Effects of six weeks of sub-plateau cold environment training on physical functioning and athletic ability in elite parallel giant slalom snowboard athletes

Participants and ethical principles

The study required all athletes participating in this trial to be in good health and free from contraindications, such as cardiovascular disease, that would make them unfit for competitive training. Nine of the 12 elite snowboarding parallel giant slalom national team athletes were found to meet the inclusion criteria. These nine athletes did not suffer any injuries during the training and testing process and all athletes completed all of the training and testing in this study under the supervision of their coaches. The study was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of the Shanghai University of Sport (ethics number: 102772020127082). All athletes understood the content and process of the test and signed an informed consent form. Demographic information about the subjects is shown in Table 1.

Training arrangements

This training program was conducted six weeks before the Olympic Test Competition held in Chongli District (altitude: 1,878–2,031 m), Hebei Province, China. The athletes were trained six days per week (Monday to Saturday) from 9:00 am to 11:30 am in a cold, outdoor, sub-plateau environment (average temperature: −10 °C ∼−20 °C) with high intensity training in specialized skiing techniques. Each athlete made eight to 10 ski trips per morning (approximately 560 m/trip). In the afternoon (15:00 to 17:00), the athletes underwent medium-to-high intensity physical training at 1,500 m above sea level. The physical training programs consisted of low-to-medium intensity dynamic stretching, aerobic training, medium-to-high intensity explosive training in upper and lower body, and stability training. The training was followed by a conditioning break on Saturday afternoon and Sunday. The Polar Team Pro team heart rate monitoring system (Polar Team Pro, Finland) was used to monitor the intensity of the training load during the indoor physical training sessions and the outdoor ski-specific technical training sessions. The Polar Team Pro team heart rate monitoring system works by transmitting each athlete’s heart rate in real time to the coach’s iPad, who then provides verbal feedback to the athlete on their heart rate information. The weekly schedule for the specialized skiing techniques training and physical training is shown in Table 2.

Blood index test and procedure

Elbow venous blood was collected from athletes at 7:00 a.m. at the following timepoints: pre-training, week 2, week 4, and post-training. The blood samples were collected from the elbow vein using an ethylene diamine tetraacetic acid anti-coagulated vacuum blood collection tube for white blood cells (WBC), the percentage of lymphocytes (LY%), the percentage of mononuclear cells (MO%), the percentage of neutrophils (NE%), red blood cells (RBC), and hemoglobin (Hb) testing (Beckman Coulter AC Tdiff-2 hemocytometer; Beckman Coulter, San Jose, CA, USA). A total of 2.5 ml of elbow vein blood was collected using a sodium heparin anti-coagulated vacuum blood collection tube for analyzing blood urea (BU), creatine kinase (CK), testosterone (T), and cortisol (C) (Beckman Coulter Access 2 Immunosav System; Beckman Coulter, San Jose, CA, USA) (Elegańczyk-Kot et al., 2011).

Athletic ability assessment

Statistical analysis

All data were processed and analyzed using IBM SPSS Statistics 26.0 software (SPSS Inc., Chicago, USA). Data normality was verified using the Shapiro–Wilk test. The Shapiro–Wilk test showed that all athletes’ blood physiological and biochemical parameters and athletic ability data were normally distributed (p > 0.05). Repeated measures ANOVA was used to test the overall differences of blood physiological and biochemical indicators during the six weeks of sub-plateau cold environment training. Post hoc pairwise comparisons of differences between different time points of the same physiological and biochemical index were performed using the least significant difference (LSD) method. A paired-samples t-test was used to analyze the variability of athletic ability indicators before and after training in a sub-plateau cold environment. An independent samples t-test was used to compare the differences between groups for the same indicators. Effects sizes (ES) in the form of partial eta squared (${\eta }_{\mathrm{p}}^2$) were used from ANOVA output (Singh et al., 2022). The magnitude of effects for ${\eta }_{\mathrm{p}}^2$ was interpreted as small (<0.06), moderate (≥0.06−0.13), and large (≥0.14) (Cohen, 1992). Data are presented as means and standard deviations (mean ± SD), and p < 0.05 was considered to be a significant difference and p < 0.01 was considered to be a very significant difference.

