Journal of
Physiological Anthropology

Numata et al.
Journal of Physiological Anthropology(2023) 42:12
https://doi.org/10.1186/s40101-023-00329-0

Open Access

ORIGINAL ARTICLE

Effects of ice slurry ingestion on bodytemperature and softball pitching performancein a hot environment: a randomized crossover
trial
Urara Numata1, Takuma Yanaoka1* , Shiho Kurosaka1 and Hiroshi Hasegawa1

Abstract
Background Although softball players are often required to play in hot environments, scarce evidence is available
regarding the effects of ice slurry ingestion on body temperature and pitching performance in softball pitchers in a
hot environment. Thus, this study investigated the effects of ice slurry ingestion before and between innings on bodytemperature and softball pitching performance in a hot environment.
Methods In a randomized crossover design, seven heat-acclimatized amateur softball pitchers (four males and threefemales) completed simulated softball games consisting of 15 best-effort pitches per inning for seven innings with
between-pitch rest intervals of 20 s. Participants were assigned to either a control trial (CON: ingestion of 5.0 g·kg−1
of cool fluid [9.8 ± 2.2 °C] before simulated softball games and 1.25 g·kg−1 of cool fluid between inning intervals) oran ice trial (ICE: ingestion of ice slurry [− 1.2 ± 0.1 °C] based on the same timings and doses as the CON). Participants
performed both trials in an outdoor ground during the summer season (30.8 ± 2.7 °C, 57.0 ± 7.9% relative humidity).
Results Ice slurry ingestion before the simulated softball game (pre-cooling) resulted in a greater reduction inrectal temperature compared with cool fluid ingestion (p = 0.021, d = 0.68). No significant differences were observed
between the trials in rectal temperature changes during the simulated softball game (p > 0.05). Compared to theCON, heart rate during the game was significantly decreased (p < 0.001, d = 0.43), and handgrip strength during thegame was significantly increased (p = 0.001, d = 1.16) in the ICE. Ratings of perceived exertion, thermal comfort, andthermal sensation were improved in the ICE compared to those in the CON (p < 0.05). Ball velocity and pitching accuracy were not affected by ICE.
Conclusions Ice slurry ingestion before and between innings reduced thermal, cardiovascular, and perceptual strain.
However, it did not affect softball pitching performance compared to cool fluid ingestion.
Keywords Ball velocity, Body cooling, Body temperature, Heat, Muscle strength, Pitching accuracy, Pre-cooling*Correspondence:
Takuma Yanaoka
yanaoka@hiroshima-u.ac.jp
1
Graduate School of Humanities and Social Sciences, Hiroshima
University, 1‑1‑1 Kagamiyama, Higashi‑Hiroshima, Hiroshima 739‑8524,
Japan

Background
The pitcher is one of the most important positions insoftball, and ball velocity is an important indicator of performance in softball pitchers. However, ball velocity generally decreases with the increase in number of pitches
thrown [1]. Possible mechanisms underlying decreasedball velocity for softball pitchers include increased pain,© The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to theoriginal author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images orother third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line
to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory
regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of thislicence, visit http://​creat​iveco​mmons.​org/​licen​ses/​by/4.​0/. The Creative Commons Public Domain Dedication waiver (http://​creat​iveco​
mmons.​org/​publi​cdoma​in/​zero/1.​0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Numata et al. Journal of Physiological Anthropology(2023) 42:12

