SUP Biomechanics: Lower Back Volume 2

Anatomy of a Paddle Stroke 3.0

Tuesday, November 1, 12022 HE

Happy Samhain (or if you’re the Christian holiday appropriative type, happy All Saints Day)!

For the backstory to this post, see my first post on biomechanics. And for more background information on general lower back anatomy and biomechanics, see this post: “Lower Back: Volume 1“. For anatomical and biomechanical information on shoulders, see here, and for hips, see here.

Full disclosure, I am a licensed physical therapist and manual osteopathic practitioner, 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 or generally, you should seek out the aid of a licensed and qualified medical professional for a diagnosis. Pain associated with an activity is often musculoskeletal but can signal something more nefarious.

  1. Anatomy of a Paddle Stroke 3.0
  2. A Preponderance of Problems
  3. Different Strokes for Different Folks
  4. Experience vs. Inexperience: Motion Capture
  5. Trade-offs: Mobility vs. Stability
    1. An Evolutionary Design Flaw
  6. Proper Prop Propulsion
    1. Hip Hinge
    2. Reaching for Power/Drive
  7. Reality meets Theory: A Motion Spectrum
  8. Spectrum Speculation
    1. What About the Kingdom?
    2. What If?
  9. Performance versus Health
  10. Take-home Tidbits

A Preponderance of Problems

Low back pain is conventionally defined as pain, muscle tension, or stiffness localized below the costal margin and above the inferior gluteal folds, with or without associated leg pain. The majority of people will experience some form of it in their life. The estimate is that up to 80% of individuals experience an episode at some point throughout their lifetimeLow back pain can be classified as acute (i.e., lasting <6 weeks), sub-acute (i.e., lasting between 6 weeks and 3 months), or chronic (i.e., lasting for more than 3 months). The majority of low back pain, 90%, is non-specific, meaning there is no clearly identified pathophysiology. Fortunately, non-specific causes of back pain have a more favourable prognosis. Specific cases are mostly due to hernias, fractures, osteoporosis, rheumatic diseases, spondyloarthropathy, infections, or cancer. Cases directly related to severe systemic diseases, such as cancer, rheumatic disorders, etc., have poorer prognoses (Mazziutti et al., 2020).

The figures below from Mazziutti and colleagues’ work show the global epidemiological burden, age distribution, and relative burden of low back pain over the last 20 years. It is worth noting that in high socio-demographic index nations, the incidence, prevalence, and burden have been on the rise and are predicted to continue. In my opinion, this reflects the mismatch between our paleogenic evolutionary origins and their current implementation in our modern holocenic lifestyles. While back pain is common and generally benign, it can be nefarious and comes with a significant societal cost. If you are reading this post because you’re experiencing low back pain, use your judgment, and seek professional medical help if warranted or in doubt. Knowledge is power, scientia potentia est. Knowing that you’ll likely experience back pain in the future leaves me wanting to take the measures to avoid that altogether in the best case or minimize the impact in the worse case. I hope this post provides some insights to help people avoid injury and maximize their potential.


Specific to SUP and musculoskeletal injuries, a 2017 study by Furness and colleagues revealed that the shoulder/upper arm was the most frequently injured body location (32.9% of all injuries). Hence why my first posts on SUP biomechanics focused on the upper extremity. The lower back was the second most commonly reported injury site, at 14.3% of all injuries. I avoided doing this post for some time due to the complex nature of the lower back and the lack of adequate research on the topic.

Different Strokes for Different Folks

Before we begin biomechanics, here is a quick note on paddle stroke phases. There are different naming systems for the stroke phases. Schram and colleagues (2019) used 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 the video below from Black Project for the phases in real-time and slow-motion).

SUPBoarder uses the five-stroke phase system too. Check out this video for an excellent, in-depth overview of the system.

There is an overlap between the two systems. The reach and catch combine as the entry in the five versus the three-phase system. And the release and recovery are coupled as the exit phase, while the power and drive phases are interchangeable. I will use either naming system where convenient. The five-phase system allows for more granularity.

