“Hallway Fights Take Energy” is the title of this post, but a more accurate one is “All About Saving Enough Energy to Save the Kid at the End of a Hallway.”
I LOVE great fight stunts and choreography, but, having studied exercise physiology, I can’t help the part of my brain that says “he should be fatigued by this point.” That’s why one of my favorite fight scenes is in Netflix Daredevil’s season one, episode 2 hallway fight. We see our masked hero fight his way down a hallway to rescue a kid, and, by the time he reaches the door at the end of the hall, he is struggling to stay standing and generate the energy to take down the last couple of goons.
There are three energy systems in the human body that are constantly working together to generate ATP to fuel all of our bodily functions. Adenosine triphosphate (ATP) is the energy compound in the muscle cell that, when split into adenosine diphosphate(ADP) + phosphate (Pi), releases energy to fuel physical activity.
The Three Energy Systems:
- Phosphagen (ATP-Pcr) System
- Glycolytic System
- Oxidative System
Based on what activity the body is doing, one system will be providing more energy than the others. For instance, sprinting over a short distance relies on a different allocation of these systems than jogging over a long distance.
The phosphagen system utilizes the ATP stored at the muscle site, which isn’t very much, so it’s the primary fuel source for quick, powerful movements that last for 3-15 seconds. It can be regenerated by taking the ADP from the original reaction and combining it with PCr (phosphocreatine). Within 30 seconds 70% of ATP is restored, with full restoration occurring within 3 to 5 minutes (Periodization: theory and methodology of training, 5th Ed., Bompa and Haff, page 22). Unfortunately, PCr takes longer to regenerate, so once that is depleted, fatigue sets in.
The glycolytic system, on the other hand, breaks down blood glucose and glycogen stores to generate ATP, and is the primary energy system for activities that last from 20 seconds to 2 minutes. The system relies on both fast and slow glycolysis. Fast glycolysis creates a by product in lactic acid, which is converted to lactate. If more lactic acid is generated faster than it can be converted to lactate, then the lactic acid builds up, which causes fatigue.
The oxidative system, similar to the glycolytic system, uses blood glucose and muscle glycogen to generate ATP, but, unlike the glycolytic system, does this in the presence of oxygen. (The presence of oxygen allocates this system as being aerobic, while the other two are anaerobic). This is the primary system when engaging in activity lasting longer than 2 minutes.
Both the glycolytic and oxidative systems use blood glucose and muscle glycogen to produce ATP. The stores of blood glucose and muscle glycogen are generated from the carbohydrates consumed in the diet. If there isn’t a sufficient amount of blood glucose or muscle glycogen available to fuel these systems, either because of a low carb diet or not having eaten recently, the effectiveness of the systems is diminished.
These systems are always working to generate ATP, so, for the approximately 2 minutes and 28 seconds that Daredevil is fighting, his body is utilizing immediate stores of ATP, is generating and using more via glycolysis of his blood glucose and muscle glycogen, is depleting his supply of PCr, and is accumulating lactic acid. While the oxidative system is contributing to ATP supply, the intensity and duration of the activity is keeping the anaerobic systems as the primary supply of energy.
Now, what’s the point of knowing all of this?
Well, Daredevil (and others engaging in athletic activity) needs to know how to delay fatigue. Now that we know why he is fatigued (other than the fact that this episode involves him recovering from a bad fight prior to this), we can alter his training and nutrition plans to make sure that he can pace his energy usage, increase his lactate thresholds, and eat properly for his activity. (I will get more in depth as how to do these things, but that’s for another post.)
If this was a little confusing, Hank Green at Crash Course has made a youtube video that relates to the subject. I also referenced the Human Kinetics text books Periodization: Theory and Methodology of Training, 5th Ed. by Tudor O. Bompa and G. Gregory Haff and Physiology of Sport and Exercise, 5th Ed. by W. Larry Kenney, Jack H. Wilmore, and David L. Costill.