Why Eccentric Work is Essential for Parkour

(I've written this article in a very simplistic language, and tried to keep the concepts as simple as possible as well, keeping in mind that many people who practice Parkour tend to be very thick headed, having no interest in the workings of the body and how it affects them at all, only desiring to go out and perform the most audacious movements. This has also been kept simple for those readers who have no biological or exercise science background, but the important knowledge within would pertain to them and their training just the same.)

A Primer on Physiology

The body's musculo-skeletal system is comprised of two main components - muscles, and bones. Bones attach to each other via joints, some of which are simple and single-planar, while others are more complex, multi-planar, but which permit two adjacent bones to move in relation to one another in space. Your skeletal muscles are the organ that attach two bones together by traveling over the joint and attaching itself on the bones on both sides of the joint. The muscles are attached in turn to nerves from your body's Central Nervous System (CNS), which produces electrical signals, which cause a certain chemical reaction within the tissue of the muscle, causing it to contract, or shorten. Because this muscle is attached to two adjacent bones on both ends, a shortening of the muscle tissue draws the two bones closer, thereby causing movement at the joint.
The bones on two ends of a joint cannot move by themselves, and need some kind of external force to cause that movement. Let's take the elbow joint for example, which is a simple hinge joint. It has one bone attached at each end, and they move back and forth to bring your wrist close to your shoulder, and back again, resembling a hinge action. Now imagine a hinge, if you will. By itself, the hinge can cause no movement. It needs an external force to move it open and shut. In this case, it would be your hand that either moves the hinge itself, or, if the hinge is attached to a door, it's your hand again that moves the door. The same way, your bones cannot move by themselves, and in their case, the external force is produced by the muscles attached to them via signals from the CNS that cause the two ends of the hinge joint in your elbow, i.e. the wrist bone (radius and ulna) and the arm bone (humerus), to open and close (i.e. unless somebody or something else produces a force against your body and causes that wrist to move close to your shoulder causing movement at that joint, but again, an external force is being applied and the bones cannot move in the joint by themselves). The above description is a very basic functioning of your musculo-skeletal system.

It is this musculo-skeletal system that is the most important part of your body in helping the body achieve any kind of external movement.
Whenever your brain signals to your body that it has to move, it is the muscles which move the joints, which move the bones, which produces movement. So it stands to reason that this is the body's system that you should pay more attention toward developing over the other body systems, if you want to improve in a discipline that is about human external locomotion.

Now, coming back to our example of the elbow joint above, we notice that there are two distinct actions that can be performed in the movement of the joint. Which is, a closing of the joint from an open state, and an opening of the joint from a closed state. This necessitates the need for the ability to produce force on either side of the joint, i.e. you need muscles on either side of the joint. One, which would cause the joint to close together, and the other to cause the same joint to open back.
Most joints in the body are structured similarly, including the complex ones which can be broken down into similar smaller elements. This is why most joint movements can be described in pairs of antagonistic or opposite movements in the same plane, and have a corresponding set of muscles on both sides of the joint to permit that opposite movement in the same plane.



With this out of the way, let us understand some basic muscle movement types. The (rather crude) diagram above represents your elbow joint. The straight lines are the bone and the joint, with the middle row representing the joint, and the curved lines are the two muscles on either side of the joint, which would be your biceps and your triceps. The one on the right side (the front side of the body, which is called the anterior side) is the biceps muscle, and the one on the left (the rear side of your body, which is called the posterior side) is the triceps. The diagram represents a locked-out elbow joint, or a straight limb. This is the normal resting position of the two muscles surrounding that joint. From this position, if you were to bend your elbow and bring your wrist closer to your shoulder, it would initiate two muscle actions - the biceps muscle would contract, or shorten, to close the joint from the anterior side and bring the two bones together, while the triceps behind, since they are also attached to both the bones and have nowhere else to go, would extend, or lengthen from the opposite side to permit that movement. At this point, your triceps are being stretched out, while your biceps are held in contraction. This movement is called flexion of the joint. When you reverse the movement, the stretched out triceps start pulling the joint from behind by shortening or contracting themselves, whereas the contracted biceps start lengthening out or extending to permit the triceps to pull on the joint from the other end. When your elbow joint reaches its normal resting position again at lockout with your arms straight, at that point, your triceps are being held in contraction, and your biceps stretched out in turn. This reverse movement is called extension of the joint.



