timing are undefined. The RevisionDojo SEHS IA ideas guide can help turn a general interest into a controlled investigation.

Check feasibility before committing

A workable SEHS IA design must fit your equipment, timetable, participant access, and school safety rules. Before committing, ask:

Can the independent variable be manipulated consistently?
Can the dependent variable be measured quantitatively?
Can important participant and environmental factors be standardized?
Can every condition be completed safely?
Will the method generate enough relevant data?
Can the mechanism be explained using SEHS concepts?

Heart rate, reaction time, respiratory rate, blood pressure, jump height, and perceived exertion can all support strong investigations when measured carefully. Expensive equipment cannot compensate for an inconsistent procedure.

The official IB SEHS subject brief describes an open-ended task in which students gather and analyse data to answer their own question. It does not prescribe one universal number of participants, trials, or variable levels. Numerical targets supplied elsewhere are therefore design advice, not official IB minimums.

Define every variable operationally

An operational definition tells another researcher exactly how a variable was changed or measured.

Variable type	Recovery experiment example	Operational detail
Independent variable	Recovery condition	Seated recovery or walking at a fixed metronome cadence
Dependent variable	Heart rate recovery	Difference between post-exercise heart rate and heart rate after 60, 120, and 180 seconds
Controlled variables	Step rate, step height, duration, room conditions	Use identical equipment, timings, instructions, and location
Participant factors	Fitness, sleep, food, prior activity	Issue consistent pre-test instructions and record deviations

Heart rate recovery can be calculated as post-exercise heart rate minus heart rate at time t. Select one primary outcome before collecting data. Measuring numerous outcomes without a clear purpose increases workload and encourages selective interpretation.

Reduce participant variation

A repeated-measures design, in which every participant completes every condition, is often suitable for physiological investigations. Participants act as their own controls, reducing the influence of fitness, body size, genetics, and baseline recovery rate.

In the recovery example, each participant completes the step test twice. Randomize or counterbalance condition order so fatigue or familiarity does not consistently favour one condition. Allow suitable recovery between sessions and keep the environment consistent.

Sleep, hydration, recent training, illness, meals, and temperature can still affect results. Standardize what you realistically can, record relevant deviations, and discuss remaining variation honestly.

Build ethics and safety into the method

Human physiology experiments require teacher approval before recruitment or testing. IB sciences experimentation guidance states that written informed consent is mandatory, parental or guardian consent is required for participants under 16, and health screening such as a PAR-Q is required for moderate-to-vigorous physical activity. Schools may impose stricter rules.

Participants must understand the procedure, foreseeable discomfort, confidentiality arrangements, data use, and right to stop without penalty. Replace names with participant codes in data files and reports.

A suitable risk assessment should include:

health screening and justified inclusion criteria
an appropriate warm-up
a safe, preferably submaximal workload
supervision and an unobstructed testing area
water and adequate recovery time
stop criteria for pain, dizziness, unusual breathlessness, poor coordination, or participant withdrawal
secure storage and disposal of identifiable information

IB guidance prohibits student experiments that administer alcohol, medicines, supplements, caffeinated drinks, or energy drinks. Experiments involving body fluids such as blood, saliva, urine, or sweat are also prohibited because of pathogen-transmission risks. Testing caffeine consumption or collecting blood lactate is therefore unsuitable.

Pilot the complete procedure

A pilot study is a small-scale rehearsal of the complete method, not one practice reading. Use it to check whether:

the workload produces a measurable but safe response
equipment records reliably during movement
measurement intervals capture the expected change
instructions are interpreted consistently
the session fits the available time
conditions differ enough to permit comparison

If heart rate approaches baseline before the first interval, measure sooner or use continuous monitoring. If the activity is too demanding, reduce the workload. Record significant revisions and explain their scientific basis. The RevisionDojo science IA experiment guide provides additional planning guidance.

Plan the analysis before testing

Decide what your raw table, processed table, graph, and statistical comparison will contain before data collection. For a two-condition repeated-measures investigation, useful processing may include:

recovery values for each participant and condition
mean or median values
standard deviation or interquartile range
paired differences between conditions
individual paired observations or summaries with variability
an appropriate paired statistical test

A paired t-test may suit approximately normally distributed paired differences. A Wilcoxon signed-rank test may be preferable when its assumptions are satisfied and normality is not defensible. Explain what the chosen test evaluates and interpret it alongside effect size, variability, uncertainty, and physiological importance.

Heart-rate monitors have sampling, movement-artifact, fit, and response-delay limitations. Record the model and settings, use equipment consistently, and explain how measurement limitations affect confidence in the conclusion.

Avoid common design mistakes

Do not choose maximal exhaustion, deliberate dehydration, supplements, or extreme conditions merely to make the investigation appear advanced. Controlled submaximal protocols are safer and often produce more consistent data.

Repeated readings from one participant are not independent biological replicates. Similarly, changing multiple variables at once creates confounding. Comparing fast running with music against slow running without music cannot isolate the effect of either speed or music.

Controls must also be practical. “Keep fitness constant” is not a method. Use repeated measures, define inclusion criteria, record training background, or measure a relevant participant characteristic. Human variation cannot be eliminated, but it can be reduced and evaluated.

Final pre-testing checklist

Before recruitment, obtain teacher approval for the question, protocol, consent process, screening, and risk assessment. Confirm that you have:

one focused question and primary outcome
operational definitions for every variable
justified participant criteria
a reproducible timed procedure
randomization or counterbalancing where needed
consent, confidentiality, withdrawal, and stop procedures
a completed pilot with documented revisions
raw-data tables with units and instrument precision
a planned graph and statistical method

The RevisionDojo SEHS resource hub and SEHS study notes can support your physiological explanation. The SEHS IA Grader can then help you review alignment with Research design, Data analysis, Conclusion, and Evaluation.

Conclusion

A successful IB SEHS IA experiment produces evidence that is safe to collect, relevant to the question, and suitable for honest analysis. Prioritize operational definitions, controlled testing, ethical judgement, piloting, and analysis planning over unnecessary complexity. RevisionDojo’s SEHS notes and rubric-based IA feedback can help refine the final investigation after your teacher approves the protocol.