The Burn: Why do our muscles fatigue during a sprint?

Part 1: Engage (Anchoring Phenomenon)

Imagine you are a world-class sprinter. You explode out of the blocks for a 100-meter dash. For the first few seconds, you feel powerful, but by the end of the 10-second race, your legs feel heavy and a “burning” sensation begins to set in.

Initial Reflections:

  1. What do you think is happening inside your muscle cells to cause this “burning” sensation?
  2. Why can’t humans maintain a full sprint for an hour, even if they have plenty of “fuel” (glucose) in their bodies?
  3. What “need to know” questions do you have about how your body produces energy during intense exercise?

Part 2: Explore (Simulation Investigation)

Launch the Cellular Respiration Energy Model to investigate how different conditions affect energy production in the cell.

Investigation A: Sustained Activity (Aerobic)

Cells typically operate in an “Aerobic” environment where oxygen is plentiful.

  1. Set Glucose Molecules to 1.
  2. Set Oxygen Molecules to 6.
  3. Click 1. Update Inputs and then 2. React.
  4. Observe & Record:
    • How many ATP molecules were produced?
    • What are the names of the “Output” molecules formed?
    • Look at the Conservation of Matter panel. Are any atoms created or destroyed during this process?

Investigation B: The Sprint (Anaerobic)

During intense exercise, your heart and lungs sometimes can’t keep up with the oxygen demand of your muscles.

  1. Click Reset.
  2. Keep Glucose Molecules at 1.
  3. Decrease Oxygen Molecules to 0.
  4. Click 1. Update Inputs and then 2. React.
  5. Observe & Record:
    • How many ATP molecules were produced this time?
    • What new “Output” molecule appeared that wasn’t there in Investigation A?
    • How does the total energy (ATP) compare to Investigation A?

Part 3: Explain (Sensemaking)

Using your data from the simulation, answer the following:

  1. Rearranging Matter: In Investigation A, what happened to the 6 Carbon atoms from the glucose? Where did they end up?
  2. The “Burn”: Based on Investigation B, what molecule is likely responsible for the “burning” sensation in a sprinter’s muscles?
  3. Energy Efficiency: Why is oxygen so important for an athlete’s performance? Compare the ATP yield of 1 glucose molecule with oxygen versus 1 glucose molecule without oxygen.
  4. Bond Breaking: The simulation shows energy (ATP) being released. According to the chemical equation and the model, where does this energy actually come from? (Hint: Think about the bonds being broken and formed).

Part 4: Elaborate/Evaluate (Argumentation & Modeling)

Final Task: Construct an Explanation

Write a scientific explanation (Claim, Evidence, Reasoning) for the following:

Prompt: Explain how cellular respiration allows a marathon runner to stay warm and move their muscles for hours, and why a sprinter’s muscles eventually “fail” and burn during a race.

Your explanation must include: