How Your Body Produces Energy (Or, Why You Felt So Bad After Today’s 1K)
Some of you may hear words like “energy systems pathways” and “glycogen stores” thrown around a lot. Or perhaps this is the first of them you’ve heard. Either way, the burn of today’s 1K followed by a mini version of DT inspired me to write about how the body converts stored energy into usable energy to rule your workouts.
A Quick Biochem Lesson
ATP. That sounds familiar right? Well, it should ring a bell from high school biology. ATP is a molecule found in all living cells that when broken down provides energy for a variety of cellular processes.
Pathway 1: The Phosphagen Pathway
This pathways is used for the first 10 seconds of exercise (so today on the rower, the first 5 or so strokes). This pathway draws on ATP stored in the muscle for about 2-3 seconds, then uses creatine phosphate to regenerate ATP until that runs out. This explains why creatine supplementation improves recovery and output for short duration, high power movements. For more on creatine you can read one of my previous blog posts. Movements that might utilize the phosphagen pathway are short duration at all out intensity (like a 100 meter sprint).
Pathway 2: The Glycolytic (Or Lactic Acid) Pathway
In this pathway, the body breaks down carbohydrates – both glucose readily available in the bloodstream or glycogen, the stored form of carbohydrate in the liver and muscles – to produce ATP as well as a molecule called pyruvate. Pyruvate can either convert to another molecule that is used to regenerate ATP or can convert to lactate, which forms lactic acid (and causes that burn in your legs when you’re sprinting or rowing). Conversion to lactate happens when your body needs more oxygen that it is getting. This pathway isn’t very efficient, producing little energy for the input, but the benefit is that it produces the energy quickly. Your body produces energy with this pathway from 10 seconds to around 2 minutes.
Pathway 3: The Oxidative (Or Aerobic) Pathway
This is the pathway often referred to as “fat burn”. During the oxidative pathway, the body uses oxygen along with carbohydrate and fat to produce energy. This pathway is used for long duration, low power and intensity exercise. Think of running 6 miles, rowing around the river for an hour (obviously slowly so you don’t tip the boat…) or chipper WODs like Eva.
An important thing to remember is that the pathways are not mutually exclusive. While it’s easiest to break them down into specific time slots, multiple pathways are used simultaneously. For example, in today’s 1K, the first few seconds were mostly the phosphagen pathway. After 10 seconds, glycolysis picks up as the predominant pathway, and the aerobic pathway takes over the lead at around 1-2 minutes. But if you look at the graph to the left, you can see how at 30 seconds for example, all three pathways are providing some energy.
Why You Felt So Bad After That 1K
Now that I’ve explained the pathways, it’s easier to understand. By the 4 minute mark (when the 1K finally ended for most of us), you’ve burned through pretty much all of your stored ATP and most of your muscle glycogen, but your body has only been creating energy via oxygen and fat stores for a few minutes. You’ve spent most of your stored energy and not had the time for your body to replenish it on it’s own.
What Should You Do
A couple of weeks ago, I wrote a blog post about how, while a lot of sugar in the regular diet can cause problems, there are times your body needs a little, especially during training. During a WOD like today’s, where we red line for a specific test, and follow it up with another challenging workout, the body would benefit from taking some sugar. I would recommend about 15 grams of very easily absorbed carbohydrate, such as:
- Coconut water
- Sport beans
- Non-fat candy
You want to eat a little something to beef up your glycogen stores, but you don’t want ANY fat or fiber to slow digestion. Of course, I made it through the WOD fine without any carbohydrate in the middle (as did the 6 and 7 am classes), but if you plan on training longer afterward, or want to go harder on the 3 rounds of DT, the carbs can help.