At the level of the joint, there is no such thing as linear movement. There are muscles that pull on tendons that pull bones in arcs and circles. By understanding this we can see linear motion as a finely choreographed sequence of arcs and rotation, that when pieced together create a straight line.
Rotational energy is one of the most overlooked aspects of movement, which by all accounts is hiding directly under our noses. Our brains are wired to understand straight lines and right angles, but it’s rotational motion doing the work behind the scenes to create this false perception of biomechanics.
There are many important concepts that stem from rotational energy in movement, which when broken down and understood, leave us with several important implications in training for elite athleticism.
Dynamics of Rotational Energy
There are many levels in which rotational ranges of motion are important in movement: arthrokinematics, osteokinematics, lines of fascia, angles of muscle attachments, etc., and then the synergy created from the connectedness of it all.
The latter point will be the main focus of these concepts, taking a wide scope look at how rotational energy is utilized for athleticism.
The Golden Ratio in Human Movement
Try this: Stick your arm straight out to your side, palm down. Now bend your fingers, bend your wrist and bend your elbow. Did your fingers just connect more or less perfectly with your armpit?
The general shape and proportions of each of our body parts is something we take extremely for granted. What would’ve happened in the example above if your humerus was twice as long as it currently is? Or if the length of your forearm was suddenly half of what it is right now? Would you still be able to touch your armpit?
Or for a better example, let’s imagine the most extreme version of disproportion in the body: If your humerus was 100 feet long, while keeping your forearm and hand the same size as they are now, would you see any semblance of linear movement? Or would the movement of your hand be at the mercy of the gigantic, sweeping arc of your upper arm? It definitely wouldn’t be pretty, and you for sure wouldn’t be able to scratch your armpit.
Maybe these are silly examples, but the fact is that one of the biggest factors in much of what we consider human (movement and attractiveness are two big ones here) is the presence of the Golden Ratio throughout our bodies.
It is ultimately the Golden Ratio that allows for the seamless translation of rotational joint kinematics into the linear movement that we are familiar with in day-to-day life.
Synergy in Joint Layout
Another aspect of our body we take extremely for granted is the joint-by-joint layout of our body. Why are our hips and shoulders ball and socket joints? Why are our knees and elbows hinge joints? Why is it all arranged in the way that it is? Or if “why” is too existential of a question, how does our body utilize this “socket-hinge” layout for movement?
There are a few very important points on this. First is that our joints are arranged in opposing directions of motion, allowing the body to “fold” and “unfold.” This concept of opposing joint torque is a huge principle of posterior chain tensegrity that allows for big time utilization of elastic energy in athletic movement.
Second is that this allows for easy energy transfer proximally to distally (as well as from the ground back up the kinetic chain due to the posterior chain tensegrity principle mentioned above). There is a huge relationship between the hip and knee based off the conservation of angular momentum. Understand that the knee is really just the point of connection between the femur and shin.
In open chain movement (swing phase of running/bounding), the knee is nothing more than a vessel for energy from the hip through the femur to the shin, into the foot, into the ground.
When the femur/knee reaches its highest point, and the glutes begin drawing femur back, there will be a whipping effect through the knee due to angular momentum at the distal end of the femur. This is only possible because of the knee as a hinge joint, and is only possible because of the direction of the hinge. As bizarre as it is to imagine, if the human body were such that the knees faced backwards instead of forwards, this whipping effect from the hip through angular momentum would not be possible.
In closed chain movement (ground contact), the knee is a vessel for the loading of the Achilles through forward shin movement, which is driven by a combination of knee extensor relaxation/force of gravity and hip extension pushing knees farther over toes (hip extension driving Achilles impulse through the knee joint is a common theme in elite athletes Olympic lifting huge weight for their size).
On a similar note, because of conservation of angular momentum (e.g. the whip effect), proximally driven movement through the hip helps drive stiffness through the posterior chain. Consider that there is nothing more stiff than a joint at its end range of motion. This is why you will sometimes see elite javelin throwers hit positions of hyperextension in their block leg. If you plant at the right angle with femoral angular momentum from the pawback mechanism of glutes (i.e. proximally driven movement), the knee has no choice but to be locked out, purely because of the layout and mechanics of the knee and hip joints.
This is also why sprinting is posterior chain dominant, despite the massive vertical forces that we would expect the quadriceps to have to handle if viewed from a typical “muscularly-driven” paradigm: The fascia through the posterior chain gets stretched like crazy because of momentum.
