Versión original del autorThe purpose of this study was to identify if awareness of water loss could impact thirst perception during exercise in the heat. Eleven males participated in two sessions in random order, receiving true or false information of their water losses every 30 minutes. Thirst perception (TP), actual dehydration, stomach fullness, and heat stress were measured every 30 minutes during intermittent exercise until dehydrated by ~4% body mass (BM). Post exercise they ingested water ad libitum for 30 minutes. Preexercise BM, TP, and hydration status were not different between sessions (p>0.05). As dehydration progressed during exercise TP increased significantly (p= 0.001), but it was the same for both sessions (p=0.447). Post-exercise water ingestion was almost identical (p=0.949) between sessions. In this study, thirst was a good indicator of fluid needs during exercise in the heat when no fluid was ingested, regardless of receiving true or false water loss information.Gatorade Sports Science InstituteUniversidad de Costa Rica/[VI-838-B4-309]/UCR/Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Sociales::Centro de Investigación en Ciencias del Movimiento Humano (CIMOHU

Aragón Vargas, Luis Fernando

Capitán Jiménez, Catalina

English

Repositorio Institucional de la Universidad de Costa Rica

1 Awareness of water losses does not impact thirst during exercise in the heat: a 1 double-blind study (PREPRINT) 2 Catalina Capitán-Jiménez1-2 & Luis Fernando Aragón-Vargas1 3 4 1Centro de Investigación en Ciencias del Movimiento Humano, Universidad de Costa Rica 5 2 Universidad Hispanoamericana, Costa Rica 6 7 8 The purpose of this study was to identify if awareness of water loss could impact thirst perception during exercise in 9 the heat. Eleven males participated in two sessions in random order, receiving true or false information of their water 10 losses every 30 minutes. Thirst perception (TP), actual dehydration, stomach fullness, and heat stress were measured 11 every 30 minutes during intermittent exercise until dehydrated by ~4% body mass (BM). Post exercise they ingested 12 water ad libitum for 30 minutes. Preexercise BM, TP, and hydration status were not different between sessions 13 (p>0.05). As dehydration progressed during exercise TP increased significantly (p= 0.001), but it was the same for 14 both sessions (p=0.447). Post-exercise water ingestion was almost identical (p=0.949) between sessions. In this study, 15 thirst was a good indicator of fluid needs during exercise in the heat when no fluid was ingested, regardless of receiving 16 true or false water loss information. 17 18 Keywords: thirst perception, dehydration, voluntary fluid intake 19 20 Abstract word count: 148 21 Body of manuscript word count: 22 23 24 Key points: 25 26 1. Thirst perception during exercise in the heat is not influenced by the received information27 about water losses even when percentage of dehydration is more than 3% body mass.28 2. Thirst perception can be used as a parameter of fluid needs as long as no liquid is29 ingested during exercise.30  1  31  32  33  34 INTRODUCTION 35 Hydration is always a factor to take into consideration when exercising, especially in the heat, 36 where liquid intake is very important; thirst, as a mechanism of hydration control during exercise, 37 has been widely studied, but whether it is good enough to drive hydration is still controversial 38 (7,12–14).  39 Thirst can be easily affected by environment, dehydration levels, and especially by drinking (11), 40 studies have clearly shown that the major issue with thirst-driven intake  is the rapid decrease of 41 the desire to drink, even when people replace less than 60% of what they lost (2,5). 42 Manipulation of thirst perception has been studied to see how it can affect performance (1,9), using 43 protocols to control thirst through saline infusions and mouth rinsing. However, we don’t know if  44 thirst can be affected by received information or if people can change the perception of thirst 45 because they know how much their water losses are. 46 Therefore, the aim of the study was to identify if thirst perception (TP) can be affected by 47 awareness of water losses during exercise in the heat. 48  49 METHODS 50 The current investigation used a double-blind design to determine whether thirst perception (TP) 51 can be affected by received information about water losses during exercise in the heat. Subjects 52 completed two randomly assigned sessions. Experimental testing procedures required subjects to 53 exercise in the heat until they reached ~4%BM. Subjects were asked to complete the thirst 54  1 perception scale every 30 minutes from the onset of exercise until they reached the target level of 55 dehydration, and then to drink as much as they wanted for 30 minutes.  