The Aerobic/Anaerobic difference

There is often confusion about the true difference between aerobic and anaerobic training. And how to use the information to train in the smartest way. Looking through the forums and blogs it looks like a common question is how to create an aerobic base. So a little info on physiology is a good weapon to have. When you train smart, you race fast!!

It all happens at the small capillaries in your body. The tiniest blood vessels in your muscles where nutritional exchange happens. When you start to exercise a muscle group, there are several things that start to happen at once. The two most important to the athlete are the fact that your muscles start to take up a lot of oxygen, O2, from the blood. This causes a depletion in oxygen. The other is that a by product of muscle energy expenditure is carbon dioxide, CO2. Both these things cause the blood vessel to dialate. This widening of the blood vessel allows more blood flow to the working muscle, and thus more O2! So depending on the size of the muscle group and exercise, there is a demand on the heart to get the blood flow there. This is where another system in your body is working. The parasympathetic nervous system. It is a complex network of nerves that are on autopilot. With complex chemical stimulation throughout your body your brain sends appropriate signals to take care of yourself without you having to think!

The parasympathetic nervous system does a couple of great things for the athlete. One, it increases the work of the heart by increasing its rate and also increasing its ability to contract, so with each contraction you are pushing more blood out to your muscles. The second thing it does, is to cause vasoconstriction to blood vessels throughout your body. The result then, is you get blood flow increasing like mad directed to the muscles that need it. So depending on the exercise and the conditioning, people will experience possibly different max heart rates, and threshholds with different exercises, like running versus biking. The brain and heart are spared this vasoconstriction, and you can survive the punishment you willingly give your body! In some extreme examples of long distance racing, like Ironman, this is why you have seen athletes with severe digestive ischemia. Minimal relative blood flow to the intestines along with dehydration can cause cells to die. It is most important to also consider the kidneys here and to keep hydrated during long events, and be careful not to take too many NSAIDS, the pain relief drugs like ibuprofen, naprosyn......These drugs cause a double vasoconstriction to the arteries of the kidneys. Something you do not want dead!

The difference between aerobic exercise and anaerobic exercise is the point when the body can no longer self regulate and supply enough O2 to the muscles, and a build up of metabolites, like lactic acid occurs at a rate higher than what the body can carry away. There are many threshholds physiologists like to define. Aerobic threshhold, lactate threshhold, ventilatory threshhold. The word is less important than just knowing what is going on. An important thing to know is the change is dynamic. You do not switch from aerobic to anaerobic instantly when you cross a related heart rate. It happens over a gradual curve. So when keeping your base aeorbic, I do not think you will hurt your ability to develop your aerobic capacity with short intense efforts. In fact I think this is good to do to keep your muscle strength intact during a rebuilding base. As long as your efforts are short enough that you are not creating a large build up of lactate in your muscles.

The aerobic base phase to a training program is your body preparing for a higher level of intensity. The efficiency of energy transfer and utilization increases at the cellular level. Your muscles will grow and your blood vessels and nerves will grow to accomodate your new fitness. Your heart increases its efficiency at pumping blood and your heart rate will come down as your body changes to a better and improved economy. This is why it is good to assess your maximum heart rate and, I'll call it lactate threshhold throughout the year. They will change! As will your bodies ability to take in and process O2 maximally, your VO2 max. This is a topic for another article down the road.

So for those that are trying to build a base, a good 8-12 weeks is often suggested to get your ideal benefit. But this clearly depends on where you are starting from. And any longer, without anaerobic phases, may cause your body to lose what it had developed in your prior phases. When recovering from an injury it is something to always fall back to (I am sure my aerobic base must be excellent!!!).

To accurately define your bodies heart rate where you start developing an overlaod of lactic acid, you need to get a lactate threshhold test. Not readily available. So that is why there are so many formulations to define average max heart rates, and percentage levels of exercise to achieve goals. Just remember this, we are not all 5 ft 10 inches, with 2.3 kids and 1.3 dogs/cats. Everyone is different! So keeping a log of your workouts is the best way you and a coach can look at what is most likely "your" physiology. Keeping a blog with athleteinyou.com is a great way to share your plans. Feel free to ask any questions in the forums. And as always, train hard but train smart.

Ted Rasoumoff, MD USAT certified coach