Experimental variable and control variables in a science experiment?

im doing a science project, its about the average heart rates of people who regularly exercise vs. people who don't exercise, when they are both simply sitting down in a chair. what would be the experimental variable and control variable in my experiment?Experimental variable and control variables in a science experiment?
control: not sitting


experimental: sittingExperimental variable and control variables in a science experiment?
OK, an important starting question: are you running an experiment (taking two groups of people, having one exercise regularly and one not exercise to observe the effects of exercise), or are you doing a correlational study (looking at people's heart rates and how much they exercise to discover a correlation between the two)?





This is an important difference because if effects the conclusions you can make. If you do an actual experiment, where you start out with people who are the same and then alter some aspect of their lives to see the effect, you can say with a fair degree of certainty that the change to you made to their exercise schedules actually caused the change in their heart rate. However, if you're merely observing people with different exercise levels, there could be other factors involved. For example maybe people who exercise a lot also eat healthier, which could change their heart rates. So you can't definitely say that exercise changes heart rate--you can only say that people who exercise more have lower (or higher, as the case may be) heart rates.





If you do a correlational study, then the two variables you're correlating are exercise and heart rate. There won't be a control and experimental group because there's no experiment taking place. If you do an actual experiment, here's how experimental groups work:





You have an independent variable and a dependent variable; the variable you change is the independent variable, in this case, exercise. Then, the dependent variable is the variable which you think is dependent on exercise, in this case, it's heart rate.





The experimental and control groups are two groups of experimental subjects. The control group is a normal, unaltered group--you don't make any changes to the control group, so that you can see how they develop without increasing their exercise levels. The experimental group is the group whose exercise levels you would increase. That way, if the control group stays the same and the experimental group changes, you know it was the change in exercise that did it. The control group is necessary for experiments to make sure the changes you observe are the result of your experimental changes; if BOTH the control group and the experimental group had the same heart rate changes over the course of the study, you would have to blame something else in the environment. But by using the control group, you can find out if there are any other things in the environment that cause changes and skew your results.





Hope this helps! Science is complicated but the results of a good study or experiment are powerful.