Effects of post-exercise cold-water immersion on performance and perceptive outcomes of competitive adolescent swimmers

There is increased demand in the competitive swimming field to explore aspects related to training biomechanics and physiology for performance enhancement (Crowley et al. 2017). Resistance training is commonly practiced before swimming training sessions and has been recommended to be included as part of training routine instead of high volume of swimming training alone (Crowley et al. 2017). Strength training or swimming-specific dry-land training programs have shown benefits in enhancing swimming performance (Girold et al. 2007; Aspenes and Karlsen 2012; Arsoniadis et al. 2022), but they also result in increased rating of perceived exertion (RPE) and acute physiological and biomechanical alterations (Arsoniadis et al. 2019). Therefore, researchers have been investigating the stress-recovery balance mainly by means of post-exercise recovery strategies aiming at the return of metabolic and neuromuscular function (Kellmann et al. 2018).

In this scenario, cold-water immersion (CWI) stands out because of its relatively low cost and easy applicability. The implementation of post-exercise CWI between dry-land resistance training and swimming training can be the key to this stress-recovery balance, since it has been suggested that CWI may improve subsequent training load and quality (Barnett 2006; Kellmann 2010). Previous studies have extensively researched CWI acute responses (Chaillou et al. 2022) and found significant improvements in delayed-onset muscle soreness (DOMS) (Batista et al. 2023) and general RPE (Hohenauer et al. 2015). However, CWI has been frequently used by coaches and athletes regardless of physiological and scientific rationale (Allan et al. 2021). Considering that the period between resistance and swimming training needs to be adequate to facilitate performance improvements (Arsoniadis et al. 2022), CWI could be an asset to enhance swimmer’s recovery.

Since athletes are constantly exposed to high training loads, researchers are currently interested in the effects of repeated use of CWI (Ihsan et al. 2021; Tavares et al. 2020, 2019; Chaillou et al. 2022) and its possible detrimental effects on training adaptations (e.g., decreased functional performance, and impaired hypertrophy), mainly because its effects on exercise-induced muscle damage is still controversial (Broatch et al. 2018). However, studies found no harm to performance when CWI was applied repeatedly (Tavares et al. 2020; Halson et al. 2014; Rowsell et al. 2011). In fact, recent research suggests that CWI may actually improve endurance performance, and discrepancy between findings may be found because different types of training (e.g., resistance, endurance and sprint exercises) may be affected differently (Chaillou et al. 2022; Malta et al. 2021; Ihsan et al. 2021). Although CWI may decrease swim performance immediately after its application (Parouty et al. 2010), 2 weeks of daily application have shown to improve sleep quality, reduce muscle soreness and promote faster return to homeostatic parasympathetic activity (Al Haddad et al. 2012). If CWI could improve swimmers’ perceptions of recovery from resisted exercises and, consequently, swimming training quality, we may be able to observe enhancements in different aspects of performance, such as power measured by functional tests and, ultimately, swim performance.

Researchers are recommended to use an integrated approach to evaluate post-exercise recovery (Kellmann et al. 2018; Micheletti et al. 2019). The evaluation of functional tests, for example, provides a more comprehensive understanding of the athletes’ overall physical capabilities (Smith et al. 2017) and enables the isolation of the specific effects of CWI on swimming performance. It also may offer valuable insights for coaches, professionals and athletes by identifying areas for improvement that extend beyond the scope of traditional swimming assessments. Moreover, because performance is the main goal in sport, perceptive outcomes are usually neglected. Due to the multifactorial nature of recovery, studies should investigate both physiological and psychological outcomes by integrating a method that explores different aspects of performance as well as perceptive variables (Kellmann et al. 2018; Micheletti et al. 2019). This approach has been previously used in swimmers and suggested to contribute to a better understanding of post-exercise recovery process (Carvalho et al. 2023). Therefore, our objective was to investigate the effects of repeated use of CWI, compared to thermoneutral water immersion (TWI) and passive recovery (PAS), on performance and perceptive outcomes of competitive adolescent swimmers. We hypothesized that CWI would improve both swimmers’ perceptions and performance, while PAS and TWI would not provide changes on any outcome.

The analysis utilized data from 20 participants who completed all three interventions. However, due to missing data, the total number of participants considered for each intervention varied: 19 for CWI, 16 for TWI, and 16 for PAS. These dropouts were attributed to participants missing one or both testing sessions within specific conditions (Fig. 1).

We monitored the training load throughout the study due to the crossover design. Our repeated measures ANOVA of internal training loads found no significant main effects and, therefore, we can ensure that all interventions were performed under the same conditions (Supplementary file 2).

Table 1 presents the detailed results of interventions on performance outcomes. There were no interaction effects (intervention*time) for swim or functional performance outcomes. We only observed time effects for sprint time (p = 0.01) and FINA points (p = 0.01) of which, regardless the intervention, the athletes improved swim performance at post-intervention compared to baseline (Fig. 3). We found no significant main effects for any functional performance outcomes.

Figure 4 presents the results of swimmers’ perceptions regarding the 100-m sprint. As expected, there was a time effect (p < 0.01) for all perceptive outcomes in which the last stages of the sprint yielded the worst perceptions as observed by the increased chances of reporting pain, poor well-being, discomfort, tiredness and heaviness. There was a main intervention effect for pain (p = 0.04) and tiredness (p = 0.04); however, when looking at post-hoc comparisons, we observed no differences between interventions. No significant intervention*time interaction effects were observed.

After the trial, the participants were asked regarding their preference between the recovery interventions. Thirteen athletes (65%) felt more recovered after CWI, four athletes (20%) preferred TWI, and three athletes (15%) found both CWI and TWI effective. None of the athletes preferred passive recovery.