Sources: Schram B, Furness J, Kemp-Smith K, Sharp J, Cristini M, Harvie D, Keady E, Ghobrial M, Tussler J, Hing W, Nessler J, Becker M. 2019. A biomechanical analysis of the stand-up paddle board stroke: a comparative study. PeerJ 7:e8006

Lastly, on stroke mechanics generally. While the phases of a stroke are universal, so too are individual variations within each phase. We all have unique structures and neuromuscular regulations that make up our biomechanics. There is no one-size-fits-all for form. There are better-or-worse, more efficient-less efficient, high risk-lower risk tradeoffs for technique. The costs and benefits must be individually assessed and determined.

Experience vs. Inexperience: Motion Capture

The video below is from the paper by Schram and colleagues (2019). It shows the generalized paddle mechanics of an experienced paddler on the left and an inexperienced paddler on the right. Of relevance to this post, is how much more motion occurs around the lumbopelvic-hip complex in the experienced paddler.

Source: Schram B, Furness J, Kemp-Smith K, Sharp J, Cristini M, Harvie D, Keady E, Ghobrial M, Tussler J, Hing W, Nessler J, Becker M. 2019. A biomechanical analysis of the stand-up paddle board stroke: a comparative study. PeerJ 7:e8006

Unfortunately, measuring spinal motion is inherently challenging, even more so without using the ‘gold-standard’ radiographs. The motion capture used by Schram and colleagues cannot capture the subtleties of spinal motion. The image below is the setup used in the study by Schram and colleagues. They had markers at the posterior superior iliac spines and thoracolumbar junction. So their data only records the lumbar spine motion as a group, not the individual segments. I am unaware of other attempts to quantify this motion outside of visual observation in SUP. As such, we’re left to theoretical speculation and visual observations in our interpretation and analysis.

For an excellent commentary on the kinematics of the SUP stroke, check out this excellent video of the anatomy of a SUP paddle stroke by the team at Quick Blade Paddles below. They highlight the individual difference in stroke mechanics and emphasize burying the blade into the water. In the study by Schram and colleagues (2019) (video above), the data was collected with the paddlers using a  KayakPro SUP ergometer. There was no water involved. In real life, the maximum power potential for an equivalent stroke, and thus the greatest propulsion, is achieved when the entire surface area of the paddle blade is engaged in the water. The blade should be submerged before initiating the drive/power phase of the stroke.

A third take on SUP biomechanics can be seen here in this video from SUPBoarder. You can see the trailer (below), but the full video is only available on their Pro site. I think their content is well worth the membership fee. However, they offer a 14-day free trial if you’re the doubting Thomas-type and want to check it out yourself.

Schram and colleagues’ data showed that experienced paddlers use more range of motion from their hips and less from their shoulders versus inexperienced paddlers. You can observe this in the biomechanics video above as more motion of the trunk (lumbopelvic-hip complex). On average, the experienced paddlers had approximately 15 degrees more of hip range of motion, 66 versus 50 degrees. It is worth noting that there was much more variance in the inexperienced group (i.e., greater standard deviations). You can see the joint range of motion values collected here in Table 1 from Schram and colleagues (2019) or the raw dataset.

Trade-offs: Mobility vs. Stability

Mobility and stability in physical medicine circles are considered the cornerstones of coordinated movement. I tried to find out the origin of the terms in physical medicine but had to settle on just looking at the Google Ngram Viewer plot, which shows the usage in the corpus of English books. After a brief uptick in print popularity in the 11850s HE, the terms became prominent in the 11950s HE. Whether the initial uptick in the 11850s HE was the Crimean WarBleeding Kansas in the lead up to the American Civil War, or Darwin‘s on The Origin of Species is openly debatable. But I’d put my money on the second rise as the post-World Wars practice of rehabilitation. But I digress…

Source: Google Books Ngram Viewer

Like many bodily processes, mobility and stability must work in balance. Too much mobility and it becomes more challenging to maintain stability. Too much stability and freedom of movement will be compromised. From our anatomy knowledge from “Volume 1,” we saw that the back morphology leads to an inherent susceptibility to injury and pathology.

