Training Methodology Part 3: Metabolic Pathways

Training Methodology Part 3: Metabolic Pathways

This is the third part of my blog series on Training Methodology. This series is designed to help athletes have a general and basic understanding of training principles and practices to understand our programming. It can also be used to adapt or design their own programming, and determine a good program from a bad one. In this article we will discuss the 3 basic systems the body uses to produce energy for muscle contraction and how we use metabolic specificity in program design to target the systems we need the most for performance. If you haven't read my first two articles, go back and check out Part 1 and Part 2.

Metabolism and ATP (Muscle Energy)
I'm going try  my best to not nerd-out with a bunch of science mumbo-jumbo, but there are some basic terms and principles we need to understand before we talk about how the body uses it's metabolic pathways to replenish our energy stores. First and foremost, when we talk about metabolism, we are referring to all of the chemical reactions in the biological system that build up (anabolic) or breakdown (catabolic) molecules. In other words, how the body breaks apart molecules to use energy and builds them together to replenish energy. The molecule that we are most concerned with when talking about training is adenosine triphosphate (ATP). ATP allows muscle contraction and muscle growth, so it is important for us to understand how our training affects it's break down (called hydrolysis when we talk about ATP) and replenishment (rebuilding ATP so we can break it apart again). I won't bore you with the chemistry lesson about the reactions and the micro-structure of muscle for now, but you can find more detailed information in Chapter 3 of The Essentials of Strength Training and Conditioning or Physiology of Exercise and Sport.

The 3 Energy Systems
Basically we use ATP to contract muscles and we have 3 different energy systems (metabolic pathways) to replenish new ATP. The energy systems are called the Phosphagen System, Glycolysis, and the Oxidative System. Although each of these systems are pretty much working all of the time during exercise, different intensities and durations demand more of a contribution from one system over another. Because of this, we can target which system we want in programming workouts.

Phosphagen System
The Phosphagen system is what we might call the first line of defense in energy, or perhaps our emergency source of energy. This system uses creatine phosphate (CP) stored in the body to quickly replenish ATP. If you need to jump out of the way of a fast moving car, quickly dodge that projectile vomit your 1 year-old baby is sending your way, or doing a 1 rep max snatch, you'll be using the Phosphagen System. This system is used for short-term, high intensity exercise and is also very active at the start of any exercise. Because of limited stores of CP in the body, this system is only good for about 5-10 seconds of work. Short sprints, low rep and high weight lifts, and quick plyometric drills are how we train this system (more on that later).

Glycolysis
Both the Phosphagen system and Glycolysis are anaerobic, which means they do not require oxygen to replenish ATP. Because of this, they are able to replenish ATP quicker, but they cannot last as long (compared to the aerobic Oxidative system that requires oxygen). Glycolysis requires the breakdown of carbohydrates in the form of of Glycogen (stored in muscle) and Glucose (delivered in the blood) to resynthesize ATP; hence the name Glycolysis. Although the Phosphagen system is much quicker at replenishing ATP, Glycolysis can produce a lot more ATP because of the abundance of glycogen and glucose (compared to CP). Before glycogen and glucose can be used to produce ATP it is first converted into pyruvate. Without getting too nerdy about all of this, the body decides what to do with pyruvate in 2 ways. If energy demand is high, pyruvate will quickly be converted into lactate and ATP is created quickly. This is called "fast glycolysis. If energy demand is low enough, meaning exercise intensity is lower, the pyruvate will be shuttled to the mitochondria of the muscle cell to undergo a slower process of making ATP. This is called "slow glycolysis". This is a very basic description of very complicated process, but for the purposes of this article all we need to know is that glucose and glycogen can be used for energy through Glycolysis in a fast and slow manner to replenish energy. Glycolysis, both fast and slow, are used from about 10 seconds to 3 minutes. More specifically, the Phosphagen and Fast Glycolysis systems work together from about 6-30 seconds, and Fast Glycolysis works from 30 seconds to about 2 minutes. The Oxidative system (which we will talk about next) starts to kick in and works with Slow Glycolysis from about 2-3 minutes. Each energy system is used in relation to intensity and duration. High intensity exercise uses the Phosphagen and Fast Glycolysis systems until duration demands that intensity slows down. As intensity decreases and duration increases emphasis will gradually shift to Slow Glycolysis and then to the Oxidative System.

Oxidative System.
The Oxidative system is used when we are at rest or during low-intensity exercise. It predominantly uses carbohydrates and fats as energy substrates, but will use protein if exercise is super long (>90 minutes) or if you're starving to death. When we are at rest or during low intensity exercise (like walking) the Oxidative system is using fats. As I mentioned earlier, the use of carbohydrates kicks in when intensity picks up and we need to replenish ATP quickly through the Phosphagen and Glycolysis systems. During prolonged, sub-maximal, steady state exercise (what most people call cardio) the Oxidative system kicks in and the reliance shifts from carbohydrates back to fats (and to some extent protein). Because the Oxidative system works on fat, and because we have an abundance of energy dense fat stored, we can use this system for a very long period of time as long as exercise intensity is low enough.

