Comparison of the effects of cold water and ice ingestion on endurance cycling capacity in the heat

Takashi Naito,Tetsuro Ogaki

Graduate School of Human-Environment Studies,Kyushu University,Fukuoka 40218,Japan

Comparison of the effects of cold water and ice ingestion on endurance cycling capacity in the heat

Takashi Naito*,Tetsuro Ogaki

Graduate School of Human-Environment Studies,Kyushu University,Fukuoka 40218,Japan

Purpose:The purpose of this study was to examine the effects of pre-cooling and flui replacement with either crushed ice or cold water.

Cold water ingestion;Pre-cooling;Rectal temperature;Thermoregulation

1.Introduction

A moderate elevation of the body core temperature(Tc) enhances exercise performance.1However,an excessive increase in the Tcresults in a deterioration of exercise performance.2,3Numerous studies have reported that the attainment of a critical Tcis the main limiting factor inhibiting exercise performance,4–6as evidenced by a reduced central nervous system drive to the skeletal muscle7and other adverse effects, including cardiovascular strain and metabolic disturbances. Therefore,the development of hyperthermia is associated with an earlier voluntary termination during exercise performance.4,8

Several strategies,such as pre-cooling and water ingestion during exercise,have been proposed to improve exercise performance and prevent hyperthermia in hot environments.9–11The theoretical mechanism of pre-cooling is to reduce the Tcbefore exercise in the heat,thereby increasing the heat storage capacity and prolonging the duration before reaching a critical Tc.9–11The ingestion of ice,including ice slurry or crushed ice (ICE),appears to be an effective and practical method for lowering the Tc.12–14In particular,the reduction in the Tcresulting from ice ingestion may prevent the decline in the central neural drive that contributes to decreased performance in hot environments.7,15

Moreover,many studies have reported that internal cooling via flui ingestion during exercise is effective for preventing hyperthermia,and for improving endurance performance in the heat.16,17The ingestion of ice during exercise also appears to be effective for cooling with respect to the Tcand for improving endurance performance.18,19Stevens et al.19showed that 10 g/kg body mass(BM)of ice slurry ingestion during the cycle leg of a simulated Olympic distance triathlon decreased the gastrointestinal temperature,and subsequently improved the 10 km running performance time by 2.5%.

The use of combined cooling methods with pre-cooling and flui ingestion during exercise may increase the ergogenic benefit on performance via a decrease in thermoregulatory strain. Hasegawa et al.20reported that combined methods employingpre-cooling and water ingestion(14°C–16°C)during exercise widened the thermoregulatory margin before the critical Tc, thus enhancing exercise capacity in a hot environment.Lee et al.21reported the effects of cold(4°C)vs.warm(37°C)water ingestion before and during exercise on cycling performance in hot,humid conditions.In that study,cold water ingestion reduced the rectal temperature(Tre)by 0.5°C±0.1°C before exercise and significanty increased the cycling time to exhaustion(TTE)by 23%±6%as compared to warm water.However, thus far,there has been no direct comparison of the effects of both pre-cooling and flui ingestion during exercise with icevs.cold water during exercise.Combining both solid and liquid H2O into a ICE solution has the added heat sink benefi requiring the heat capacity from both the solid and liquid H2O,as well as the enthalpy of fusion required for the phase change,and provides a far greater cooling effect than water at a similar temperature.22The sum of these thermodynamic properties in a ICE mixture results in a larger heat storing capacity than liquid H2O alone(cold water,CW).

The purpose of the present study was therefore to investigate the effects of the ingestion of ICE before and during exercise on exercise capacity and thermoregulatory responses as compared with CW.We hypothesized that ingesting ICE before and during exercise would reduce the Trebefore and during exercise,and hence improve exercise capacity as compared with CW ingestion.