Physical functional status

Athletic ability

Figure 1 shows that after 6 weeks of intervention, the relative maximal oxygen uptake (Fig. 1A) and snow race performance (Fig. 1D) of both males and females, as well as the 30 m sprint performance (Fig. 1C) of females were considerably higher than their pre-training levels (p = 0.000 − 0.007). In addition, Wingate 30 s relative mean power for both male and female athletes (Fig. 1B) and 30 m sprint performance for male subjects (Fig. 1C) were both noticeably higher than pre-training (p = 0.013 − 0.027). As for comparisons between gender, the male athletes were very significantly higher than the female athletes in all indicators of athletic ability (p = 0.000 − 0.001).

Effects of 6 weeks of sub-plateau cold environment training on the oxygen transport system of elite parallel giant slalom athletes

Snowboarding parallel giant slalom has a competition single trip skiing time of approximately about 35–45 s. Athletes who participate in this sport rely on glycolytic metabolism for energy supply and train and compete in cold alpine environments. There are significant differences in the physiological functions of the human body when exercising in altitude and cold environments compared to plains and ambient environments (Acosta et al., 2018; Brajkovic, Ducharme & Frim, 1998). Normally, when training at altitude, the body is more deeply stimulated than in a plain environment due to the relatively low oxygen concentration of the altitude environment (Ramos-Campo et al., 2018; Schmutz et al., 2010). RBC and Hb reflect the oxygen-carrying capacity of the blood and the functional status and their reserve levels in the body reflect aerobic metabolism. A number of studies have shown that plateau training can improve the aerobic metabolic capacity of athletes by increasing the density of skeletal muscle capillaries and the number of mitochondria, increasing blood volume and total Hb. This, in turn, enhances the ability of skeletal muscle to buffer BLA, oxidize fatty acids, utilize energy efficiently during exercise (Saunders et al., 2013; Tannheimer et al., 2010). In this study, the RBC and Hb of both male and female athletes were higher than pre-training in the other weeks of the 6 weeks sub-plateau cold environment training, except for the female athletes whose RBC and Hb were slightly lower at week 6. This effect suggests that the 6 weeks of training promoted the production of RBC and increased the RBC reserve, thereby possibly contributing to the enhancement of maximum oxygen uptake. In addition, the changes in RBC and Hb of the athletes in this study indicate that the oxygen transfer capacity of the subjects improved in contrast to the pre-training level, which is consistent with other studies observing the increase of Hb level and oxygen-carrying capacity of the Hb after plateau training (Bonne et al., 2014; Nummela et al., 2021; Wachsmuth et al., 2013). Furthermore, this study found that both RBC and Hb were significantly lower in female athletes than in males throughout the 6 weeks of training in a sub-plateau cold environment, suggesting that there are significant gender differences in human RBC and Hb production. Lastly, this study also found that the RBC and Hb levels of athletes were significantly higher than those engaging in summer Olympic sports (Ma, Gao & Li, 2019). This may be due to the fact that the cold hypoxic environment of the plateau stimulated the body’s erythropoietin (EPO) response (Kasperska & Zembron-Lacny, 2020; Wisniewska, Ploszczyca & Czuba, 2020).

