Introduction

Throwing performance, including velocity and accuracy, is crucial in baseball (Freeston and Rooney, 2014). During routine training or competition, baseball athletes repeatedly exert maximal throwing efforts with brief recovery periods. Hence, it is crucial to explore potential ergogenic aids that can assist baseball players in achieving excellent repeated throwing performance and accelerating recovery between rest intervals. This is essential for preventing performance decrements and succeeding in competition.

During baseball training or competition, athletes commonly apply ice packs directly to their shoulders or arms during rest intervals to alleviate discomfort from high-intensity exercise. Gradually, cooling strategies are frequently used as ergogenic aids in baseball games. In a study, Verducci (2001) applied 3 min of cooling treatments using ice packs filled with ice cubes to the shoulder and the forearm of six pitchers between four innings of 22 pitches per inning. The cooling strategy increased mean pitching velocity, whereas no differences were noted in accuracy. In a repeated-measures crossover design study, Bishop et al. (2016) instructed eight pitchers to pitch five innings including 12 pitches per inning in a simulated baseball game, separated by 6 min of the recovery period with local cooling on the deltoid muscle and the forearm of the pitching arm for 4 min or without cooling. That study found that intermittent local cooling attenuated velocity loss in baseball pitching and lowered the rating of perceived exertion (RPE) (Bishop et al, 2016). Previous research suggests that pain relief and diminished tissue temperature from intermittent local cooling may account for the attenuated velocity loss and facilitated recovery during repeated pitches (Bishop et al., 2016; Verducci, 2001). However, Huang et al. (2021) revealed that cooling interventions during real games may be limited because most pitchers prefer to keep their pitching arms warm rather than cold between innings. Furthermore, during short-term, explosive exercise, it is important to maintain the working muscles within the optimal temperature range (Olberding and Deban, 2017). If the muscles cool significantly, both concentric and eccentric isometric strength, as well as explosive strength, decreases (Cross et al., 1996; Ruiz et al., 1993). This may be due to vasoconstriction and reduced calcium release from the sarcoplasmic reticulum, impairing crossbridge formation (Ruiz et al., 1993). Additionally, it may impede the sensitivity of the neuronal discharge and diminish the sensitivity of muscle spindles, which in turn affects muscle contractile function (Ruiz et al., 1993). Therefore, direct cooling working muscles may not be beneficial for explosive movements.

Cooling working muscles directly can reduce performance, and hence, some have examined the benefits of cooling peripheral extremities, such as palms (Caruso et al., 2015; Grahn et al., 2012; Kwon et al., 2010) and feet (Cai et al., 2021), instead of the muscles themselves to avoid performance reduction due to decreased muscle temperature (Cross et al., 1996; Ruiz et al., 1993). These areas have abundant arteriovenous anastomoses and are sensitive to cold (Walløe, 2016). Therefore, peripheral cooling may maintain the facilitation of A-alpha motor neurons mediated by the activation of the cutaneous cold receptors (Manuel and Zytnicki, 2011), potentially causing a higher afferent stimulus (De Keyser et al., 2018). Although the mechanism of peripheral cooling in increasing strength performance is unclear, it seems to elicit a higher arousal level (Hopkins et al., 2002; Palmieri-Smith et al., 2007; Pietrosimone and Ingersoll, 2009; Wu et al., 2021, 2023), increase motor unit recruitment (Cai et al., 2021; Kwon et al., 2010; Wu et al., 2021), and delay the onset of fatigue (Caruso et al., 2015; Kwon et al., 2010; Wu et al., 2023), which may be the reason for its effectiveness.

During exercise, palm cooling (PC) is a more convenient and easily implemented method. Previous studies have determined that intermittent PC increased the number of repetitions and total exercise volume during a 4-set 85% of 1-repetition maximum (1RM) bench press workout accompanied with a reduced RPE (Kwon et al., 2010), increased the number of repetitions to failure in pull-up exercise (Grahn et al., 2012), and delayed the average power decrements in a 4-set 8-repetition of concentric flywheel leg press resistance exercise at a submaximal level of effort with hastened blood lactate clearance (Caruso et al., 2015). These findings indicate that intermittent PC has a beneficial effect on strength performance. Baseball throwing is an exercise that requires explosive strength. However, the effect of PC on baseball throwing speed is uncertain.