reduced muscle strength, and decreased flexibility [2]. A
crossover effect of muscle fatigue from exercised to nonexercised upper extremity muscles has also been reported[1]. These findings suggest that the decrease in ball velocity with the increase in number of pitches thrown may
result from central fatigue (e.g., the ability to voluntarily
activate motor units) as well as peripheral fatigue.
Although softball players are often required to playin hot environments, little evidence is available regarding the magnitude of increases in body temperature anddecreases in pitching performance during softball games
played in hot environments. Exercising in a hot environment, compared with a temperate environment, results
in a faster rise in body core (Tc) and mean skin ( T sk)
temperatures [3]. In a hot environment, a concurrent risein Tc and T sk can lead to greater cardiovascular, metabolic, and perceptual strain, resulting in impaired exercise performance and an increased risk of heat-related
illness [3]. Moreover, hyperthermia-induced central
fatigue downregulates skeletal muscle recruitment anddecreases the maximal voluntary isometric contraction [3]. Previous studies have reported that the tympanic temperature in heat-acclimatized baseball players
reached 39 °C or higher after a 3-h practice session in a
hot environment [4]. The gastrointestinal temperature inbowlers increased to 38.8 °C during bowling simulations
in cricket matches [5]. In addition, Huang et al. reported
that an extremely hot environment resulted in decreased
pitching performance, although this did not affect hitting
performance in the Chinese Professional Baseball League
games in Taiwan [6]. Accordingly, it can be assumed thatin a hot environment, Tc in the softball pitcher increases
significantly with an increase in the number of pitches
thrown, resulting in a greater increase in the magnitudeof ball velocity decrement. Therefore, it is important todevelop practical strategies for aggressive cooling in softball pitchers.
Cooling the body may be an effective approach as thisstrategy can alleviate physiological (elevated ­Tc, T sk,and heart rate [HR]) and perceptual (increased rate ofperceived exertion [RPE], thermal sensation [TS], andthermal comfort [TC]) strain in a hot environment [3,7]. Body cooling strategies may be classified as internal and external cooling strategies. Several studies haveinvestigated the efficacy of external cooling strategies forbaseball and cricket players [5, 8–11]. External coolingof cricket pitchers was shown to prevent increases in Tc,
T sk, HR, RPE, and TS during bowling simulations in a
hot environment [5]. In another study, external coolingof baseball pitchers prevented decreases in ball velocity
during simulated baseball games in a thermoneutral environment [10]. However, there is currently no evidence
regarding the efficacy of internal cooling strategies on

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pitching performance. Ingestion of ice slurry before exercise can effectively lower Tc compared with the ingestion of cool fluid [12]. Previous studies have suggested
that ice slurry ingestion may improve hyperthermiainduced central fatigue by decreasing brain temperature[13] and by cold stimulation of internal thermoreceptors
in the mouth, throat, and stomach regions [14]. Moreover, repeat ingestion of ice slurry during breaks in atennis-simulated game was found to increase its cooling power [15, 16]. Therefore, ice slurry ingestion before
and between innings could improve physiological andthermal strain as well as pitching performance in softball
pitchers.
Although evidence suggests an improvement in physiological and thermal strain following ice slurry ingestion, the efficacy of this strategy can be affected by theheat-acclimatization status of the players [17] and nowind velocity and solar radiation due to laboratory settings [18]. Moreover, many studies used an ambient temperature fluid as a control condition, although athletes
often ingest cold fluid during sports competitions [19].
These methodological limitations suggest that previous
findings may have overestimated the physiological andergogenic benefits of ice slurry ingestion. Therefore, thisstudy aimed to investigate the effects of ice slurry ingestion before and between innings on body temperatureand softball pitching performance in a hot environment.
This study included heat-acclimatized softball pitchers,
simulated softball games in an outdoor ground, and useda cool fluid (10 °C) as a control condition. We hypothesized that ice slurry ingestion before and between innings
would decrease thermal (Tc), cardiovascular (HR), andperceptual strain (TS, TC, and RPE) and attenuate thedecrease in ball velocity that occurs with the increase in
the number of pitches thrown.

Methods
Participants

A sample size of seven participants was required based ona power calculation (G*Power 3) [20], with an α of 0.05, aβ of 0.20, and an effect size (Cohen’s d) of 1.43, calculated
from the difference in Tc following repeated ice slurryingestion demonstrated in a previous study [16]. Seven
heat-acclimatized softball pitchers participated in thisstudy (four male participants: age, 22.8 ± 1.8 years; height,
1.69 ± 0.04 m; body mass, 65.7 ± 6.1 kg; three female participants: age, 22.0 ± 0.8 years; height, 1.60 ± 0.05 m; andbody mass, 58.6 ± 4.5 kg [mean ± standard deviation]).
All participants were amateur softball pitchers with nohistory of elbow or shoulder injury within the 6 months
before the study. The female participants experienced
regular menstrual cycles and did not use oral contraceptives. The participants dressed in a softball attire,

