In North American history, canoeing played a critical role for commercial purposes; however, it was overshadowed by the construction of transcontinental railways (Shephard, 1987). Nonetheless, interest in canoeing as a sport continues to increase, and the International Canoe Federation (ICF) currently considers more than 10 canoeing disciplines, with the sprint and slalom challenges in the Summer Olympic Games (ICF, 2021). While sprint takes place on flatwater courses, the slalom discipline occurs in natural or artificial rivers, also called whitewater. This “simple” difference does not only drastically affect the specificity of the sport, but the number of scientific reports in each. While considerable research has been conducted on sprint athletes (Shephard, 1987; Michael et al., 2008, 2009), there are few studies on canoe slalom athletes.

Slalom courses are inconsistent in terms of obstacles, routes, and gates, offering large performance variability (Nibali et al., 2011). Canoe slalom athletes must negotiate courses with a maximum of 25 gates, including upstream and downstream gates, and an approximate length of 300 m. The challenge includes a competitive course with eddies, waves, and stoppers. Therefore, it is clear that canoe slalom complexity is purposeful rather than chance. Such factors directly impact scientific studies designed to understand the relevant factors underlying canoe slalom athlete performance. Thus, the science of this sport is challenging. Moreover, the Olympic Games comprise K1 (kayak single) and C1 (canoe single) classes. In addition, the canoe double category (C2) is challenged at the international level. In canoe (both C1 and C2), a single-blade paddle is used by the athlete while their legs are maintained at the knees and tucked under their body. In the kayak category, the double-bladed paddle is used, and the athlete is kept in a seated position in the boat (ICF, 2021).

Studies published until 2010 have triggered relevant discussions on energy metabolism during races (Sidney and Shephard, 1973; Shephard, 1987; Zamparo et al., 2006), as well as the biomechanical (Hunter et al., 2007, 2008; Hunter, 2009), and psychological aspects of slalom athletes (Males et al., 1998; Moran and MacIntyre, 1998; White and Hardy, 1998; MacIntyre et al., 2002; Macintyre and Moran, 2007). Zamparo et al. (2006) verified that both aerobic and anaerobic metabolism are relevant during slalom tasks. Moreover, strokes performed during competitions were properly addressed (Hunter et al., 2007), and strategies to negotiate upstream gates have been discussed in detail (Hunter et al., 2008). However, among these studies, few have compared and/or associated the collected results with slalom performance (Hunter et al., 2008).

In a later narrative review, we initiated a discussion on this matter (Messias et al., 2014), but the lack of published studies until that moment precluded deeper inferences. Since then, research groups have tried to identify the relevant components associated with canoe slalom athlete performance. Slalom tasks require great physical fitness and precise technical skills (Messias et al., 2014). Therefore, mechanical, physiological, and technical components play important roles in canoe slalom races. However, no systematic review has focused on demonstrating which of these parameters are associated with canoe slalom performance. In this way, the present manuscript aimed to systematically review studies that evaluate and compare mechanical, physiological, and technical parameters with the performance of slalom athletes.

This systematic review showed that mechanical, physiological, and technical components may affect the performance of canoe slalom athletes. Nonetheless, despite the increase in the scientific interest of this sport over the last 7 years, more studies are necessary to understand the demands of slalom trials and improve the assessment of these parameters with increased ecological validity. Regarding the performance measurement, great variability in terms of course, gates, and obstacles were identified among the eligible studies. This is not surprising, since slalom championships are projected to be inconsistent, offering a great challenge for athletes, coaches, and researchers.

With respect to mechanical parameters, Messias et al. (2015) showed inverse correlations between race time and force (peak, mean, and impulse) from a maximal 30-s all-out test. This ergometer was proposed to preserve forward stroke characteristics while measuring the technical and/or physiological parameters. Additionally, the tethered system was suggested as an alternative training tool that is not affected by the climatic conditions, since it can be used in a swimming pool. Macdermid et al. (2019) assessed slalom athletes in a flatwater course with a kayak paddle shaft (Macdermid and Fink, 2017) and suggested that peak force and its rate of development are relevant during races, although correlations between these parameters and race time were not significant. Moreover, these authors visualized that impulse and the time to develop peak force per stroke remained similar throughout the performance task, while the peak force magnitude decreased. Hence, both Messias et al. (2015) and Macdermid et al. (2019) corroborate that a high stroke force level is important for slalom race performance.

Studies not eligible for this systematic review may shed some light on these aspects. The early work of Sidney and Shephard (1973) suggested that the trunk muscles and upper extremities are engaged in rhythmic work during slalom, which may depend more on cardiorespiratory power rather than strength. We believe that over the last 40 years, the canoe slalom has evolved and strength training has gained higher importance, as has been found in other sports (Hebert-Losier et al., 2014, 2017; Styles et al., 2016; Kniffin et al., 2017). However, the mean power of bench pulls and presses appears to have a deeper influence on canoe sprint as opposed to slalom (Bielik et al., 2020). Canoe slalom paddlers use narrower hand grips, which results in shorter, more powerful strokes with increased elbow flexion than that reported for a top-level sprint (Zahalka et al., 2011). The narrower hand-grip of these athletes strongly engages the arm muscles to produce rapid movement. Conversely, hand-grip of canoe sprint athletes primary engage the trunk muscles (McKean and Burkett, 2014).