Furthermore, previous studies examining the impact of PC on exercise performance have excluded participants who did not experience or report cooling-induced pain sensation (Caruso et al., 2015; Grahn et al., 2012; Kwon et al., 2010). Pain can induce changes in motor performance, motor unit recruitment, and rate coding that varies across different contraction speeds (Martinez-Valdes et al., 2021). Given that cooling-induced pain varies individually (Soeda et al., 2021), and cooling reduces force production in the presence of pain (Chi et al., 2012; Roatta and Farina, 2011), it is important to evaluate the effect of PC on explosive power performance categorized by cooling-induced pain. Moreover, considering that hand cooling has been shown to decrease fingertip dexterity and hand gross movement (Cheung et al., 2008, 2023) and muscle contraction due to shivering disrupts fine motor control (Wakabayashi et al., 2015), the effect of PC on throwing accuracy should be further investigated.

Within this framework, this study aimed to investigate whether the application of intermittent PC would have an ergogenic effect on throwing velocity and examine whether PC would affect throwing accuracy. Perceptual responses during the workout were measured as a secondary outcome. The results were divided into two groups based on whether the participants experienced pain from cooling. We hypothesized that PC would increase baseball throwing velocity, but decrease throw accuracy in participants who did not feel cooling-induced pain and decrease baseball throwing velocity and throw accuracy in participants who felt cooling-induced pain.

Methods

Study Design

This study was conducted for 3 days during the off-season period, including 1 day of familiarization followed by 2 days of experimental sessions. A randomized, counterbalanced, within-group research design was used to compare the effects of PC and test our hypotheses. During each experimental session, participants were instructed to aim at the target as accurately as possible and throw with maximal speed. The target was 18.75 m away (distance between the pitcher’s mound and the home plate). The throwing protocol consisted of five sets (3-min interval) of 10 fastballs, totaling 50 throws, under NC and inter-set PC conditions, within a 5-d interval.

To further explore the potential effect of PC-induced pain on experimental results, participants experiencing varying levels of pain during the PC process were categorized into the no pain group (NPG) and the mild-to-moderate pain group (PG) according to the 4-point verbal rating scale (VRS) score (Relvas et al., 2016) measured after the PC condition for statistical analysis (Figure 1).

Figure 1

Schematic diagram of the experimental testing protocol and the flow chart of data analysis.

FAS = felt arousal scale; RPE = rating of perceived exertion; VRS = verbal rating scale

Results

After classifying by pain, this study included 10 NPG (point 0, n =10, no pain) and 12 PG (point 1, n = 6, mild pain; point 2, n = 6, moderate pain; point 3, n = 0, severe pain) adult participants. The demographic data are presented in Table 1.

Figure 2 shows that for the NPG, PC treatments resulted in significantly higher mean throw velocity (107.9 ± 9.9 vs. 106.9 ± 10.2 km/h, t = 2.071, p = 0.034, ES = 0.323), maximal throw velocity (112.5 ± 9.0 vs. 111.2 ± 9.8 km/h, t = 2.112, p = 0.032, ES = 0.331), and throw accuracy (48.8% ± 7.1% vs. 42.6% ± 7.7%, t = 3.615, p = 0.003, ES = 0.566) compared with the NC condition. However, for the PG, PC treatments resulted in significantly lower mean throw velocity (101.0 ± 11.1 vs. 105.2 ± 10.5 km/h, t = −2.959, p = 0.007, ES = 0.443) and maximal throw velocity (105.0 ± 10.8 vs. 108.7 ± 9.8 km/h, t = −2.836, p = 0.008, ES = 0.422) when compared with the NC condition, and no significant difference in throw accuracy between the PC and NC conditions (38.5% ± 2.2% vs. 43.0% ± 2.1%, t = −1.497, p = 0.08, ES = 0.157).