Effects of 6 weeks of sub-plateau cold environment training on the immune system of elite parallel giant slalom athletes

The acute exposure to high altitude typically causes an inflammatory response in the body and reduces immunity, while long-term altitude training may improve the stability of the immune system (Aksel, Corbacioglu & Ozen, 2019; Gallagher & Hackett, 2004; Hackett & Roach, 2001). Several studies have shown that short or intermittent plateau hypoxia exposure rapidly activated the sympatho-adrenal system to regulate the activity of immune cells and the secretion of related cytokines (Jung, Kim & Park, 2020; Park et al., 2020; Svendsen, Hem & Gleeson, 2016), while longer plateau training or hypoxia exposure may affect the immune system by regulating the proliferation and differentiation of immune cells via the hypoxia-inducible factor (HIF) signaling pathway (Domingo-Gonzalez et al., 2017; Taylor & Colgan, 2017; Wang, Huang & Gao, 2021). The proliferative capacity of T lymphocytes and the activity of NK cells are suppressed at the beginning of the hypoxia exposure (Facco et al., 2005; Morabito et al., 2016), the activity of NE cells is increased (Chouker et al., 2005; Wang et al., 2019), and the body experienced a certain inflammatory response. In contrast, after prolonged hypoxia and plateau training, the expression of CD55 and CD59 on the surface of leukocytes and CD4/CD8 of T lymphocytes increases, which in turn improves the regulatory function of the immune system (Wang, Huang & Gao, 2021). Theoretically, when training in a hypoxic environment on the plateau, the lack of oxygen combined with the training load causes the athelete enough stimulation. Once cold is added to the stimulation, the organism is subjected to a more serious burden, and the function of the organism’s systems will undergo more complex changes. However, little research has been reported on these changes. In one study, however, the results demonstrated that when training in hypoxic and cold environments at plateau, the body may experience a series of physiological stress responses similar to those seen when training at plateau or in hypoxic environments, such as a decrease in WBC and LY% reflecting immune function, and an increase in NE% reflecting inflammation during early training in cold environments on the plateau (Thompson-Torgerson et al., 2007). In our study, WBC and LY% were lower at week 2 of training in a sub-plateau hypoxic cold environment prior to the Olympic Games Test Competition compared to pre-training, while MO% and NE% were higher than pre-training, indicating that the athletes’ immune system function was somewhat suppressed and the body experienced a certain inflammatory response during the first 2 weeks of training. Moreover, from week 4 to 6, the LY% level gradually increased and was higher than pre-training at the end of the sub-plateau hypoxic cold training, which was suggestive of recovery. On the other hand, WBC increased at week 4 and remained lower than pre-training at the end of the sub-plateau hypoxic cold training, while MO% and NE% gradually decreased from week 4 to the end of the training. This is generally consistent with Gao et al. (2018) and Wang, Huang & Gao (2021), who reported the changes in indicators such as WBC, LY%, MO%, and NE% in rowers during hypoxic training. Therefore, the elite parallel giant slalom athletes’ bodies adapted to the training load and the hypoxic cold environment of the sub-plateau, the stability of the regulatory functions of the body systems improved, immunity gradually recovered, and the inflammatory response was progressively reduced during the training period.

Effects of 6 weeks of sub-plateau cold environment training on the musculature of elite parallel giant slalom athletes

Previous studies have found that the human body becomes less adapted to training at the early stage of sub-plateau training, as indicated by increased protein and amino acid catabolism and BU and CK levels (Wang, Gao & Gao, 2013; Yu et al., 2016). As the body adapts to the plateau training environment, the BU and CK levels gradually stabilize and change regularly with the training volume or intensity (Li & Wang, 2017; Zhang, Gao & Zhu, 2017). In our study, the CK for both genders and BU for male were lower at week 2 compared to pre-training. This is consistent with Wang, Gao & Gao (2013), who reported the same change in blood BU and CK levels in rowers when training at plateau for longer than 1 week. As for this phenomenon, this may be related to the adaptation of the athletes’ body to the hypoxic environment of the plateau and the improved ability of the body to withstand the training load. In addition, the BU and CK levels of both male and female in this study were significantly higher at the end of week 6 compared to pre-training and week 4, which may be related to greater stimulation of the athlete’s body caused by the 6-week multiple competition-intensity specific skiing technique training. Further analysis revealed that although elite parallel giant slalom athletes’ BU and CK were significantly higher at the end of week 6 of training, they were still in the normal range. BU and CK did not significantly exceed the normal range during the last 2 weeks of high intensity training, and the body remained stable in terms of the functional status and muscle fibers. This indicates that training adaptation ability of the athletes’ body also improved during this process, though the stimulation of the training load on the body gradually deepened with the increase of the training load. Previous studies have shown that prolonged hypoxic exposure can promote HIF-1 gene expression and induce adaptive changes in the body to the hypoxic environment and improve exercise performance (Cimino et al., 2012; Rocco et al., 2014; Yeo, 2019). As a result, prolonged and repeated cold stimulation can promote adaptation through adrenergic and non-adrenergic mechanisms and reduce the physiological fluctuations during exercise in cold environments (Castellani & Young, 2016; Saltykova, 2016; Young & Castellani, 2007).