Numata et al. Journal of Physiological Anthropology(2023) 42:12

consisting of a cap, softball pants, socks, softball shoes,
practice jerseys, and belts. This study was approvedby the Ethics in Human Research Committee of the
Graduate School of Humanities and Social Sciences at
Hiroshima University (approval number: 2021074). All
participants provided written informed consent to participate in this study.
Experimental design

All participants completed two experimental trials
using a randomized crossover design in an outdoor
softball ground. The trials were separated by at least
7 days and were performed at the same time of the day(09:30–15:00) for each participant to avoid any circadian rhythm-related variations. Female participants were
tested between days 2 and 10 of their menstrual cycle.
Participants refrained from consuming alcohol and caffeine for 24 h prior to each experimental trial and fasted
for 2 h, excluding the consumption of water, before eachexperimental trial. The participants were asked to avoid
altering their regular lifestyle habits, exercise, and dietthroughout the study. This study was completed during
the summer season (30.8 ± 2.7 °C, 57.0 ± 7.9% relative
humidity, 1.6 ± 0.8 m/s for air velocity).
Simulated softball games

Figure 1 demonstrates the testing protocol. Upon arrival,
the participants first emptied their bladders. Nude bodymass and urine-specific gravity were then measured in allparticipants. After that, the participants were then fittedwith the measuring instruments. After the standardized
warm-up (2-min jogging, 5-min active stretching, andPage 3 of 9

13-min practice throwing, with gradually increasing ballvelocity), participants sat in a dugout for 15 min (REST).
After REST, participants threw 15 best-effort pitches per
inning to a catcher for seven innings, with between-pitch
rest intervals of 20 s [21]. A 6-min interval was allowed
between the innings. The participants were instructedto throw fastballs into the strike zone. Three practice
pitches were allowed prior to each inning. For the besteffort pitches, the batter was made to stand.
Cooling intervention

Participants were assigned to either a control trial(CON: ingestion of 5.0 g·kg−1 of fluid during REST
and 1.25 g·kg−1 of fluid between the inning intervals;
9.8 ± 2.2 °C) or an ice trial (ICE: ingestion of 5.0 g·kg−1
of ice slurry during REST and 1.25 g·kg−1 of ice slurry
between the inning intervals; − 1.2 ± 0.1 °C). The participants undertook both interventions in a dugout. The ice
slurry was made from conventional sports drinks (Pocari
Sweat, Otsuka Pharmaceutical, Japan) containing 6.2 g ofcarbohydrates, 49 mg of sodium, and 20 mg of potassium
per 100 mL. A commercially available ice shaver was used
to create the ice flakes. The ice flakes and 4 °C conventional sports drink were mixed in a 3:1 ice-to-drink ratio
to create an ice slurry. The fluid used in the CON had thesame components as those in the ice slurry.
Measurements
Physiological index

Rectal temperature (Tre) was measured using a thermistor (LT-ST08-21, Nikkiso-Therm, Japan) at a depth of
10 cm from the anal sphincter at 1-min intervals. T sk

Fig. 1 Schematic representation of the experimental protocol. Tre, rectal temperature; T sk, mean skin temperature; TS, thermal sensation; TC,
thermal comfort; RPE, rating of perceived exertion

Numata et al. Journal of Physiological Anthropology(2023) 42:12

was measured using a wireless surface temperature datalogger (Thermochron SL, KN Laboratories, Japan) at
1-min intervals. The thermistor was attached to four sites(chest, upper arm, thigh, and calf ). T sk was calculated asfollows: T sk = 0.3 (chest + upper arm) + 0.2 (thigh + calf )[22]. For simplicity of the statistical analysis, body temperature data are presented as the 1-min sample measured immediately before and after warm-up and innings.
Moreover, changes (Δ) in Tre during REST (i.e., 15-min
rest between the post-warm-up and post-REST) and thesimulated softball games (i.e., between the post-REST
and seventh inning) were calculated.
HR was measured using a wireless HR monitor(RS800CX, Polar Electro, Finland) at 1-min intervals.
The towel-dried nude body mass was measured using ascale (InBody 470, InBody Japan, Japan) before and after
the experimental trial. Gross sweat loss was estimated byadjusting for fluid intake. The urine-specific gravity wasmeasured using a refractometer (PAL-09S, Atago, Japan)
before and after the experimental trial.
Perceptual indices

