SUP Biomechanics

Friday, December 31, 12021 HE

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1. Disclaimer
2. What is SUP? Benefits and Risks
3. A Little Bit of History
4. Other Resources
5. Different Strokes for Different Folks
6. A Bit on Biomechanics
7. Crash Course Anatomy
8. Crash Course Physiology
9. Take Aways

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Disclaimer

Full disclosure, I am a licensed physical therapist, but the following is purely for informational purposes. For formal guidance concerning your stand up paddleboard (SUP) biomechanics, you should enlist the help of a qualified professional. If you are experiencing pain associated with SUP, you should seek out the aid of a licensed and qualified medical professional for a diagnosis. Pain associated with a physical activity is often musculoskeletal but can signal something more nefarious.

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What is SUP? Benefits and Risks

Stand up paddleboarding is a growing aquatic recreational and sporting activity. It is conceptualized most familiarly as a combination of modern surfing and paddle-based sports (Schram et al., 2019). In SUP, the rider balances on a board (~3–5 m long, ~1 m wide) and grips a single-bladed paddle (~2 m long) to propel themselves through the water (Schram et al., 2019). Stand up paddleboarding is easily accessible to most people since it requires minimal equipment and is easy to learn. It can be practiced on almost any body of water and provides a low-impact, full-body physical challenge, suitable for all ages and skill levels. But like any activity, it is not without risk. A 2017 study by Furness et al. revealed that the shoulder/upper arm was the most frequently injured body location (32.9% of all injuries), followed by the lower back (14.3%), and the elbow/forearm (11.8%). In other paddling disciplines, sub-optimal stroke biomechanics are associated with injury. For anyone getting into paddling, particularly if you plan to participate in endurance paddling, attention to your stroke mechanics is a consideration of concern. Check out this post for general information on basic safety guidelines regarding SUP participation.

While modern SUP is seen through the lens of surfing and paddle-based sports, it has a long history dating back to well before these sports became popular. See the post and video below for more details.

A Little Bit of History

The History of Stand up Paddling

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And a small addendum. I recently came across this 5-minute history of SUP on SUPBoarder‘s site by Robert Stehlik of Blue Planet Surf.

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Other Resources

The 2019 paper by Schram and colleagues lists some of the non-scientific sources on optimal paddling techniques for SUP, both online as instructional videos and written guides. Anyone who wants to delve into the topic deeply should check out those sources. The following will be more of a general overview. And then, I will post more specific articles on shoulder, lower back, and hip biomechanics.

Different Strokes for Different Folks

There are different stroke phase classification systems. In the paper by Schram and colleagues (which is where the feature image for this post is from), they use a three-phase classification system: entry, drive, and exit. Another commonly used system uses a five-phase classification: reach, catch, power, release, and recovery (see this video from SUPBoarder for a great overview of the five-stroke phases). There is obvious overlap, with reach and catch combining as the entry in the five versus three-phase system, respectively. And, release and recovery are combined as the exit phase. The five-phase system allows for more granularity. Throughout this biomechanics series, I will use either system where convenient.

Stand up paddleboarding is a full-body activity. And, like many sports, the development of force and power can be augmented by using more of the lower body via the lumbopelvic-hip complex (i.e., the hips, pelvis, and lower spine). The force developed from the lower body must then be transferred through the trunk to the upper limbs through the paddle and into the water to propel the board. The main finding from the Schram et al. (2019) paper was that experienced SUPers used less shoulder movement and more hip movement than inexperienced paddlers. A caveat to mention for the study is the biomechanics measured were on a KayakPro SUP ergometer. The device has been previously validated in other studies but is still not the same as a real-world evaluation.

A Bit on Biomechanics

The video below is supplementary material from the paper by Schram and colleagues (2019). It shows representative stroke mechanics for an experienced (left animation) and inexperienced (right animation) paddler. You can see that the experienced paddler is more fluid throughout their stroke. And their motion is much more of a full-body action. There is much more of a hinging action through the hips. This action results in a further forward reach for the entry of the stroke. In addition, you can see how the rotation of the hips and torso also allows for more excursion. Also evident is the power transfer to the paddle in the drive or power phase of the stroke. The upper extremities actively force the blade down while the action of the lower extremities and hip complex is in unison to create a more powerful looking stroke. For the inexperienced paddler, on the right, you can see how the stroke is performed more with the upper extremities. There is minimal motion through the trunk and lower extremities.