Effects of 6 weeks of sub-plateau cold environment training on the endocrine system of elite parallel giant slalom athletes

T has the function of promoting anabolism in the body, inhibiting the breakdown of muscle glycogen and activating glycogen synthesis, increasing muscle glycogen and creatine phosphate reserves, and enhancing immunity and resistance to bacterial infection (Chiu et al., 2015; Ouergui et al., 2016). In contrast, the main role of C is to accelerate the breakdown of fats and proteins into sugars, and accelerate catabolism (Ouergui et al., 2016; Pesce et al., 2015). T and C reflect anabolism and catabolism from different perspectives, and can be used to assess the effect of training load on an athlete’s functional status. The training loads in different environments have unique effects on the body. When exercising in hypoxic or cold environments on the plateau, the athletes were stimulated by the training load and experienced the hypoxia and cold stimuli (Ramos-Campo et al., 2018; Schmutz et al., 2010). Wang (2020) showed that elite modern pentathletes had a high anabolic capacity and peak serum T levels during the sub-plateau adaptive training phase of moderate intensity training, while a certain decrease in serum T occurred during the increased sub-plateau training load phase. These results suggested that changes in serum T in athletes were associated with training load during the subalpine period. Zhao, Li & Lu (2008) showed that the serum T and C of male weightlifters decreased significantly at the beginning of sub-plateau training compared to the pre-training period, increased slightly at the middle of training period, and decreased slightly at the end of sub-plateau training. Serum T and C were lower throughout the sub-plateau training period compared to the pre-training period. Zhao, Li & Lu (2008) concluded that this was related to the greater maladjustment of the body to the training load and plateau environment during sub-plateau training in male weightlifters. In our study, serum T and T/C levels were significantly lower in both males and females during the first 2 weeks of training in a sub-plateau cold environment compared to the pre-training period, while serum C was significantly higher compared to the pre-training period. These results suggested that the training load at the beginning of training, combined with the hypoxic and cold plateau environment, caused some pressure to the participants’ body. From weeks 4 to 6, the athletes’ serum T and T/C gradually increased rather than decreasing due to the increase in training load. These results suggest that as the training progressed, the body systems gradually adapted to the sub-plateau cold environment. Moreover, the anabolic levels of the elite parallel giant slalom athletes improved and the physical function status was higher after 6 weeks of training in a sub-plateau cold environment.

Effects of 6 weeks of sub-plateau cold training on the aerobic metabolic capacity of elite parallel giant slalom athletes

