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This question was triggered by an exam question that I was doing on the following paper (Q2 part (b)(i)): http://qualifications.pearson.com/content/dam/pdf/A%20Level/Biology/2013/Exam%20materials/6BI05_01_que_20120307.pdf Here is the markscheme: http://qualifications.pearson.com/content/dam/pdf/A%20Level/Biology/2013/Exam%20materials/6BI05_01_msc_20120215.pdf

I do not understand why the decrease in pH results in the lack of of increase in speed, despite hours of research. Here are my best attempts:

The build up of lactate will have to keep the power output of the muscles, as a whole, constant, rather than allowing it to continue increasing. Therefore, there must be a link between the increased acidity of the muscle cells and the limiting of the power output. Now, if the markscheme is correct and the increase in acidity causes a decrease in the ATP production, this means that the ATP concentration within the cell decreases. However, the decrease in ATP concentration should decrease the power output rather than limit it, because less myosin heads will be able to contribute to the pulling of the actin filaments during the contraction of a sarcomere. Am I correct, or is there more to this? If so, why is there a limiting of the power output of the muscles rather than a decrease in it?

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  • $\begingroup$ There is not complete shift to anaerobic respiration. $\endgroup$ – JM97 Mar 12 '17 at 16:43
  • $\begingroup$ @JM97 may you please elaborate? How does that ansswer my questions? Moreover, what are your comments on my deductions? What am I missing? $\endgroup$ – Mathematician Mar 12 '17 at 18:08
  • $\begingroup$ During sprinting the runner maintains constant output not only just because of anaerobic respiration but also aerobic respiration, limited supply of oxygen limits the output. $\endgroup$ – JM97 Mar 13 '17 at 2:01

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