Anaerobic Respiration and Lactic Acid Formation

Name Accelerated Biology Date Period

Background A muscle exercised strenuously for a prolonged period may lose its ability to contract, a condition called fatigue. Interruption in the muscle’s blood supply or, rarely, lack of acetylcholine in motor neurons may cause fatigue. However, fatigue is most likely to arise from accumulation of lactic acid in the muscle as a result of anaerobic respiration. In anaerobic respiration, the simple process of glucose decomposing into 2 pyruvic acid molecules is quickly followed by the conversion of the pyruvic acids into lactic acid. Lactic acid is named for its occurrence in sour “milk.” It is also produced by muscle and other body cells during anaerobic catabolism of glucose. When a human being runs very rapidly, for instance, the fibers (cells) in the leg muscles cannot get oxygen fast enough to allow them to utilize it for metabolism. Hence, glucose is broken down by anaerobic catabolism. Excess lactic acid molecules quickly accumulate, and they irritate local nerve endings within the muscle fibers. This creates leg cramping and pain. In this lab, you will experience the effect of muscle fatigue on repeated and sustained muscle contractions with small muscle groups and large muscle groups.

Question: Do sustained or repeated muscle contractions result in muscle fatigue faster?

Hypothesis: Develop a hypothesis in an if…then…because… format that predicts and explains what you think will happen.

Procedure: You will need to develop a procedure that examines the four following categories:  Repetitive contractions with small muscles  Repetitive contractions with large muscles  Sustained contractions with small muscles  Sustained contractions with large muscles Large muscles include those found in your arms and legs, such as your biceps or quads. Small muscles include those that control your fingers and feet.

Keep in mind that you should maintain good scientific practices, including multiple trials.

Analysis Questions: (To be answered in your lab notebooks) 1. What is muscle fatigue? 2. Based on your observed results, which conditions caused the muscles to fatigue the most? Explain your reasoning. 3. What happens in muscle tissue when oxygen demand is not met? 4. How would someone experiencing muscle fatigue still be able to participate in physical activities? Explain your reasoning. 5. How does fitness or regular exercise improve the ability of muscles to resist fatigue?

Conclusion: (To be answered in your lab notebook) What conclusions can you draw from this activity? What did you learn? How do your results relate to your hypothesis?

Write Up: You will create a CER poster, one per group, that demonstrates reflects your investigation.