The diagram above depicts a (partially) flexed elbow joint. The middle row again is the joint, the middle column is bone, and the curves lines on either side of the middle column are the biceps and triceps muscle, where the biceps are in a shortened position, and the triceps are in a lengthened position.

Just remember - Joints go through Flexion and Extension (depending on which side of the body the joint is being moved on), and flexion and extension are not interchangeable for the movement of the joints when the action is reversed. When a joint closes on the anterior side, it is called flexion, and when the joint opens on the posterior side, it is called extension. The only exception to this rule is the knee joint, which flexes when bent (and the lower leg travels in a posterior direction), and extends when straightened out and the lower leg travels back in a frontal direction. (There are other movements of joints as well depending on the plane of movement, but they are outside the scope of this discussion, since we are mostly focusing on using the simple hinge joint example for later demonstrating eccentric contractions and their importance to Parkour training.)
Whereas Muscles go through Contraction and Extension (same term, but different meaning), and at any given time during a movement, a muscle is either contracting or extending, and the terms are interchangeable for the same muscle depending on the direction the muscle is moving in. Regardless of the direction of movement (anterior, posterior, lateral, or otherwise), when a muscle shortens, it is called contraction, and when a muscle lengthens, it is called extension.

So now you have two basic muscle actions - contraction and extension. So when you say you are exercising a muscle, the majority of the times it means you are working on contracting the muscle with force, where the muscle on the opposite side of the joint assists that movement by passively relaxing and permitting the first muscle to do its job, and when you say you are stretching a muscle, or doing flexibility work, you are extending a muscle (often times with force) to the limit of its range of motion, with the muscle on the opposite side of the joint is being passively contracted to permit the closing of that side of the joint which in turn permits the muscle on the first side of the joint to reach its lengthening point.

Now that was about two opposing muscle actions, contraction and extension. Muscle contractions themselves comprise of three distinct actions in turn - concentric contractions, isometric contractions, and eccentric contractions.
Concentric contractions refer to the shortening of a muscle under load, usually against the force of gravity. An example is the raising of a weight during a bicep curl, where your biceps are contracting concentrically.
When a muscle lengthens under load, usually along the force of gravity, it is called an eccentric contraction of the muscle. Although the motion is the same as an extension of the muscle, it is not the same as a muscle which is passively extending while the opposing muscle contracts, as here the extension of the muscle is happening while the muscle is still under tension. This tension can be greater than the tension on the same muscle under the same load when it is contracting concentrically. An example of an eccentric contraction would be setting an object down, the reverse of the example of concentric contraction above. The arm flexors (biceps) must be active to control the fall of the object, and hence, are contracting eccentrically here.
Isometric contractions happen when a muscle is held immobile in contraction under load, usually against the force of gravity. Under an isometric contraction, the muscle neither shortens, nor lengthens. An example of an isometric contraction would be carrying an object in front of you. The weight of the object would be pulling downward, but your hands and arms would be opposing the motion with equal force going upwards. Since your arms are neither raising or lowering, your biceps will be isometrically contracting.

Let us just be clear here that the concentric contractions we are concerned with are the ones happening against the force of gravity, and not the contractions that happen along the force of gravity, and vice versa for eccentric contractions. To use the previous elbow joint example - when you start from a locked out elbow position, your biceps muscle are extended, your triceps are contracted fully and held in isometric contraction. Now when you grab something in your fist and start to move your arm upward to bring your fist toward your shoulder, your biceps start to concentrically contract whereas your triceps muscle start extending and not eccentrically contracting, because they are not actively assisting the biceps in their contraction, nor are they trying to resist or slow down the rate of contraction of the biceps, but are instead, merely relaxing and allowing the opposing muscle to do its job. When you reverse the motion however, the triceps start to concentrically contract, yes, but they aren't really doing anything to bring the arm back down. If you leave it to itself, the arm will come down by itself at the speed of gravitational pull or faster, because the force of gravity acting on the mass of the object will automatically accelerate your limbs back down in the absense of any countering force (where your eccentric contractions come in). So this isn't really a proper contraction since an external force is acting upon your joints to displace them with no effort from your own self, even though technically, your muscle is contracting from an extended position. Coming back to the movement of the arm back down to the thigh from the shoulder, your biceps here, although technically extending, are actually eccentrically contracting to resist the force of gravity acting upon the mass of your arm (and the mass of the object in your fist if any) from accelerating the speed of descent to the rate of gravitational pull or faster, and prevent it from going down too fast and crashing.


