Human movement is a marvel of nature – a complex interaction of forces, muscles, bones, and nerves that allows us to walk, run, jump, and throw with precision and efficiency. From the effortless grace of a dancer’s pirouette to the explosive speed of a sprinter, movement is much more than meets the eye.
Beneath these seemingly simple actions lies an intricate system of biomechanics, combining physics, anatomy, and neurology to create the fluid motions of movement. Chiropractors inherently possess the specific skill set to appreciate the biomechanics of human movement and how this may apply to injury and recovery.
What happens behind the scenes when you leap for a basketball, sprint across a soccer field, or even stroll down the street? The study of biomechanics helps us uncover the science of these everyday and extraordinary movements, revealing how our bodies coordinate and produce motion.
By understanding the principles of biomechanics from the moment the foot hits the ground, we can optimize performance, prevent injuries, and improve rehabilitation for athletes and non-athletes alike.
Kinematics and Kinetics: The Science of Motion and Force
Biomechanics can be broken down into two key areas: kinematics, which focuses on the description of movement, and kinetics, which examines the forces that cause or result from movement. This distinction is important to the health care practitioner because it addresses the corrective care plan.
The kinematics tells us if the technique of the movement is causing the injury, pain, or dysfunction. The kinetics of movement tell us if the forces resulting from that action are the causative factors in the injury, pain, or dysfunction.
Imagine a sprinter launching off the starting blocks at the beginning of a race. The kinematics of that motion include how fast they accelerate, the angle of their leg as it pushes off the ground, and the trajectory of their arms as they swing forward. These are purely descriptive aspects of movement, allowing us to quantify motion without necessarily worrying about what causes it.
On the other hand, kinetics digs into the forces behind this motion. In the sprinter’s case, their muscles generate force that travels through tendons and bones, while the ground exerts an opposing force called ground reaction force.
Proper control of these forces is critical for injury prevention. If a sprinter pushes too hard without the right muscular balance, they risk overloading many muscles or tendons, such as the Achilles-gastroc-soleus complex, which could result in a painful strain, tendinopathy, or rupture.
Consider a patient who presents with chronic low back pain following activity. A kinematic analysis might reveal excessive lumbar lordosis or altered pelvic mechanics. However, a kinetic assessment would focus on the forces acting on these structures, such as excessive ground reaction forces or compensatory movement due to foot biomechanics.
Research has shown that excessive pronation, for instance, increases forces on the lumbar spine, contributing to low back pain.1 This would be an example of kinetic forces acting on the lumbar spine to promote pain or injury. In instances such as this, a custom flexible orthotic will greatly assist in the unwinding of the kinetic chain, decreasing injury and promoting enhanced performance.
Chiropractors must analyze the kinetic and kinematic factors in each patient. Often, an issue such as low back pain isn’t isolated to the spine, but results from compensatory mechanisms in the kinetic chain. Looking into the forces from the feet to the head as they present in the patterns of the five primary kinetic chains is a solid start in uncovering the key driving force of injury, pain, or decreased performance.
The Five Primary Kinetic Chains
The five primary kinetic chains are the intrinsic, deep longitudinal, lateral, posterior oblique, and anterior oblique. Each offers a specific task in the biomechanics and force generation of movement.
Evaluating a patient’s gait and movement patterns allows us to determine very quickly which kinetic chain is faulty. This critical information then translates into which corrective care plan will most effectively drive the patient toward improved, efficient, and sustainable recovery.
Activation of the deep intrinsic chain is the first and most important step for almost every patient we see. This chain is the master organizer. Its primary function is core stabilization, which is active during all movement and gait cycles. It consists of many core muscles extending from the pelvis to the cranial bones.
In the intrinsic chain, the primary focus is on the diaphragm, pelvic floor, transverse abdominis, and multifidus. Efficient contraction and synchronization of this group of muscles will create a stable base of support for all movements. Not only does the intrinsic chain stabilize during straight plane actions such as walking and running, but it also acts as the pivoting point for all rotational activities.
An interesting point is the synchronization of the pelvic floor and diaphragm in core stabilization. These two muscles need to work together to subsequently activate the transverse abdominis, and internal and external oblique, for core stability. Inhalation drops the diaphragm and the pelvic floor, and exhalation contracts and raises these two muscles in synchronicity.
Unfortunately, so many of us are breathing asynchronously, so these two muscles are not working in this manner. When this occurs, we cannot effectively contract the core to stabilize and protect the spine and body from injury.
Activating the Intrinsic Kinetic Chain
Retrain breathing: Step one is to take a deep breath through the belly without raising the shoulders. The patient is trained to breathe in through the abdomen, expanding the belly with inhalation. During exhalation, the abdomen contracts and moves inward toward the spine.
Raise the foot arches: A custom flexible orthotic is placed to raise all three arches of the foot. There is some emerging and exciting research on the changes in lumbopelvic position and pelvic floor muscle activation, hence core activation.2 An interesting caveat is that 78% of women with low back pain have urinary incontinence.3 This is not, in my opinion, a coincidence.
Women are socially trained to “suck in your stomach.” This is asynchronous breathing perpetuated into pelvic floor disengagement. Here again, orthotics are an effective tool to redistribute forces along all five kinetic chains from the feet upward.4
Synchronize the pelvic floor / diaphragm: Progress the patient to raise the pelvic floor while exhaling to gain synchronicity with the diaphragm contraction. This is best described to the patient as imagining they are attempting to stop urinating midstream; and also imagine they are trying not to pass gas, which leads to a more robust and effective pelvic floor contraction.
The complete raising of the pelvic floor requires both actions. The patient should notice the increased strength of the contraction when doing this.
Take-Home Points
As chiropractors, we examine the symmetry, mobility, and stability of our patients’ musculoskeletal systems. These are the very components that create and support movement. The biomechanics of movement is frequently the basis for peak performance or redundant injury.
For this reason, we evaluate the functionality of our patients. Assessing the functionality of the five kinetic chains is an essential component of the why of injury and the corrective care plan. Of the five kinetic chains, the intrinsic chain is the basis for core stability and the starting point for all corrective care plans.
Lastly, it’s critical to understand that as the foot hits the ground, the kinetic chain can perform optimally or be significantly hindered. Looking at the feet and providing an intervention such as a custom flexible orthotic can assist the practitioner in executing the goal of a full patient recovery.
References
- Yazdani F, Razeghi M, Karimi MT, et al. Foot hyperpronation alters lumbopelvic muscle function during the stance phase of gait. Gait Posture, 2019 Oct;74:102-107.
- Capson AC, Nashed J, Mclean L. The role of lumbopelvic posture in pelvic floor muscle activation in continent women. J Electromyography Kinesiol, 2011;21(1):166-177.
- Eliasson K, Elfving B, Nordgren B, Mattsson E. Urinary incontinence in women with low back pain, Manual Ther, 2008;13(3):206-212.
- Bonifácio D, et al. Influence and benefits of foot orthoses on kinematics, kinetics and muscle activation during step descent task. Gait & Posture, 2018;65:106-111.