2.Methods

2.1.Participants

Nine non-heat-acclimatized,physically active male recreational cyclists(age=23±4 years,height=1.72±0.06 m, BM=64.0±9.6 kg,maximal oxygen uptake (VO2max)= 47.7±8.7 mL/kg/min)were recruited for this study.All participants were non-smokers,normotensive,free from any known autonomic dysfunction or cardiovascular disease,and were not taking any medications.The study protocol was approved by the Ethics Committee of Human-Environment Studies,Kyushu University,Japan,and all participants gave their written informed consent prior to commencing the study.

2.2.Preliminary measurements

In order to determine the VO2max,on the firs visit to the laboratory,each participant performed a progressive exercise test on a cycle ergometer(Ergomedic 828 E;Monark,Varberg, Sweden)at room temperature(25°C and 50%relative humidity (RH)).Their height and BM were measured to the nearest 0.1 cm and 10 g(TBF-210,Tanita Co.,Tokyo,Japan),respectively.The protocol consisted of progressive exercise beginning at 90 W for 3 min,followed by increments of 30 W every 3 min until volitional exhaustion.23Respiratory gases were measured every 30 s during the test using a pre-calibrated automatic gas analyzer(AE-310s;Minato Medical Science,Tokyo,Japan). The heart rate(HR)was monitored continuously via telemetry using an HR monitor(DS-3140;Fukuda Denshi,Tokyo,Japan). The test was considered to be valid if 2 of the following 3 criteria were met:(1)oxygen consumption reached a plateau, (2)HR remained within 10%of the predicted maximum(220?age),or(3)the respiratory exchange ratio was above 1.05.23On the second visit,between 4 and 14 days later,the participants performed a familiarization trial involving cycling to exhaustion at an intensity of 60%VO2maxin the same hot environment as the experimental trials.4,14,21

2.3.Experimental trials

In a randomized counterbalanced design,the participants performed 2 trials,ingesting either ICE or CW.During the 24 h period before the experimental trial,the participants were instructed to avoid strenuous exercise,as well as the consumption of alcohol,caffeine,nonsteroidal anti-inflammato y drugs, and nutritional supplements.All participants completed a diary that was replicated prior to the second trial.Each participant arrived at the laboratory after having refrained from eating for 6 h and drinking any type of beverage for 2 h.They were instructed to drink 500 mL of plain water 2 h before all tests to help promote euhydration prior to the start of each trial.For each participant,the 2 trials were commenced at the same time in the afternoon to control for circadian variations in the Tc, separated by 4–14 days.

Upon arrival at the laboratory,the participants’height and BM were recorded before they entered a climate-controlled room(35°C and 30%RH).A rectal thermistor(ITP010-11; Nikkiso-Therm Co.,Ltd.,Tokyo,Japan)was inserted approximately 15 cm into the rectum.Three skin thermistors were affi ed using hypoallergenic polyacrylate adhesive tape (ITP082-24;Nikkiso-Therm Co.,Ltd.)at the left rectus femoris,forearm,and sternum.An HR monitor was then fi ed to each participant’s chest before a 5-min rest period to gather baseline data.

ICE was made using a commercially available food blender (TM8100;Tescom Co.,Ltd.,Tokyo,Japan).The participants were given 1.25 g/kg BM of ICE(0.5°C)or CW(4°C)every 5 min for 30 min to ensure a standardized ingestion rate.13,14The participants then mounted the cycle ergometer to start the cycling exercise at an intensity equivalent to 60%VO2maxuntil voluntary exhaustion,approximately 5 min after fully ingesting the last drink.The participants were asked to maintain a pedal cadence of 60 rev/min throughout the exercise.Exhaustion was define as being unable to maintain 60 rev/min for 10 s.The participants subsequently ingested 2.0 g/kg BM of the same treatment drink at 15 min,30 min,and 45 min after the commencement of the exercises.After the exercise period,the participants dried themselves with a towel and were weighed again to determine their BM.

