Kinetic Chain: A Missing Link in Surfing Rehabilitation after Amputation
By: Resident Fellow Council
Tags: Sports Medicine, Physiatry In Motion, Physiatry, Adaptive Sports, Surfing

by Claudia Jimenez, MD

Photo from Aaron Lieber/Freestyle Releasing per LA Times. Link in references below.

Movement is produced by the synchronization of 3 systems in our body: skeletal, muscular, and nervous. The nervous system acts as a conductor to integrate the ambiance of our surroundings and communicate via organized signals with the musical groups in our body including muscles and bones to produce a coordinated motion. If one of the elements in these three systems is not functioning properly, it will lead to impairments in the chain of motion. So what happens when one of the links in the chain is missing? Well, we may make the rest of the chain stronger. This is a lesson that athletes with amputations who have excelled in their sport have taught us, such as surfer Bethany Hamilton, through competing in sports as complex as surfing. This sport has unique challenges, requiring precise orchestration of motion that combines endurance, strength, power, stability, balance, and coordination. While many might think that missing a link in the chain of motion would be a fatal flaw for this sport, surfers like Bethany have gone above and beyond what we ever thought imaginable. In order to understand how to make the rest of the chain stronger, it is important to understand the kinetic chain and how this has been applied to the sport of surfing to bypass the missing links in the chain and allow optimal performance.

The knowledge of how our body is interconnected to produce movement as a unit is as important to a surfer as their connection to the ocean by reading the waves. The kinetic chain, a concept established in engineering by Franz Reuleaux, has been adapted to understand movement in linked systems such as the human body. In a system of overlapping rigid segments linked into a chain via pin joints, movement produced at one segment will affect movement in other segments. Therefore, a force applied to one segment will be transferred to adjacent segments and produce predictable patterns of movement at all the joints in the chain. Applying this concept to the human body, bones act as rigid overlapping segments that are linked at joints. In this way our foot, leg, thigh, pelvis, spine, ribs, arms, forearms, hands, skull are neatly connected into a chain by joints at the ankle, knee, hip, ribs, cervical, shoulder, elbow, and wrist. The kinetic chain principle helps to understand how movement in our body transfers force to adjacent segments in a chain reaction producing predictable patterns of movement. Based on this concept, human movements have been classified in two groups: closed and open kinetic chains, depending on whether the most distal segment is met by sufficient resistance or not. A kinetic chain is closed when the most terminal segment in the chain meets resistance considerable enough to restrain it from moving freely. This fixation markedly affects movement in other segments. In contrast, a kinetic chain is open when the terminal segment of the link is free to move in space. This allows for better isolation of the terminal joint during movement.

Most movements in exercise possess elements of both open and closed kinetic chains. However, most exercises can be classified as open or closed chain based on the characteristics at the specific joint targeted by the exercise. In surfing, the definition of closed kinetic chain raises an interesting question. As the feet are in continuity with the free moving surfboard, over freely moving water, this could potentially make surfing an open kinetic chain exercise. However, Kibbler has recently defined closed kinetic chain as a sequential combination of joint motions in which the distal segment of the kinetic chain meets considerable resistance, but does not have to be fixed. This clarifies that surfing is a closed kinetic chain exercise as the feet, which act as the terminal segment, are met by sufficient resistance from the surfboard to restrain them from moving freely. Muscles are therefore activated in a chain from distal to proximal as force is transferred upward from force generators including the lower limbs and trunk, towards mobile distal segments including the arms. Body segments along the chain must have optimal flexibility, strength, proprioception, and endurance to enhance and harmonize mobility and stability to surf successfully. In order to catch waves, surfers must perform the following cycle of events: paddle out, duck dive to push the board under crashing waves, paddle for a wave, push to stand, ride the wave, and perform maneuvers on the wave. Additionally, surfers must simultaneously interact with external forces including gravity, buoyant force keeping the board afloat, shear forces with the board, and torsional forces of their desired movements.