The existing studies concerning plateau or hypoxic training have demonstrated that plateau or hypoxic training lasting 3 weeks or more could increase the RBC and Hb counts of the athletes, improve oxygen transport capacity, enhance the removal of BLA, thereby improving aerobic metabolic capacity (Bonne et al., 2014; Saunders et al., 2013; Shaw et al., 2020; Tannheimer et al., 2010; Wachsmuth et al., 2013). It has been shown that plateau or hypoxic training not only improves indicators related to oxygen transport and oxygen utilization capacity (e.g., EPO, Hb, RBC, 2, 3-DPG) but also promotes maximal oxygen uptake and specific aerobic athletic ability (Gao et al., 2018; Liu & Zhang, 2015; Wang, Gao & Gao, 2013). Our results showed that 6 weeks of training in a sub-plateau cold environment resulted in a significant increase in the relative maximum oxygen uptake levels in elite parallel slalom athletes. The data suggested that 6 weeks of specialized ski technique training and physical training in a sub-plateau cold environment may improve aerobic metabolism capacity. This trend was also consistent with the changes of RBC and Hb levels. RBC and Hb levels remained elevated and stable after training, and there was a significant increase in maximum oxygen uptake. This was also consistent with the findings of Wang, Gao & Gao (2013) that sub-plateau training could improve rowers’ RBC and Hb levels and improve their aerobic metabolism capacity. Therefore, it could be concluded that this training was effective in improving the aerobic metabolism capacity of athletes in snowboarding parallel giant slalom.

Effects of 6 weeks of sub-plateau cold environment training on anaerobic metabolic capacity in elite parallel giant slalom athletes

Some studies have shown that plateau or hypoxic training enhances aerobic metabolism and promotes anaerobic metabolism (Bădău et al., 2016; Christoulas, Karamouzis & Mandroukas, 2011; Holmberg, 2015). Hypoxia can induce the expression of HIF-1 and HIF-1-related genes (Cimino et al., 2012; Yeo, 2019). As a DNA-binding protein, HIF-1 induces an increase in the expression of several genes, including glycolytic metabolism enzymes, which promotes adaptation to hypoxic environments (Tang & Jiang, 2004). Semenza & Wang (1992) showed that both EPO-synthesizing Hep3B cells and non-EPO-synthesizing HeLa cells were induced by hypoxia to increase mRNA transcription of three key enzymes of glycolytic metabolism, aldolase A (AL-DA), phosphofructokinase (PFK), and pyruvate kinase (PK). Therefore, it can be suggested that hypoxia may promote an increase in glycolytic metabolic enzymes induced by hypoxia via the induction of HIF-1 expression. Wang (2013) and Li (2014) showed that hypoxic training stimulated the body more deeply and improved BLA levels of athletes compared to training in a normoxic environment. Their studies confirmed that 3 to 4 weeks of hypoxic training can improve anaerobic levels in boxing and sparring athletes who are mainly energized by anaerobic glycolytic metabolism. This may improve the specific athletic ability of these athletes. In addition, some studies have shown that 4 weeks of hypoxic training can significantly improve the levels of all indicators of the Wingate 30 s anaerobic work test in aerobic and cycling athletes, and can promote the reduction of BLA and CK levels (Li, 2020; Ma et al., 2013). In our study, subjects had significant improvements in anaerobic exercise capacity such as Wingate 30 s anaerobic power levels and 30 m sprint runs, as well as significant improvements in competition performance. These results indicate that the 6-week training was beneficial to improving anaerobic metabolism and increase competitive performance.

Limitations

The aim of this study was to investigate the effects of six weeks of training in a sub-alpine cold environment on the physical functioning and athletic ability of elite snowboarding parallel slalom athletes. This study showed that elite national snowboarders had significant improvements in aerobic and anaerobic capacity and race performance after six weeks of medium intensity physical training and high intensity ski-specific technical training in a sub-alpine cold environment. The small sample size of this study (only nine elite national team snowboarding parallel giant slalom athletes) is a limitation of this study that may impact the generalizability of the results. However, as there are only nine athletes in the entire snowboarding parallel giant slalom national team, these athletes are some of the best snowboarding parallel giant slalom athletes in China. Therefore, this study may provide some reference value for the national team in the future in terms of training methods, even for athletes of other competitive levels and other winter snow sports. Of course, in order to improve the applicability of the training methods in this study and to provide a greater reference value for other sports, we believe that the sample size of the study should be expanded. It would be of value to conduct a randomized controlled trial based on this (e.g., both the test group and the control group use the same training arrangement, with the test group training in a cold sub-alpine environment and the control group training in a plain environment) to investigate the extent that the content and the training environment improved athletic performance, respectively.