2.4.Measurements

The VO2was measured at 9–14 min,24–29 min,and 39–44 min during the exercise.The HR was monitored continuously throughout the trial,and reported as the average for each 5 min interval.Throughout the 2 trials,the Treand skin temperature(Tsk)were recorded continuously via a data logger (N542R;Nikkiso-Therm Co.,Ltd.)and logged intermittently at 30 s intervals.The mean Tskwas calculated using the formulafrom Roberts et al.:24Tsk=0.43×(Tchest)+0.25×(Tarm)+ 0.32×(Tthigh).The mean body temperature(Tb)was calculated using the formula from Colin et al.:25△Tb=0.8×(△Tre)+ 0.2×(△Tsk)+0.4.Heat storage was calculated at 5 min increments using the formula described by Adams et al.:26heat storage=0.965×m×△Tb/AD,where 0.965 is the specifi heat storage capacity of the body(W/kg/°C),m is the mean body mass(kg)over the duration of the trial,and AD is the body surface area(m2):AD=0.202×m0.425×height0.725.27A rating of the subjective thermal sensation28(RTS;9-point scale ranging from 1=very coldto 9=very hot)was recorded every 5 min throughout each trial,while a rating of the perceived exertion29(RPE;20-point scale)was recorded every 5 min during exercise.

2.5.Statistical analysis

All statistical computations were performed using the IBM SPSS Statistics Version 21.0 software package(IBM Corp., Armonk,NY,USA).A two-way(Drink×Time)repeatedmeasures ANOVA was performed to compare the changes in the Tre,Tsk,HR,RPE,and RTS between the experimental conditions.The BM,TTE,heat storage,VO2,and physiological variables at exhaustion between the 2 experimental conditions were examined using attest.When a significan main effect or interaction effect was identifie,the differences were delineated using a Bonferroni adjustment.The VO2at 39–44 min was not analyzed,because 4 participants in the CW trial reached exhaustion before 45 min.For all comparisons,significanc was set at apvalue<0.05.All figure represent means±SEM for clarity of presentation,and all other data are presented as the mean±SD.

3.Results

The volume of beverage consumed during the pre-exercise period was 480±72 g for all treatments,and the volume of beverage consumed during exercise was 316±67 g for all treatments.There were no significan differences in the pre-exercise measurements of the BM between the ICE(64.0±9.7 kg)and CW(64.2±9.4 kg)trials.At the conclusion of the TTE,the BM values were significanty lower in both the ICE(62.2±9.0 kg,p=0.001)and CW(62.5±8.7 kg,p=0.001)trials.However, the loss of BM did not differ significanty between the 2 conditions(p=0.690).

3.1.Cycling TTE

The cycling TTE finding for all participants are shown in Fig.1.Eight of the 9 participants cycled for a longer time in the ICE trial as compared to the CW trial(50.0±12.2 minvs.42.2±10.1 min,p=0.02).

3.2.Treand Tsk

Fig.1.Cycling time to exhaustion under the 2 experimental conditions.The lines denote the raw data from individual participants(n=9).*p<0.05.

Fig.2.Rectal temperature(A)and mean skin temperature(B)under the 2 experimental conditions.The arrows denote when the drink was ingested.The values are expressed as means±SEM of all 9 participants.Time×Drink effect ICEvs.CW:*p<0.05,#p<0.10.CW=cold water;ICE=crushed ice.

There were no significan differences in Trebetween the 2 conditions from 35 min(ICE:37.09°C±0.28°C;CW: 37.20°C±0.18°C)to 15 min prior to exercise(Fig.2A).However,the ingestion of the ICE caused the Treto fall by 0.37°C to 36.74°C(p=0.001).Consequently,the Trebefore the start of exercise was 0.32°C±0.09°C lower after ICE ingestion than after CW ingestion(p=0.01).The Treincreased progressively in both ICE and CW trials during exercise,but remained lower in the ICE trial for the firs 30 min of exercise(p=0.001). The rate of rise in the Treduring exercise was not significanty different between the 2 conditions(ICE:0.23°C±0.07°C, 5 min;CW:0.22°C±0.07°C,5 min;p=0.942).At exhaustion, the Trewas not significanty different between the 2 conditions (ICE:38.87°C±0.38°C;CW:38.93°C±0.52°C;p=0.575). No significan differences in the Tskwere observed between the conditions at rest(p=0.868;Fig.2B).During the preexercise period,the Tskincreased from 34.87°C±0.45°C to 35.29°C±0.42°C in the ICE trial,and from 34.91°C±0.53°C to 35.24°C±0.29°C in the CW trial(p=0.002).The rate of rise in the Tskat 15–30 min during exercise was significanty slower after the ingestion of ICEvs.CW(0.14°C±0.01°C,5 minvs.0.18°C±0.01°C,5 min;p=0.005).However,there were no significan differences in the Tskbetween the 2 conditions either prior to the commencement of exercise or during exercise.

