As educators we are continually designing new methods and procedures to enhance learning. During this process good ideas are frequently generated and tested, but the extent of such activities may not be adequate for a full manuscript. Nonetheless, the Illuminations is a column designed to facilitate the sharing of these ideas (illuminations). The format of the column is quite simple: a succinct description of about one double-spaced page (less title and authorship), without figures or references, of something you have worked up for the classroom, teaching lab, conference room, etc. Submit your column entry directly to Daniel Richardson, Illuminations Column Editor, Department of Physiology, University of Kentucky, College of Medicine, Lexington, KY 40536–0298.

Estimating ATP resynthesis during a marathon run: a method to introduce metabolism

Most physiology classes have several lectures devoted to the study of metabolism and bioenergetics. A basic tenet of such study is that the human body uses substrate level and oxidative phosphorylation to continuously resynthesize ATP from birth until death.

It has been our experience that an ingenious student will ask why humans have not evolved to simply store all the ATP that they need instead of having to use metabolic pathways to continuously oxidize foodstuffs. Clearly, a dramatic example is needed to restore students’ faith in the “wisdom of the body” and to refocus attention to the task at hand. In our classes, we have successfully used the following example to introduce metabolism and bioenergetics.

Initially, we ask the class “how much ATP does it take to run a marathon (42.3 km)?” Usually, answers range from several ounces to several pounds. The correct answer quite surprisingly and dramatically illustrates the importance of ATP resynthesis. The current world record in the men’s marathon is 2:05:42 held by Khalid Khannouchi set at the 1999 Chicago Marathon. His weight was 55 kg, and we estimate his maximal aerobic power (|$$˙Vo2 max) to have been 80 ml · kg-1 · min-1 or 4.36 l/min. Furthermore, we estimate that Khonnouchi’s average energy expenditure corresponded to 80% of his |$$˙Vo2 max in which he would have utilized a total of 438 liter (STPD) of O2 to complete the race.

With the use of the molar equation for the oxidation of carbohydrate, the amount of ATP resynthesized per mole of glucose is C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 36 ATP.

When the reactants and products are expressed in common metric units and by taking into account molecular weights and volumes per mole of ideal gasses, the equation looks like: 180 g glucose + 134.4 liter O2 → 134.4 liter CO2 + 108 g H2O + 18.25 kg ATP. Thus 0.136 kg of ATP are resynthesized for each liter of O2 consumed. Because 438 liters of O2 were used for the marathon, this means that a staggering 60 kg of ATP were resynthesized by Khonnouchi’s muscles in slightly over 2 h.

After seeing the magnitude of this estimate, most students readily comprehend the problem of attempting to store all the ATP that a human would need for existence. The fact that Khannouchi resynthesized ∼60 kg of ATP during his race drives home the physiological rationale for using metabolic pathways to resynthesize ATP on a need basis rather than storing it.

In conclusion, the same ingenious student who started this discussion usually states that he/she does not plan to run a marathon and that our example, although dramatic, exaggerates the need for ATP. At this point, we simply smile and state, “An average college student typically consumes 400–500 liters of O2 per day, which, coincidentally, is about the volume of O2 used by Khannouchi during his historic marathon run. Thus, every student in this class is resynthesizing ∼60 kg of ATP everyday! Now, let’s start our discussion on how you accomplish this feat.”


Departments of 1Biology and 2Exercise and Nutritional Sciences, San Diego State University, San Diego, California 92182–7251

Colored letters: a tool to increase class participation in a large classroom

It is often difficult to hold students’ attention during a 50-min class. This is especially true when students have 2–4 consecutive 50-min classes, as is common in medical school. In fact, studies document that students’ attention dramatically wanes after only 15 min of a lecture (Stuart J and Rutherford RJ, Medical student concentration during lectures, Lancet 2: 514–516, 1978). In an effort to enhance students’ attention as well as increase class participation, we include five colored sheets of paper labeled A (red), B (white), C (blue), D (green), and E (yellow) in the students’ lecture notes. Students use these colored letters to answer questions during the class. For example, at 15- to 20-min intervals during the class, a multiple-choice question related to the specific topic that was just discussed appears in the PowerPoint presentation. Students answer the question by holding up the appropriate colored letter. All students hold up their choice of colored letter at the same time. These procedures increase class participation as well as allow us to immediately determine whether students understand a particular concept by observing the sea of colors. If the majority of students answer correctly, we feel comfortable moving on. However, if a significant number of students answer incorrectly, the concept is reviewed. Students enjoy this activity and appreciate the opportunity to assess their own understanding as well as participate in class. For example, one student stated that “the letters are a fun way to test my knowledge and help me see if I really knew the material.” Furthermore, students report that these activities help to hold their attention. Finally, we get an immediate idea of students’ learning.


Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan 48201

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