“The vertical forces in sprinting come not from the quads, but from the fascial trains coming up from the foot, via the posterior chain”
Another important consideration is that proximally to distally, our joints go from more to less degrees of freedom. That is, your hips can move in directions that your knees or feet can’t. The same idea applies to the shoulder/elbow/wrist.
Why does this matter? As joints go from more to less degrees of freedom, energy from the transverse plane gets “funneled” into sagittal plane energy. To understand this we also have to understand the role of end ranges of rotational motion in energy transfer. Here is a small section of a previous article I wrote using the throwing motion as an example:
“Look at how energy gets transferred through the kinetic chain in a baseball or javelin throw: Energy of internal rotation of the right side of the pelvis gets stopped and absorbed by the stiffness of the left hip (Think about a bicyclist crashing into a curb and flying over the handle bars to help visualize this example). The linear and angular momentum of the body causes this energy to get transferred up the spine, where end range of thoracic extension and rotation acts as another “curb” that transfers energy to the scapula. The end range of scapular retraction and posterior tilt acts as another “curb” that forces glenohumeral external rotation. When the shoulder hits its end range of external rotation, it acts as a “curb” for the transfer of energy into elbow extension, whose end range acts as a “curb” for glenohumeral internal rotation and forearm pronation.”
So consider that the femurs (from the hips) move naturally in a “figure 8” pattern during the running motion: hip flexion is linked to internal rotation, while extension is linked to external rotation. As the hip reaches the end range of internal rotation and hip flexion, the leg then swivels around into external rotation and extension. This extra rotational energy from internal to external femoral rotation gets transferred to the hinge of the knee, where it is translated into sagittal plane energy to extend the knee and then load the foot through the ground.
Momentum and Energy Relationship
Momentum and energy are two very related values in physics. As a reminder:
Momentum = Mass * Velocity
Kinetic Energy = ½ * Mass * Velocity^2
(Angular momentum and rotational KE have slightly different equations, but relationship is the same)
Both are based off of mass and velocity, but the key difference lies in the fact that kinetic energy is exponentially related to velocity. This is massively important in human movement, where the conservation of angular momentum plays a huge role in athletic movement.
Proximally to distally, each segment of our body decreases in mass. That is, our trunk is bigger than our thigh, which is bigger than our shin, which is bigger than our foot (See: Golden Ratio). So if our body follows the principles of passive energy transfer through proximally driven movement, angular velocity will increase from segment to segment in order to conserve angular momentum as mass decreases.
This is important in and of itself, but what is even more important is that because of the relationship between momentum and energy, kinetic energy will increase from segment to segment. This is important because of our foot’s role in transforming rotational kinetic energy into elastic energy upon ground contact.
Now remember that force is really another name for energy transfer, and can therefore only exist in collisions. Also remember that the ground will always give back what you put into it. Tying these two ideas together, how much energy you put into the ground is how much energy the ground will give back to you (This is actually only true in a completely elastic collision, which is not the case in human movement, but the point is that energy is where we should be looking as opposed to force).
“The force put into the ground is the force returned from the ground, but this is ONLY true in elastic collisions. Stomping or punching the ground can reduce the elasticity of these collisions and nullify this law”
A really important point to consider here is that the true physics behind angular momentum, kinetic energy, force and collisions goes so much deeper than what is typically brought up in the sports performance field. We cannot draw complete conclusions using incomplete physics.
Joint Rotation as Waveforms
I’ve talked before about energy transfer occurring through the body as different forms of waves: Longitudinal (elastic), and Transverse (joint rotation). Elastic waves of energy would be the loading and unloading of elastic elements in the body (muscles/tendons/fascia), while the angular displacement of joints moving in their respective arcs and rotational pathways would create the transverse waves.
While this may sound unnecessarily abstract, synchronizing these two kinds of waveforms is where principles of timing in elite athleticism stem from.
On a local level the synchronization is inevitable: due to attachment points of muscle/tendon/fascia to bones, any angular displacement of bones will cause a stretch. But ultimately, we want to utilize the entire body to contribute energy synergistically in movement. Therefore, we have to understand how to “connect” parts that aren’t typically viewed as connected.
By seeing movement in terms of waves of energy, and understanding fundamental principles of waveforms and rotational energy, we are given an all-encompassing point of reference to determine optimal timing and motion of any given body part, in any given movement.
