In a model, each contraction makes lactic acid in proportion to the share of the ATP that is made…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
In a model, each contraction makes lactic acid in proportion to the share of the ATP that is made without oxygen. If all of the ATP were made without oxygen, one contraction would make unit of acid. A fibre is tired when it has made units. A fibre makes of its ATP with oxygen.
- How much acid does one contraction make?
- How many contractions can it make before it is tired?
- Another fibre makes only of its ATP with oxygen. How many contractions can it make?
Need a reminder? The key ideaShow
Repeated contraction makes lactic acid from the anaerobic breakdown of glycogen, and this causes fatigue. Red fibres have much myoglobin, plenty of mitochondria and work with oxygen. White fibres have little myoglobin, fewer mitochondria and much sarcoplasmic reticulum, and they depend on anaerobic breakdown.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Limit: units. Share with oxygen: and .
Plan. Find the acid for one contraction. Then divide the limit by it.
Step 1. The first fibre. Without oxygen: , so one contraction makes unit.
Step 2. Contractions. .
Step 3. The second fibre. Without oxygen: , so unit in one contraction. .
Answer: unit; contractions; contractions.
Check. The second fibre makes twice the acid in each contraction, so it is tired after half as many.
Watch out. This is a teaching model, with round numbers. Real fatigue has more causes than lactic acid.
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