INTRODUCTION
Surfing is a sport that involves skillful maneuvering up and down the slopes of waves crashing onto the shore. In the Championship Tour (CT), where world-class athletes participate, the maneuvers performed during surfing are scored by five judges based on subjective criteria, which include the following: 1) commitment and degree of difficulty, 2) innovative and progressive maneuvers, 3) combination of major maneuvers, 4) variety of maneuvers, and 5) speed, power, and flow [1]. Among many maneuvers included, an aerial is defined as completely separating the body and board from the waves, launching them airborne, and then landing again [2]. The aerial includes Frontside Air, Frontside Air Reverse (FAR), Frontside Air Reverse 360, and Backside Air Reverse, with the FAR being the most frequently performed maneuvers [3]. The inclusion of this maneuver scores, on average, 2.3 points higher than normal maneuvers where no separation from the waves occur [4]. Considering that a single maneuver can be rated up to 10 points, a successful aerial maneuver is significant and contributes to victory in a match [5].
The high score reflects the maneuver's likelihood of failure due to the low success rate (50-60%) [4]. A failed attempt results in a missed opportunity to try another maneuver and expose the surfer to injury from a poor landing [6,7]. To better understand these risks, as well as to reduce injuries and improve performance in aerial maneuvers, many previous studies have stimulated aerial maneuvers under experimental conditions and quantitatively analyzed biomechanical variables [8,9]. As a result, it has been reported that appropriate increases lead hip extension and decreases in lead knee flexion range of motion are beneficial for performing aerial maneuvers, and greater lead foot dorsiflexion angle and trail hip extensor mobility may reduce the peak vertical force generated upon landing [10]. In previous study that qualitatively analyzed performance variables based on a deterministic model of aerial maneuvering, it was reported that dorsiflexion of the lead ankle upon landing and keeping the center of weight in the middle of the board contributed to the successful performance of aerial techniques and stable landings [11]. However, since most technical analysis studies focused on performance improvement in surfing have been conducted with male surfers, it may be difficult for female surfers to directly apply this information to improve their performance [12].
In addition to many studies identifying gender-based anatomical, physiological, and functional differences [12,13], it has been found that among the pop-up movements used by surfers to catch waves on the force plate, female surfers generate less maximum force (13.41 N·s-1 ·kg-1 vs. 20.23 N·s-1 ·kg-1, respectively), and speed (1.21 m·s-1 vs. 1.69 m·s-1, respectively) than male surfers [14]. Additionally, in 5 m, 10 m, and 15 m sprint paddling, female surfers took longer time (female 4.34 s, 7.65 s, 11.01 s vs. male 3.74 s, 6.65 s, 9.59 s) and had lower maximum speeds (female 1.55 m·s-1 vs. male 1.77 m·s-1) compared to male surfers [15]. Even in diverse measurements such as 400 m paddling time (male 321.1 s vs. female 361.3 s), peak height from squat jump (male 53.4 cm vs. female 40.4 cm), and peak force in isometric midthigh pull (male 33.6 N·kg-1 vs. female 27.8 N·kg-1), male surfers outperformed female surfers [16]. These results may imply that female surfers have lower wave catching ability and skills compared to male surfers [16,17], suggesting differences in the performance variables required for maneuvering [12,18]. In the case of female surfers, compared to male surfers, attempts and successful examples of aerial maneuvers are extremely rare, and female big wave surfing has only recently begun to be recognized for its achievements [19]. Additionally, since most studies conducted with female surfers focused on improving physical functions [14,16], potentially limiting the information available to female surfers and coaches for performance improvement.
In 2021 CT, one female surfer executed a perfectly grabbed FAR and she won the Rip Curl Newcastle Cup presented by Corona. When observing the performance of a female surfer, technical coaches can gain a better understanding of the requirements and technical aspects of the surf-specific skill. Therefore, this study aims to 1) explore variables related to the success and failure of FAR by professional female surfers and 2) verify the differences in these variables depending on gender. This study intends to provide a basis for recommending useful information and technical improvements that can contribute to improving the performance of successful FAR by female surfers.