Understanding the kinetic chain in surfing can advance rehabilitation of surfers after an amputation. Particularly in upper extremity amputees, the following issues must be addressed: kinetic chain alterations, weight imbalances, challenges to duck diving, paddling, pushing to stand, and balance. Rehabilitation programs should focus on maximizing the kinetic chain by improving flexibility of joints and soft tissues, strengthening muscles of the lower limbs and core, and improving muscle endurance. Flexibility of the involved joints and soft tissues including the residual limb should be targeted first through muscle reeducation and soft tissue mobility. Failing to address inflexibilities of both upper and lower extremities early leads to limitations in mobility and hinders progression. Early stages should also focus on residual limb care to optimize mobility and functionality. This includes: positioning to prevent muscle and tissue shortening by extending the residual limb as much as possible, compression bandages to reduce swelling and aid circulation, appropriate skin care, desensitizing the skin by accustoming it to textures, and catching any phantom limb pain or sensitivity issues early to initiate any pharmacologic treatment or therapeutic modalities.

The next priority is the strengthening of the lower limbs and core muscles to aid balance and strength. Proper activation of the lower limbs is crucial to generate power and create a stable base of support that will allow dynamic stability so both arm and residual limb can direct the resultant energy during cuts and turns on the wave by facilitating scapular motion. Proper core muscle activation also aids balance and posture as the loss of weight on the amputated side can lead to imbalance and poor posture. When establishing balance on the board, the arms spread out instinctively to spread mass away from our feet that act as the pivot point. This increases the body’s moment of inertia or resistance to rotational forces so that more torque would be required to rotate the surfer making it more difficult to fall from the board. Therefore, optimizing core and lower extremity activation, mobility, strength, and proprioception are essential to surfers with an upper extremity amputation. Closed kinetic chain exercises should start early after the amputation to provide a stable axially loaded static setting to the residual limb in a more controlled environment, work at specific snapshots of the range of motion, and unload the rotator cuff muscles by activating inhibited muscles emphasizing normal activation patterns to reestablish proximal stability and control in the links of the kinetic chain such as the pelvis and trunk. This will not only help maneuvering on the board, but also in pushing to stand and duck diving under waves which are both closed chain motions initiated by the legs and core. Once the normal activation pattern has been restored, more challenging isolated open kinetic chain exercises should be implemented. This should be done later in the program due to their increased demand on the soft tissues. These open chain exercises will help the unaffected arm in developing power and endurance to be able to withstand paddling with one arm.

While it may seem that the amputee population has a disability, a much better description for this population is that they are adaptive. They have changed the mindset that certain activities are not possible with a missing limb. Further, they have adapted the equipment to bolster performance, the possibilities in their sport, the way we approach rehabilitation, and their body to reach heights that no one thought imaginable. In summary, these athletes are enabling what once seemed impossible by adapting our mindset and approach to sports.

Claudia Jimenez is a PGY-1 at the Department of Physical Medicine and Rehabilitation at University of Puerto Rico School of Medicine. You can follow her on Instagram @pm_and_art.

References:

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2. Sciascia, A., & Cromwell, R. (2012). Kinetic Chain Rehabilitation: A Theoretical Framework. Rehabilitation Research and Practice, 2012, 1–9. doi: 10.1155/2012/853037

3. Information for upper limb amputees and their families. (n.d.). Retrieved April 19, 2020, from https://www.ottobockus.com/prosthetics/info-for-new-amputees/information-for-upper-limb-amputees-and-their-families/

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5. Airaksinen, Lisa. The Role of Core Stability in Surfing According to a Delphi Panel. Bachelor’s Thesis. Mikkeli University of Applied Sciences, Finland. https://core.ac.uk/download/pdf/38093862.pdf

6. Article photo link: https://www.latimes.com/entertainment/movies/la-et-mn-mini-bethany-hamilton-unstoppable-review-20190711-story.html