Where Do We Get All That Energy.
Exercise physiology is essentially two concepts: the DELIVERY of oxygen to the working muscles and the USE the delivered oxygen (I’ve just summarized eight years of college).
Everything else simply supports the delivery and use of oxygen. I personally think coaching books either go too far into physiology and biochemistry or just ignore it altogether. I’ll be gentle in my discussion in this four-part series.
To deliver oxygen, it has to be carried and most people remember from biology that oxygen is carried by hemoglobin in red blood cells. Sure, there are details about how oxygen is carried, but just understand that a red cell has only so much space to carry oxygen and blood can only have so many red cells before it becomes too thick.
Want to carry more oxygen? You need more red cells, thus the illegal attempts at blood doping where a very specific protocol is used to remove, store, then reinsert the red cells to increase oxygen carrying capacity sometimes used by hard core endurance athletes like cycling and cross country skiing.
I’ve never heard of anyone attempting blood doping in soccer. The other way is to use drugs that simulate red cells production (erythropoietin, nicknamed EPO). The point is that the blood will only hold so much oxygen, so there must be other ways to move more oxygen to the working muscles.
Appreciate that the heart is one remarkable organ. It works hard for a fraction of a second when it beats and only needs fractions of a second to rest, whether the heart rate is 50 or 200 beats per minute.
Let’s start at rest. When at rest, the body is at its “idle” — the minimum to operate. You have a certain minimum energy requirement needed to keep things operating and your energy needs are met mostly through energy production with oxygen.
During exercise, the muscles (and other cells) must produce much more energy and they want to do this using oxygen. Now the body has two options. So the muscles just take all the oxygen out of the blood, right? Nope, muscle doesn’t suck the blood dry of oxygen; blood leaving muscle still has quite a lot of oxygen left in it.
The other option is for the muscles to take about the same amount of oxygen out of the blood, but in this option, more blood goes through the muscle and despite the shorter time in the muscle’s capillaries, the “same” amount of oxygen is taken by the muscles.
Increased blood flow is comes about by increasing both the heart rate as well as how much blood pumped is pumped with each heart beat and is called the stroke volume. The product of heart rate and stroke volume is a critical feature called the cardiac output.
Simply put, to deliver more oxygen to the body, you must increase the cardiac output. Now, during exercise, both the heart rate and stroke volume increase up to a point. But stroke volume increases only so much, up to about 40% of a personís capacity, then levels off.
Thus, in order to increase the cardiac output, heart rate must increase.
There are a many cardiac adaptations to training. Probably the most obvious changes are to the heart rate. At rest, you energy needs are roughly the same whether you are fit or not.
When you are fit, your resting heart rate is reduced. Oxygen consumption is very closely related to the cardiac output. So, at rest your oxygen consumption is the same after training (thus, cardiac output is also about the same after training).
Therefore, with cardiac output being the product of heart rate and stroke volume, with the resting heart rate lower, the stroke volume MUST be higher.
During exercise by the fit player, the stroke volume follows the same relative pattern (increase to ~40% of max, then plateau), just that this new pattern is at a much higher level.
One cardiologist I knew used to say the stroke volume of a fit athletes looked like a toilet flushing, so much blood was ejected each beat. After training, the heart rate at the same workload is reduced.
Let’s say, your heart rate before training for a 10-mile jog is 170. Now lets say, you heart rate is 150 at that same pace after training. The oxygen requirement for that 10-mile run is still about the same, so the stroke volume at this pace is greater, the heart isn’t beating as often, and your perception of intensity isn’t as high.
Your maximal heart rate is affected little and may actually drop by a few beats. This explanation is an oversimplification of a complex process.
Next month: Using that oxygen