An Evolutionary Design Flaw

The lower back is a series of stacked articular triads. The big intervertebral joint at the front and two smaller zygapophyseal joints on either side at the back of the spinal column. I always think of a tricycle, with a big wheel at the front and two little wheels at the back. The segmental bioarchitecture allows for motion between vertebral levels, but as we saw in the past post, the shift to bipedalism came at a spinal cost for all the upper extremity manipulative benefits. Our quadruped ancestors do not seem to be plagued by the same spinal problems. There is evidence to suggest that those amongst us with morphology most similar to the spines of our non-human primate relatives are most susceptible to pathology. The so-called “ancestral shape hypothesis” (fun fact is that two of the authors of this paper have Vancouver affiliations – woot, woot, 604). I would venture that on evolutionary time scales, the spine is segmented, just because it is. At some point, it was advantageous to have a segmented central axis to animal bodies. And it still is today, as we are blessed with the inheritance of this motion and manipulative ability. We’re not SUPing today without a spine and the adoption of bipedalism. However, with a spine not fully adept at verticality, our bipedalism comes with a cost, namely potential back troubles. Thus, it follows that taking advantage of the surrounding, more motion-adapted joints to spare the spine is a smart system. To do this, the lumbopelvic hip complex must work in coordination to take advantage of the greater mobility available at the ball-and-socket bioarchitecture of the coxofemoral joints and maintain relative stability through the spine’s fibrocartilaginous and synovial joint complexes.

In my lower back anatomy post, I mentioned the tendinous intersections between the segments of the rectus abdominis. The rectus abdominis is commonly referenced as a flexor of the spine. While this is true, it fails to consider the role of tendon intersections in what is typically a fascicle-form structure, the muscle belly. Many muscles in the body that span multiple joints that are apt to create angular motion conspicuously lack these perpendicular tendons (the quadricepshamstrings, and biceps muscle groups all come to mind). If the rectus abdominis’ role was to flex the spine, it would likely be fluidly fascicular in form, not intersected. For this reason, it has been hypothesized that the role of the tendon intersections is to limit the deformation of the rectus abdominis from the laterally directed contractions of the lateral abdominal muscles (e.g., external obliqueinternal oblique). In this light, the tendinous intersections likely have a role in resisting the ripping of the abdominal musculature, and aid in controlling the motion of the trunk, rather than primarily creating it.

When the hips are mobile, the trunk can be more stable since it does not have to give up its stability to gain mobility. Mobility and stability work together. While they are not mutually exclusive, increasing one can often decrease the other. However, this is not inevitable, and a high degree of motor control can keep mobile structures stable. In some sense, this is inherent to the spinal system via the complex interrelationship between multi-articular and uni-articular muscles. The uni-articular muscles of the spine (i.e., the transversospinales group) are rich in proprioceptive receptors allowing them to provide sensory information to the central nervous system about the state of affairs. Your body is equipped with the circuitry to provide real-time data about where your spine is in space. This way the larger and more motion-adept multi-articular muscles (e.g., erector spinae group, latissimus dorsi, external obliquus) can create and control movement.

Proper Prop Propulsion

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). To do this, the rider reaches forward with the paddle submerging it into the water before pulling themselves forwards relative to the paddle placement. A further reach generally translates to greater propulsion, with the caveat of tradeoffs to the force-length and force-velocity relationships. Nothing comes for free. A good way to conceptualize paddle technique and gear is the one espoused by Danny Ching in his “Paddle Like a Pro” technique video. He stresses that everything has pros and cons and that kit or technique choices manage the tradeoffs between these costs and benefits. You can watch the two parts of his video on YouTube (Part 1 and Part 2). Speed and efficiency in paddling are achieved through the balance between the stroke rate and stroke distance.

It is best to adopt a hip hinge motion to maximize stroke reach and, thus, distance. As past posts have highlighted this is the most efficient way to take advantage of the large muscles of the body that surround the hip complex.

Hip Hinge

During a hip hinge, the hip joint acts as a pivot, allowing the torso to swing forward. At the same time, the knees are slightly bent, allowing the pelvis to shift posteriorly, countering the anterior motion of the torso. The torso re-orientation ultimately permits a longer reach and paddle stroke by moving the arms and paddle forward in space. The large posterior muscles of the hip must keep the torso upright as they eccentrically contractlowering the torso forward in the field of gravity. At the same time, the muscles of the trunk must work together to maintain a relatively extended spine. A sort of reversal of this action must be completed through the power/drive phase of the stroke to bring the body back to an upright stance.

