Recording Your Biorhythms

The combined action of the nervous and the endocrine systems is responsible for much of our daily behavior. Usually when we think about how these systems work, we think about specific events. You get "scared" at a horror movie, or "pumped up" just before a big exam. There are, however, more subtle changes in the operation of our physiological systems. Some of these changes are rhythmical and tend to recur in regular cycles. These cycles are referred to as circadian rhythms, or biorhythms. For example, we have a fairly regular sleep-wakefulness cycle: most of us spend about 7 or 8 hours out of every 24-hour period sleeping. Usually that period comes at about the same time every day. Can you think of any other body functions that may exhibit a circadian (or biological) rhythm? Perhaps you have heard that when a child has a fever, it always seems to get worse just before bedtime and is best when the child wakes up in the morning. Have you ever wondered if there is any scientific support for the idea that body temperature follows a daily rhythmical pattern? This experiment will investigate the question of whether body temperature follows a circadian rhythm.

Experimental Procedure

In this experiment, you will act as your own subject. To collect the necessary data, you will need a body thermometer. You will be able to see more clearly the results of this experiment if you use a basal body thermometer, because it can measure body temperature more precisely than a regular thermometer. These thermometers are widely available at drugstores.

Step 1 Take your temperature four times a day every day for two weeks. Be sure to take your temperature at the same time every day. You should take it just after you wake up (perhaps at 7:00 a.m.), sometime during the middle of the day (perhaps at 12:00 noon), sometime in the late afternoon (perhaps at 5:00 p.m.), and before you go to bed at night (perhaps at 10:00 p.m.). If you miss a regularly scheduled time, omit that piece of data. Do not record your temperature if you are more than an hour earlier or later than usual.

Step 2 Record your temperature readings on the chart provided here. Try to be accurate to one-tenth of a degreeÑfor example, 98.6°, not just 98° or 99°.

Analyzing the Results

Step 1 Calculate your average daily temperature for each of the four time periods and record the averages at the bottom of the chart. To get your averages, add up all the readings for each time period and divide the total by the number of readings. For example, add together all 14 of your 7:00 a.m. readings and then divide the resulting total by 14. If you did not record readings for some days at this time, you would still add together all the readings you had for that time slot, but instead of dividing by 14, you would divide by the number of readings you had actually taken.

Step 2 Plot the data you collected on the graph provided here. Sometimes it is easier to see trends when data are plotted graphically. Do your temperature readings follow the same pattern every day? What is this pattern? Are there some days that do not fit your basic pattern? If there are, can you think of any reasonsÑperhaps illness, stress, lack of sleepÑthat could explain these variations? If you are a woman, do you notice any changes in your body temperature that correspond to your menstrual cycle? What conclusions can you draw about the pattern of your body temperature biorhythm?

Step 3 If you ask a friend to record his or her body temperature at the same time you do, the two of you can compare biorhythm patterns. Do you both show the same basic temperature changes throughout the day? If not, what are the differences? Do these differences reflect different lifestyles or habits? Do you get up earlier or stay up later? Are you a morning person or a night person? What about your friend? Do you think your natural biorhythms influence how you feel at various times during the day? What other physiological functions might fluctuate according to basic rhythmical patterns?

If you are like most subjects, you will notice that your most typical pattern of temperature fluctuation should show the lowest temperature of the day when you are asleep. In fact, some research indicates that the sleep cycle is determined by your body temperature. As your body temperature begins to rise in the morning, you wake up. Then, for most people, body temperature continues to rise throughout the day. Is this the pattern your body temperature shows? If not, don't be alarmed. Some studies (e.g., Foret, Benoit, and Royant-Parola, 1982) show that there are differences between "morning people" (people who wake up feeling great, having their best time of the day in the morning, and begin to fade as evening comes) and "evening people" (those who wake up slowly, have trouble getting things done early in the day, but are very productive in the later part of the day).

Current research is also being done on factors, in addition to the sleep cycle, that appear to be related to body temperature. Even cognitive abilities may be linked to body-temperature cycles. Certainly more research in this area will help us answer questions about the function of the body-temperature biorhythm.