Sports climbing, which has been officially adopted as an Olympic sport in the 2020 Tokyo Olympics, has been gaining increasing popularity among the general public. This sport has developed into a popular sport available to individuals due to its greater accessibility compared to natural rock climbing, originating from traditional rock climbing conducted in the natural setting (Sanchez et al., 2012). Sports climbing comprises three specialized disciplines: lead, bouldering, and speed, which are classified as distinct events despite having similar competition methods and rules. In particular, lead is a discipline in which athletes compete to determine who climbs the highest within a given time limit, whereas speed determines the winner based on who climbs a set route in the shortest amount of time. Accordingly, athletes in each discipline clearly differ in the competition duration and training methods, and also relatively differ in terms of the physical conditions, fitness, and body weight. Sports climbing involves movements that engage the entire body from the fingertips to the toes, making it a complex exercise encompassing both anaerobic and aerobic metabolic processes and requiring overall muscular strength, muscular and cardiovascular endurance, and flexibility, thus demanding higher exercise intensity compared to other sports disciplines.

However, since sports climbing competitions proceed in rounds based on each discipline, the outcomes of subsequent rounds largely depend on the level of fatigue recovery during the rest periods between competitions. Therefore, fatigue recovery, in addition to the fitness factors related to athletic performance, plays a very important role. In particular, climbing involves intermittent isometric muscle contractions maintained continuously, leading to a rapid elevation in blood lactate concentrations within a short period (Mermier et al., 1997), and sports climbing, characterized by performing at high intensities within short durations, is closely related to peripheral fatigue caused by intramuscular phosphocreatine depletion and lactate accumulation (Faude et al., 2009). The accumulation of muscle fatigue induces stress, resulting in decreased muscle function and exercise performance (Komi et al., 2000). To enhance performance, systematic and continuous physical fitness training must be conducted, even for athletes possessing outstanding technical skills in all sports disciplines.

Previous studies have been conducted to attempt the construction of systematic training programs based on metabolic and cardiovascular responses occurring during sports climbing (de Geus et al., 2006) and to identify the factors influencing performance in sports climbing such as lactic acid, etc. (Watts et al., 2000). In sports climbing, the muscles primarily utilized may differ depending on the competition methods and the main climbing direction according to the routes, suggesting that the composition of efficient training programs may differ among disciplines. Although various training methods exist, circuit-type exercise, which can improve both aerobic and anaerobic capacities increasingly emphasized for sports climbing athletes. Circuit weight training (CWT) applies the concept of a circuit to weight training, performing multiple exercises consecutively while moving from one exercise to the next with minimal rest intervals between exercises.

This training method comprehensively improves cardiovascular function as well as muscular strength. However, longitudinal studies investigating the effects of CWT on blood lactate levels, stress indices, and related performance in sports climbing athletes are very limited. Therefore, this study aims to examine how CWT and traditional weight training influence changes in blood lactate concentrations, stress indices, and their subsequent effects on performance enhancement among athletes in various sports climbing disciplines.

As the exercise intensity increases, the demand for oxygen within the human body also rises, leading to elevated lactate concentrations as part of the body’s buffering mechanism to maintain homeostasis. This increase in lactate concentration until carbohydrate depletion is closely associated with accumulated muscle fatigue, which directly impacts performance deterioration (Hoff et al., 2016). Therefore, athletes, who repeatedly perform high-intensity exercise during training or competition, accumulate high amounts of lactate, highlighting the necessity to identify methods to return lactate levels to their resting state. Climbing itself can be defined as a complex exercise involving both anaerobic and aerobic metabolic processes that require muscular strength, muscular endurance, and cardiovascular endurance (Mermier et al., 2000). An increase in the capillary density within the body has been associated with the reduction of blood lactate (Kraemer et al., 1987), and an improved ability to remove lactate is anticipated to enhance the climbing performance (Giles et al., 2006).