3.3.Heat storage

Heat storage in the ICE(?5.52±2.25 W/m2)trial during the 30 min pre-exercise period was lower than that observed in the CW trial(?1.46±1.22 W/m2,p=0.01).During exercise,the amount of heat stored was not significanty different between the ICE(67.53±5.94 W/m2)and CW (68.76±6.76 W/m2)trials,including that noted at exhaustion.

3.4.RTS,RPE,and perceptual responses

Measurements of the RTS and RPE are presented in Fig.3. There were no significan differences in the RTS between the ICE(6.0±0.9)and CW trails(6.3±1.0)at rest.However, the RTS in the ICE trial decreased significanty from 20 min prior to exercise to the firs 5 min of exercise,as compared with that observed in the CW trial(p<0.05).Both RTS and RPE increased significanty(p=0.001)during exercise.The RPE in the ICE trial tended to be lower than those noted in the CW trial for the firs 5 min of exercise(p=0.07).The RTS and RPE at exhaustion were similar between the ICE and CW trials (p=1.00).In the pre-exercise period,3 of the 9 participants experienced headaches while consuming ICE,whereas none experienced this symptom with CW ingestion.No participants reported any headaches or gastrointestinal discomfort during either trial when exercising.

3.5.VO2and HR

There were no significan differences in the VO2between the 2 conditions during the firs 9–14 min(ICE:34.5± 5.5 mL/kg/min;CW:33.3±5.5 mL/kg/min)and at 24–29 min (ICE:32.0±5.0 mL/kg/min;CW:32.2±5.9 mL/kg/min).The HR values are shown in Fig.4.The HR did not differ signifi cantly between the 2 conditions in the rest period(ICE: 72±5 bpm;CW:74±6 bpm,p=0.309)and the commencement of exercise (ICE:70±9 bpm;CW:72±6 bpm,p=0.215).The HR increased continuously(p=0.001)during exercise,but was unaffected by the beverage type(p=0.398). At exhaustion,the HR was similar between the ICE (191±7 bpm)and CW(189±5 bpm)conditions(Fig.4).

Fig.3.Rating of the thermal sensation(A)and perceived exertion(B)under the 2 experimental conditions.The arrows denote when the drink was ingested. The values are expressed as means±SEM of all 9 participants.Time×Drink effect ICEvs.CW:*p<0.05,#p<0.10.CW=cold water;ICE=crushed ice.

4.Discussion

The main finding of the present study are as follows:1)The ingestion of ICE rather than a cold drink before and during prolonged cycling exercise resulted in a longer cycling TTE(by 7.8 min:16%)in a hot environment;2)ICE ingestion before exercise reduced the Treas compared with CW.

Fig.4.Heart rate under the 2 experimental conditions.The arrows denote when the drink was ingested.The values are expressed as means±SEM of all 9 participants.CW=cold water;ICE=crushed ice.