TS (− 6 [very cold] to 6 [very hot]) and TC (− 6 [veryuncomfortable] to 6 [very comfortable]) were measured
before and after warm-up and innings [23]. The RPE (6[no exertion] to 20 [maximal exertion]) was assessed
after each inning [24].
Pitching performance and muscle strength

The ball velocity was measured using a radar gun (Speedster V, Bushnell, USA) positioned 3 m behind the home
plate. Video images were recorded using an HD 60 fps
camera (GZ-E780, JVCKENWOOD, Japan) positioned
3 m behind the home plate. These video images wereused to determine the pitching accuracy (i.e., the percentage of pitches crossing the strike zone during flight).
Accuracy was determined by the same investigator. The
handgrip strength of the dominant hand was measured
using a handgrip dynamometer (T.K.K.5401, Takei,
Japan) after the warm-up, REST, and each inning.
Statistical analysis

Statistical analysis was performed using SPSS software(Version 29.0, SPSS Japan Inc., Japan). Statistical significance was set at p < 0.05. Unless otherwise stated, allvalues are presented as the mean ± standard deviation.
The Shapiro–Wilk test was used to assess the normalityof distribution, and all parameters, except for the perceptual indices, were found to not differ significantly
from normal. Differences in environmental variables
between trials were analyzed using linear mixed models(fixed effects: trial). Differences between trial, time, andtrial × time for the changes in thermal, cardiovascular,

Page 4 of 9and performance variables were analyzed using linear mixed models (fixed effects: trial and time; random
effect: participant). This analysis was preferred because
it allows for missing data. It also accurately models different covariate structures for repeated-measures data
and models between-subject variability [25]. Changes(Δ) in Tre during REST and the simulated softball games
were calculated and analyzed using linear mixed models to adjust for potential confounding covariates (i.e.,
Tre at the end of the warm-up or the commencement of
the first inning and wet bulb globe temperature). Where
significance was found, the values were subsequently
analyzed using the Bonferroni multiple comparison
test. Differences in perceptual variables between trials
were analyzed using the Wilcoxon’s matched pairs test.
Cohen’s d effect size was also calculated where necessary, whereby > 2.0 was categorized as a very large effect,
1.2–2.0 as a large effect, 0.6–1.2 as a moderate effect, and
0.2–0.6 as a small effect [26].

Results
The mean data for all participants, male participants,
and female participants are presented in Supplementary Tables 1, 2, and 3, respectively. No significant differences were observed in the ambient temperature(CON: 31.1 ± 3.9 °C, ICE: 30.5 ± 2.2 °C, p = 0.539), relative humidity (CON: 53.4 ± 12.7%, ICE: 60.6 ± 6.5%,
p = 0.124), and air velocity (CON: 1.1 ± 0.9 m/s, ICE:
1.5 ± 1.3 m/s, p = 0.573) between trials.
Body temperature

Tre responses are shown in Fig. 2A. No trial × time interactions were observed for Tre (p > 0.05) and T sk (p > 0.05,
Supplementary Table 1). However, there was a main
effect of the trial for Tre (p < 0.001). Tre was significantly
lower in the ICE than in the CON (p < 0.001, d = 0.46).
ΔTre during REST and simulated softball games areshown in Fig. 2B and C, respectively. The ICE resulted
in a greater reduction in Tre during REST than the CON(p = 0.021, d = 0.68, Fig. 2B). No significant difference
between the trials was observed in ΔTre during the simulated softball games (p > 0.05, Fig. 2C).
Heart rate and body fluid balance

There was no trial × time interaction for HR (p > 0.05), but
a main effect of the trial for HR was observed (p < 0.001,
Supplementary Table 1). HR was significantly lower in
the ICE than in the CON (p < 0.001, d = 0.43). Changes intowel-dried nude body mass, gross sweat loss, and urinespecific gravity remained comparable between the trials(p > 0.05).