With that out of the way, let me just define Strength in a quick and simple manner (so that the rest of the article stays consistent and on the same page).
Strength is nothing but the ability of a muscle to generate force against an object. That's it. Pretty simple concept, innit? Your muscles do not distinguish between the kind of objects they are producing force against, they merely contract to produce force or resist force. If the joint movements are produced by your own willful action, then the measurement of the force produced is the Strength of the muscles contracting.
If your joints are moved by an external force however, that is not a willful contraction by you, and hence cannot be termed Strength, because it is the object that is producing the force making your muscles contract/move in the direction to redirect your bones, not the muscles producing the force to move the object.
Muscles are a tissue, just like any other tissue in the body. And just like any other tissue in the body, your muscles respond to stress, and adapt to the level of stress that is placed on them on a regular basis. In this case, the load placed on the muscles forcing them to produce force to contract is the stress. Therefore, in order to get stronger, or in other words, to get your muscles to produce more force than before, you have to subject your muscles to a greater stress (or load) than before each time you train for that adaptation to take place.

So What Does This Have to Do with Parkour?

Everything!

An oft ignored aspect by most traceurs when training for Parkour Strength & Conditioning is the ability to withstand impact. Many traceurs today would wisely nod their heads and state that building Strength is crucial for Parkour, because Strength is what gives them the ability to progress, and be able to jump higher and better. It has become almost fashionable in the Parkour world today to tout the word 'conditioning', despite people not understanding what it really means, or that training for Strength actually has two sides, and they only end up focusing on the one, non-important side. This is all good, and you're making one good case for Strength, but in all this, people tend to neglect the other all-important aspect of impact-resistance, or making your muscles strong enough to resist and bear that impact from all your plyometric-heavy activities day in and day out. Infact, I would argue that the strength to withstand impact is far more important than the strength to create force, even at smaller levels of jumps, because the ability to jump higher is not a very good or accurate indicator of progress in Parkour, but the ability to withstand any kind of impact - small or large - will keep you safe and capable throughout your life. Not to mention techniques in which impact is properly absorbed are very graceful and aesthetically pleasing to watch, and at the same time, show other attributes of Parkour skill such as control and flow, which when taken together, are a more accurate indicator of how much you have truly progressed in Parkour.^[1]

When teaching Parkour, I always tell people that it's not the going-up part that I'm worried about, it's the coming-back-down part that I'm worried about. Gravity has given us the law that 'what goes up must come down', and 'the higher they go, the harder they fall'. (I know, the second quote is actually a corruption of the original American proverb 'the bigger they come, the harder they fall' that I saw in a DuckTales episode once, but its meaning is apt in this scenario.) You cannot just expect to jump with all your might, exerting all your strength/force, and then forget about what will happen on the way down once you have achieved the target height/distance you were aiming for in your jump. When you go up, you will come down, and when you do, your body had damn better be ready to withstand what's coming next, or it's bye-bye joints. No, this is not just about proper landing technique or rolling when you land, although those are important as well. But no matter of landing and/or rolling technique practice will prepare you for taking the impact of a landing if your muscles aren't strong enough to withstand the impact and control and slow the body down during landing. And landing and rolling to absorb and dissipate impact-force come into play when you are landing on your feet. But what about when you are landing on your hands? Has anyone given a thought to that? Don't the upper limbs go through the same motions, and are required to absorb the same force when you are doing something like a cat-leap, or landing from a leap with your hands on a horizontal bar?

It is exactly here that the eccentric portion of your muscle contractions come in, if you haven't figured that out already. When you land it's always the eccentric strength of your muscles that is being called into play and not the concentric strength, and the ability to withstand impact by a muscle should always be a far more valued attribute in a traceur than the ability to produce a great deal of force from the same muscle.



