How Our Bodies Move: The Kinetic Chain Explained

How Our Bodies Move: The Kinetic Chain Explained

We first introduced you to the concept of the kinetic chain during our mini series on understanding low back pain. Since the kinetic chain is such an important principle in movement, injury, and injury prevention, we thought it would be a great stand-alone topic. Today’s article explores the background and theories behind the kinetic chain principle, its relationship to injury, and ways to use the kinetic chain to your advantage. 



There’s a lot of ground to cover, so let’s get started.

From birth, our bodies are ergonomic works of art. If you study toddlers’ movements, you will most likely see perfect technique as they squat to pick up scattered toys or climb stairs. They also have excellent landing skills while splashing in puddles of water or reaching for things that they shouldn’t have. 

But, what you may not realize is that these are carefully coordinated acts that involve over 200 bones and 650 muscles in the human body. This idea that our movement has the ability to affect multiple muscles, tendons, ligaments, and joints at one time is the foundation to understanding the kinetic chain.

What Is the Kinetic Chain?
Franz Reuleaux, an engineer from Germany, is credited for defining the kinetic chain as a chain reaction of events in machines that have stationary or fixed-end points.

Reuleaux proposed that an outside force applied to machine systems with fixed-end points will produce an internal chain reaction, similar to a domino effect, with each segment in the machine transferring force to its neighbor. He also realized that outside forces will create patterns throughout the chain reaction, thus making it possible to predict outcomes of various forces that are transmitted throughout the system. 

But, it wasn’t until a few decades later that the kinetic chain principle was applied specifically to the human body. By definition, the kinetic chain in the human body describes how parts of the body act together as a system of chain links, where energy generated by one link (or part of the body) is transferred to the next. And, thanks to our physics lessons, we know that energy is never truly created or destroyed, but simply transferred. This fact becomes even more important when it comes to injury and injury prevention. 

A helpful example to visualize the kinetic chain at work is the act of throwing a ball. Although the arm is responsible for moving the ball to its target, the legs and torso begin the movement by generating a majority of the force before the actual throw occurs. Then, the force is transferred through the shoulder, down the arm, and ultimately out to the ball.

Another way to think about the kinetic chain is the movement that occurs during a squat. To successfully perform a squat, your body must coordinate motion at the ankles, knees, and hips on both sides of the body. Unfortunately, limited mobility at any one of these joints will alter movement quality and place increased demands on the other joints. Remember, the energy has to go somewhere since it is never destroyed. 

Besides limited mobility, other factors that can influence the kinetic chain include core strength, strength, body mechanics, footwear, stress, stability in your pelvis, scar tissue formation, and prior injuries.

Old Theories of Human Movement
Human movement can be deciphered in many ways. Traditionally, it was analyzed as one part moving at a time: to take a step, your foot moves forward and the rest of the leg follows, joint by joint.

However, that concept of motion, also referred to as isolated movements, fails to consider the interaction between body parts, which is arguably the most important part of human movement. 

Instead, consider how the body interacts in a holistic sense. By looking at movement as one event rather than isolated parts that move one at a time, we can begin to see specific patterns arise. These specific patterns of movement are commonly referred to as muscle synergies and are defined as a group of different muscles that work together to produce a coordinated movement. 

But, depending on whom you ask, muscle synergies are controversial at best. Multiple research studies have refuted their importance, though some experts claim that they play a crucial role in the nervous system and are especially affected after someone suffers a cerebrovascular event, like a stroke, or brain injury.

Applying the Kinetic Chain Principle to Exercise
According to the National Strength and Conditioning Association (NSCA), there are two types of movement when it comes to the kinetic chain: closed-chain and open-chain kinetic exercises.

Open-chain kinetic exercises, sometimes referred to as isolated movements, occur when the ends of the chain (i.e., the limbs that are doing the movement) are not rooted to the ground. Examples of open-chain kinetic exercises are biceps curls, triceps extensions, lateral raises, knee extensions, hamstring curls, or donkey kicks. In each example, the leg or arm can freely move against gravity and, therefore, is considered to be “open.”

In closed-chain kinetic exercises, the end of the limb is fixed in place. They generally activate large, prime movers of the body (such as the glutes and quads), but also require smaller stabilizing muscles to fire as well. Classic examples of closed-chain kinetic exercises include the squat, deadlift, and pushups. As you can see, these exercises require your hands or feet to be “closed,” or in contact, with the ground.

There’s an age-old debate about closed-chain kinetic exercises versus open-chain kinetic exercises, and which one is more effective. The truth is, both types of kinetic chain exercises belong in your workout routines. However, the ratio of open- to closed-chain kinetic exercises will vary depending on your workout goals. Those who are interested in gaining strength will probably benefit from a higher ratio of closed-chain to open-chain exercises. Conversely, open-chain kinetic exercises are typically best for isolating specific muscle groups, especially after an injury. 

Understanding the Kinetic Chain and Injuries
By now, our understanding of Reulaux’s machine theories has evolved dramatically. We are currently able to identify specific muscle synergies, distinct patterns of injury, and predictable outcomes by applying the kinetic chain principle to the human body. 

We discussed above that movement comes from energy within the body that is transferred from one area to the next. In order for energy to transfer efficiently and effectively, our body must be functioning properly to produce well-timed and coordinated movement, otherwise, injury can result. In general, the body segments (aka, joints) closest to the problem area are going to be most affected.  

Take the hip, as an example. Muscle tightness, weakness, or restrictions within the hip joint are going to have a significant influence on the pelvis, low back, and knee. However, the elbow and shoulder joints are less likely to be affected by problems at the hip. 

If one segment in the body is not working correctly, then the neighboring areas are forced to compensate. Unfortunately, compensatory movements place stress on areas that are not accustomed to handling the extra work, eventually leading to injury. In the example of the throwing motion, if the legs and torso do not produce enough force, then the shoulder and elbow must work harder to offset this, placing them at high risk for injury. 

On the contrary, applying the kinetic chain principle can work to your advantage when it comes to injury  prevention and rehabilitation. Because of the relationship among body segments, strengthening one area can create improvements elsewhere in the body. An example of this is the notion of strengthening your core, glutes, and hip stabilizing muscles to address low back pain. Training different segments along the kinetic chain not only makes these areas stronger, but can also help the whole body become more efficient. 

Isn’t the human body fascinating? We love delving into the science behind the ways that our mind and body work. Let us know what we should tackle next! 

Written for Fitness Blender by Kayla C, PT, DPT
Board-Certified Neurological Clinical Specialist

References

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Karandikar N, Vargas OO. Kinetic chains: a review of the concept and its clinical applications. PM&R. 2011;3(8):739-745. doi:10.1016/j.pmrj.2011.02.021

Ellenbecker TS, Aoki R. Step by Step Guide to Understanding the Kinetic Chain Concept in the Overhead Athlete. Curr Rev Musculoskelet Med. 2020;13(2):155-163. doi:10.1007/s12178-020-09615-1

Wojtara T, Alnajjar F, Shimoda S, Kimura H. Muscle synergy stability and human balance maintenance. J Neuroeng Rehabil. 2014;11:129. Published 2014 Aug 30. doi:10.1186/1743-0003-11-129