For athletes, the purpose of training is to improve performance on game day.  In the sport of fitness, performance is the ability to utilize physiological characteristics to produce a higher work rate.  Training programs should focus on enhancing these physiological characteristics and turning them into performance results.  The widely accepted model for “conditioning” in the sport of fitness is misguided.  As such, athletes in our sport are generally lacking in power production compared to what they could achieve if properly trained.  We use lessons learned from athlete development in other capacity sports and focus on

Raw Capacity:  Physiological adaptations which enhance the body’s energy production capability

Functional Capacity:  The integration of raw capacity with functional capabilities, to maximize the contribution of capacity toward performance


Raw Capacity

This is the ability to produce energy.   Physiological adaptations which increase energy production include:

Stroke Volume:   The amount of blood pumped per heartbeat.   Evidence indicates that in well-trained athletes, stroke volume does not plateau as heart rate increases.    Therefore, increased stroke volume can improve performance at all intensities.  

Muscle Capillary Density:   The amount of capillaries which supply oxygen and nutrients to muscle cells.  Increased MCD increases the amount of oxygen that can be delivered, as well as the rate at which lactate can diffuse out of working cells.

Aerobic Enzyme Activity:   With proper training, the size and number of mitochondria in your muscle cells increase.  This means greater enzyme content in each cell for aerobic energy production.  Increased aerobic enzyme activity is critical for increasing work rate at a specific percentage of VO2Max.  In fact, by enhancing all these markers, you can attain a higher work rate at a lower percentage of VO2Max.

In other words, raw capacity is substantially the ability to deliver oxygen to working cells and the ability of those cells to use oxygen.   The limiting factor of the aerobic energy system is delivery of oxygen by the cardiorespiratory system, not extraction of oxygen by muscle cells.  This is why the Olympic Training Center is at high altitude, and why so many elite cyclists use EPO: to improve the delivery of oxygen.  Increasing raw capacity requires a combination of endurance training, threshold training and high intensity interval training.   Our Engine Builder 1 program is an example of a raw capacity – focused training program.


A very brief discussion of muscle fiber types

Muscle fibers are commonly grouped by type:  Type 1 (slow) Type 2 (fast), with additional divisions in type 2.  This can be a little bit misleading, and arises from analytical techniques which allowed only simple categorization.   Newer techniques have revealed that muscle fibers exist along a spectrum from pure slow to pure fast.  The presence of certain types myosin heavy chains determines the fiber's position on the spectrum; myosin is the main contractile component of muscle.  However, the older categories persist, so a muscle fiber that is 60% slow and 40% fast is considered Type 1, as is as muscle fiber that is 95% slow and 5% fast, yet these fibers exhibit different characteristics during exercise.  Slower muscle fibers are preferentially recruited for long-duration, lower intensity work. While the idea of complete slow-to-fast transformation is not widely supported by evidence, some movement along the spectrum is possible with focused training.  Furthermore, with the proper combination of intensity and duration, the oxidative capacity of fast fibers increases tremendously.  Generally, interval training is used for high intensity efforts, enabling recruitment of the faster muscle fibers, and subjecting them to a sufficient volume of contractions to increase their oxidative capacity. 


Functional Capacity 

When exercising, the brain cycles muscle fibers through work and rest intervals to conserve capacity.  Increasing work rates lead to greater energy needs, increased muscle fiber recruitment, and shorter rest cycles for muscle fibers.  Raw capacity is the ability to respond with adequate ATP production.  Functional capacity enables us to maximize our raw capacity by taking advantage of two important concepts:

Economy of movement: A measurement of the work accomplished vs the total energy expended.  Double-unders are a great example.  Advanced athletes use only their forearms to turn the rope.   Less experienced athletes may rotate at the elbows, recruiting their entire upper arm and shoulder.    This increases the total energy expended without doing any more work; the rope isn’t turning any faster.   The more advanced athlete gets the same work done at lower energy expenditure.   For a stunning example of economy of movement, check out Molly Metz completing 153 double-unders in 60 seconds.