Adarian Barr’s concept of ground impulse as a biomechanical lynchpin is a game-changer in this regard. Remember: movement only happens from the transfer of energy from our feet into the ground back through our feet.
Also remember: transfer of energy only happens in the form of collisions. Tying these ideas together leaves us with two key ideas.
First idea is the importance of knowing when the ground gives you energy. It is not necessarily when your feet contact the ground. It will vary from movement to movement, but there has to be a series of collisions (starting with the ground, moving from joint to joint, and ending with our center of mass) caused in some part through opposing torque of joints and/or end ranges of rotational motion.
The best example of this is in a javelin throw. The throw happens only once the hips are fully squared into the throw and collide with the block leg. Therefore, the ground can’t give energy to the thrower through the block leg until hips are squared into the throw, because this is when the collision happens.
https://www.instagram.com/p/BrSpz6Cni9V/?utm_source=ig_web_copy_link
Second idea is using the “non-elastic” energy of joint rotation (or limb movement) for two jobs:
The first job is to set up the body to be in an optimal position for a “full-body” collision with the ground. Understanding the ideas of opposing joint torque and tensegrity, as well as the role of end ranges of rotational motion is key here. This concept goes hand in hand with the Frans Bosch idea of eliminating “muscle slack.”
An important point though is that we do not need to train our muscles to fire faster to eliminate slack, we’ve got to train our muscles to put our joints in optimal positions to utilize gravity and momentum to eliminate slack through tensegrity priniples and collisions.
“We do not need to train our muscles to fire faster to eliminate muscle slack, we’ve got to train our muscles to put joints in the optimal position to utilize gravity and momentum!”
Going back to the javelin example from above, we could say that to shorten the timeframe, and maximize impulse from block foot planting and hips colliding, the thrower should time their hips to be open at the moment of block leg planting. This effectively clears up the “slack” before collision takes place.
The second role of joint rotation in movement is to contribute momentum into loading of elastic tissue and/or into the direction of movement.
From the perspective of waveforms, we want to time the moment of maximal angular momentum of limbs with the maximally loaded phase of the stretch shortening cycle of elastic tissue. This is where Adarian Barr’s ground impulse idea is such a game changer: In most athletic movement, the Achilles being maximally loaded is the moment that the ground gives back energy. This means that limb positioning and timing should be based around this.
In sprinting: Knee lift, arm swing, shin angle are all linked according to Achilles impulse.
Can you see the Achilles loading and unloading throughout the sprint cycle in this famous video?
In Javelin release phase (for right handed thrower): Hips opening and left arm driving upper body opening (hips first, then upper body) are timed with the impulse from the block leg hitting the ground. The idea being that rotational energy is maximized from the uncoiling of hips/upper body when everything is squared into throw, so this is the optimal time to “combine” the waves of energy from elastic components and ground impulse.
If hips are still closed when block leg plants, impulse is lengthened and energy is lost. If hips open too soon, momentum from hips will be lost.
https://www.instagram.com/p/BrDtgnwH1rq/
Here you can see that the throw happens instantly when the block hits. The hips open from back foot contact to right foot contact and the center of mass collides with the block leg. The knee does not bend at all in this throw because the collision (plus angle of block and pawback mechanism of glutes) forces stiffness through posterior chain of block leg.
https://www.instagram.com/p/BtgFL4sH3bu/?utm_source=ig_web_copy_link
Here you can see that the hips are not fully squared into the throw when the block leg plants. As a result there is no collision and the block leg knee collapses briefly as a result of the forward momentum of the thrower.
This is a lot of information that isn’t new, but the implications that come with connecting the dots on these ideas allow us to better cut through the noise on what matters and what doesn’t in elite athleticism.
With that being said there are a few key applicable takeaways from all of this.
Coaching Cues
Because our natural tendency is to break movements down into straight lines, right angles, and planes of motion, coaching cues need to be selected much more carefully to preserve the body’s natural system of energy transfer.
- Cueing high knees in running can “disconnect” the swing leg from the Achilles ground impulse.
- Cueing a long arm in the javelin (i.e. locking out the elbow) can obstruct the rotational-to-linear energy transformation allowed by the golden ratio concept mentioned earlier.
- Cueing a “cheek to cheek” arm action in running can disconnect the arms from loading the Achilles ground impulse.
