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E1.1 · Assess effects of performance-enhancing substances on the body

Learn to assess effects of performance-enhancing substances on the body through clear examples and targeted practice.

Ontario Grade 12 Biology

Homeostasis

Assessing possible benefits, biological effects, and risks

A substance may improve one part of performance while placing stress on other parts of the body. For example, a substance that increases red blood cell production may help transport oxygen, but can also make blood flow more difficult. To assess a substance, consider both the intended effect and the possible effects on body systems. Assessment also requires careful attention to evidence: a result in one person or one study does not prove that the same result will occur in everyone.

What you will learn

Describe how selected performance-enhancing substances can affect body systems.
Compare a possible performance benefit with effects on health.
Use evidence carefully and explain what a result does and does not show.

1. Bridge from SBI3U: bodies are connected systems

In SBI3U, you learned that body systems work together to keep the body functioning. The circulatory system transports materials, the respiratory system brings oxygen into the body, and the nervous and endocrine systems help coordinate responses. The endocrine system is the set of glands and organs that release hormones, which are chemical messengers.

A performance-enhancing substance is a substance used with the aim of improving athletic ability, such as strength, speed, endurance, or alertness. Some substances act in ways similar to hormones. Others affect how active or alert the body feels. A substance can affect more than one body system, so an assessment should not focus only on whether performance changes.

The basic question is not simply, “Does it work?” Ask: What performance effect is intended? Which body systems may be affected? What harms may occur? How strong is the evidence?

Body systems interact, so an effect in one system can affect another.
Assess both the intended performance effect and possible health effects.
A performance change alone does not establish that a substance is safe.

2. Examples of effects on body systems

Anabolic steroids are substances related to the hormone testosterone. They can increase muscle-building processes, which may increase muscle size or strength. However, they can interfere with the body's own hormone regulation. Possible effects include changes to reproductive function, mood, skin, and the liver. The type and severity of effects can vary with the substance, amount, duration of use, and person.

Stimulants are substances that increase activity in parts of the nervous system. They may increase alertness or reduce the feeling of tiredness. Some can also raise heart rate and blood pressure. This may put extra strain on the cardiovascular system, which includes the heart and blood vessels. Feeling more alert does not mean the body is less tired or protected from harm.

Erythropoietin, often shortened to EPO, is a hormone that signals the body to make more red blood cells. Red blood cells carry oxygen. More red blood cells may increase oxygen transport, which can support endurance. But a higher red blood cell concentration can make blood thicker and harder to move through blood vessels. This can increase the risk of dangerous circulation problems.

These examples show why effects must be considered together. An intended benefit can occur alongside an unwanted effect. A person's health, the dose, and the length of use can change the outcome. A general description is not a prediction for a particular person.

Anabolic steroids may affect muscle development and hormone regulation.
Stimulants may affect alertness as well as heart rate and blood pressure.
EPO may increase oxygen transport while also making circulation more difficult.

3. A model for assessing evidence

A useful assessment separates three ideas: the intended effect, the measured result, and the possible health cost. A measured result is an observation collected in a study, such as a change in strength or heart rate. It is not automatically proof that the substance caused every change. Other factors, such as training, sleep, health, or the way a study was conducted, may also matter.

Consider a hypothetical comparison in which one group uses a substance and another does not. If the first group shows a larger average change in a performance measure, that is evidence of a possible effect under those study conditions. It does not show that every user will benefit, that the benefit will last, or that the substance is safe. Stronger conclusions require suitable comparisons and evidence about both benefits and harms.

A percentage change can help describe a measurement, but it cannot by itself judge whether a substance is safe or worthwhile. Compare the result with the health effects and the quality of the evidence. For example, a small performance improvement may not outweigh a serious possible effect on the heart or circulation.

The evidence has limits. A short study may not detect harms that develop over a longer time. A study of adults may not describe effects in adolescents. Also, people may respond differently. These limits do not prove that a substance is harmful or harmless; they show where conclusions should remain cautious.

\text{percentage change}=\frac{\text{new value}-\text{starting value}}{\text{starting value}}\times100\%

Distinguish an observed change from a proven cause.
Consider study conditions, duration, participants, and both benefits and harms.
A calculation describes a result; it does not make the health decision.

4. Reaching a balanced conclusion

A balanced conclusion names the possible performance benefit, the body systems affected, and the important risks or unknowns. It avoids saying that a substance is safe simply because a performance measure improved. It also avoids claiming that every person will experience the same harm.

Use cautious wording that matches the evidence. For example: “In this comparison, the group using the substance had a larger average increase in the measured outcome. The result suggests a possible performance benefit under these conditions. It does not establish long-term safety or predict the effect on every person.”

This approach keeps the assessment focused on the expectation: effects on the body. It connects the desired performance change to body-system effects and evaluates how much confidence the evidence supports.

State what the evidence suggests and what it cannot establish.
Weigh performance effects against possible body-system harms.
Do not turn a general finding into medical advice for an individual.