Interval Training
Now that we have a very basic understanding of our energy systems and how they work we can begin to understand how we must program training to target the systems we use most. One of the common mistakes among conditioning programs is wasting time training energy systems that athletes will never use. For example it is pointless for a football player or a baseball player to do endurance training and maximize the Oxidative system. Rarely do they work longer than 7-10 seconds and they never do long sub-maximal work. Likewise, although a CrossFitter needs a strong Oxidative system, they won't get far competitively without a robust Phosphagen and Glycolysis system because the sport requires an excess amount of high intensity exercise. In order to put ourselves in the best position to succeed, we must target the systems we need most (or perhaps the systems we are weakest at), by programming work to rest intervals.
The more you target a specific system or combination of systems, the better and more efficient they become. We can do this by controlling how many reps we do or how long a work interval is compared to the rest between sets. When training the Phosphagen system we generally do heavy weight and low rep sets with a good amount of rest between. Over time, the system will be become better at recovering quicker and we can decrease the rest and increase the amount of sets we can perform at heavier weights. Likewise, by training fast and slow glycolysis, we increase the ability to do more high intensity work longer and to recover quicker. Intervals can also helps improve the amount of substrate the systems need. For example a lot of Phosphagen system intervals will increase the amount of CP stored in the body and Glycolysis training will increase stored glycogen and glucose. Additionally, by training certain systems you can actually improve the other "supporting" systems that are working in the background. For instance it is possible to increase the efficiency of the Oxidative system by training the 2 anaerobic systems (it's important to note however that the inverse is not necessarily true and that endurance training tends to diminish anaerobic efficiency and even strength).

The Importance of Intensity
A good strength and conditioning coach is going to have a firm grasp of the energy systems, which ones you need to improve the most, and the specific work to rest ratios to target them. The other important factor to this equation is work intensity of the athlete There has been some confusion, at least with some of my athletes, on the intensity that is needed for intervals. Because this is a crucial factor in the success of targeting the pathways, we need to be clear about the type of effort required for successful adaptation.
At the Chamber we do intervals several days a week in some form or fashion. It may be our typical glycolytic intervals on Monday, or Phosphagen intervals theough different timed EMOMs (Every Minute On the Minute). We also do a form of Oxidative/Slow Glycolysis Training through multiple metcons in a workout with moderate rest between. What is important to understand about all of this is that intensity is the most important aspect of an interval once the work duration and rest is established. One of our typical Glycolytic interval workouts might look something like this...
6 rounds
1'30" AMRAP
10 pull-ups
8 hang cleans
6 burpees
Calorie Bike
Rest 2'
In this workout the athlete works for 1'30" attempting to get through each of the exercises (pull-ups, cleans, burpees) before getting as many calories on the rower as possible in the 1 minute 30 second time limit. She rests for the entire 2 minutes then completes another interval for a total of 6 intervals or rounds.
One of the issues that we have had with athletes at our gym, generally the experienced competitive athletes, is that they "pace" the interval to get a better score or to win workout. What I mean by that is, they will hold back on intensity early in the interval rounds to get more calories on the bike throughout the entire workout. This is an effective strategy if your sole purpose is to get more calories than anyone else, but you will not get the full benefit of the interval in the long term. You can generally tell if an athlete paces an interval if there is no drop off in score throughout the rounds. For instance if an athlete completes 6-6-7-6-6-5 bike calories across the 6 intervals of our workout, there is no drop off in score. Most of the time a big drop off usually occurs around the 3rd or 4th round and might look like this: 6-6-6-4-3-1. Most competitive athletes want to win and that us understandable, but pacing intervals will compromise it's integrity and will not get the desired result. So this should be kept in mind during training.
It also possible for an athlete's conditioning level to be above a given interval. For example they may be so well trained in the Glycolytic system that it is impossible for them to go any faster during the time duration. They move incredibly fast for the entire work interval and never see a drop off across rounds. In this case the athlete should modify the interval by increasing weight in the lifts (increasing the hang clean weight from 95 to 135) or the difficulty of the movement (switch a pull-up to a chest-to-bar). In any case, in order to increase the efficiency of an energy system the intensity of the work interval must exhaust that energy system. You better make it hurt.
Interval training is one of the best ways to specifically target the conditioning you need for your sport without wasting time training things you don't need. Additionally, high intensity intervals are on e of the best ways to burn fat without losing muscle size or strength. Just be sure to know what you are training for and the best way to get it done.
In my next article we will talk about exercise selection and exercise economy.