Figure 2

Individual (dotted lines, open circles) and average (solid line, filled circle) throwing performance under NC and PC conditions with the individual values. (a) Mean throwing velocity in participants classified as experiencing no pain (n = 10) by the verbal rating scale (VRS) after the PC condition; (b) Mean throwing velocity in participants classified as having mild or moderate pain (n = 12) by the VRS after the PC condition; (c) Maximal throwing velocity in participants classified as experiencing no pain (n = 10) by the VRS after the PC condition. (d) Maximal throwing velocity in participants classified as having mild or moderate pain (n = 12) by the VRS after the PC condition; (e) Mean throwing accuracy in participants classified as experiencing no pain (n = 10) by the VRS after the PC condition; (f) Mean throwing accuracy in the participants who were classified as having mild or moderate pain (n = 12) by the VRS after the PC condition

Two-way ANOVA and post-hoc analysis of FAS and RPE data (Table 2) revealed that the NPG exhibited significantly higher FAS under the PC than the NC condition (F = 7.484, p = 0.23, ES = 0.454). However, for the PG, there was no significant main effect of condition on the FAS score (p = 0.91). A significant main effect was only observed in the set (F = 7.075, p < 0.001, ES = 0.391; Table 2).

For RPE data, comparisons between PC and NC conditions showed significantly lower RPE values in both the NPG (F = 26.561, p = 0.001, ES = 0.747) and the PG (F = 33.702, p < 0.001, ES = 0.754). Additionally, RPE values increased significantly during the throwing workouts in both the NPG (main effect of set, F = 31.171, p < 0.001, ES = 0.776; Table 2) and the PG (main effect of set, F = 31.138, p < 0.001, ES = 0.739; Table 2).

Discussion

The present study used intermittent PC at 10°C for 2.5 min as an ergogenic cooling strategy. The strategy of peripheral cooling has been demonstrated to improve muscle strength performance (Cai et al., 2021; Kwon et al., 2010; Wu et al., 2021). In contrast, in this study, a cooling temperature of 10°C seemed to reach the 15°C cooling-induced pain threshold (Barati et al., 2017). Individual differences in cooling-induced pain could affect strength performance (Chi et al., 2012; Roatta and Farina, 2011), thus participants were divided into a NPG (n = 10) and a light-to-moderate PG (n = 12) for analysis. To the best of our knowledge, this study is the first to investigate the effect of various levels of PC-induced pain on baseball throwing performance. The primary findings of this study mostly confirmed our research hypothesis, indicating that intermittent PC increased arousal levels and enhanced both the mean throwing velocity and maximal throwing velocity in skilled baseball athletes who did not experience pain following intermittent PC treatment. However, intermittent PC decreased the mean throwing velocity and maximal throwing velocity in trained baseball athletes who experienced pain after intermittent PC treatment. Interestingly, intermittent PC increased throwing accuracy in trained baseball athletes who did not experience pain.

In the present study, the NPG participants exhibited higher arousal levels under the PC than the NC condition. Although the present study did not delve into the precise mechanisms of how arousal would affect strength, previous research has indicated that elevated arousal levels can enhance motor cortex excitability (Hajcak et al., 2007). Additionally, Schmidt et al. (2009) conducted a functional magnetic resonance imaging study to investigate the effect of arousal on motor command and force production. Their findings demonstrated that the arousal-related brain regions contributed to motor command and facilitated force production. Those researchers suggested that heightened arousal levels could benefit sports requiring maximal power, where performance could thus be enhanced in highly arousing situations. The present study found that cooling the palm during repeated baseball throwing had a similar effect on arousal levels to cooling the feet in a previous study (Wu et al., 2021, 2023). It has been observed that elevated arousal by foot cooling plays an ergogenic effect on lower limb strength performance (Wu et al., 2021). Conversely, PC yielded an ergogenic effect on strength performance in high-intensity bench press workouts and flywheel leg press exercises (Caruso et al., 2015; Kwon et al., 2010). Extending from previous studies that have found that PC is beneficial to strength performance, the present study further demonstrates that PC enhances throwing velocity, including mean and maximal throwing velocities, which are indicators of explosive strength performance. The intermittent PC increased both maximal and mean throwing velocity, indicating enhanced peak power performance and anti-fatigue by maintaining a higher average baseball throwing velocity during repeated throwing exercises. Moreover, unexpectedly, PC increased throwing accuracy, contrary to previous findings that hand cooling at 10°C for 5 min significantly decreased fingertip dexterity and hand gross movement (Cheung et al., 2023) and affected the accuracy of shoulder flexion performance due to cold shivering (Meigal et al., 1998). Methodological differences, such as cooling sites (palm vs. hands and forearms) and duration (immersion for 2.5 min vs. 5 min) may contribute to the observed discrepancy. Our study findings suggest that intermittent brief PC may not induce hypothermia or trembling in participants who do not experience cooling-induced pain, and therefore does not affect exercises requiring accuracy. The data in this study provided limited evidence to explain the exact mechanism of how PC increases throwing accuracy. Given that the optimal arousal level benefits sports requiring accuracy (Doyle et al., 2016), it is plausible that the moderately increased arousal levels in the present study may provide some rationale. In addition, compared to a previous study on baseball throwing using intermittent cooling of arms and shoulders without increasing accuracy (Verducci, 2001), the present study suggests that applying PC is a more effective strategy for improving the accuracy of baseball throwing.