Examples of intended effects and possible body effects

Substance	Possible intended effect	Possible body-system concern
Anabolic steroids	Greater muscle development or strength	Interference with hormone regulation; possible effects on reproductive function, mood, skin, or liver
Stimulants	Greater alertness or reduced feeling of tiredness	Possible increase in heart rate and blood pressure
EPO	More red blood cells may support oxygen transport and endurance	Thicker blood can make circulation more difficult

Worked example

Comparing possible benefit and body-system effects

A student is asked to assess EPO for endurance performance. Explain one possible benefit and one possible harm using a body-system connection.

Identify the intended effect
EPO signals the body to produce more red blood cells. Red blood cells carry oxygen, so increased oxygen transport may support endurance.
Connect the effect to a possible harm
A higher red blood cell concentration can make blood thicker. This can make circulation more difficult and increase the risk of serious problems in the cardiovascular system.
State a balanced assessment
EPO may support endurance through oxygen transport, but the same change can create a circulation risk. The possible benefit does not establish that use is safe.

Answer: EPO may support endurance by increasing the number of oxygen-carrying red blood cells. However, increased red blood cell concentration can make circulation more difficult and raise health risks.

Check: The answer links a possible performance effect to both the circulatory benefit and a possible harm.

Worked example

Calculating a percentage change

In a hypothetical classroom example, a performance measure changes from 40 units before a program to 46 units after it. Calculate the percentage change. The numbers are invented for practice and are not experimental findings.

Find the change
Subtract the starting value from the new value. This gives the increase in the same units as the measurement.
$46-40=6$
Compare with the starting value
Divide the increase by the starting value, because percentage change is measured relative to where the result began.
$\frac{6}{40}=0.15$
Convert to a percentage
Multiply by 100 to express the decimal as a percentage. This describes the size of the change, not its cause or safety.
$0.15\times100\%=15\%$

Answer: The measure increased by 15%.

Check: The calculation uses the starting value, 40, as the comparison point.

Worked example

Judging what a study result supports

A hypothetical short study reports that a stimulant group had higher average alertness scores than a comparison group. The study did not measure long-term health effects. Write a conclusion that matches this evidence.

Report the observed result
The evidence supports saying that the stimulant group had higher average alertness scores in this study.
Avoid claiming more than was measured
The result does not establish that the stimulant caused every difference, improved all forms of performance, or was safe over a longer period.
Include a relevant body-system concern
Stimulants can affect the nervous system and may also raise heart rate or blood pressure. Since long-term health was not measured, the study cannot settle those possible effects.

Answer: The study suggests that the stimulant may increase alertness under the study conditions. It does not establish long-term safety or show that every user would have the same response.

Check: The conclusion reports the measured finding and clearly states an important limit.

Common mistakes and how to avoid them

Concluding that a substance is safe because one performance measure improved.

Correction: Assess the possible health effects as well as the performance result. Improvement in one measure does not establish safety.

Treating a study result as proof that the substance caused every difference.

Correction: Describe what was observed and consider other factors and study limits before making a causal claim.

Assuming every person will have the same benefit or harm.

Correction: Responses can vary. Match the conclusion to the people and conditions studied.

Lesson summary

Performance-enhancing substances can affect several body systems.
An intended benefit may occur alongside unwanted effects.
Assess evidence by considering the measured result, study limits, and possible harms.
A percentage change describes a measurement; it does not prove cause or safety.

Check your understanding

Question 1

Which statement best assesses EPO's possible effects?

It may support oxygen transport, but increased red blood cell concentration can make circulation more difficult.
It improves endurance and therefore has no important effect on other body systems.
It affects only muscles because endurance is a physical performance.
It guarantees the same benefit for every person.

Show answer and explanation

It may support oxygen transport, but increased red blood cell concentration can make circulation more difficult.

This choice identifies a possible performance benefit and a possible circulatory harm without claiming a guaranteed outcome.

Question 2

A study measures alertness for a short time but does not follow participants' health over a longer period. What conclusion is best supported?

The study proves the substance is safe over the long term.
The study may show a short-term alertness effect under its conditions, but it cannot establish long-term safety.
The study proves that every participant will become more alert.
The study shows that no body system other than the nervous system can be affected.

Show answer and explanation

The study may show a short-term alertness effect under its conditions, but it cannot establish long-term safety.

A short study can support a conclusion about what it measured under its conditions, but it cannot settle effects it did not measure.

Question 3

A result rises from 50 units to 55 units. What is the percentage change?

5%
10%
50%
110%

Show answer and explanation

10%

The increase is 5 units. Relative to the starting value, the change is

\frac{5}{50}\times100\%=10\%

Key terms

Performance-enhancing substance: A substance used with the aim of improving an aspect of athletic ability.
Hormone: A chemical messenger released by a gland or organ that affects body processes.
Stimulant: A substance that increases activity in parts of the nervous system.
Cardiovascular system: The heart and blood vessels, which move blood through the body.
Evidence: Information, such as measured results, used to support or assess a conclusion.

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Published by DoAssignment. This reviewed lesson follows Ontario Grade 12 Biology (SBI4U), expectation E1.1. It is a study resource, not an official curriculum publication.

Before publication, content is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability. Errors can still occur, so corrections are welcomed.

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