Practical Biology

A collection of experiments that demonstrate biological concepts and processes.

Observing the effects of exercise on the human body

Class practical

In this activity, your students are participating as subjects to provide data for analysis. This raises ethical issues, some of which could be addressed by using the briefing sheet and consent form attached. The activity involves students exerting themselves in light exercise and monitoring their heart rate for a period afterwards. Collating class data allows you to develop ideas about averages and variation within a population.

Lesson organisation

Adapt and use the attached briefing and consent form before the lesson to prepare your students for the activity. Develop a text-based alternative, or devise a non-exercising role for students who cannot or do not want to take part in the exercise activity. Set out a personal results table for individual students. Set up a class results table (on whiteboard or computer) to collect the data from the activity. If you can use a spreadsheet it will be easier to analyse the input data later. Make sure the students know how to take their pulse to measure their own heart rate. Give students an appropriate exercise to do for an appropriate time and collect the data for analysis. Identify and remove anomalous results before calculating mean averages.

Apparatus and Chemicals

For each group of students:

Stopwatch or stopclock

Access to a pulse oximeter (optional)

Bench or step to exercise on

Chocolate (optional) (Note 1)

Health & Safety and Technical notes

Doing low impact exercise as described in this procedure should be safe for most students. Ensuring that any individuals with identified health issues do not take part, and ensuring that the activity does not become competitive (and hence boisterous) should reduce the risk of the activity causing damage. Ensure that any equipment used on which students exercise is well-constructed and stable. If you choose a staircase as the site for exercise, instruct them to use the handrail and ensure by supervision that this is obeyed.

1 If you choose to observe the effects on heart rate of sucking a small piece of chocolate, you will need to think how to give students chocolate without the risk of contamination from the laboratory. This will be easier if you are working in a regular classroom, not a laboratory space.

Ethical issues

In effect, this practical uses students as participants in a piece of research. Ethical procedures associated with using students in this way should be followed. This should include:

  • explaining the purpose of the activity (openly and with no deception)
  • outlining likely results
  • being sensitive to and on the lookout for any participant who finds the results upsetting
  • offering the students a chance to opt out before beginning, or at any stage of the procedure, as well as offering the option of not submitting their data to the group set
  • providing a debrief on the activity explaining the results gathered
  • taking care about how individual results are presented in the context of the average results from the group – avoid confusion between the term ‘average’ and an idea of what is ‘normal’ or ‘expected’.

 Student briefing and consent form.


SAFETY: Supervision of activity by teachers will ensure that the activity does not become competitive or too boisterous. The activity should be appropriate to footwear and clothing worn by students, for example, walking briskly up/ down stairs or steps up onto a low bench in the lab. Students with identified physical/ health conditions should not be involved. Asthmatics may be able to take part if they use their inhalers before starting the exercise.


a Check student health status, and discuss any issues with colleagues in PE.


b Take resting heart rate and O2 saturation (if a pulse oximeter is available).

c Show the range of resting heart rate. Plot on a frequency histogram with bands of heart rate 51-55, 56-60, 61-65 etc.

d Show the range of resting O2 saturation. There will be less variation in O2 saturation than in resting heart rate.

e Discuss variation across a population. Establish that variation of some sort is what we expect to see in any measured feature of the population, but that the amount of variation may be different for different factors.

f Tell the students that they are going to do some exercise. Take heart rate again.

g Note that the warning about exercise increases the heart rate a little, and explain that some of the systems in our body can be consciously or deliberately controlled.

h Give each group of students an exercise to do – some vigorous, some less vigorous. Take heart rate again during exercise if possible. Calculate percentage increase in heart rate and plot average percentage increase in heart rate for each exercise.

i Get some student volunteers (perhaps you could select members of school sports teams as those likely to be the fittest) to do more exercise – the same exercise, but for different times.

j For each student, note how long they exercise. Take heart rate at the end of the exercise, and then every minute until the heart rate returns to near their normal level. for few minutes. Plot heart rate against time after exercise. Plot recovery time against duration of exercise.

Teaching notes

A common weakness in examination answers on this topic are that candidates do not correctly identify the beginning of the exercise.

Take care that students’ personal responses are anonymised to the rest of the group – so although each individual may see their own position in the range, the group will not identify individuals at the extremes.

Factors affecting resting heart rate:

  • The fitter you are the lower your resting heart rate. Fitness relates to how efficiently your body can release useful energy (ATP) from your food and oxygen. If you regularly do exercise then your body is more efficient. You therefore need less oxygen to produce the same amount of ATP, and therefore have a lower heart rate as you do not require a higher blood flow.
  • Caffeine makes the heart beat faster, so if you drink a lot of coffee, cola or caffeine-loaded drinks your heart rate can rise. Sucking a piece of chocolate also increases your heart rate. Your students’ heart rate could rise by around 20 beats per minute if they suck on a piece of chocolate. Although there is some caffeine in chocolate, the increase is actually due to the fact that using your mouth muscles increases your energy requirement and also to the feelings of pleasure we get from chocolate.
  • If you feel stressed, your body releases more adrenaline and this increases heart rate. So just before an exam you would expect your heart rate to increase. Your body releases adrenaline in response to chronic pain and in other situations too.
  • Even thinking about exercise – anticipating the activity – increases our heart rate by a few beats per minute. This allows the muscles to increase production of the ATP before we actually need it.

Control of heart rate from brain via autonomic nervous system
The autonomic nervous system is a specialised nervous system that controls our automatic responses, for example heart rate, digestion and breathing. These are things we do without conscious thought. Heart rate is determined by a group of specialized cells in the heart itself called the sino-atrial node. These cells act as a pacemaker to set how fast our heart beats. However, the autonomic nervous system can alter this as necessary, so that our heart beats faster or more slowly, and the force of heart muscle contraction can change, too. Signals from the brain to the heart are important in exercise (both in anticipation and once the exercise starts), in response to thoughts (such as stressful situations or the pleasure of chocolate) and in the regulation of blood pressure.

Adrenaline, intensity of exercise and recovery
Our body produces adrenaline in response to frightening, stressful or exciting situations. Adrenaline makes the heart beat faster and prepares the body for either flight (running away from danger) or fight (using the muscles to fight off a competitor or predator). More intense exercise requires a higher heart rate because the muscles need more oxygen and more food, so the heart pumps faster to deliver more blood carrying those vital components. We produce adrenaline in response to high intensity exercise over a long period. After high intensity exercise, then, the recovery period may be longer, as it will take time for the body to respond and reduce the level of adrenaline.

Oxygen debt and recovery
When we exercise, we reach a point where there isn’t enough oxygen reaching the tissues to provide the energy we need. We can shift to anaerobic respiration – releasing energy without oxygen. This generates lactic acid. When we stop exercising, our heart rate remains elevated until we have broken down the lactic acid. We need oxygen for this breakdown process, so producing lactic acid is sometimes called having an oxygen debt. So the more lactic acid you have produced, the longer it takes for your heart rate to come back to normal. If you are fit you release energy more efficiently; you tend to produce less lactic acid, and show a faster heart rate recovery than someone who is not fit. The size of the oxygen debt is the main factor in the length of the recovery period if there is little adrenaline circulating. Lactic acid in your muscles makes them painful.


Include a Student briefing and consent form and set some answers and questions in a student sheet.

Health & Safety checked, December 2008

Web links
This link is to an article called 'Just what is average?' on the BBC’s magazine area, where Michael Blastland presented a summer school in statistics. It presents the idea that most people have an above average number of legs – and explains why.

(Website accessed October 2011)