In contrast, an opposite outcome was noted in throwing performance between PG and NPG players, exhibiting a decrease in both maximal throwing velocity and mean throwing velocity. The decrease in force production due to cooling is often accompanied by cooling-induced pain (Chi et al., 2012; Roatta and Farina, 2011) and a reduction in cutaneous sensory feedback (Caminita et al., 2020), which depends on cooling temperature and duration. As demonstrated by Roatta et al. (2011), pain caused by cooling decreases electrically stimulated muscle force. Another similar investigation observed that strength was reduced in the presence of pain (Chi et al., 2012). Caminita et al. (2020) also reported that reducing cutaneous sensory feedback by peripheral cooling at foot soles at 0°C for 15 min decreased squat jump height and vertical ground reaction force. Although pain data were not available in the study, previous investigations using the same cooling temperature and duration have shown that cooling-induced pain typically occurs (Chi et al., 2012; Roatta and Farina, 2011). This pain may decrease explosive performance by interfering with afferent stimulus to cutaneous cold receptors, resulting in reduced activation of A-alpha motor neurons. Regarding throwing accuracy, intermittent PC did not significantly affect the PG participants, supporting the idea that increased arousal levels may be partly responsible for the improved accuracy in the NPG. However, the present study found that half of the participants (Figure 2f) decreased throwing accuracy under the PC condition. Therefore, more attention should be paid when practically applying PC to training.

Various intermittent cooling strategies have been demonstrated to reduce the RPE during exercise, such as resistance exercise (Kwon et al., 2010), high-intensity exercise (De Koning et al., 2011), and baseball throwing (Bishop et al., 2016; Verducci, 2001). Previous research has shown that perception of effort is a key element in the development of fatigue, and improvements or impairment of performance are partly mediated by it (Pattyn et al., 2018). Performance improvements during repeated exercises are often accompanied by decreases in the RPE (Kwon et al., 2010; Verducci, 2001), and high-intensity exercise is partly regulated by the RPE (De Koning et al., 2011). Intermittent cooling strategies made participants feel like they were exerting less effort during exercise, and facilitated recovery, potentially leading to improved performance (Bongers et al., 2017; Verducci, 2001). In the present study, intermittent PC significantly decreased RPE values during the five sets of baseball throwing for all participants; however, those who experienced cooling-induced pain did not see performance improvement. In the present study, data classified by pain after PC reveal that cooling-induced pain may counteract the benefits of reduced perceived effort on improvements in athletic performance.

This study has some limitations. First, participants in the current study had undergone years of baseball training. Thus, the results should be cautiously extrapolated to non-well-trained athletes. Second, PC was a novel treatment to the players; hence, the results may not be appropriate for extrapolation to populations who are accustomed to cold pain. Therefore, future studies are warranted to determine whether PC would provide an ergogenic effect for cold adaptation in participants performing baseball throwing.

Conclusions

In conclusion, intermittent PC reduces perceived exertion during baseball throwing regardless of whether trained baseball players experience cooling-induced light-to-moderate pain. Furthermore, for trained baseball players who do not feel pain during intermittent PC treatment, inter-set PC (10°C, 2.5 min) elicits higher arousal levels, greater mean throwing velocity, higher maximal throwing velocity, and better throwing accuracy during repeated baseball throwing. However, intermittent PC does not provide an ergogenic effect in well-trained baseball players who experience cooling-induced pain during repeated baseball throwing. Additionally, athletes exhibit decreased mean throwing velocity and maximal throwing velocity. The findings of this study show that a pain-free baseball player from PC could use PC as an ergogenic aid to enhance baseball throwing performance; the presence or absence of pain after PC can serve as an initial assessment of whether to use PC as an ergogenic aid strategy.