Although the generation and removal of fatigue substances in the blood are significantly influenced by the exercise intensity, frequency, duration, and physical fitness level of subjects, making interpretation context-dependent and necessitating caution, regular training generally reduces fatigue substances (Messonnier et al., 2005; Theofilidis et al., 2018) and stress responses (Timmerman et al., 2008; Zhang and Sim, 2024), which are positively related to an improved performance. A recent study by Zhao and Sim (2023) conducted on highly trained middle-distance runners demonstrated that reductions in blood muscle damage indicators and fatigue substances after 10 weeks of high-intensity interval training influenced improvements in middle-distance running performance. Additionally, Du and Sim (2021) reported significant effects of 8-week interval training on reducing blood fatigue substances and ACTH levels on changes in the 100-m sprint records of short-distance runners. In the current study, an analysis of differences in the blood lactate levels after 10 weeks of two forms of weight training showed a significant reduction in the blood lactate levels in the circuit weight-training group. In contrast, although the traditional weight-training group exhibited a trend toward reduced lactate concentrations after training, no significant change was observed, thus showing differences between the groups. These results may be attributed to elevated lactate levels due to individual sports climbing athletes not regularly performing supplementary exercises. However, continuous physical fitness improvement through CWT is believed to have gradually restored lactate accumulation, resulting in reduced lactate levels observed in posttraining measurements.

On the other hand, exercise imposes stress on the human body, and the level of stress varies according to the training volume and individual training status (Tianlong and Sim, 2019). The increase in stress hormones, such as cortisol, ACTH, epinephrine, and norepinephrine caused by acute exercise occurs because glucocorticoids are temporarily activated, increasing the adrenal sensitivity to ACTH (Campbell et al., 2009). In contrast to short-term, high-intensity, and acute exercise, one of the general effects of regular training is a reduction in stress responses. Compared to the general population, athletes typically show a trend of decreasing ACTH levels through regular exercise compared to the pre-exercise levels (Du and Sim, 2021; Duclos and Tabarin, 2016; Soslu et al., 2023). In this study, the blood ACTH concentrations differed between the two groups, with the circuit weight-training group showing a significant reduction, while the traditional weight-training group displayed a decreasing trend, though not statistically significant. Regarding these results, Zhang and Sim (2024) reported that, in athletes, repetitive and continuous training processes improve adaptive responses to stress, such as reductions in antidiuretic hormone and lactate concentrations, leading to decreased ACTH secretion. Catecholamine secretion rates are not significantly changed at lower exercise intensities; however, blood concentrations increase at exercise intensities above 60% of maximum oxygen uptake, and this increase is proportionally related to the exercise intensity (Tan and Yip, 2018; Wheatley et al., 2015). Changes in catecholamine levels can vary depending on training intensity or type (Kraemer and Ratamess, 2005). In this study, the resting norepinephrine concentrations released through the two forms of training showed no significant differences between groups but decreased in both groups. The variability in these outcomes may be explained by differences in adaptive processes due to the training environment and control factors, indicating neuromuscular adaptations capable of tolerating continuous high-repetition, weight-bearing exercises.

Furthermore, salivary α-amylase, known as an external stress marker reflecting blood catecholamine levels, is measured non-invasively and is highly sensitive to stress, significantly changing when psychological stress occurs (Kang, 2010). In the present study, no differences were observed between the two training methods; however, α-amylase levels were reduced after training compared to pretraining in both groups. Yamaguchi-Shinozaki et al. (2001) reported that human salivary α-amylase increases with negative stress and decreases with positive stress; thus, regardless of the training type, it is considered that repeated physical stimulation through the 10-week training process enhanced resistance and tolerance to stress, positively affecting changes in stress indicators. It is noteworthy that the performance records for the speed and lead disciplines of sports climbing improved through both forms of training, with no significant difference between groups for changes in speed records; however, lead records showed greater improvement in the circuit weight-training group. Particularly, reductions in the blood lactate levels resulting from CWT and traditional weight training affected performance changes in the lead discipline, whereas reductions in stress indices affected performance changes in both speed and lead disciplines. However, the influence of lactate and stress indices changes due to CWT and traditional weight training on performance changes in speed and lead disciplines did not significantly differ between the two groups. Although fatigue may initially increase at the beginning of training, the application of a continuous 10-week training program appears to improve the ability to break down blood lactate, which induces muscle fatigue, thereby enhancing both aerobic and anaerobic performance capacities of sports climbing athletes. This can be regarded as an outcome resulting from overcoming the factors affecting performance and leading to improved physical functions.

Summarizing these results, it was confirmed that blood lactate and stress indicators, which represent fatigue substances, are important variables affecting performance in sports climbing athletes. In particular, considering that the athletes participating in the lead and speed climbing disciplines showed greater improvements in blood lactate removal capacity and stress resistance through continuous 10-week CWT, this training method could be proposed as an exercise program that contributes to improved performance as a method of enhancing physical fitness and managing condition. It is expected that implementing diverse training programs that consider the specific exercise characteristics of individual sports climbing athletes, including appropriate intensity, as well as durations for rest, training, competition, and recovery periods, could further enhance functional performance in the future.