I usually smile when I see people in Spin/Rev/Indoor Cycling Classes pushing to their max... While I always appreciate their efforts, I wonder if they have ever been told about lactic acid, heart rate training and the difference between aerobic and anaerobic respiration...
It should be obvious by now that I am a science geek and I like to hear stuff about mitochondria and the Kreb's Cycle... Most people's eyes glaze over when those topics are mentioned so I have looked for a few simple explanations so we can all get more from our cardio.
Lets start with anaerobic respiration aka OVERTRAINING...
Did you know we humans have about 639 muscles in our body, with each of them having their own name? Most of these muscles are attached firmly to the bones of the skeleton, which make up the framework of the body. They are highly important parts of the body because without them we would not be able to move, eat, breathe, talk and even the heart would stop because the blood gets pumped in and out of the heart only through muscular action! Exercise is a good way to keep these muscles in shape, but if we exercise for too long a time, the muscles start to ache very badly and this is due to anaerobic respiration.
Under normal conditions, the body cells go through aerobic respiration, which is a long process where oxygen is used to convert the stored up glucose molecules, completely into energy. This type of respiration takes place in most living creatures, but there are a few parasitic worms and lower forms of plants (bacteria and yeast) that breathe anaerobically, that is, in the absence of oxygen. Anaerobic respiration also takes place in human beings when we exercise rigorously. During this time, we tend to take in less oxygen and this lack of oxygen prevents the oxygen from breaking down completely. This 'oxygen debt' results in the formation of an acid, or rather a 'poison' called lactic acid. This lactic acid gets stored in the muscles and causes the pain. The tiredness is caused by the production of different types of toxins, which are carried by the blood throughout the body.
The only way to remove this acid is to rest for a while, take in deep breaths of air (the extra oxygen helps to convert the lactic acid into a safer form) and the pain slowly subsides. The pain is actually a good way to control the body's activities. If a person continues to exercise and ignores the warnings being given by the body, the person might faint due to lack of oxygen or seriously sprain some of the muscles.
There are many differences between the two types of respiration, the most important being the difference between the amount of energy released. In aerobic respiration, we get about 38 ATP molecules of energy from a single glucose molecule, while in anaerobic respiration only 2 ATP molecules of energy are released for the same quantity of glucose. So it is always advantageous to take breaks while exercising; while resting, body removes any waste products, the cells get rejuvenated, the brain's nerve cells get re-charged, the joints of the body replenish their supplies of lubricants and much more. The body is then fit enough to carry on with the exercise and the rest of the day as well.
The body is quite an ingenious instrument and should be handled with care!
Now to geek out on LACTIC ACID fermentation...
LOL... Only NERDS need to read more...
If oxygen is absent, many cells are still able to use glycolysis to produce ATP. Two ways this can be done are through fermentation and anaerobic respiration. Fermentation is the process by which the electrons and hydrogen ions from the NADH produced by glycolysis are donated to another organic molecule.
The point of fermentation
The reason this is done is to produce NAD+ which in tern is needed to keep glycolysis going. Remember, that unless the cell has some sort of electron transport system, the NADH is not usable. At the same time NAD+ is needed for glycolysis and its much less expensive in terms of energy for the cell to simply take the NADH that would normally go to the mitochondrion and use it to regenerate the NAD+. The NADH produced by glycolysis donates it's hydrogen ions and electrons that in aerobic respiration would have ended up powering electron transport phosphorylation.
Other fermentation pathways
There are a number of fermentation pathways that different cells use. Yeast cells produce ethyl alcohol by fermentation. Certain cells of our body, namely muscle cells, use lactic acid fermentation, while depending on the organism some of the other products of fermentation include acetic acid, formic acid, acetone and isopropyl alcohol.
Fermentation and running
In our bodies certain muscle cells, called fast twitch muscles, have less capability for storing and using oxygen than other muscles. When you run and these muscles run short of oxygen, the fast twitch muscles begin using lactic acid fermentation. This allows the muscle to continue to function by producing ATP by glycolysis.
The muscles get enough ATP for quick spurts or shall we say sprints, but quickly become fatigued as their stores of glycogen are used up. Eventually you cramp. This is in part because the muscles lack sufficient ATP to continue contracting. Also, lactic acid builds up and must be metabolized by the liver. Runners who sprint actually have more muscle cells specialized for lactic acid fermentation than do long distance runners.
White meat and dark meat
If you want to see what these muscles are like, when you eat chicken or turkey the white meat is fast twitch muscle. The dark meat is what is called slow twitch muscle. This meat is dark because it contains an oxygen holding protein called myoglobin. Note that the slow twitch muscles tend to be wing and leg muscles where long term endurance is required. The fast twitch muscles tend to be more common in the breast where quick response but not necessarily endurance is needed. Also, wild animals tend to have more slow twitch muscle than their domestic counterparts.