Graphing pulse rates at Year 6

Rhona Dick
rhona.dick@mape.org.uk
This article first appeared in MAPE Focus on Science Autumn 2000

Year 6 had been looking at some graphs of the effect of exercise on the heart. Their teacher asked me if I could take a few of them and show them how a database or spreadsheet program can take raw data and, from that, generate a graph.

That would have been easy, but I suggested that it might be a good idea to take it one stage further and get the children to produce the data for themselves.

I spent a little time talking with the children about what they had learnt about exercise and the heart. They knew that the heart speeded up during exercise and were able to tell me that this was to increase the blood flow and hence oxygen supply to the body. Some of them had sensed their heart 'thumping away' when exercising vigorously, but none of them had ever tried to measure their pulse rate.

As I had not had advance warning of this activity I hadn't come prepared with stopwatch, clipboard etc., but we compromised by using a pupil's digital watch complete with every function you could possibly imagine! After some minutes' tuition from the pupil on how this piece of technology would enable me to work out the time in every city I might ever want to phone, calculate how much longer I could stay submerged at a depth of 30 metres without getting the bends as well as several other irrelevancies, I eventually got the hang of the stopwatch function.

Before we could begin we had to decide:

Initially the children were rather bemused.

Suggestions like 'Run for a bit and then count your heart beat' and further discussion eventually prompted the questions:

  1. 'Have we anything to compare heart rate after exercise with?'
  2. 'How long should we run for?'
  3. 'How long should we count for?'
  4. 'How often should we count our pulse rate?'

1. 'Have we anything to compare heart rate after exercise with?'

One pupil suggested we start with the at-rest pulse.

The children decided they would measure their own heart rate. On reflection it would probably have been better to work in pairs, but the group I had were lively and not particularly good at collaborative work.

Herein was the first problem.

2. 'How long should we run for?'

I decided on 3 minutes running up and down the hall. This should give their hearts a chance to work hard. It was evident that some of these children were fitter than others; however, they all managed to run for the 3 minutes.

Immediately they had to record their pulse rates again.

3. 'How long should we count for?'

I had noticed that children found it difficult to keep up the count for a minute, so we decided upon 30 seconds. The children were able to tell me that to find what the pulse rate would be for a minute they would double that figure. One child in particular found it difficult to keep track of his pulse for even half a minute and so he counted for 15 seconds, doubled the figure and doubled that.

As a group we discussed this and reached the conclusion that it would give a slightly less accurate reading, but would be adequate for our needs. In fact all the children adopted this strategy.

4. 'How often should we count our pulse rate?'

This was difficult, as I had no idea how quickly their heart rates would return to normal. In the end we decided on counting every 2 minutes.

Using Excel

When everyone had collected their data to the best of their ability we loaded Excel. Most of the children had never used this before and so I had to explain briefly what it could do for us.

They were quick to pick up the main points, but spent a long time deciding on which type of pictorial representation they liked the best, regardless of how appropriate it might be. This was interesting and prompted the question 'Why do we draw graphs?'

This was met with a disbelieving look, and it took some discussion to identify the idea that it makes information easily understood at a glance.

They took some convincing that a pie chart did not clearly show what was happening to their heartbeat.

After having another look at the types of charts available to them all eventually opted for the safe bar chart, created them and printed them off.

The children eagerly compared their graphs at this point and noticed that Pupil D seemed to have a higher pulse rate 4 minutes after rest than 2 minutes after rest. It was almost unanimously agreed that Pupil D had miscounted, but which figure was incorrect? Another look at the graph suggested that it was the 2 minute reading, as all others seemed to fit a pattern.

I had hoped that at least one would have selected a line graph, but no one did so I suggested it.

The children did not seem to have met the idea of continuous data before, and without exception they found it difficult to understand why a line graph was appropriate in this instance.

What did the children learn?

They were able to experience for themselves the effect of exercise on the heart.

They learnt how to enter data in Excel and how to create a graph from the data.

They now appreciate the reason for creating graphs.

They have been introduced to the idea of continuous measurement of data.

What did I learn?

I learnt that this is not an activity to undertake with a whole class simultaneously!

How successful was the activity?

It met the learning objectives in that the children generated their own raw data, entered it in a suitable software package, and created graphs.

I had assumed that the children would be able to locate and count their pulse for 15 seconds every 2 minutes when I told them to. This was not the case, and in general I found I was doing a lot of the pulse taking.

I was initially concerned at the degree of accuracy; however, as in the case of Pupil D, this proved to be a hidden blessing as it gave us the opportunity to interpret the graphs.

How would I adapt this for future use?

1. Children should work in pairs. I'm sure some of the problems of counting arose from the fact that they were out of breath while trying to count their heartbeats.

2. If I knew there was a parent helper who was a nurse I'd probably enlist his/her help with taking pulses.

3. I'd try to find one of those natty little machines that clips on the end of your finger and appears in every episode of Casualty I've ever watched!

Links with Science Explorer (time-limited CD supplied in this pack)

Science Explorer includes a virtual experiment demonstrating the effects of exercise on the heart. I don't think it is a substitute for the real thing, but could be beneficially used in combination with empirical methods, and could throw up all sorts of interesting points for discussion such as:

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