Numata et al. Journal of Physiological Anthropology(2023) 42:12

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Fig. 2 Tre (A) and ΔTre during REST (B) and simulated softball games (C) between the trials. The values are shown as mean ± standard deviation(n = 7). *Significant difference between trials (p < 0.05). Tre, rectal temperature; ΔTre, changes in rectal temperature

Perceptual indices

The perceptual indices between the trials are shown in
Fig. 3. The ICE significantly lowered TS after the third
inning (p = 0.026, d = 2.35) and RPE after the fourth
inning (p = 0.023, d = 0.95). The ICE also lowered TS after
the second inning (p = 0.063, d = 1.20) and TC after first(p = 0.059, d = 0.88), second (p = 0.059, d = 0.96), third(p = 0.058, d = 0.51), and seventh (p = 0.098, d = 0.96)
innings; however, there were no significant differences
between the trials.
Pitching performance and muscle strength

The responses for ball velocity, pitching accuracy, andhandgrip strength are shown in Fig. 4. There were notrial × time interactions for ball velocity (p > 0.05), pitching accuracy (p > 0.05), and handgrip strength (p > 0.05).
However, main effects of time on ball velocity (p < 0.001)
and handgrip strength (p = 0.003) were observed. The ballvelocity was significantly lower in the sixth (p = 0.002,
d = 0.33) and seventh (p < 0.001, d = 0.40) innings than in
the first inning. Handgrip strength was significantly lower
in the sixth (p = 0.009, d = 0.40) and seventh (p = 0.003,
d = 0.44) inning than at REST. There was a main effectof the trial on handgrip strength (p = 0.001). Handgrip
strength was significantly higher in the ICE than in the
CON (p = 0.001, d = 1.16).

Discussion
This study investigated the effect of ice slurry ingestion
before and between innings on body temperature andsoftball pitching performance in a hot environment.
The present findings revealed that, in accordance with
our principal hypothesis, ice slurry ingestion before andbetween innings decreased thermal (Tre), cardiovascular(HR), and perceptual (TS, TC, and RPE) strain. However,ice slurry ingestion had no impact on the magnitude of

the ball velocity decrement with the increase in the number of pitches thrown.
To our knowledge, this study is the first to investigate
the influence of ice slurry ingestion on Tc in softball
pitchers playing in a hot environment. In the present
study, the ingestion of 5.0 g·kg−1 of ice slurry during
REST (i.e., pre-cooling) reduced Tre compared with
the ingestion of 5.0 g·kg−1 of cool fluid (− 0.35 ± 0.16 °C
vs − 0.25 ± 0.13 °C). A previous study reported a 0.4 °C
reduction in Tre with 7.5 g·kg−1 of ice slurry ingestion
for 15 min after warm-up [27], which is consistent withthe present findings. Ice slurry ingestion as a pre-coolingstrategy decreases Tre prior to exercise and increases heatstorage capacity, which delays the influence of hyperthermia-induced fatigue [28]. However, this strategy also
results in (1) a smaller core-to-skin temperature gradient, caused by a decrease in Tre without a concurrent
decrease in T sk, and (2) a delay in the onset of sweating during subsequent exercise [29]. These may lead to agreater rate of Tre increase during the early stages of subsequent exercise [29]. In the present study, the magnitudeof the increase in Tre during simulated softball games wascomparable between the trials (Fig. 2C), which is inconsistent with previous research [29]. This resulted from theingestion of 1.25 g·kg−1 of ice slurry between the innings.
A previous study reported that ingestion of 1.25 g·kg−1 ofice slurry in a game and set breaks during a tennis-simulated running test significantly lowered Tre comparedwith the ingestion of the same dose of cool fluid (4 °C)
according to the same timing [15]. A high dose of ice
slurry ingestion may result in gastrointestinal discomfort[30]. Therefore, the present results, which were obtainedby employing an intermediate (5.0 g·kg−1) dose before
simulated softball games and low (1.25 g·kg−1) doses
between the innings of ice slurry ingestion, are useful forsoftball pitchers playing innings in a hot environment.