If you notice the body position of the traceur in the image above carefully (disregard the cringe-worthy flat footed landing and pardon him for this gaffe, he was very new when this was taken), you will see that when he bends deep to absorb the impact of his precision, he bends his knees and flexes his hip joint. If you notice, this is the exact reverse motion of a squat or a deadlift. His hamstrings and hip flexors contract along the force of gravity, while his quadriceps on the opposite side of the knee joint and the glutes on the opposite side of the hip joint are lengthening under load along the same force of gravity, the load in this case being the downward force of the jump acting upon the weight of his body. They are undergoing the same eccentric contraction like in a squat or a deadlift, lengthening under load, and actively trying to decelerate the downward motion of the body and resist the concentric contractions of the opposing muscles of the hamstrings and hip flexors. If at this point the quadriceps and glutes fail to do their job and counter the hamstrings and hip flexors, the force of the contraction of the hamstrings and hip-flexors as forced upon them by the downward-acting force of the jump would cause the body to collapse and crash into the ground. This is exactly why eccentric contractile strength is so essential.



You can imagine the same analogy for the upper body - take a cat-leap for example. When absorbing the impact of a cat with your hands, your arms are moving backwards while staying close to your body. Which means your back muscles (latissimus dorsi) are contracting concentrically and your chest muscles (pectorals) are contracting eccentrically, decelerating and resisting the backward motion of the arm (or else your body would crash into the wall face-first).

In Parkour, it is mostly the landing stage where the ability of impact-resistance comes into play. We can divide common landing types in Parkour the following way - horizontal or vertical landings, and legs-only landings or hands-only landings or legs-and-hands landings. An example of legs-only horizontal landing would be precisions or any kind of running jumps. A legs-only vertical landing would be something like a vertical downward precision. A legs and hands horizontal landing would be a cat-leap whereas a legs-and hands vertical landing would be drops. A hands-only horizontal landing could be jumping forward to grab a horizontal bar or a ledge, or even a dive roll or kongs, or any movement where you leap forward to first place your hands for redirecting your force. Whereas a hands-only vertical landing would be jumping up to grab the same bar or ledge. You also have things like box jumps which can be a legs-only vertical landing while going up. I can envision very few situations for a hands-only vertical landing going downwards, as it is better, more efficient and safer to land on the legs, or on the legs-and-hands when going down instead of only on the hands. As you can see from all these examples, your impact-resistance activities come mostly from these types of landings, and not other movement patterns in Parkour. So it is mainly the muscles involved in these type of different landing patterns that need to be strengthened eccentrically, and not all the muscle groups in the body which do not really come into play in non-landing related work, and it should be safe to say that for the other areas of the body, even if you just focus on increasing concentric contractile force output you would be fine.
Untucking is another area where eccentric control is very important, because this is closely related to landings. In my years of teaching people how to tuck high and hard, I've seen tons of people manage to put all their might into jumping high and tucking tight, and they actually get a high enough jump at times, but these same people seem unable to control the rate of descent of their legs once the tuck reaches its peak, and crash down hard on the way back. Eccentric strength in untucking therefore would be required from the muscles involved in tucking - your spinal and hip flexors, because these are the muscles that counter the action of the reverse set of muscles that bring your legs down hard from a tucked position, the spinal and hip extensors, which are the lower back (spinal erectors) and the glutes. The lower back and the glutes being the strongest muscles in the body, if the hip and spinal flexors, which is to say a whole lot of muscles around your abdominal area, are not strong enough to counter the strong contraction of the powerful glutes and spinal erectors on the way down in an untuck, will lead to a crash-landing. So this is another area where eccentric training needs a strong focus.

On a side note, if you are wondering where the eccentric portion comes in in landings that involve going up, or whether you can call going up a 'landing' at all, either for the hands or the legs, let's look at these diagrams.

  

As you can see, (you can also try this out for yourself), taking the example of a hands-only vertical landing going up, if you are to jump up and grab a horizontal bar (first diagram), you wouldn't want to jump up to your limit only to grab the bar at the last instance, hanging by a thread, because this can cause a great amount of jerk on your joints, and you might even pull something (Newton's third law at work here, an equal and opposite reactionary force to your vertical jump force acting down upon you pulling you back down when your shoulder joint is in a completely stretched and hence compromised position). If you do this (not a recommended idea as stated before, but just from an example point of view), it would be your concentric muscles (or agonists as they are technically called) that would be forced to contract hard against gravity to pull your body up toward the bar to counter back the counter-acting force pulling you down. To prevent this and for a safer, more efficient vertical upward landing, you have to jump slightly higher than the level of the surface, giving your limbs some leeway, and travel back down a bit before you can grab it (second diagram), thereby creating a 'landing' effect while coming down, which also serves to absorb a lot of the impact of the vertical jump by the concentric muscles. But the moment you 'land' on the bar, it means the eccentric muscles start firing again in order to resist the agonistic muscles from contracting too fast due to gravity acting on them and prevent you from crashing/collapsing. As for legs-only vertical landings going upwards, it's a no-brainer that you can't land with your legs on a higher surface if your legs just come level with the surface, or you would just fall off behind. Your legs have to first go up slightly above the level of the higher surface in order to come down to a rest on that surface, thereby creating a 'landing' effect once again.