METHODS
1. Data collection procedures
Eight CT competitions held in 2021 were selected for analysis in this study because they were major competitions for qualification for the Tokyo Olympic Games. Aerial maneuvers attempted in a total of 56 matches (32 quarterfinals, 16 semifinals, and 8 finals) during these eight CT competitions were viewed using the Heat Analyzer function provided by the World Surf League (https://www.worldsurfleague.com/events/2021/wct/3858/rip-curl-newcastle-cup-presented-by-corona/heatanalyzer). The FAR was the only aerial maneuver that a female surfer succeeded in, so we decided to limit our analysis to the FAR in this study. More specifically, only one female surfer (referred to as surfer A) succeeded in performing the FAR, while other two surfers (referred to as surfer B and surfer C) attempted two unsuccessful FARs during the CT 2nd Rip Curl Newcastle Cup presented by Corona and CT 3rd Rip Curl Narrabeen Classic presented by Corona. Considering environmental factors, the scope of analysis was limited to two series (2nd Rip Curl Newcastle Cup and 3rd Rip Curl Narrabeen Classic) to confirm the difference performance variables between male and female surfers. Three male surfers showed 8 successful and 3 unsuccessful FARs in 2nd series and performed 8 successful and 6 unsuccessful FARs in 3rd series. FARs were limited to cases in which the entire board and the surfer body were airborne and completely separated from the waves, and they were divided into success and failure depending on landing. The 2nd and 3rd series were held consecutively in the same area, with a wave range of 1-4 and calm and offshore wind conditions.
2. Participants
This study analyzed the 1 successful and 2 unsuccessful FARs of 3 female surfers (age: 29.0±3.0 years; height: 167.3±4.6 cm; mass: 62.6±6.4 kg; career: 13.6±0.5 years) and the 16 successful and 9 unsuccessful FARs of 3 male surfers (age: 27.3±3.0 years; height: 175.3±6.4 cm; mass: 74.3±5.5 kg; career: 12.6±1.5 years) during the 2nd and 3rd series of the 2021 CT. The surfers included in this study were high performance surfers that were ranked between 1st and 10th in the 2021 World Pro Surfing Federation rankings and included a gold medalist at the 2020 Tokyo Summer Olympics. Participant consent was waived since all the data used in this study are publicly accessible and can be found in World Surf League. All demographic information of the surfers was gathered from the World Surfing League introduction to player profiles (https://www.worldsurfleague.com/athletes).
3. Performance variables
The FAR performance variables were defined by Forsyth et al. [11] and a total of 22 variables were used in this study, except for variables that were hard to identify. All performance variables were categorized into three phases (approach & take-off, airborne, and landing; Figure 1). The approach refers to the phase in which the surfer approaches the waves, and take-off refers to the immediately before the body or board is separated from the waves. The performance variables in the approach and take-off phase are as follows: (1) bottom turn, (2) approach angle, (3) wave condition at approach, (4) preparation for take-off, and (5) relative body position. The airborne phase refers to the time when the board and body are completely separated from the wave and are floating in the airborne, right before landing on the wave again. The performance variables at the airborne phase are as follows: (1) position of the surfer, (2) grab the board, and (3) foot movement. The landing phase refers to the point at which the board and body meet the wave and accept body weight. The performance variables at the landing phase are as follows: (1) position of the surfer, (2) wave condition at landing, (3) landing position on the surface of the wave, (4) first contact of board, (5) lead knee angle at initial contact, (6) trail knee angle at initial contact, (7) width of both feet at initial contact, (8) apparent gaze directed at initial contact, (9) center of mass position at initial contact, (10) lead arm position at landing, (11) trail arm position at landing, (12) trail knee valgus at landing, (13) trunk flexion at weight acceptance, and (14) chest position at weight acceptance. All performance variables were assessed as being suitable based on each criterion. The center of mass (COM) of body was defined as the location of the umbilicus and the open-license video analysis soft-ware Kinovea 0.8.15 for Windows (Bordeaux, France) was used to estimate the approximate joint angle and alignment [11]. All the analyses were conducted by experts with 10 years of surfing experience.
4. Statistical analysis
For female surfers, the descriptive method was used to identify variables in relation to the successful FAR. In male surfer, Fisher's Exact Test (χ2) was performed to determine variables associated with the success or failure of FAR using IBM SPSS Statistics version 27 for Windows (IBM, Armonk, NY, USA), and statistical significance levels were set as p =.05.