In the present study,the ingestion of ICE(0.5°C)reduced the Treby 0.32°C as compared with CW ingestion before the start of exercise in the heat.This result is consistent with the finding of previous studies showing that ice ingestion provided internal pre-cooling,which effectively reduced the Tcas compared with CW ingestion.12–14,23Siegel et al.13observed that the preexercise ingestion of an ice slurry(?1°C)reduced the Treby 0.32°C as compared with CW ingestion before the start of exercise in the heat.Similarly,Ihsan et al.12found that the pre-exercise ingestion of ICE(1.4°C)reduced the gastrointestinal temperature by 1.1°C as compared with tap water ingestion in a hot environment(30°C and 74%HR).Additionally, Stanley et al.23reported that consuming an ice-slush(?0.8°C) during recovery from 75 min of steady-state cycling exercise decreased the Treby 0.4°C more than cool flui ingestion.This enhanced ability of ice to cool the body may be explained by the latent heat of fusion.22Moreover,there were no significan differences in the Tskand BM between the 2 conditions in the present study;therefore,it is difficul to determine whether these changes can be attributed to water or heat loss.Hence,it is possible that the delayed attainment of the critical Tcand the increased cycling time found using ICE greatly enhanced the heat sink effect as compared with CW ingestion.

Differences in the rate of rise in the Trebetween the 2 conditions may influenc the time required to attain the critical Tcand,in turn,the end point of exercise.In the present study,the rate of rise in the Treduring exercise was not significanty different between the 2 conditions(ICE:0.23°C,5 min;CW: 0.22°C,5 min;p=0.942).This findin does not concur with the current literature.Siegel et al.13reported that the ingestion of ice slurry before exercise tended to increase the rise in Treduring exercise as compared with CW ingestion,despite the decrease in the Treprior to the commencement of exercise. Other previous studies have reported that the rate of rise in the Tretends to be higher following the ingestion of ice slurry as compared with CW.14,23It is possible that the lowerTreobserved during exercise in the ICE trial may be explained by the decreased rate of rise in the Tskachieved with ICE ingestion during exercise.A decreased rate of rise in the Tskresults in a higher core-to-skin temperature gradient,leading to a slower rise in the Treduring exercise.14Burdon et al.18reported that the Tskduring exercise tended to be lower following the ingestion of 3.5 g/kg BM ice slurry every 15 min during exercise.Indeed, the rate of rise in the Tskat 15–30 min intervals during exercise in the present study was significanty slower after the ingestion of ICE vs.CW(0.14°C,5 min vs.0.18°C,5 min;p=0.005). Therefore,the present results suggest that the ingestion of ICE before and during exercise may reduce the pre-exercise Tre,as well as maintain a lower Treduring exercise.

It is generally accepted that the attainment of a high Tcmay contribute to the subjective decision to terminate endurance exercise in the heat.4Therefore,we used the TTE to investigate the attainment of a critical Tre.González-Alonso et al.4demonstrated that well-trained participants(VO2max=65.8 mL/kg/ min)fatigued at the same esophageal temperature(40.1°C)at the end of cycling at 60%VO2peakin a hot environment(40°C), despite any differences in the initial esophageal temperature (35.9°C vs.37.4°C)induced by immersing the participants in water of different temperatures for 30 min.Although the Treof the participants at exhaustion in the present study did not reach 40°C,Cheung and McLellan30showed that untrained participants(VO2max<50.0 mL/kg/min)were exhausted when theirTrereached 38.7°C.The authors reported that the critical limiting temperature may be associated with the level of aerobic fitness Therefore,in the present study,considering the participant’s VO2max(47.7 mL/kg/min),we hypothesized that the Treat exhaustion reached the critical Tcbetween the 2 conditions.

Consuming larger volumes of flui may cause gastrointestinal discomfort in some athletes.Byrne et al.31reported that ingesting 900 mL of CW(2°C)over 35 min in the pre-exercise period produced a mean 0.4°C reduction in the Treat the start of exercise and resulted in a lower Treduring exercise than did the ingestion of warm water(37°C).Previous studies have also demonstrated that ingesting CW before exercise reduces the Tre by 0.4°C–0.6°C as compared with warm water(37°C).21,31In the present study,we provided the participants with a total volume of approximately 500 g of ICE to consume during the pre-exercise period in a hot environment,which subsequently reduced the Treby 0.32°C as compared with CW ingestion. Previous studies provided participants with approximately twice the total volume of beverage to consume than that used in the present study.Hence,ICE may serve as a practical precooling maneuver during cycling-based exercise,as ingesting small volumes of ICE was more effective in decreasing the Trethan ingesting CW,and was not associated with any gastrointestinal discomfort.