Reaching for Power/Drive

In addition to a hip hinge, when paddling, the upper extremities must flex forward to prepare the paddle for entry into the water or the catch. During the reach phase, the shoulder joints are flexing (i.e., the arms are moving forward) while the hip is relatively flexed. The extremity joints are in flexion (i.e., the hip and shoulder), while the spine is more in extension. As the shoulders flex, the upper back is in extension. The lower back is relatively in extension, too, but as will be highlighted later, this appears to be more variable. As the stroke enters the catch phase, the shoulders extend slightly as the arms are drawn down and back to engage the paddle with the water. At the same time, the hips flex, lowering the torso and allowing the blade to enter the water. During the power/drive phase, the shoulders continue to extend, while the hip/trunk flexes. The trunk also undergoes some lateral flexion and rotation. It is difficult to determine where this motion comes from, however. Lumbar spine motion is notoriously difficult to quantify compared to other body parts since the boney segments are buried deep within a meat suit. The data from Schram and colleagues depict comparable values between experienced and inexperienced paddlers. In fact, the group average range of motion values for trunk abduction and flexion is greater in the inexperienced group. I don’t have a good explanation for this, as it flies in the face of conventional wisdom. Perhaps it is the variability in the inexperienced group. The representative motion capture video appears to demonstrate much more range of motion than the dataset reveals. It may be that the apparent rotation and flexion observed is a summing of the motion happening in the lower extremity (i.e., knee and hips), as rotation in these joints was not reported. Enter reality…

Reality meets Theory: A Motion Spectrum

The theory does not always translate into practice. The video below, which is slow-motion of some of the top paddlers from the 2016 Fastest Paddler on Earth Lost Mills Event, demonstrates what happens in practice. Keep in mind that this is a short-distance, maximum-speed event where the form may give way to function. What stands out to me is the amount of spinal flexion/extension. In my eyes, the spinal motion is seen as a wave-like action of the torso through the power/drive to the recovery phase of the stroke. I have looked at footage of longer distance races to see if the wave-action is a short duration maximum effort effect or is truly their technique.

My conclusion is that the ‘spinal wave’ is the technique of the paddlers. Though, the intense effort of the sprint event magnifies the effect. To be fair, there are many individual differences in form. Other paddlers tend to demonstrate form with stiffer, more erect spines. Check out some of the paddlers in the video below, again from the team at Quick Blade Paddles.

They all are on the straighter spine/hip hinge side of the spectrum. The caveat is that their technique is being watched and scrutinized so they may be altering their form for assessment. Additionally, they’re only paddling a short distance, so fatigue and maximum competition speed are not factors. My take home is that the reality is there is a continuum of paddle forms ranging from spinal wave to hip hinge. The former involves more motion of the lumbar (and spine generally) segments, and the latter is characterised by a straighter (i.e., more extended), less mobile lumbar spine.

Spectrum Speculation

What remains unanswered is which of these techniques is better for performance and which is better for health/injury avoidance. Are there differences? Anecdotally and speculatively, it seems that the spinal wave may be more conducive to speed, purely since it seems to be the style employed by the fastest SUPers. It seems the top racers utilize some degree of spinal wave in both short-duration sprints and long-distance endurance races. However, it may be that the distinction suggested between performance and durability is artificial. Perhaps there is no tradeoff. The wave action, which involves more lumbar flexion/extension may not pose any harm to the intervertebral discs. Many people are familiar with the occupational recommendations surrounding back health and lifting. We’ve been taught to limit loads and avoid bending, particularly in combination with twisting. As we saw in Volume 1, the recipe for disc herniation is repetitive flexion and extension, especially with rotation, under load. The occupation lifting advice is sound, but lost in the intricacies, are the key points about load and twisting (i.e., rotation). Too often, lifting advice is boiled down to the basics of don’t bend, leading to an ethos of spinoflexophobia. At the risk of falling to the fallacy that flexion is faulty, I think it is worth highlighting that the increased flexion/extension motion that comes with the spinal wave style of paddling is under low load and with minimal rotation. Perhaps, there is not enough of all three risk factors to pose a threat to the spine. The lack of excess spinal disc injury in the upper echelon of professional SUP racing would seem to corroborate this hypothesis. Though, I will caveat this contention with the caution that a survivorship bias may be at play. It could be that some other spinal-saving mechanism is at play in protecting the population of premier paddlers. If this is true, anyone with a soft spine is not going to endure in the sport long enough to reach elite status. A sort of offshoot of the ancestral shape hypothesis. But this is purely speculative.

