• Question: how do we have lactic acid e.g. in our arm when we put it above our head, but not be out of breath, because I thought that you used anaerobic respiration when there is not enough oxygen present?

    Asked by 698hrmc35 to Craig, Laura, Saffron on 25 Jun 2015.
    • Photo: Laura Wales

      Laura Wales answered on 25 Jun 2015:

      You’re right that lactic acid is a product of anaerobic respiration.

      When exercising, muscle cells do extra work and therefore need more oxygen that the respiratory system can supply. Increasing breathing rate and heart rate will increase the supply of oxygen through the blood to generate ATP, but after a while the muscle can’t generate enough ATP through aerobic respiration

      During prolonged exercise/endurance training, cells use anaerobic respiration to generate ATP to keep the muscles functioning. Although energy is still produced, it is in smaller amounts for each molecule of glucose. Glucose is not fully oxidised to carbon dioxide and water, and forms lactic acid instead. Lactic acid is thought to cause the pain and cramps associated with prolonged exercise.

      I’m not sure about the arm above the head thing. With rock climbers, because of the type of sport it is, their breathing is generally very controlled and slower than that of a sprinter. Some climbers will “shake out” their arm if there is pain cause by a build up of lactic acid in their forearm – by dangling their arm and shaking it out a bit, blood flow can resume to normal and relieve some pain.

    • Photo: Craig Doig

      Craig Doig answered on 26 Jun 2015:

      698hrmc35

      When your arm is above your head you are not using the muscles in it. Instead a lot of the blood in your arm is draining out as it is too high up for your heart to pump it up there. So your arm feels like is has lactic acid in it but it doesn’t because the muscle in it are not doing anything. And because of this you don’t need to breathe harder.

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