Ever wondered why feel all stiff the day after doing lots of exercise, in order for you to contract your muscles they need the energy that is released in respiration. However, when you’re doing heavy exercise for a long time the muscles can’t always get the oxygen they need to carry out aerobic respiration. In this case the muscle cells can switch to carry out another type of respiration called anaerobic respiration. this is respiration without oxygen so why don’t we just do this respiration all the time if we don’t need oxygen that we don’t need to bother breathing. Well unfortunately anaerobic respiration is not as good as aerobic firstly it only produces a small amount of energy compared to aerobic respiration and also it produces a nasty waste product called lactic acid. The muscles in your forearm which control the fingers been out carrying out anaerobic respiration. After a while the lactic acid will start to build up in the muscles and it causes pain. When you stop exercising you will need to break down this lactic acid. To do this lactic acid needs to travel in the blood to deliver. Here it is broken down using oxygen into carbon dioxide and water.  After vigorous exercise, you may find you are still breathing very heavily for a time afterwards. This is to get the oxygen into the blood needed to break down lactic acid. We say after doing anaerobic respiration that you’re an oxygen debt, if you need to pay back the oxygen to the body. So, to answer the question at the start of the video, why do you feel stiff after exercise? it’s all to do with lactic acid if you stop moving straight after exercise then the blood does not return to deliver and the lactic acid stays and the muscles. This is what makes them stiff the next day. So, it’s very important to warm down after exercise or a gentle jog and stretching SUBSCRIBE to the FuseSchool YouTube channel for many more educational videos. Our teachers and animators come together to make fun & easy-to-understand videos in Chemistry, Biology, Physics, Maths & ICT. VISIT us at www.fuseschool.org, where all of our videos are carefully organised into topics and specific orders, and to see what else we have on offer. Comment, like and share with other learners. You can both ask and answer questions, and teachers will get back to you. These videos can be used in a flipped classroom model or as a revision aid. Find all of our Chemistry videos here: https://www.youtube.com/watch?v=cRnpKjHpFyg&list=PLW0gavSzhMlReKGMVfUt6YuNQsO0bqSMV Find all of our Biology videos here: https://www.youtube.com/watch?v=tjkHzEVcyrE&list=PLW0gavSzhMlQYSpKryVcEr3ERup5SxHl0 Find all of our Maths videos here: https://www.youtube.com/watch?v=hJq_cdz_L00&list=PLW0gavSzhMlTyWKCgW1616v3fIywogoZQ Twitter: https://twitter.com/fuseSchool Access a deeper Learning Experience in the FuseSchool platform and app: www.fuseschool.org Follow us: http://www.youtube.com/fuseschool Friend us: http://www.facebook.com/fuseschool This Open Educational Resource is free of charge, under a Creative Commons License: Attribution-NonCommercial CC BY-NC ( View License Deed: http://creativecommons.org/licenses/by-nc/4.0/ ). You are allowed to download the video for nonprofit, educational use. If you would like to modify the video, please contact us: [email protected]