Understanding the 3 energy systems of the body

Most of you are familiar with the three core principles that comprise the CrossFit strength and conditioning program: "Constantly varied, functional movements, executed at a high intensity."

The movements however, are not the only variable in CrossFit programming. The level of power, that the athlete must generate is also a variable in the CrossFit workouts. Power output is also closely related to time or the duration of the work involved.

There are three energy systems or metabolic pathways that the body utilizes to generate power. These are the phosphagen, glycolytic and oxidative systems. The first of these three metabolic pathways, the phosphagen system, is responsible for fueling the highest power outputs, but has limited fuel available. Thus, the phosphagen system is utilized by the body for very short bouts of extreme power output. The phosphagen system can produce peak power output only for about 11 seconds. Examples of this system at work are the clean and jerk and snatch, 100 meter sprints, max plyometric jumps. The second metabolic pathway, the glycolytic system, utilizes a power output of about 60%. Activities that utilize glycolytic metabolic pathway include things like a 200m and 400m sprint. These are activities that last anywhere from 45 sec to a minute. The oxidative pathway is utilized by the body for activities that are over several minutes, such as a 2 km row, running a marathon and walking. The oxidative pathway has a low power output.

These pathways, and their corresponding output of power make sense when you compare the bodies of athletes involved in different sports. A marathon runner only has a power output of about 10% percent as compared to an olympic lifter, whose power output is 100%. Olympic lifts only last a second so a maximum power output is possible. It is impossible for an athlete to run a marathon with 100% power output given that a marathon lasts over an hour. The physicality of a marathon runner is obviously very different from a sprinter, and this is because of the different degree of power that is required. Athletes adapt to the stimuli that they undergo. Thus, sprinters and olympic lifters develop more strength and power than distance runners.

Muscle fibers are also an important consideration in a discussion of power output. Fast twitch muscles are made of both 2a and 2b fibers. 2b fast-twitch muscle fibers are recruited for extreme bursts of energy - near maximal lifts and sprints are two examples. These fibers produce a lot of force but they also fatigue quickly. Type 2a fast twitch muscle fibers also generate force, but not as rapidly as type 2a and thus they are more fatigue resistance. One of the reasons CrossFit is so successful is that its programming does not specialize in any one energy system. The olympic lifts and very short sprints are obviously capable of generating tremendous power; but specialize in these two activities at the expense of ignoring the glycolytic and oxidative pathways and your stamina will be adversely affected. Likewise, if you train only at a lower intensity, with minimal power output, you will never develop explosive power and speed.

Soooo, how to train for a 400m sprint and a 200m sandbag sprint? You need to train all three metabolic pathways!

Interval training is a good place to start: Interval training is simply intense periods of work followed by periods of rest. The classic example from the CrossFit workouts would be the traditional tabata workout of 20 sec of work followed by 10 sec of rest. You can play around with the numbers obviously as well. 1 min of work followed by a min of rest. Or 30 sec of work followed by a minute of rest.

If your goal is to do each of these as fast as you can then you need a ratio of sprinting to resting of about 1:4. So if you run 400m in 2 min you need about 8 min of rest. As Tony Leyland explains, when you change the time on the rest interval you change the nature of the workout. If you decide to take shorter rest periods your body cannot fully recover and your intensity will decrease. This is not in and of itself a bad thing but just be aware that you have changed the nature of your workout. Tony Leyland recommends that for training 100m sprints the work/rest ratio should be anywhere from 1:12 to 1:20.

"One of the most common errors for many specialized athletes, both distance runners and lifters, both beginners and advanced, is overtraining. Lured by the 'more is better' mantra, many seem to think that if we train longer, harder, and more often, we'll get the best possible results [...] This is an error" (Tony Leyland, CrossFit Journal Issue 56, April 2007).