There were also no significan differences in the VO2or HR during exercise between the 2 trials.This result is consistent with previous studies which reported that the use of ice ingestion to provide internal pre-cooling does not reduce the VO2or HR as compared with CW ingestion.These data suggest thatICE ingestion has no effect on any markers of physiological intensity.

One limitation of the present study is that we cannot rule out whether the placebo effect is responsible for the increase in exercise capacity.Due to the inability to blind pre-cooling research using a true placebo,the participant’s expectations of a beneficia effect from using pre-cooling in hot conditions cannot be eliminated.A further limitation of this study is related to the use of a time to exhaustion protocol.We used a time to exhaustion protocol to assess the attainment of a critical Tre.Further study is needed to examine the results of performance tests that are more ecologically valid(i.e.,discrete tests set for time or distance).Finally,the sample used in the present study is not representative of participants who would potentially undertake prolonged exercise during hyperthermic conditions.Further research should recruit highly fi individuals or elite athletes.Although the current participants appeared to give their full effort,a highly fi group would be more appropriately motivated to exercise,in addition to having the ability to reach a greater core temperature.32

5.Conclusion

The present study demonstrated that ICE ingestion before and during exercise in a hot environment effectively increases the endurance cycling time as compared with CW ingestion.In addition,ICE ingestion reduced the pre-exercise Treand attenuated the increase in the Trethat occurs during exercise in a hot environment.A reduction in the Treat the start of the TTE and the lower Treobserved during TTE were evident in the ICE trial as compared with CW,which may have resulted in a greater heat storage capability,thereby improving exercise capacity. The ingestion of ICE before and during exercise in the heat may be a preferred and effective approach for minimizing thermal strain and for improving exercise capacity.

Authors’contributions

TN carried out the studies of concept,conceived of the study,participated in its design,performed the statistical analysis,and drafted the manuscript;TO participated in the study design and helped to draft the manuscript.Both authors read and approved the fina manuscript,and agree with the order of presentation of the authors.

Competing interests

Neither of the authors declare competing financia interests.

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Received 8 February 2015;revised 12 May 2015;accepted 2 July 2015 Available online 17 December 2015

Peer review under responsibility of Shanghai University of Sport.

*Corresponding author.

E-mail address:naito-t@students.ihs.kyushu-u.ac.jp(T.Naito)

http://dx.doi.org/10.1016/j.jshs.2015.12.002

2095-2546/?2017 Production and hosting by Elsevier B.V.on behalf of Shanghai University of Sport.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Methods:On 2 separate occasions,in a counterbalanced order,9 recreationally-trained malesingested 1.25 g/kg(80–100 g)ofeithercrushed ice(0.5°C) or cold water(4°C)every 5 min for 30 min before exercise.They also ingested 2.0 g/kg(130–160 g)of the same treatment drink at 15 min,30 min,and 45 min afterthe commencementofcycling to exhaustion at60%VO2maxuntilvoluntary exhaustion in a hotenvironment(35°Cand 30%relative humidity).Results:The cycling time to exhaustion in the crushed ice trial(50.0±12.2 min)was longer than the cold water trial(42.2±10.1 min;p=0.02). Although the rectal temperature fell by 0.37°C±0.03°C(p=0.01)at the end of the resting period after the crushed ice ingestion,the rates of rise in rectal temperature during the exercise period were not significanty different between these 2 conditions(crushed ice:0.23°C±0.07°C,5 min; cold water:0.22°C±0.07°C,5 min;p=0.94).

Conclusion:Crushed ice ingestion before and during exercise in a hot environment may be a preferred and effective approach for minimizing thermal strain,and for improving endurance performance as compared with cold water ingestion.

?2017 Production and hosting by Elsevier B.V.on behalf of Shanghai University of Sport.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).