Numata et al. Journal of Physiological Anthropology(2023) 42:12

Page 6 of 9

Fig. 3 TS (A), TC (B), and RPE (C) between the trials. The values are shown as mean ± standard deviation (n = 7). *Significant difference between
trials (p < 0.05). TS, thermal sensation; TC, thermal comfort; RPE, rating of perceived exertion

In the present study, neuromuscular function following ice slurry ingestion was assessed because reduced
muscle strength was shown to be related to decreasedball velocity for softball pitchers [2]. Exercise-induced
hyperthermia in a hot environment impairs neuromuscular function in both exercised and non-exercised muscle

Numata et al. Journal of Physiological Anthropology(2023) 42:12

Page 7 of 9

Fig. 4 Ball velocity (A), accuracy (B), and handgrip strength (C) between the trials. The values are shown as mean ± standard error (n = 7)

groups [31]. Impairment was found to be associatedwith central fatigue, which is triggered by an increasein Tc including brain temperature [3]. A previous study
revealed that ingestion of 7.5 g·kg−1 ice slurry reduced
brain temperature, as measured by proton magnetic resonance spectroscopy [13]. A previous study also demonstrated that ingestion of 1.25 g·kg−1 ice slurry attenuatedreductions in maximal voluntary contraction following
exercise-induced hyperthermia without causing physiological changes [14]. The authors postulated that the
improvement in neuromuscular function resulted fromthe ice slurry by (1) altering afferent feedback by stimulating internal thermoreceptors in the mouth, esophagus, and stomach regions and (2) stimulating the reward/
pleasure centers of the brain [14]. The present study
demonstrated that ice slurry ingestion attenuated the
reduction in handgrip strength compared with cool fluid
ingestion. This result is consistent with the findings ofa previous study [14]; therefore, the improvement may
result from Tc reduction, including brain temperature,and sensory mechanisms.
The present study demonstrated that ice slurry ingestion lowered HR by approximately 10 bpm comparedwith cool fluid ingestion, which is consistent with thefindings of a reduction in HR by ingestion of 1.25 g·kg−1
of ice slurry during game and set breaks in a tennissimulated running test in a previous study [15]. We areunable to conclude the mechanism of reductions in HR
with small decrements in Tre during the simulated softball game (i.e., approximately 0.1 °C) due to a lack of cardiovascular measurements (i.e., skin blood flow, strokevolume, cardiac output, and mean arterial pressure).
However, given the results of a previous study [32], we
speculate that this effect resulted from an enhancement of heat storage capacity by ingesting ice slurry.
In support of this, Ng et al. reported that, compared totepid fluid, ice slurry ingestion during exercise at 60% of
maximal oxygen uptake decreased HR by 9 bpm without significantly changes in Tre, skin blood flow, cardiac

output, mean arterial pressure, or local sweat rate [32].
The authors suggested the possibility that ice slurryingestion provided a sufficient heat sink to decrease heatstorage and thereby reduce cardiovascular strain [32].
The other study also reported that ice slurry ingestion
during walking at 4.0 km·h−1 on a 12% incline wearing
firefighter-protective clothing decreased HR by approximately 10 bpm at 5 min of the commencement of walking
compared to cold fluid [33]. However, this is only speculative, and further research is warranted to investigate
the mechanism of the decrease in HR following ice slurryingestion.
Although ice slurry ingestion improved thermal (Tre),
cardiovascular (HR), and perceptual (RPE, TS, and TC)
strain, pitching performance was not affected by ice
slurry ingestion. This may be due to the low thermal
strain (i.e., low magnitude of the increases in Tre) during the simulated softball games in this study. A recent
review suggested that it is easier to avoid an increase inthermal strain by employing less intense exercise protocols or protocols interspersed with moments of lowerintensity recovery periods (intermittent efforts); thus,
the benefits of ice slurry ingestion are minimized [34].
Indeed, the magnitudes of the increases in Tre during CON in the present study were lower than thoseobserved in previous studies, which investigated changes
in body temperature during a 3-h baseball practice [4]and bowling simulations in cricket matches played [5] ina hot environment. Therefore, future research is needed
to investigate the ergogenic effect of ice slurry ingestion
on pitching performance in environments with high thermal strain, such as actual softball games.
The strength of the present study includes its methodological setting: (1) trials were conducted in an outdoor ground, (2) pitchers were heat acclimatized, and(3) cool fluid (10 °C) was employed for CON. Previous studies were conducted in the laboratory; however,environmental factors, including wind velocity [18] andsolar radiation [35], have a significant influence on bodyNumata et al. Journal of Physiological Anthropology(2023) 42:12

