How can you plan an experiment that you could carry out with your class to measure their fitness

So the question in whole is this:

The time a person takes to recover after exercise is often used as a measure of fitness. A program of activities involving measuring the time for recovery is one of the methods used by the army to judge the fitness of new recruits.
(The recovery time is the time the pulse rate takes to return to normal after exercise.)
Plan an experiment that you could carry out with your class to measure their fitness.

Would really appreciate help with this :)

Okay, so consider all the things you need in an experiment. You need a way to measure fitness (btw, is your class really using the term 'fitness' for this? Because 'fitness' is also the term used to describe the number of viable offspring an organism has--I was totally a little worried when I read your question, lol), and data to compare. This means you need a control.

Here is what I would do.

I would have you class measure their pulse rates for 30 seconds three separate times in a five minute window (or you, knowing more about this than I do, can adjust the time). This would be our baseline measurement, or our control. I'd then have them exercise for 5-10 minutes (remember to be consistent!) and then have them measure their pulse rates for 30 seconds three times within five minutes again.

You might want to repeat a couple times to get the most accurate data you can. At this point, I would find a way to normalize the data (because everyone has different fitness, and some super jock is obviously going to have greater fitness than someone who never works out).