- Cueing to “punch the ground” in running can destroy the synergy that comes from rotation and the whipping effect of conservation of angular momentum.
There are so many more examples but the idea is that cueing needs to take these concepts into consideration.
Horizontal vs. Vertical Force Production
By understanding the concepts of tensegrity and angular motion, we can come to realize that the horizontal versus vertical force production debate is entirely pointless.
The truth is that our body takes care of both simultaneously, purely as a function of the mechanics of our joint-to-joint layout. The glutes (“horizontal”) extend the knee (“vertical”), which loads the foot (“vertical” and “horizontal”). Hip internal rotation on the stance leg in running has a horizontal component. The knee drive in running/jumping has a horizontal and vertical component of momentum to it.
The nature of circles and rotation is that horizontal turns into vertical, which turns back into horizontal, all as a function of time. The nature of our feet, knees, and hips, combined with the power of proximally driven movement gives our body a natural ability to move horizontally forward. This same layout of the feet, knees, and hips also provides us with a natural ability to maintain upright tension through the connectedness of the fascia network. There is no separation of horizontal and vertical force production in movement.
Rate of Force Development
As I briefly alluded to earlier in the article, there is much more to “force” when viewed from the lens of energy. In fact I would argue that the entire concept of “rate of force development” only exists in the paradigm of muscularly driven movement.
Again, force is just another name for transfer of energy. It only exists in collisions, and the force that gets measured is based entirely on how well the energy gets transferred. Even when force is muscularly driven, it comes from the collisions of myosin heads on actin filaments.
Viewing it in this light, force then depends on two key ingredients:
- The amount of energy going into a collision
- The quality of energy transfer from the athlete to the ground to the athlete
Looking at it in this way requires us to completely let go of our view of force as muscularly driven. Elite athletes do not put multiple times their bodyweight into the ground because they are freakishly “explosive.” It’s not because of their ability to “push” against the ground harder and faster than anyone else.
Elite athletes utilize the synergistic pathways of energy transformation that are intrinsic to the joint-by-joint layout of the human body. Elite athletes are the best at bringing energy into their collision with the ground.
Is Juan Miguel Echevarria’s long last step just “quirky” or does it lend to the manner by which he produces an incredible collision with the ground that launches him through the air?
On top of that, elite athletes are the best at accepting this energy back into their body. Ground reaction force is ultimately what drives movement. But the secret to GRF is that the pathway of energy from the hips to the feet to the ground is the same pathway that drives energy transfer from the ground to the feet to the center of mass.
That is, the nature of the interaction between our hips, feet, and fascia is such that maximizing the energy into the ground will also create immediate reflexive tension through the posterior chain fascial pathway upon collision with the ground. Whipping the foot down to the ground has the effect of locking out the knee and creating vertical stiffness through momentum to transfer the elastic energy back to the center of mass.
Proximally driven movement that utilizes rotation, relaxation, gravity, momentum, and fascia has the power to create huge forces easily and instantaneously. There’s a reason that the greatest athletes who produce the highest amounts of force in the least amount of time have a knack for making it look so easy (see: Usain Bolt, Jonathan Edwards, Jan Zelezny). If you are trying to produce force quickly, you’ve already lost. The athletes with the best RFD utilize collisions.
Looking at the dynamics of rotational energy in movement, it’s clear that there are sources of energy that remain largely untapped in many training programs. Elite athletes find this energy intuitively, but it’s something that can be taught and trained.
But it won’t be found through periodization schemes or barbell exercises. Rather, it can be trained by understanding principles of energy, mindfulness in training and a good coaching eye.
If nothing else, these concepts show that there is still a world of coaching ideas yet to be fully explored. These ideas aren’t necessarily new or groundbreaking, but can help us break out of our quantitative boxes and bodybuilding paradigms.
About Kevin Foster
Kevin is a former Division I javelin thrower for the University of Connecticut. He is currently training to compete post-collegiately while working as a personal trainer and javelin coach in Southeastern Connecticut.
He runs the Javelin Anatomy Instagram page whose mission is to break down and simplify the anatomy and physics that go into the javelin throw in a logical, critical, and holistic manner. Follow the page @javelin.anatomy to learn more about the science of javelin throwing and training. For any questions or feedback, email javelin.anatomy@gmail.com.
Want to apply for Javelin training with Kevin? This option is now in our store: Online Javelin Training. So apply today for this tremendous opportunity.
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