What About the Kingdom?

I am (slowly) reading Daniel Lieberman‘s book Exercised, and just after writing this post, I got to the section “The Trouble with Two Legs.” Using Usain Bolt as the exemplar of human speed, Lieberman demonstrates that even the fastest human over short distances is slow in the animal world. One reason for that is our bipedalism. Roadrunners and ostriches, as bipedal speedsters, have been clocked at maximum speeds of 40 and 70 km/h, respectively. Bolt’s top speed was 45 km/h, and his average speed over the 100 metres was 38 km/h. That’s incredibly impressive, considering the average human is probably running at 12 km/h, but this pales in comparison to the top land speed animal, the cheetah, which ranges from 80-130 km/h.


Professor Lieberman highlights that “being upright has another disadvantage: when running, we lost the use of our spines as stride-extending springs.” He makes the comparison to a greyhound or cheetah galloping. The forelimbs come together to meet the hindlimbs in the air before reaching apart (see example below). The quote and visual are striking to me after having analyzed the spine during the SUP stroke. It seems the top SUPers have found a way to take advantage of the stroke-extending spinal spring!

What If?

A few more speculations come to mind. One is that perhaps the hip hinge style is not protective of the spine. I am inclined to think that it is, but that may be false logic and falling for the fallacy of spinoflexophobia. From a material mechanics perspective, more motion will lead to faster material failure. In this view, the hip hinge should be spine-saving since the segments are somewhat static. However, when your muscles contract, they shorten and in the process, compress the joint structures they cross. Could it be that the cost of contracting to control the spine is too compressive in a pure hip hinge pattern? Another view is that maybe the spinal wave style is sparing. The biological building materials of your body have regenerative capacity. Through mechanotransduction, your cells respond to mechanical stimuli in the environment to drive cellular processes. To maintain tissue integrity your cells require a certain amount of physical deformation to stimulate their cellular machinery. It may be that the spinal wave paddling style readily meets that requirement. Rather than distress the system, perhaps it serves as eustress or is neutral.

A final take is that perhaps the action of paddling is spine-saving despite going through repetitive flexion/extension cycles. Many paddling coaches cue the catch of the stroke to be a leaning or transferring of body weight onto the paddle. As the blade, with its positive blade angle, engages the water, the paddler should lean onto the paddle using their body weight to help pull themselves forward. After reading Daniel Lieberman’s comments on quadruped speedsters and their spine-springing strides, I wondered if leaning onto the paddle in SUP serves as a spine-saving strategy. Arguably, our bipedal-ness is being reduced, to a degree, by the extra points of contact with the paddle shaft and ultimately the paddle in the water. The question is how much and if it is significant.

Performance versus Health

We tend to revere high-performance sports and the elite athletes that make it possible. It is great entertainment and inspirational to test the limits of human performance. But all too often, we tend to conflate performance with health. While the two are often related, they are not inextricable. While there is evidence to suggest that elite performance provides longevity and health benefits, there is data supporting the opposing view. The conclusion from the end of the Bauman and Blair paper is worth quoting at length.

Although the evidence points to a small survival effect of being an Olympian, careful reflection suggests that similar health benefits and longevity could be achieved by all of us through regular physical activity. We could and should all award ourselves that personal “gold medal.”

Bauman AE, Blair SN. Republished editorial: Elite athletes’ survival advantage. British Journal of Sports Medicine 2014;48:1008.

The pursuit of prime performance is not always the most healthy. Hippocrates often referred to as the father of medicine, is believed to have said, “Everything in excess is opposed to nature,” and that, “Walking is man’s best medicine.” I’ve always liked the adages, “Moderation is the key to life,” or, “Too much of anything will kill you.”

Take-home Tidbits

Where does this leave us? Like many things, with more questions. But I do think there are a few take-home messages that can be gleaned.

• Back pain is commonplace throughout life. Knowing this, take measures to avoid it, but take solace in knowing that it is generally benign and that you can thank evolution for your misfortune should you have it.
• There is no one-size-fits-all to paddling form.
• Experience SUPers tend to use more movement around the lumbopelvic hip complex.
• Using big muscles and big joints seems like a sensible SUP strategy.
• You should hinge at the hip, but how much your spine should move is open to debate.
• Moderation is the key to life.

That’s my current take on SUP biomechanics. Happy paddling!

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