This study aimed to investigate the effects of repeated use of CWI in competitive adolescent swimmers compared to control and placebo. Our main finding showed that repeated use of CWI during a training week did not change functional (flexibility, shoulder proprioception, lower and upper body power) nor swim performance (100 m freestyle sprint time). We also found a main intervention effect for pain and tiredness during the sprint.

Considering training-recovery balance, the interest in the effects of repeated use of CWI has risen considerably in order to speed-up recovery and improves training quality (Ihsan et al. 2021). Our results did not support our initial hypothesis that the repeated use of CWI between resistance and swim training would improve swim performance. Nevertheless, our results also do not support the belief that CWI could impair training adaptations (Kwiecien and McHugh 2021; Yamane et al. 2006), as we observed improvements in swim performance (sprint time and FINA points) regardless of intervention. This finding corroborates previous studies that found similar improvements in cycling performance between repeated use of CWI and passive recovery (Aguiar et al. 2016; Halson et al. 2014; Vaile et al. 2008).

Similarly, we found no differences in functional performance outcomes (flexibility, power, and proprioception) among interventions. The evaluation of these variables provides a more nuanced and detailed analysis of the impact of CWI on various aspects of athletic performance. A systematic review found that the repeated use of CWI decreased performance gains for 1RM (one-maximal repetition), maximal isometric strength and endurance (Malta et al. 2021), parameters which were not assessed in our study. In addition, it is worth noting that the duration of the CWI protocols in the studies included in this analysis ranged from four to 12 weeks. Other studies, applying CWI for 3 weeks, reported favorable effects of CWI on countermovement jump performance in volleyball (Tavares et al. 2020) and rugby (Tavares et al. 2019) athletes. Given these findings, it appears that a one-week evaluation may not provide sufficient time to observe changes in these functional parameters and, therefore, future studies assessing the effects of long-term CWI on swimmers are needed.

It is also important to emphasize that a neutral result should not be underestimated and, perhaps, the benefit of the cold is elsewhere (e.g., perception outcomes). Ihsan et al. (Ihsan et al. 2021) support the current findings highlighting that, when time to recovery is limited, CWI can improve training performance which might outweigh possible decrements to hypertrophy, especially when hypertrophy is not the main goal. For instance, our examination of perceptive outcomes during sprints revealed main intervention effects for pain and tiredness without significant post-hoc comparisons, which usually happens due to lack of statistical power. Although not significant, a trend for reduction of pain over the last strokes was observed favoring CWI in relation to PAS (p = 0.05). We believe that the repetitive use of CWI may help athletes feel more tolerant to pain, given its documented advantages in alleviating muscle soreness (Batista et al. 2023) and increasing pain threshold (Klich et al. 2018). These benefits could potentially be enhanced with a repeated application protocol. As training progresses and symptoms become more frequent, the impact of CWI could potentially become more pronounced.

Interestingly, pain perception did not differ between CWI and TWI. In the present study, we led participants to believe that TWI with the skin cleanser solution would be beneficial for post-exercise recovery. A placebo intervention can elicit expectations and promote health benefits via brain-body responses, thereby, contributing to perception of recovery (Wager and Atlas 2015). This was confirmed by the preference for TWI expressed by 20% of the participants. In fact, some athletes might not tolerate CWI protocols which can affect post-training experiences and, therefore, their opinion should be considered during the decision making of interventions to be used.

Some researchers discuss the appropriateness of the use of CWI in sight of its modest effect sizes (Wilson et al. 2021). One of the aims of recovery strategy is to improve the athlete’s experience between training stimuli so they can be recovered not only physically but also psychologically, by promoting general well-being. CWI is known to anticipate metabolic and autonomic recovery after exhaustive exercise (Bastos et al. 2012) in addition to reduce fatigue and swelling, which may alleviate perceptions of discomfort, thereby allowing participants to perform better during training sessions (Roberts et al. 2014). Despite our results not affirming this rationale through the absence of improvements in performance outcomes, it gains support from the high acceptance rate among swimmers, as none favored passive recovery, while 65% expressed a preference for cold-water immersion.

Some strengths and limitations of the present study should be addressed. The crossover design can be considered as a strength, since it allowed assessing the same sample in different conditions/interventions, but it restricted the intervention duration to a single week. Although it was enough time to observe performance enhancements in response to training, it may not be sufficient to study differences between experimental conditions. The study included individuals from 12 to 20 years old which may be a heterogeneous sample considering hormonal differences and, therefore, these results may not be extrapolated to the adult population. However, considering that this age range is a decisive period for preparation to elite competition we believe that our results may help coaches to improve adolescent swimmers training. Although we provided participants with instructions, we could not guarantee they gave their best when performing performance tests or rating their perceptions. Finally, swimmers could be conditioned to water immersion, which possibly influenced our findings and, therefore, this should be considered when extrapolating these results to other sports.

The debate surrounding the implementation of post-exercise recovery programs for competitive athletes persists, with the objective of optimizing their performance. Although CWI is a commonly used post-exercise recovery intervention, studies in the literature present inconclusive results regarding its effectiveness, especially because training characteristics are not considered when implementing it. When applied during training sessions, we did not observe detriments in performance, and athletes felt more recovered after doing CWI or TWI, in comparison to PAS (no intervention), emphasizing the importance of recovery in training routines.

In summary, we found that the repeated use of CWI throughout a training week did not impact functional or swim performance outcomes of competitive adolescent swimmers. Although perceptive outcomes during sprinting were also similar across interventions, athletes indicated a preference for both CWI and TWI in relation to PAS. Professionals and coaches may consider incorporating CWI as a recovery intervention for competitive adolescent swimmers during training weeks, with a focus on enhancing recovery rather than explicitly aiming for performance improvements. However, it is imperative to consider the athletes’ preferences and tolerance when incorporating CWI into their recovery protocols.