RESULTS
1. Difference in approach and take-off phases
Table 1 shows the difference of each performance variable in the approach and take-off phases between the success or failure of FAR for female and male surfers. Female surfer A, who successfully attempted FAR, had an approach angle of the board nose less than 45 degrees from the vertical when approaching the wave. In contrast, female surfers B and C who failed had an approach angle exceeding 45 degrees. It was observed that most male surfers maintained an approach angle of the board nose less than 45 degrees from the vertical, regardless of success in FAR. During preparation for take-off, female surfer A, who succeeded in FAR, and surfer C, who failed, used their upper extremities to initiate rotation and generate angular momentum. However, female surfer B, who was unsuccessful in FAR, did not initiate her rotation. It was shown that all male surfers, regardless of success in FAR, had rotation initiated during preparation for take-off.
Table 1.
Description of performance variables in approach and take-off phases for success or failure of FAR
2. Difference in airborne phase
Table 2 shows the difference of each performance variable in the airborne phase between the success or failure of FAR for female and male surfers. While female surfer A, who succeeded in FAR, was on the board (position of the surfer) during the airborne phase, female surfers B and C, both of whom failed, were unable to maintain their position on the board and fell into the water. All male surfers, whether they succeeded or failed in FAR, maintained their position on the board during the airborne phase. Also, all female surfers hold the rails of the surfboard with one or two hands during airborne, but most male surfers did not grab the board regardless of success in FAR. In foot movement in airborne, while female surfer A succeed in FAR and surfer C with failure did not move their feet excessively on the board, surfer C who failed moved her feet off the board. All male surfers kept their feet on the surfboard, regardless of success in FAR.
Table 2.
Description of performance variables in airborne phase for success or failure of FAR
3. Difference in landing phase
Table 3 shows the difference of each performance variable in the landing phase between the success or failure of FAR for female and male surfers. Female surfer A with success in FAR landed on the board, but both surfers B and C with failure did not land on their board leading to fall into the water. And almost male surfers with success or failure in FAR landed on their board. When returning to the surface of the wave, female surfer A and C landed on the mid-face of the wave and many male surfers who succeed in FAR landed on the bottom of the wave (also known as the flats). While the contact the surface of the wave for all female surfers was the nose of the surfboard first. most male surfers, regardless of success in FAR, used the center of board in first contact of the surface of wave. Both lead and trail knees angle of female surfer A who succeeded were less than 90 degrees when landing, but those of almost male surfers were greater than 90 degrees, regardless of success in FAR. At initial contact with the wave, the width of the feet for female surfer A and most male surfers with succeed or failure were greater than their shoulder width, and female surfer A and male surfers with succeed in FAR gazed toward the water in front of their hips. Also, they kept their center of mass over the center of the surfboard. During landing, both lead and trail arm of female surfer A and most male surfers with succeed or failure were positioned over the toeside rail, and during weight acceptance, surfer A and male surfers with succeed displayed their knees valgus. Also, during weight acceptance, they moved through a large range (>45 degrees from vertical) of trunk flexion, and their trunk bended over the lead knee.
Table 3.
Description of performance variables in landing phases for success or failure of FAR
DISCUSSION
In this study, we explored the influencing variables for success and failure of FAR maneuvers for female surfers. Since there were few cases of aerial maneuvers in female surfers, we confirmed the gender-based differences of performance variables. In this study, considering that remaining on the board or not signifies success or failure, it was found that female surfers failed in the airborne phase, while males failed in the landing phase. Female surfers succeeded in FAR, during approach phase, when the board's approach angle was less than 45 degrees from vertical and when they performed upper extremities to initiate rotation. In contrast, male surfers approached regardless of success or failure, the board angle of less than 45 degrees from vertical and, performed upper extremities to initiate rotation. Additionally, during airborne phase, female surfers succeeded when gripping the board in the airborne phase, whereas male surfers did not grip the board regardless of success or failure. In terms of foot movement, female surfers exhibited foot movement during failures, whereas male surfers showed no foot movement regardless of success or failure. During landing phase, female surfers succeeded when their front and rear knee angles were less than 90 degrees, whereas male surfers had knee angles greater than 90 degrees regardless of success or failure. Furthermore, female surfers succeeded when the board landed at the center of the wave with the nose making contact first. In contrast, male surfers landed on relatively flat waves, with the center of the board making the first contact with the wave, a pattern observed regardless of success or failure.