Distributed Power Output:  This means using as many muscles as possible to accomplish a task.   In butterfly pull-ups, athletes use the hips and legs to generate force.   By including more muscles, an advanced athlete can do 30 or even 50 butterfly pull-ups without loss of intensity.  This volume of strict pull-ups would be taxing to all but the most elite.  This same phenomenon is observed in most kipping movements such as muscle ups and others.    By sharing the load, each working cell is required to produce less energy, delaying fatigue of any specific muscle group or region.

Collectively, functional capacity reduces the stress of exercise and delays fatigue, enabling the more complete and powerful expression of raw capacity.  Maximizing functional capacity is complex.  Superior technique produces superior functional capacity, and this requires rigorous attention to detail from the gross movement patterns all the way down to fine details like optimal joint angles to maximize energy storage and return in connective tissues.   If you don’t have access to elite gymnastics coaches and movement specialists to fine tune your movements, don’t worry!  The main ingredient in functional capacity is doing a high number of reps of each task.  Functional capacity is about muscle fiber recruitment and work/rest cycling.  Developing these neuromuscular adaptations requires lots of reps.  An example of a functional capacity training session would be:

  • 3 rounds for time:    
  • 100 DU
  • 50 wall balls

or perhaps

  • AMRAP 10
  • 7 muscle ups
  • 20 box jumps

By performing large numbers of reps, the body will determine the optimal movement patterns for energy conservation.   That is exactly the goal of functional capacity.  


Hey, what about the glycolytic system? 

Glad you asked.  Most of the time, intensity in a WOD is based on the joint contribution of our aerobic and glycolytic systems.  Intensity is usually

Aerobic Power + Glycolytic Power (just above lactate threshold)

Increasing the power output of either system increases total intensity.   Adding aerobic power requires more oxygen, and aerobic capacity can be added almost without limit.  Adding glycolytic power requires more glycolysis and produces more lactic acid.   Therefore, to increase glycolytic power without hastening the onset of fatigue, one must increase the ability to remove lactic acid.  Muscle Capillary Density is correlated with lactic acid removal as well as oxygen delivery.  Furthermore, improved aerobic capacity increases fat oxidation and spares glycogen, so more energy stays in the tank for high intensity efforts, like strength training.  Therefore, increased aerobic capacity also benefits the glycolytic system indirectly.  We don’t ignore the glycolytic system.   In fact, our Engine Builder series targets the glycolytic system explicitly at least once a week, and secondarily in lots of our training.   But the best way to increase your “race pace” is to develop tremendous aerobic capacity, and that is our primary focus.   One last thing…Some common tests, such as Isabel or Grace, are very much within the “glycolytic time frame” for advanced athletes.  However, studies have shown that strength is the best predictor of performance in these events, rather than traditional measures of anaerobic capacity.   For additional information on this phenomenon, see:



We have established that a comprehensive conditioning program should include development of raw and functional capacity, via a combination of:

Classic endurance training:  This long-duration, steady state work enhances stroke volume, muscle capillary density and aerobic enzyme activities. 

Interval training:  High intensity sessions (above race pace) demand recruitment of fast muscle fibers.   Short rests keep the focus on aerobic energy, increasing the oxidative capacity of these fast fibers.  Keep the work intervals longer than, or equal to, the rest intervals. 

Threshold training:   To improve your race pace, you sometimes have to work at your race pace.

Functional capacity development:  High rep sessions improve economy of movement and distributed power output and facilitate neuromuscular adaptions to optimize work / rest cycling of muscle fibers. 

Many popular training programs include high reps of various movements and therefore develop some functional capacity, but economy of movement and distributed power output are only as beneficial as the underlying raw capacity.  There is little value to developing functional capacity without raw capacity; what’s the point?   Over-emphasizing functional capacity (doing too many MetCons) is akin to building the penthouse before the foundation is in place.   Perhaps the commercial success of some programs lies not in their results, but in their implied shortcuts.