Then there are other related aspects of a strong eccentric contraction, like the myotatic-stretch-reflex, which refers to a reflex property of your muscles to contract forcefully or 'bounce back' in the opposite direction when they reach the end of their range of motion when being extended or stretched.
Let's take the example of a drop or a drop-roll. As the wisdom behind absorbing impact from vertical landings goes in Parkour, there are two accepted methods of abosrbing and disspiating the force and preserving momentum, depending on the situation - a standard drop, slap and go; or a drop roll. And in both methods, you don't just want to absorb the impact by going deep, but want to bounce-off and dissipate it as fast as possible. In a standard drop, slap and go, you drop down under control, slap your hands as the final act to absorb impact, and try to bounce up as quickly as possible using the stretch in your muscles that are contracting eccentrically on the way down to explode back up and start running. Same way, in a drop and roll, the eccentrically contracting muscles explode back in the opposite direction, with the body traveling horizontally, parallel to the ground, instead of going back up vertically, because you use the explosion from your hips to push you forward in a roll. Once again, a control in your eccentric motion is what makes this controlled explosion back in the direction you want using the myotatic stretch reflex possible. Without the control in the eccentric part, although the stretch reflex would have kicked in, but it wouldn't have given you a proper control in the subsequent explosion of the muscle making your subsequent movements post-explosion uncontrolled, jerky and off-balance, with you not really ending up where you wanted to be - in this case back on your feet and running, or going in a proper roll.
(Since the ability to generate impact is far greater in a vertical motion than in a horizontal one or one involving jumping/landing with the hands, we do not have anything like rolling out of a cat-leap in our horizontal leaps when landing on our hands, but have to roll or bounce back when landing on our feet. Which is why the topic of myotatic stretch reflex in relation to eccentric contractions cannot be discussed for cat-leaps and other similar upper-body landings. This is not to say there is no myotatic stretch reflex involved in any upper body movement, only it is not involved in Parkour in movements that involve landing primarily with your upper body.)


"But I'm already doing a lot of training, am I not getting sufficient eccentric strength built alongside?", you would say. A lot of people train with the right intentions, but do not realize the small shortcomings in the approaches they take.
Here's the thing - eccentric strength cannot be built without training the eccentric phase in resistance training, and responds to the same overload principle as the concentric phase does for producing greater force by the muscle. If you only ever train the concentric or isometric phases of contraction, you will only build concentric force generating capabilities in your muscles, but the eccentric resisting capabilities will suffer and degenerate.
Whereas studies and experiments have shown time and again that training just the eccentric phase of resistance has a significant carry-over to increasing concentric phase contraction as well, in addition to improving the said eccentric force resisting capability.

For instance, it has been noticed that professional cyclists with no previous lifting experience are pretty strong in the squat, and can lift relatively heavy loads. However, the activity of cycling itself lacks a significant eccentric component in the pedaling action, and the pedaling itself only goes through a short range of motion, not utilizing full range of motion for the lower limbs. Which means that although these cyclists have tremendous force producing capability in the concentric portion of the squat, they are unable to control the same weight while going down, thereby increasing chances for injury and becoming a major safety concern for these athletes if left to train with heavy weights unsupervised.^[2] This also means that other methods of training that involve an elimination of the eccentric component, like gymnastic bodyweight isometric hold progressions, or heavy lifting with dropping the weights instead of lowering them, most forms of aerobic exercises (like the cycling example above), are all ineffective methods to train for Strength for Parkour. Some of these might be very good at building higher levels of strength, but these only help build the concentric half, or in some cases the isometric part, and neglect the all-essential eccentric half.

Gymnastic Bodyweight Isometric Hold progressions have been proven to be a great method to increase upper-body contractile strength. By putting the body in disadvantaged leverage positions and then increasing the length of the lever arm and holding through it or performing dynamic range-of-motion movements into and out of these positions, they force a great amount of adaptation on the muscles because of the higher intensities involved in contractile output. However, these holds are still primarily isometric in nature, with a small amount of concentric contraction involved in the progression leading to the hold or in the dynamic movements performed from the hold, but very very little to nil eccentric motion involved. Which is why this kind of training for strength building makes it ineffective for sports which require a good amount of eccentric strength along with concentric.