Crash Course Anatomy

The main finding from the study was that experienced paddlers used their hips more and their shoulders less. Intuitively this makes sense when the anatomy of the hips and shoulders are taken into consideration. Both the hips and shoulders are classified as ball-and-socket joints, but their anatomy is quite different. The size of the boney articulations involved is different. The femur at the hip is larger than the humerus at the shoulder. The hip is a deeper ball-and-socket that provides more inherent stability from an osteologic standpoint. The cavity at the hip, the acetabulum, is much deeper than the cavity at the shoulder, the glenoid fossa. In addition, the pelvic girdle is inherently more stable as both sides of the pelvis are articularly connected to the axial skeleton through a stable planar joint, the sacroiliac joint. Despite being a planar joint, the sacroiliac joint still possesses six degrees of freedom, meaning it has rotational and translational movement around and along all three cardinal axes. The shoulder girdle is only attached to the axial skeleton at the scapula via the clavicle at the sternoclavicular joint. The sternoclavicular joint is a saddle joint with two degrees of freedom. There is a pseudo-arthrosis between the scapula and thoracic cage, the scapulothoracic junction, but it is not a true articulation. Though, it does provide some stability to the scapular girdle.

Beyond the osteologic differences, there are anatomical muscular differences, with the hip joint having much more muscular bulk. Many people are familiar with the rotator cuff of the shoulder. It is a group of four muscles that help keep the arm bone congruent with the socket of the shoulder blade. With joint congruency, the larger, multi-joint muscles of the shoulder can do their jobs of motion and force development more efficiently. An apt adage from the strength and conditioning world is that you can’t fire a cannon out of a canoe. That is, if you are trying to generate motion or power from an unstable base of support, the conditions are suboptimal. The hip socket also has a rotator cuff, which depending on the source, is the six deep hip rotators or will also include some of the gluteal complex (i.e., gluteus minimus and gluteus medius). In both cases having adequate arthrokinematic stability from the joint cuffs allows for more motion and power at the osteokinematic level.

Crash Course Physiology

Bringing this back to SUP, for power, speed, and efficiency, the longer, more powerful, and faster the stroke is, the faster and more powerful the vessel will be. Though, there are trade-offs between these variables. Generally, a paddler that can get a longer stroke can pull more water per stroke, resulting in higher power production. However, a longer-reaching stroke does not always result in greater propulsion. Biomechanical properties like the force-length relationship (aka., the length-tension relationship) and force-velocity relationship of muscle govern where and when optimal force development occurs. Muscles can generate the greatest force at their ideal length, which is their resting length. The least amount of force development occurs when shortened or stretched relative to resting length (see graph below). Force development is due to the degree of overlap of the myofilaments of a muscle. Myofilaments are proteins that are the subcellular contractile elements of the myofibril of a muscle cell. For your muscles to contract, these filaments need to interlock (couple) and then pull each other to slide along, shortening the muscle. The so-called sliding filament theory. A schematic of the overlap is shown below on the x-axis of the graph. An analogy would be being in the middle of the rope during a tug-of-war. You can easily pull or release the rope from the middle because you have more rope to grab. Whereas, if you are at either end of the rope you will not be able to pull or hold the rope easily as there is nothing to pull or hold.

Furthermore, the power production of a muscle is also governed by the force-velocity relationship. Optimum power output occurs at one-third of maximum contraction (or shortening) velocity (see graphs below). This phenomenon is a result of the subcellular biomechanics of myofilament coupling. Borrowing again from the tug-of-war analogy, this is akin to the optimal speed of changing over your hands to pull or release the rope. Too fast, and you are not able to get a solid grip and too slow, and you are inefficient in the tugging battle.

In addition to these biomechanical factors at the microscopic scale, macroscopic factors also contribute to power, speed, and efficiency. Using a greater range of motion at the hips optimizes these parameters compared to using the upper extremities. Utilizing the larger muscles of the pelvis and trunk to apply force to the water is more efficient for the power developed as well as energy metabolism. For these reasons, experience paddlers exhibit less upper body motion. By using their upper appendages as rigid extensions of their hips and trunks, experienced paddlers can transfer force to the water more efficiently. It is worth noting that individual variations in these parameters exist and account for differences above and beyond skill and training.

Take Aways

The following are a few key takeaways to lower your risk and possibly improve your performance on the water:

•Every body is unique – don’t try to fit a square peg into a round hole
•It’s hard to perform if you’re hurt (durability outweighs performance)
•Listen to your body, and if in doubt, seek professional help
•Performance and durability can be in competition
•It makes sense to maximize the use of the bigger muscles and efficient joints of the lower body
•Your bodies tissues will adapt to the stress imposed on them provided they do not surpass their current capacities – start low and progress slow (slow and steady wins the race)

For more on the specific biomechanics of the shoulder, lower back, and hip joints, stay tuned for future posts…