The way they train is more endurance focused and bodyweight training. The reason you see people get big is because they eat big and lift heavy and PKGEN doesn't lift very much and keep their reps high.

When you think about it, lighter is better.

Move and accelerate faster, less force, etc.

PK Gen does not strength train AFAIK -- they train for endurance.

Compare the Bar-Barians to PKGen and you will see a huge difference.  The Bar-Barians focus on constantly getting stronger even with bodyweight only skills.  Look at livewire vs. PKGen and you will see that Livewire is more "built" than most of PK gen because he does a ton of strength work for his upper body such as handstands, flags and general strength training.

If you want to get bigger you need to eat and train for it and PK Gen just doesn't do that.  Hopping on 1 foot for an hour does not make you bigger (nor does it make you better, really.)

I'm unclear whether you're saying chimps are gracile ("slender and graceful") or robust (big, "bulky" musculature), but I've seen some pretty robust wild male chimpanzees.  The dominant males tend to be pretty bulky.  Before taking anthropology my image of chimps was that of the typical female, but after seeing a few documentaries I realized there's quite a bit of variation within the species.

There, Shae, I fixed that for you.

If you want to be strong, then train like STRONG people.  Bar-barians, Steve Low, Jim Bathurst, Gymnasts, Power Lifters, Olympic Lifters, Traditional Strongmen.  The guys at PK Gen aren't what I would consider strong - though they are very good traceurs.  Much of parkour is skill/coordination work so that explains a lot.

David Belle, for example, does a lot more strength work than PK Gen as far as I am aware.  DB can do thumb pushups - you don't get those by doing little circles at the bottom of your pushups for 4 hours a day or running a marathon's worth of running while mixing in some skill work like PK Gen trains.

Agreed 100%.  PK Gen is called on to teach parkour for several hours a day, several days a week, on top of other projects, many of which are parkour-related.  It's quite understandable that they train for endurance to withstand that kind of constant punishment.  They can definitely move their bodies and what gear they carry on them, so why not bias their training toward endurance?

To look at it from the other direction, having greater endurance allows them to be involved in more parkour-related projects, and therefore do more for the parkour community.  Seems like a good idea to me.

One other thing that I would like to add is that this question was brought up regarding their musculature.  If you are interested in musculature at all then any sort of extremely high volume of movement is not going to put you closer to being more muscular.

Strength training does make you bigger and supplementing that with hypertrophy training makes you biggest.  Thats 3-5 RMs for strength and 8-12 RMs for hypertrophy.  PK Gen is doing things in the hundreds and thousands of RM range. That is nowhere near either strength or hypertrophy.

Really, I don't care how you train.  The fact that a marathon runner trains endurance and I train strength is meaningless when you consider how many people are training vs. sitting on the couch.  Me and the marathoner are pretty damn similar in that regard and I respect anyone who trains for any reason towards any goal so long as they do it seriously and with conviction.

With that said, I get really annoyed when I opt out of PKGen style workouts because I view them as a waste of time and people seem to think this means I am being a bitch or I am not cut out for the workouts.  Additionally, many people who think that these PKGen style workouts are good ALSO think that they make you strong.  Both of these assertions (the former implications about me and the latter about the results of these workouts) are entirely false but after the 100th time it happens it gets really annoying....

Maybe I'm just on a soapbox, now.

Chris... TripplepostedPwnage.

Agreed, 100%. You would think that of all people, PKGen as traceurs would value efficiency, especially in their workouts. It's a shame to see them propagating the same sort of nonsense as seems to be displayed at fitness clubs all across... everywhere probably.

Again I must thank you, Chris, as you've made me actually scrutinize some things I took for granted and change my opinion on some PK Gen exercises.  However, I must still disagree with you on your assertion that their training is useless and ineffective as endurance training

I think you're fixating on only one aspect of their training.  I agree that many of their exercises such as those circle push ups are not likely to give any translation to actual parkour movement.  However, there is plenty of stuff that seems fine.  The majority of what I've seen of their trainings has been a large volume of skill and coordination work with constant, low-level exercise in between.  I don't understand why this would be particularly "bad", if one does not tout that it will make you strong.

?? I don't understand your point here, Chris. I don't think you understood my post? Having a strong Cardiorespiratory/pulmonary system will only aid in your lifting abilities due to the increased strength of the heart, as well as the capacity of the lungs. With more cardiovascular endurance, you are more able to supply the muscles with what they need during exercise.