56 Subjects 57 Eleven apparently healthy, physically active males provided written informed consent prior to 58 participation in this study. The protocol was approved by the Institution Ethics Committee. 59 Procedures  60 In one session subjects received information about their real water losses (RI) and in the other 61 session they received information corresponding to 60% of their real water losses (FI), which is 62 the average voluntary drinking reported in other studies; sessions were randomly assigned. Each 63 participant arrived in the laboratory after an overnight fast, performed the baseline procedures, 64 exercised in the heat, and rehydrated ad libitum.  At different points during the protocol, self-65 reported measures were obtained for thirst, fullness and heat perception.  66 On testing days participants reported to the laboratory and voided their bladders completely. Urine 67 was collected and analyzed with a refractometer for urine specific gravity (manual refractometer 68 ATAGO® model URC-Ne, Minato-ku, Tokyo, Japan, with a spectrum of 1.000 to 1.050). Urine 69 osmolality (Uosm) was also measured via freezing point depression (Advanced Instruments 3250 70 osmometer; Norwood, MA). Nude baseline body weight was measured to the nearest 10 g 71 (Accura® scale, model DSB291, Qingpu, Shanghai, China).  72 Self-reported thirst was recorded with a visual analog scale. The scale consisted of a continuous 73 100 mm line with a mark on the left end indicating “not at all” and on the right “extremely”, 74 responding to the question “how thirsty do you feel?”. Perceived heat sensation was measured with 75 an analog scale with a score from “1: incredibly cold” to “8: incredibly hot”.  Finally, for the 76 feeling of fullness, the question was: “how full do you feel?” with a score between 1 (not at all) 77  1 and 5 (very, very). Each participant ingested a standardized breakfast after baseline measurements 78 (750 kilocalories: 24.6% fat, 20.7% protein, and 54.7% carbohydrate; 250 mL of fluid, 1500 mg 79 sodium).  After resting for thirty minutes, baseline measurements were taken, and the exercise 80 session started.  81 On both sessions each participant exercised intermittently (30 min bicycle-30 min treadmill, at 70-82 80% HRmax) in the heat (WBGT= 28.8±0.1°C and 28.9±0.3°C, for RI and FI, respectively), to a 83 target dehydration near 4% body mass (BM). Subjects were weighed every 30 minutes to monitor 84 their water losses; after every weighing, subjects received information according to the session. 85 Thirst perception was measured every 15 minutes after they received information. Water ingestion 86 during exercise was not allowed. Heat stress was monitored with a Questemp36® monitor. (3M, 87 Oconomowoc, WI, USA). 88 Upon exercise termination, participants were instructed to drink as much as they needed from 89 previously weighed bottles, while monitoring water intake with an OHAUS® Compact Scales, 90 model CS2000 (Parsippany, NJ, USA) food scale, every 15 minutes for a total of 30 minutes. Urine 91 specific gravity (USG) and osmolality (Uosm), fullness, heat sensation, and thirst perception (TP) 92 were measured pre- and post-exercise, and post-rehydration.  93 Statistical analysis 94 Mean and standard deviation were used for descriptive statistics. A t-test was performed to identify 95 differences between sessions for each variable (body mass, USG, Uosm, thirts, WBGT, fullness, 96 and heat sensation). One-way analyses of variance were performed to see differences over time 97 for each variable (Urine osmolality, thirst, heat sensation, and fullness). Where ANOVA showed 98 a statistically significant main effect, Tukey’s post hoc tests were performed to compare time 99 differences. 100  1  101 Results 102 Participants were 23.0±3.0 years old, 1.75±0.07 m tall, and weighed 76.7±4.9 kg. Pre-exercise 103 conditions were the same for both sessions, see table 1. 104 Participants exercised for 110.0±24.8 vs. 115.0±22.3 minutes (t=-1.27; p=0.232) during the RI and 105 FI sessions and achieved a body mass loss of 76.7±5.2kg and 76.8±5.2kg (t= -0.389; p=0.706) 106 respectively, which represent an actual dehydration of 3.88±0.43 vs. 3.81±0.38 (t=-0.30;p=0.756), 107 respectively. Subjects ingested the same amount of water at the end of both sessions (1220±249 108 mL and 1228±422 mL; t=-0.66, P=0.949).   109 Table 1.  Pre-exercise conditions for each session 110 Variable Real Information (S1) False Information (S2) t p Body Mass (kg) 77.1±4.9 77.1±5.0 -0.389 0.706 USG (a.u) 1.017±0.007 1.017±0.007 0.135 0.895 Uosm (mmol∙kg-1) 654.3±296.4 663.2±297.4 0.279 0.786 Thirst perception (mm) 12.8±10.8 14.1±7.5 -1.38 0.199 WBGT (°C) 28.8±0.1 28.9±0.3 -0.814 0.461 Fullness 2.9±1.0 2.9±0.5 -1.27 0.232 Heat sensation 3.8±1.0 3.7±1.0 1.02 0.860  111 Figure 1 shows urine osmolality between conditions over time, pre-exercise (RI:654.3±296.4 and 112 FI: 663.2±297.4), postexercise (RI:630.1±295.5 and FI: 579.1±279.3) and rehydration (RI: 113 695.2±259.5 and FI: 665.9±288.5).  