Research on the physiological parameters of slalom athletes has provided important data for coaches and athletes. Except for the incremental running test in two studies (Bielik et al., 2019, 2020), all reports adopted distinct ergometers and tools to assess the physiological parameters of slalom athletes. The weak and non-significant correlations of Vieira et al. (2015) regarding heart rate/blood lactate and race time can be explained by the low number of athletes tested in this study. Ferrari et al. (2017) have confirmed the importance of aerobic metabolism in slalom athletes, suggesting that the oxidative system may indirectly affect performance by improving the training load and leading to faster recovery between races. In summary, slalom races require great anaerobic participation during paddling efforts in order to surpass obstacles (Baker, 1982; Messias et al., 2015; Vieira et al., 2015). On the other hand, the aerobic metabolism demand is also considerable (Zamparo et al., 2006) and related to performance (Ferrari et al., 2017). These factors, however, may not increase the chances of winning medals according to Bielik et al. (2019, 2020).

Although the technical aspects of strokes performed by slalom athletes have been described in detail (Hunter et al., 2007), few studies have assessed the relevance of these for performance. Hunter et al. (2008) verified in the top 10 runs of the 2005 World Championship that 67–71% of the strokes performed were in the forward direction, while 30% of strokes were performed to turn the boat. These authors also noticed that race time and the total time that athletes spent with their blades in the water were positively correlated, which was expected. However, the same was not observed for the percentage of time the paddlers spent with the blade in the water, suggesting that regardless of race time, this percentage was unchanged. Vieira et al. (2015) tracked the strokes performed during two simulated races, and their results suggest that athletes may vary their strategy from race to race even in an identical course. Such results strengthen the idea of a purposeful challenge offered by this sport to coaches and athletes. Therefore, further studies on the paddler's strategy and performance are necessary.

Baláš et al. (2020) proposed an alternative way to verify the influence of a specific skill on the athlete's performance over a flatwater course. Pivot turns were added in the time paddling tests over 40, 80, and 200 m. Interestingly, high-performance athletes at the international level presented better results in every trial than those at the national level. This result adds to the previous discussion on the measurements to be considered by coaches when evaluating performance enhancement. The course proposed by these authors can be easily reproduced, and further studies are also required to create a group of trials that can offer insights on performance by measuring other technical skills. In addition, identifying associations with these results in simulated trials or situations mirroring real slalom conditions can strengthen the importance and use of such assessments. These should consider the rules provided by the ICF, such as a maximum of 25 gates and a length of 300 m. In this scenario, canoe slalom athletes should accomplish the race between 90–110 s and require great force, velocity, and power development in addition to anaerobic metabolism.

The athletes evaluated in the eligible studies were mostly men. Only the investigation by Hunter et al. (2008) also considered slalom runs in female athletes. Further research with females' slalom athletes is encouraged, especially because female K1 and C1 classes are challenged in the Olympic Games. Another interesting fact noted in this systematic review was that slalom athletes from only four countries were tested. It must be recognized that Slovakia, the Czech Republic, and New Zealand won medals at the last Summer Olympic Games. Still, other countries from Europe and Oceania have also won medals in both Olympic and World Championship tournaments. Accordingly, to improve the scientific knowledge of slalom athletes, further studies are required with athletes from different nationalities. In addition, none of the eligible studies provided a deep discussion on the performance of the different classes (i.e., kayak and canoe). Hunter et al. (2007) concluded that athletes in the C1 category may perform fewer strokes during races than K1 athletes, but this does not impact performance time. The studies included in this systematic review did not compare these parameters between classes, precluding a thorough discussion on this matter. However, further research comparing the physiological, biomechanical, and technical aspects of classes is strongly encouraged.

A further point worth discussing is the variability in performance measurements. Although general characteristics are mandatory, such as a minimum/maximum number of gates, approximate distances, and interval durations of 90–110 s (ICF, 2021), great variability still occurs from race to race. Therefore, we did not include studies with specific performance trials. Some of the eligible studies tried to follow such recommendations in both whitewater (Messias et al., 2015; Vieira et al., 2015; Ferrari et al., 2017) and flatwater (Macdermid et al., 2019) tasks; nonetheless, considerable variability was also seen in these. The idea of creating a standard performance protocol—identical courses, obstacles, eddies, waves, and stoppers—for this sport with strong ecological validity is likely utopic because canoe slalom competition preserves the unpredictability (Nibali et al., 2011). Thus, others opted for a different strategy and focused on a particular technical skill (Baláš et al., 2020) or used the results from slalom championships (Hunter et al., 2008; Bielik et al., 2019, 2020). Overall, it is too early to affirm or suggest the most suitable strategy to evaluate canoe slalom performance, but without further investigations, this issue will not be resolved.

This study concludes that mechanical, physiological, and technical factors may play important roles in canoe slalom performance. Further studies are recommended on these issues along with slalom performance assessments, which deserve significant attention in terms of standardization and ecological validity. Together, these studies should confirm the presented outcomes and advance the science surrounding this sport, helping coaches and athletes throughout the training period and, most importantly, in competitions.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

LM: proposal of ideas, the conception, design of the work, acquisition, interpretation and analysis of data, the writing of the main manuscript text, and preparing figures and tables. IR and AG: acquisition, interpretation and analysis of data, the writing of the main manuscript text, and preparing figures and tables. VB: writing of the main manuscript text and preparing figures and tables. CG and FM-G: proposal of ideas, the conception, interpretation and analysis of data, and the writing of the main manuscript text. All authors contributed to the article and approved the submitted version.

The authors thank the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP—Proc. 2012/06355-2, Proc. 2010/17134-1 and Proc. 2021/12447-6) and VEGA (1/0260/21) for financial support.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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