FAR is a technique that requires the board to separate from the wave and includes rotation while airborne [2]. The approach angle and ability to generate angular momentum is crucial for enabling high jumps and turns. In our study, female surfer A, who successfully attempted FAR, had an approach angle of the board nose less than 45 degrees from the vertical and she used her upper extremities to generate angular momentum. However, a previous study indicated that the approach phase of male surfers did not necessarily correlate with the success of FAR [11]. This suggests females’ approach angle would be the potential to succeed in the FAR.
In the airborne phase of FAR, the likelihood of failure increases with the separation of the board from the body or feet [11]. In this study, female surfer A who succeeded in the FAR held the board rail with her hands to prevent separation of her board and body, and she did not move her feet excessively on the board. But female surfers B and C who failed the FAR were characterized by excessive foot movement even when holding the board. On the other hand, male surfers, regardless of their success in FAR, did not grab the board rail and did not have excessive movements of their feet. It was obvious that the minimum foot movement in the airborne was crucial for the success in the FAR [11]. For keeping their feet on the board in the airborne, female surfers, un-like males, grabbed the board rail, and it related to make up for in insufficient force to perform high jumps and turns with the board. That was to maintain the angular momentum gained through torso rotation and their center of body closer to the axis of turning board for reducing the inertia during the aerial phase [11]. Actually, male surfers had a higher jump height and a greater maximum force than female suffers [16], leading to lift the board and body into the air. Therefore, for female surfers, grabbing their board could be considered a unique performance variable influencing to success in the FAR. Also, a previous study established that the greater lower extremities’ strength was related to the performance of higher scoring turning maneuvers during the airborne [20]. In skateboarding that is a land sport derived from surfing, experienced skaters with a higher strength in lower extremities had an increased jump height when performing an air jumping technique called as an ollie [21]. Further studies are needed to see if female surfers should be considered to the important of their strength for lower extremities.
In this study, while a female surfer succeeded in FAR had the angle of the lead and trail knees less than 90 degrees during the landing phase, both the lead and trail knees angle of male surfers were greater than 90 degrees for keeping the body's center of gravity close to the board and providing a stable base [22]. A surfer's landing is characterized by a more difficult compared to a general landing because of challenging landing surface such as flat, slope and rapids, so many surfers had various strategies depending on the wave conditions. Thus, it is conceivable that the landing strategy of female surfers who had a lower jump height compared to male surfers [16] was that both knees flexion angle were less than 90 degrees for the landing stability and the aerial effectivity [11].
The peak force during landing on the ground ranged from 8.2 to 11.6 times of the body weight [23]. Bending knees during the landing phase were for absorbing the force of impact so that the force is not sudden and large [24], and it was important for preventing knee injuries. However, female surfers who had a smaller knee flexion angle compared to male surfers during the landing phase have an inefficient shock absorption. Considering the higher incidence of knee injuries in female athletes compared to male athletes [25], these findings might indicate a higher potential risk to the knees for female surfers during landing.
To enhance the performance of surfers, research has focused on functional improvement and technical analysis. Because of the competitive characteristics of surfing in natural conditions, there was research on direct technical analysis is insufficient. Moreover, studies that had qualitatively investigated performance variables to improve skills in female surfers were unknown. As you known, this study was the first to identify the performance variables of female surfers for success in the FAR. However, since it was conducted using an explanatory method rather than a statistical method, it would be difficult to generalize the findings to all female surfers. Additionally, it is important to interpret the results considering that they are based on a single successful case observed in females. Recently, the analysis of athletes’ movement using inertial measurement unit sensors, which are lightweight and do not restrict movement, had quantified despite of environmental factors such as extreme water conditions [26]. Further research should be needed to consider the quantitative evaluation of variables contributing to successful airborne maneuvers among female surfers for a better understanding of factors impacting airborne maneuver success and safety.
CONCLUSION
This study, for female surfers, focusing on preparation for the airborne phase or refining techniques during this phase may play a key role in the success of FAR. During approach phase, the approach angle of the board and the angular moment generated by using upper extremities for female surfers might affect the success in FAR. Whilst airborne, female surfers might benefit from grabbing the board with one or both hands. During the landing phase, especially when returning to the surface of the wave, female surfers could consider the landing point of the wave in mid-face and the first part of the surfboard to contact the surface of the wave. Additionally, it may be helpful to consider bending the female surfer's legs to an angle smaller than 90 degrees.
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