The neuromechanical control of surfboard paddling

Wynand Volschenk

doi:10.25918/thesis.181

Background: In recent years, surfboard paddling has received increased research interest due to its importance and impact during a surfing competition. Paddling is fundamental to reaching the line-up, position within the line-up, and most importantly to catching waves. Wave priority during surf competitions is given to the surfer who reaches the line-up first. Additionally, surfers with a better paddling performance capability (endurance and speed) may have an improved ability to reach the line-up first and catch waves more efficiently and effectively, thus enabling them to maximise their scoring opportunity. Previously, surfboard paddling research has largely been conducted using ergometers, e.g., swim bench ergometer, due to methodological constraints of water-based assessments. However, a dearth of research exists in understanding the neuromechanical control differences between paddling on water or on a swim bench ergometer or between paddling intensities when in the water. Additionally, with the increased female participation and competition within surfing, an understanding of neuromechanical differences between sex is warranted. Research Aim: The overall aim of this thesis was to investigate the neuromechanical control of surfboard paddling under differing environmental conditions and at different paddling intensities for both males and females. Methods: Two individual studies were designed and undertaken within this thesis. Study 1 focused on exploring the neuromechanical control of surfboard paddling on either a swim bench ergometer or in water. Each paddle stroke was broken down into two distinct phases: propulsion and recovery, to aid in analysing and distinguishing any differences between conditions. Surface electromyography (sEMG) signals across eight shoulder complex and torso muscles were collected in addition to 2-D video footage during the experimental paddling trials. A 20 second (s) window was recorded during the swim bench ergometer trial, and two 20 m paddling distances were recorded during the pool paddling trial. Of all stroke cycles recorded, seven successive stroke cycles of each paddling condition were then analysed and averaged for statistical analysis. Kinematic data were analysed using Dartfish software, which helped to identify the start of each stroke cycle and phase. Raw sEMG data were smoothed using an RMS with a 0.3 s running window within LabChart software, and synchronised with the kinematic data to determine peak muscle activity and discrete temporal points within the stroke cycle. Both the kinematic and sEMG data were statistically analysed using a 2-way repeated measures ANOVA (condition x sex) to determine whether there were any significant main effects within and between conditions and sex. Study 2 focused on exploring the neuromechanical differences between a steady-state paddling bout and a sprint paddling bout within four distinct phases, namely the hand entry, pull, push, and recovery phases, respectively. The experimental setup, i.e., sEMG and video recordings, was similar to that of Study 1. Data acquisition for the sprint paddling protocol was completed over two 15 m all-out sprint bouts. Of all stroke cycles recorded, seven successive stroke cycles of each paddling condition were then analysed and averaged (as in Study 1) for statistical analysis within four distinct phases. Data were statistically analysed using a 2-way repeated measures ANOVA (condition x sex) to determine any significant main effects within and between conditions and sex. Major Conclusions: The results from Study 1 revealed the latissimus dorsi and triceps brachii to be the main contributors to propulsion, while the middle deltoid, upper and middle trapezius contributed mainly to recovery within the stroke cycle. The erector spinae contributed to trunk ipsilateral stabilisation during propulsion. Interestingly, surfboard paddling on a swim bench ergometer elicited similar peak muscle activation intensities, similar muscle onset timings, and similar muscle activation burst duration to paddling in the water. However, differences were found in peak intensities of some muscles (i.e., medial deltoid and right erector spinae) and in some temporal aspects of the activation patterns (i.e., medial and posterior deltoid, middle trapezius, and latissimus dorsi). Thus, paddling on a swim bench ergometer may lack some ecological demands of paddling, reducing its specificity for muscle or limb coordination training. Moreover, it was found that paddling on the swim bench ergometer had a significantly longer propulsive phase and a significantly shorter recovery phase compared to paddling in water. This revealed that, when paddling on the swim bench ergometer, surfers preferred a superposition arm coordination pattern rather than an absolute opposition pattern found in water paddling. This may be due to a lack of proprioceptive feedback provided on the swim bench ergometer. Notwithstanding this, surfboard paddling on a swim bench ergometer may be a viable alternative and possibly the most sport-specific land-based training and testing tool when surf access is limited. No sex differences were found for any of the kinematic or sEMG variables between conditions. Study 2 revealed significantly shorter stroke cycle times, a shorter hand entry phase, and a longer pull phase when sprint paddling. Furthermore, it was revealed that higher peak muscle activation intensities accompanied similar temporal activation patterns when sprint paddling. However, sprint paddling was accompanied by higher variability of the temporal aspects of muscle activation patterns. We conclude that the neuromechanical control elicited by sprint paddling differed to steady-state surfboard paddling with only certain similarities. Therefore, surfers should undertake sprint paddling sessions separate to steady-state paddling to help decrease temporal variability of neuromechanical control and improve power when sprint paddling. Females had a shorter hand entry phase accompanied by a longer recovery phase; however, no further kinematic or sEMG differences were found.

The neuromechanical control of surfboard paddling

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The neuromechanical control of surfboard paddling

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