Couple benefits to Aerobic training:
1. Decrease Heart Rate at any submaximal effort, including rest. (Heart Rate: The number of times the heart beats per minute [bpm])
2. Increased Stroke Volume at rest, and at all intensities. (Stroke Volume:  the amount of blood pumped from each ventricle each time the heart beats)
3. Increased maximum cardiac output (The amount of the blood that flows from each ventricle in one minute)
4. Increased capillary density
5. Increased number of mitochondria
6. Increased activity of mitochondrial (aerobic) enzymes

Capillaries: very narrow, thin-walled vessels across which the exchange of gases, nutrients, and cellular waste products occurs between the blood and the cells of the body.

Mitochondria: The site of aerobic energy(ATP) production. The greater number of mitochondria in a cell, the greater the aerobic energy production capabilities of that cell.
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ATP (Adenosine Triphosphate) "The Energy Cell": Where the energy used to exert force and contract muscle fibers primarily comes from.
Muscle cells must produce more ATP to continue working, because only a limited amount is stored, therefore muscle cells must produce more ATP. The ATP supply is replenished using three distinct biochemical pathways, or separate series of chemical reactions: the aerobic system, anaerobic glycolysis, and the creatine phosphate system.

The aerobic(with oxygen) system produces more ATP than the anaerobic(without oxygen) systems.

The primary source of of anaerobic ATP production is glucose, which is carried in the blood and is also stored in the muscles and the liver and glycogen (A large molecule made up of chains of glucose).
A second source of anaerobic ATP production is Creatine Phosphate, a molecule that can be quickly broken apart to help produce ATP. There is an extremely limited supply of creatine phosphate. The muscles store only enough creatine phosphate and ATP, together referred to as Phosphagens, to last for about 10 seconds of maximal effort.

As long as a muscle cell is aerobic, it uses both fatty acids and glucose to produce ATP. The aerobic system produces more ATP than the anaerobic systems, primarily because fat yields 9 calories of energy per gram, while carbohydrate (glucose) and protein yield only 4 calories of energy per gram. The end products of aerobic ATP production are water and carbon dioxide, both of which are relatively easy for the body to deal with, so that aerobic energy production does not lead to fatigue.
When an exercising muscle becomes anaerobic, it relies on glucose (and to a limited extent the phosphagen system) to produce ATP. Not only is much less ATP produced, anaerobically than aerobically per molecule of substrate used, the byproducts of anaerobic ATP production include lactic acid, heat, and hydrogen ions. As the level of lactic acid and other by-products increases in the muscle, continued contraction of that muscle is soon inhibited. Lactic acid is thought to be the principal cause of the immediate soreness (the "burn") in an exercising muscle.

In addition to lactic acid build-up, the muscles give other signals when they can no longer produce enough ATP aerobically. One is hyperventilation, defined as "breathing faster than is necessary at a given pace", an indication that anaerobic ATP production is predominating. When inadequate oxygen is available, the muscle signals the brain to increase the rate and depth of breathing. The limiting factor is not usually the ability to increase the rate and depth of the breathing. It is primarily the ability to extract and use oxygen at the muscle, therefore hyperventilation is an almost useless process.
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One change in response to aerobic training is that new capillaries are produced in the active skeletal muscles, increasing the area for the exchange of oxygen. In response to aerobic training is a significant increase in the mitochondrial density, which means more of the muscle cell is occupied by mitochondria.

The increased aerobic enzyme capacity allows for a greater use of oxygen; thus, exercising at greater intensities can still be accomplished "aerobically".

The increased maximum cardiac output combined with the increased extraction capability yields not only a greater maximum aerobic capacity, but also an elevated anaerobic threshold.

Anaerobic Threshold: The intensity at which adequate oxygen is unavailable. Corresponds to the upper limit of sustainable aerobic exercise and it generally occurs in the range of 50 to 85% of maximum effort.

As long as enough oxygen can be delivered into the mitochondria to meet this increased energy need, ATP production will proceed primarily through the aerobic system.

Now yes, Lifting weights is primarily Anaerobic, but I would think it be foolish to classify cardiovascular training as useless when the benefits of aerobic training are clear. (Also note the previous statement)

I would only think it a benefit to increase your aerobic abilities through cardiovascular endurance training and increasing the strength and efficiency of the cardiorespiratory/pulmonary system.