This also once and for all refutes the age-old 'movement based conditioning' fallacy that a lot of traceurs cite. The concept (fallacy, rather) has been discussed in S&C circles before and refuted from the point of view of building concentric strength so I won't go into it, but as you can see, it doesn't do much to help build eccentric strength either. Let's examine a precision jump for example. Proponents of the 'movement based conditioning' viewpoint state that in order to obtain the ability to jump higher and farther in a precision, the only thing that needs to be practiced is the technique (in this case the precision) itself, and you would get more distance over time with practice and thereby also increase your strength in a 'functional' movement through a more 'natural' method. But by practicing the precision and trying to aim to reach a farther distance in it every time you train, you are focusing all your energy on just increasing the concentric output of the muscles involved in jumping through a very inefficient method, and are thereby subjecting your already weak muscles which have never experienced any eccentric training before to a high amount of shock and impact upon landing, which I'm sure would not be controlled the way a strong muscle would be, and therefore would not be counted as a valid eccentric contraction training, but would instead, just end up ruining your joints through repeated impact experiences. This kind of high-impact bearing plyometric activity does not produce the kind of systematic overload on the muscles, either in the concentric phase or eccentric, to drive the adaptation process in order to come back stronger than before, but just shocks and stuns the muscles and joints, especially on the landing part.
This also means that the frequently quoted line in traceur circles to help keep newcomers in line and prevent them from trying out big drops, "For the first three years of your training, if you can't box jump up to a certain height, you shouldn't jump off that height either", while a good measure to instill the right training attitude in newcomers, is still kinda misleading and incorrect, because the concentric explosive jumping ability needed for going up high in a box jump alone is not a good indicator of strength to resist the jump while coming back down, as seen from the discussion above. Once again, in all my years training people, I have seen people with various levels of ability be able to jump up pretty high. Just recently some of my trainees matched world records in Box Jumps. Two of the guys who set the highest jumps also embody the two very reasons I often state why certain people can naturally jump so high - being taller gives you a comparative advantage in jumping up to an absolute height, and certain people are genetically gifted jumpers and can jump high even without any training. But the same people do not show that much control yet while coming down. So once again, just the ability to Box Jump up is not a good indicator of control in coming back down.

So it stands to reason that in any kind of resistance training, in order to get optimal results, a full range of motion technique involving both eccentric and concentric contractions is essential. Not only that, but to build optimal power output and resistance capability, it is ideal to follow the training maxim - Fast concentric, slow eccentric. That is to say, explode hard and fast in the concentric half of the motion, this helps you to build speed and power in your contractions, and go as slow as you can and under control in the eccentric, this helps build control and resistance in the muscle when it needs to lengthen under load.
Infact, if you want to get better at eccentric training, you can even take it a step further. This concept was shared with me by a friend, Mohammad Azmat, who is a strongman, powerlifter and a former bodybuilder, who squats and deadlifts in excess of 600 lbs. He once mentioned this thing called 'stealth lifts' for deadlifts (actually you can use it for any exercise which begins/ends at the floor), where you're supposed to be so soft with the deload on the eccentric that the neighbors below (assuming you live in an apartment structure and are not on the ground level) do not hear a sound or get any clue whatsoever that you're training. (Actually, it's high time I implemented this myself, my neighbor below has already complained to the apartment superintendent that the dude above puts his 'dumbbells' down too hard when he works out, which makes her ceiling shake. Dumbbells, hahaha. If she only knew that what she imagined were light, 10 pound dumbbells were actually 250 pound barbells...) I'm sure the idea of stealth lifts would catch the fancy of traceurs, after all, we all love doing stealth drops, stealth rolls, stealth precisions, stealth QMs, stealth vaults, stealth runs, and stealth what-nots. 'Stealth' and 'Ninja' are our bread and butter. Why not stealth with lifts as well? We need that eccentric training more than we imagine.


- NOS on Jun 17, 2011

This article was written by Parkour Mumbai Reproduced here with permission.

References:
1 ^ Skill in Parkour
2 ^ Practical Programming. Rippetoe, Kilgore, and Pendlay, 2006