temperature during exercise. In addition, heat-acclimatized individuals may experience ceiling effects of body
cooling strategies on thermal and performance variables[17]. Moreover, using an ambient-temperature fluid asa control condition may overestimate the extent of thephysiologic and ergogenic benefits of ice slurry ingestion.
Therefore, the present results, which were obtained using
a method with high ecological validity, suggest that ice
slurry ingestion is a physiologically effective heat mitigation strategy for softball pitchers.
This study has three limitations. First, the type of participants employed in this study (i.e., amateur softball
pitchers) did not allow for comparison with professional
athletes. Regarding the pitching accuracy, a previous
study has reported that the strike rates in 480 regularseason Chinese Professional Baseball League games wereapproximately 50% [6]. In addition, intercollegiate baseball pitchers from University Baseball League Division I
in Taiwan had approximately 45% of strike rates during
the simulated baseball games [21]. These rates are consistent with the present result. Because ball velocity andpitching accuracy may interact during actual softballgames, and pitching accuracy in professional baseballpitchers was significantly higher than in amateur baseballpitchers [36], further research is needed to investigate
the effect of ice slurry ingestion on pitching performance
during professional softball games. Second, we did not
perform ambient-temperature fluid trials or no-ingestion
trials. However, cold fluid ingestion is a common practiceamong many athletes [19]. Third, the pitching accuracy
was subjectively determined by an investigator. Althougha single umpire is responsible for calling balls and strikes
in softball games, the lack of objective determination of
the strike zone and whether the ball passed the strikezone could lead to human error.

Conclusions
This study demonstrated that ice slurry ingestion before(5.0 g·kg−1) and between (1.25 g·kg−1) innings improved
thermal (Tre), cardiovascular (HR), and perceptual (RPE,
TS, and TC) strain compared with cool fluid ingestion. However, this strategy did not affect pitching
performance.
Abbreviations
CON	Control trialHR	Heart rate
ICE	Ice trial
REST	Seated rest in a dugout for 15 min
RPE	Rate of perceived exertion
Tc	Body core temperatureTC	Thermal comfortTre	Rectal temperatureTS	Thermal sensation

Page 8 of 9

T sk	Mean skin temperature
Δ	Change

Supplementary Information
The online version contains supplementary material available at https://​doi.​
org/​10.​1186/​s40101-​023-​00329-0.
Additional file 1: Supplementary Table 1. Mean data in for all participants between trials (mean ± standard deviation, n = 7).
Additional file 2: Supplementary Table 2. Mean data of male participants between trials (mean ± standard deviation, n = 4).
Additional file 3: Supplementary Table 3. Mean data of female participants between trials (mean ± standard deviation, n = 3).
Acknowledgements
The authors would like to thank the participants for their cooperation.
Authors’ contributions
UN, TY, and HH conceived and designed the study. UN collected the data. UN,
TY, SK, and HH analyzed and interpreted the data. UN wrote the first draft ofthe manuscript. All authors contributed to manuscript revision and read andapproved the submitted version.
Funding
This study was supported by JSPS KAKENHI (under Grant Number 20K19599)
and the National Strength and Conditioning Association JAPAN (under Grant
Number NA).
Availability of data and materials
The datasets during and/or analyzed during the current study are available
from the corresponding author on reasonable request.

Declarations
Ethics approval and consent to participate
This study was approved by the Ethics in Human Research Committee of the
Graduate School of Humanities and Social Sciences in Hiroshima University(Approval number: 2021074). All participants provided written informed
consent to participate in this study.
Consent for publication
Not applicable.
Competing interests
The authors declare that they have no competing interests.
Received: 1 March 2023 Accepted: 20 June 2023

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