Anatomy of a Paddle Stroke 2.0
Thursday, January 27, 12022 HE
The video below shows the generalized paddle mechanics of an experienced paddler on the left and an inexperienced paddler on the right. Relevant to this post is to note how much more motion occurs around the lumbopelvic-hip complex in the experienced paddler.
For a different commentary on the kinematics of the Stand Up Paddleboard (SUP) stroke, check out this excellent video of the anatomy of a SUP paddle stroke by the team at Quick Blade Paddles below. Importantly 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, and thus the greatest propulsion, is achieved when all of the surface area of the paddle blade is engaged in the water. To do this, the blade must be efficiently 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. They offer a free 14-day trial if you’re the doubting Thomas-type want to check it out for yourself.
Schram and colleagues’ data showed that experienced paddlers seem to use more range of motion from their hips and less from their shoulders compared to inexperienced paddlers. This is observed in the biomechanics video above as more motion of the trunk (lumbopelvic-hip complex). On average, the experienced paddlers had 15 more degrees 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 all of the joint values collected here in Table 1 from Schram and colleagues (2019).
Sources: Schram, Ben et al. “A biomechanical analysis of the stand-up paddle board stroke: a comparative study.” PeerJ vol. 7 e8006. 1 Nov. 2019, doi:10.7717/peerj.8006
Below is a quick note on paddle stroke phases. There are different naming systems for the stroke phases. In the paper by Schram and colleagues, they 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 this video from SUPBoarder for a great overview of the five-stroke phases). There is overlap between the two systems. The reach and catch are combined as the entry in the five versus the three-phase system. And release and recovery combine as the exit phase, while the power and drive phase are interchangeable. I will use either naming system where convenient. The five-phase system allows for more granularity.
Greater motion at the coxofemoral joints allows for more motion of the torso into an anterior tilt. This re-orientation of the torso ultimately allows for a longer reach and paddle stroke. The paddlers’ trunk tilting forward in space along with their arms reaching forward shifts their centre of mass anteriorly. To maintain balance, this change in the centre of mass must be counter-balanced posteriorly. This is done through the lower extremity by way of a hip hinge action (see above), which incorporates knee flexion. The large posterior muscles of the hip must keep the torso upright as they eccentrically contract, lowering the torso forward in the field of gravity. That action must then be reversed through the power/drive phase of the stroke to bring the body back to an upright stance. However, during the power phase with the blade engaged in the water, the torso must be rigid for efficient power transfer. The ground (uh, water) reaction force from pulling the paddle in the water is causing an extension moment to the spine that must be balanced with activation of the trunk flexors. Specific to the hip are the hip flexors (iliopsoas) which arise from the pelvis, lumbar spine, and even have connections to the diaphragm at the crus. There must be co-contraction of the muscles controlling the spinal column to create a rigid lever to pull the body forward in space. When paddling, because water is a relatively incompressible medium the board and paddler are essentially pulled past the point where the paddle blade catches, resulting in relative forward propulsion.
I mention the hip flexor-diaphragm attachment relationship above due to the curious case of locomotion-respiratory entrainment. Essentially, this is a phenomenon seen in quadruped animals, where a coupling of locomotion and respiration, or entrainment, occurs. Animals, such as horses, rabbits, rats, cats, and dogs, when at a gallop, exhale as they draw their forelimbs back and inhale as they extend their forelimbs. This respiratory entrainment does occur in human physical activities (e.g. wheelchair use, rowing, cycling, and cross-country skiing). Perhaps SUP is another activity where it occurs or it might be advantageous to use entrainment for trunk stiffness and respiratory efficiency?
For the hip hinge motion, adequate mobility of the posterior chain (i.e., the soft tissues at the back of the hip) is required. The tissues at the back of the hip that need to be extensible include the muscles (e.g., gluteus maximus, adductor magnus (anterior and posterior heads), hamstring, and lateral rotators of the hip), fascia, posterior joint capsule, ligaments (particularly ischiofemoral ligament when the hip is medially rotated and adducted), and nervous tissue (e.g., sciatic nerve). The extensors of the hip need to be extensible enough to allow hip flexion (i.e., an anterior tilt of the pelvis) to keep an erect trunk. If the hip is too stiff or immobile then flexion of the body will occur more through the spine. It is not that the spine should not bend. Contrary to that, it needs to bend and receives rich proprioceptive input from the motion between its segments. However, with external load and repetition, excessive spine motion can result in disc injury. Work by spine biomechanist Stuart McGill in porcine animal models has shown that repetitive flexion-extension motions can cause disc herniation. As such, it is mechanically more efficient (and safer) to repetitively flex and extend the ball-and-socket joint of the hip versus amphiarthrosis and synovial planar joints that make up the intervertebral and facet (zygapophyseal) joints of the spine.
Another aspect of gaining more reach for the paddle stroke comes from hip and pelvis rotation. As described in my Shoulders Volume 2 post, there is a contralateral trunk rotation toward the paddle side during the reach. That rotation stems from the hips which, allows the pelvis to be globally rotated away from the paddle side (i.e., think of where your umbilicus is pointing for the rotational direction of the pelvis). To rotate the pelvis globally in space, the ipsilateral coxofemoral joint must laterally rotate while the contralateral coxofemoral joint medially rotates. This occurs during the recovery and reach phases of the stroke. The rotation of the hips and pelvis is reversed through the power/drive phase. This requires contraction of the medial and lateral rotators of the ipsilateral and contralateral hip, respectively.
