Nick Keough
Cardio and strength training: what order to perform them in.
6/31/06
Why you should do Cardio after Strength Training
Why should you always do intense strength training before cardio? There is a reason for this that involves in depth analysis of cellular respiration in the muscles.
Many athletes are not sure while their training if they should do their cardio workout first before strength training or after strength training. The answer to this issue is that Cardio should always be done after any type of strength training.
Before I go into the justifications of my claim, let me explain to you some of the mechanisms of cellular respiration in the muscle cells.
Within our muscle cells, there are membrane bound organelles called mitochondria. These organelles allow us to perform work with a molecule called ATP. The process of utilizing this molecule for energy to perform work is called cellular respiration. There are two different metabolic pathways in which ATP is generated and used for energy. There is Aerobic respiration and Anaerobic glycolysis. Aerobic literally means “with oxygen”. During Aerobic respiration, glucose is broken down completely into carbon dioxide and water. Some of this energy that is released as the bonds are broken is captured in the bonds of ATP molecules. (Marieb 166). Aerobic respiration provides a rich ATP harvest, ( 36 ATP molecules per one glucose unit to be exact). This process is slow and requires continuous supply of oxygen and nutrient fuels to keep the muscle active. (166).
What about the short burst interval training that requires 100 percent strength for short periods of time of muscle activity. There is a high powered molecule called Creatine Phosphate (CP) that donates a phosphate molecule to ADP to convert it into ATP so it can be used for energy. This process is called Anaerobic ( without oxygen) glycolysis. Although 5 times more CP is stored in our muscle cells compared to ATP, Creatine stores are depleted extremely quickly (within 20 seconds) (166).
Why is Anaerobic glycolysis run out so much faster then Aerobic respiration? The reason why is that Oxygen can replenish ATP molecules and no other element can keep the cellular respiration cycle going. The first steps in breaking down glucose molecules happen through a pathway called glycolysis, which does not utilize oxygen. During glycolysis, glucose is broken down into pyruvic acid while small amounts of energy are captured in ATP bonds. As long as Oxygen is part of this equation, the pyruvic acid then enters the aerobic pathway to produce ATP. (166). During an intense lift or exercise, Oxygen is too slow to meet the demands of the work being done. When this happens, pyruvic acid is then converted to lactic acid. Lactic acid contributes to muscle soreness and muscle fatigue. (166). Lactic acid creates an acidic environment in which muscle cells do not have the ability to work as efficiently with oxygen. The muscle fatigues because of lactic acid from oxygen debt.
What does all of this complex biology have to do with exercising? Well it has a lot to do with my theory that I proposed about not doing Cardiovascular activity before strength training. While someone is engaged in Cardiovascular activity, Aerobic respiration is occurring and the muscle cells are working efficiently. At some point in time during this activity, people can get short of breath. This is a sign that the muscle cells are not getting enough oxygen to perform the work of a cardiovascular activity. The time in which one becomes fatigued varies from certain people with different fitness levels. When someone is disengaged from cardiovascular activity, they become short of breath if they worked their muscle cells to exhaustion. Being short of breath means that the muscle cells require oxygen to restore the cellular respiration cycle. This also means that there is Lactic acid accumulation within the cells. The acidic environment that lactic acid produces a situation where muscles can not go through cellular respiration efficiently.
If one starts doing strength training right after cardio, they are obviously not going to perform well. During weight lifting of any kind, Cellular respiration only occurs through Anaerobic glycolysis. Through this pathway, the muscle cell is not able to get rid of the lactic acid due to the lack of oxygen.
I used to do cardio before lifting. I thought it was beneficial because it got the blood flowing and got the muscle cells active. I was completely wrong by thinking this. During my workouts after doing cardio, I would find myself feeling like I have no energy to do the lifts that I want to. I did not have the stamina because the lactic acid could not be transferred back into useful energy without oxygen. I was not getting adequate amount of oxygen because my lifts only last 20-30 seconds which in this case Anaerobic glycolysis occurs and oxygen can not keep up with the demands that I put on my muscles.
The process of these two pathways of cellular respiration truly support the theory of not doing cardio before performing any type of heavy strength training.
Reference
Marieb, Elaine. Essentials of Human Anatomy and Physiology. 5th. California: 1997.
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