Uosm was no different between sessions (f=0.134; p=0.722) 114 also, there is no difference over time (f=0.65; p= 0.804) and no interaction (f=0.243; p=0.633) 115  116  1  117  118  119 Figure 1. Urine osmolatity values (mean ± s.d), no difference between sessions (p=0.722) or time 120 (p= 0.804). 121 Thirst perception shows no difference between sessions (F=0.661; p=0.447). There is a difference 122 over time (F=44.6; p= 0.001) from pre-exercise, but no interaction (F=0.382; p=0.559). Fullness 123 shows no differences between sessions (F=3.74; p=0.205) nor time (F=3.74; p=0.304).  124 Meanwhile, heat sensation does not differ between sessions (F=0.982; p=0.360) or over time 125 (F=2.88; p=0.140). Figure 2, A, B and C, respectively.   126 02004006008001000Pre Post RehyUrine Osmolality RealFALSE 1 127  128  129 Figure 2. Values shown are mean ± s.d. A. Thirst perception shows no difference between sessions 130 (p=0.447). There is a difference over time (p= 0.001) from pre-exercise, but no interaction 131 (p=0.559). B. Fullness: no differences between sessions (p=0.205) nor time (p=0.304).  C. Heat 132 sensation did not differ between sessions (p=0.360) or over time (p=0.140). 133  134 DISCUSSION 135 020406080100120Thirst perception (mm)RealFALSE01234Fullnes (a.u)0246810 Pre 30 60 90 120 150Heat sensation (a.u)Time (min)* * * A B C  1 The aim of the study was to identify if thirst perception (TP) can be affected by awareness of water 136 losses during exercise in the heat. The main finding of this study was that thirst perception during 137 exercise in the heat was not influenced by true or false information about water losses. After 138 exercise, subjects drank one-third of their losses (≈1.2 L),  a large volume for 30 minutes of 139 rehydration, independently of the information they received.  140  141 This study design differs from others because we manipulated thirst through the information of 142 water losses of the subjects, contrary to others that manipulate thirst with saline infusions, mouth 143 rinse or small quantities of water (1). We also focused only on thirst perception during exercise 144 and not on performance as other studies (2,4,8,11,15); this could be relevant because an important 145 proportion of  the physically-active population may be relying on thirst to drive their hydration. 146 This study confirms that thirst perception can detect dehydration and it will go higher as the level 147 of dehydration increases, but thirst perception stops working as soon as subjects drink anything 148 (2–5,10).  149  150 Even when WBGT and exercise intensity were high, thirst perception between sessions was the 151 same and had the same behavior over time, regardless of receiving true or false information about 152 water loss. It should be noticed that in this study drinking during exercise was not allowed; we 153 expect that this behavior can change when drinking or mouth rinsing is allowed, as others have 154 shown (6). 155  156 Thirst perception is widely used as a reference of hydration needs, especially in physically active 157 persons (not necessarily athletes).  Moreover, thirst can be used as a parameter as long as no liquid 158  1 is ingested during exercise. From this particular study, it may be added that internal signals seem 159 to be adequate to indicate dehydration, despite inaccurate external information that people may 160 receive about their hydration status. 161  162 In conclusion, thirst perception (TP) was not affected by received information about water losses 163 during exercise in the heat. This might suggest that awareness of water losses during exercise 164 cannot override the dehydration-induced hypothalamic signal for thirst.  165  166  167 CONFLICT OF INTEREST 168 Authors declare no conflict of interest 169 REFERENCES  170 1.  Adams, JD, Sekiguchi, Y, Suh, HG, Seal, AD, Sprong, CA, Kirkland, TW, et al. Dehydration 171 Impairs Cycling Performance, Independently of Thirst: A Blinded Study. Med Sci Sports 172 Exerc 2018; 50: 1697–1703. 173 2.  Armstrong, LE, Johnson, EC, Kunces, LJ, Ganio, MS, Judelson, DA, Kupchak, BR, et al. 174 Drinking to Thirst Versus Drinking Ad Libitum During Road Cycling. J Athl Train. 2014; 175 49: 624–631. 176 3.  Armstrong, LE, Johnson, EC, McKenzie, AL, Ellis, LA, and Williamson, KH. Endurance 177 Cyclist Fluid Intake, Hydration Status, Thirst, and Thermal Sensations: Gender Differences. 178 Int J Sport Nutr Exerc Metab. 2016; 26: 161–167. 179 4.  Berkulo, MAR, Bol, S, Levels, K, Lamberts, RP, Daanen, HAM, and Noakes, TD. 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Awareness of water losses does not impact thirst during exercise in the heat: a double-blind study

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Awareness of water losses does not impact thirst during exercise in the heat: a double-blind study

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