Source: Kapandji, I A. The Physiology of the Joints: Volume 2 The Lower Limb, 2011.
It follows that adequate ranges of coxofemoral rotational motion should be a benefit to paddling. Adequate range of motion allows for a longer paddle stroke reach and should limit the chance of compression/abutment type injuries (e.g. femoroacetabular impingement, labral tear). There is no way to completely limit the risk of injury but adequate joint mobility is a good starting point. An ounce of prevention is worth a pound of cure. Or for the non-imperialists among us, a gram of prevention is worth a kilogram cure. Though it doesn’t quite have the same ring to it metricized. It is worth noting that the osseous anatomy of the hip plays the ultimate role in determining the limits of motion. That is to say, you cannot stretch or mobilize yourself out of a structural bone issue. After the age of skeletal maturation, this is essentially a non-modifiable characteristic. Similar to the adage in athlete development, that you can’t make a racehorse out of a plowhorse. Some things are non-modifiable and in the body need to be accommodated or compensated for. In the case of someone with a structurally immobile hip, they should be doing everything to maximize the surrounding structures to compensate for their weakest link (e.g. maximize hip flexion/extension, thoracic rotation, shoulder mobility, etc.).
Balance is a major part of SUP as you are standing on an inherently unstable surface in a dynamic environment. Simplified, the body relies on three sensory input systems (visual, vestibular, somatosensory) to maintain postural equilibrium in the field of gravity. Successful balance requires a complex interaction between dynamic sensorimotor processes to control the body’s centre of mass. The lumbopelvic-hip complex plays a key role in the process. Just think of the last time you almost lost your balance. You likely needed to shift your hips to regain balance. Or if the perturbation was large enough to move your centre of mass outside of your base of support, then you would have used a stepping strategy to regain your balance. On a SUP being mobile in your hips as well as fleet of foot are valuable assets. These talents must be coupled with practice and experience to develop skillful balance on a paddleboard.
Source: Kapandji, I A. The Physiology of the Joints: Volume 2 The Lower Limb, 2011.
When paddling the centre of mass will shift laterally to the opposite side of the paddle stroke. This is due to the lateral trunk flexion or list needed for the paddle to clear the edge of the board to enter the water. To counter this shift in the centre of mass and maintain equilibrium, the hips must shift to the opposite side. In order to do so in the coronal plane, the ipsilateral hip must abduct while the contralateral hip adducts. However, since this occurs throughout the stroke the hip is going through flexion and extension movements. The movement is therefore coupled with medial and lateral rotations as the hip moves out of the coronal plane and more into the transverse plane. Overall, this results in movement of the hip that is coupled with the other motions and equates to a circumduction of the coxofemoral joint.
As the second-most mobile and the second-largest joint in the body, the hip is proficient in both joint mobility and stability. This makes sense as bipedal animals. Our hips need to support us so they need to be stable and strong, and capable of developing high levels of stiffness. But at the same time, they must be mobile so that we can harness their motion for ambulation and locomotion. The largest muscle of the body (gluteus maximus) crosses the hip and the joint is, therefore, the powerhouse of the body. When paddling, it is best to take advantage of the large musculature and osteokinematics of the hip for a powerful and efficient stroke. The larger, polyarticular muscles of the trunk, hips, and legs should be the basis for the power development during the drive/power phase of the stroke. This power is transferred through the trunk to the shoulder girdle and arms, and ultimately to the water via the paddle for propulsion. The upper limbs are relatively static and stiff to allow the transfer of energy.
As put forward in my Shoulders Volume 2 post, the recovery phase of the stroke can vary with the paddling goal (e.g. speed versus endurance). When paddling for speed, the goal is to keep the paddle pulling water as much, and as quickly as possible. The faster the recovery phase of the stroke is, the quicker the next reach, catch/entry, and power/drive phase are initiated. Keeping the paddle more vertical during the stroke recovery phase makes for a faster stroke. To do this, the shoulders remain at a higher angle of flexion, and the trunk is brought into a more upright posture. The hips must extend for this to happen. The paddler stands more upright to create clearance for the vertical paddle. In a more leisurely paddle stroke the hips are often extended too, but more so to relax the legs so that the mass of the body can be supported by the osseous structures rather than muscular activity.
I have alluded to it previously, but the hips do not function in isolation. They are beholden to the osteokinematics and arthrokinematics of the surrounding joints and overall bodily system. This is the idea of regional interdependence or the “concept that seemingly unrelated impairments in a remote anatomical region may contribute to, or be associated” with someone’s primary complaint (Wainner et al., 2007, p. 658). This is a similar idea to Mike Boyle‘s joint-by-joint approach. Essentially, the joint-by-joint generalizes that joints in the body tend to alternate between a need for mobility to a need for stability. As a simple heuristic, it is a useful concept but requires joints to be grouped as complexes to really hold true (e.g. the lumbar spine is a complex of 18 joints when considering all the intervertebral discs and facet joints, and the ankle complex includes three joints, talocrural, subtalar, and inferior tibiofibular joints). So while this post was focused on the hip specifically, the hip doesn’t operate in a vacuum. It is part of a complex organism and proficiency in SUP must consider that, as well as other environmental factors that influence the biomechanics of the activity.
Hopefully, there was something new in there for you. And if not perhaps, something old that you could look at in a new light. For me, it was a great anatomy review to compose this post. And in addition, it had me really think through some of the biomechanics of SUP, which had previously been a more implicit motor learning endeavour. I had learned them through practice and feel. Creating this post, I had to explicitly consider what I am actually doing through my various stroke phases.