Energy Systems say, "Don't Cherry Pick!"
CrossFit is defined as,”Constantly varied, functional movements, performed at high-intensity, across broad time and modal domains.” Breaking that down this means that we perform movements that mimic actions we take in our daily lives. We perform them at higher speeds and loads relative to how we may traditionally do them. And we take on these tasks in various rep schemes, for different lengths of time, matched with various other movements.
If you were to look back at a year, a month, or even a week of programming you’d notice that some of the sessions have strength components such as a 1 or 3 rep max lift. High intensity interval (time) components such as 1 minute of max wallballs followed by rest. Or maybe, yes, a 5K run for time. These 3 examples are clear cut representations of programming to our body’s 3 energy systems: phosphagen, glycolytic, and oxidative. These 3 systems are how our bodies turn ADP into ATP, what we use for energy. CrossFit is highly effective because in addition to sticking to the clear cut programming models, it blurs the lines between the 3 of them, in turn making each system operate more efficiently over time.
A common thought is that each energy system operates independently. The fact is that although they dominate energy reproduction in certain time/effort intervals, in all activities, each of the 3 energy systems is contributing to your energy level to a small and/or large degree.
The phosphagen system (an anaerobic system producing energy without the presence of oxygen) dominates explosive, high power activity lasting 10 seconds or less. This system is known for very high power output, short duration activity such as a 1 rep max snatch attempt or a 40 yard dash test in football. This system produces ATP at a very high rate so that it can power those quick explosive efforts. However, it’s capacity to recover and do so over and over again at that rate is very low, usually requiring passive rest intervals of about 5:1.
The glycolytic system (also anaerobic) dominates energy production in intervals less than 90 seconds-2 minutes. This system powers high output activities such as a 400m run or the first 21 thrusters in the workout FRAN. Your glycolytic system produces ATP at a high rate, not as high as the phosphagen, yet recovers a little more quickly than it usually at a rate around 3 or 4:1.
And finally, the oxidative system (aerobic-producing energy with oxygen) dominates low output activity lasting over 2 minutes in length. A 2000m Row comes to mind here. This system produces ATP at a low rate but with a high capacity to continue generating energy for long durations of time. This is why a marathon runner can run 26+ miles without slowing down.
Notice the use of the word dominate. Each system, while being the primary source of energy production for its activity type and time frame, is not the only being used. During any given activity, your body will recruit energy (ATP) from all 3 of the energy pathways. This becomes especially evident as you hit the end ranges of each pathway where the lines blur, or when you implement interval style training at less than maximal recovery periods for the pathway you are training. CrossFit workouts are great at blending the lines because of the transitions from movement to movement. A workout like last weeks 1 minute on 1 minute off of: 3 Heavy power cleans followed by max wallballs. The power cleans were very high output and lasted about 6-15 seconds unbroken. This is your phosphagen system. The wallballs were high output and about 40-50 seconds in duration, glycolytic. With the minute of rest, the power cleans received about an 8:1 rest, plenty of time to recover while the wallballs about 1.5:1 rest, clearly not enough for a full recovery. So what happened in that workout was that most found that they could continue to clean the weight quickly yet the wallball repetitions began to fall off. As the wallball reps fell off the glycolytic system was maxing out and our body was forced to recruit the oxidative system which doesn’t produce energy at as high a rate. So this workout was effective in forcing our body to use all 3 energy systems, A in the ranges in which they dominate and B in the ranges in which they assist.
So what does this mean? What this means is that we need to effectively train all 3 systems in those manners. A) in their traditional sense, oxidative = 5K run or phosphagen = lift heavy and B) in their blending the lines sense, traditional CrossFit workouts. If you love to do the strength days and want your lifting to go better, you need to recover better across all 3 systems meaning that you should never skip the random cardio days or the days with medium length runs mixed into the wod. If you love to run and row and you want to get better at duration, you also need to recover more effectively and have strength to last, you should not skip a strength training day. In the U.S. cherry season is from April to August so there aren’t anymore to pick 🙂