Exercising in the heat can adversely influence performance if fluid balance is not maintained leading to dehydration and a potential risk of heat ailments (28). The risk of dehydration may be further amplified during consecutive days of training if fluids are not adequately replaced between sessions, which could increase the risk of chronic progressive dehydration (27). Athletes commonly subject themselves to an involuntary dehydration of 1–2% of body mass loss during practices and athletic events (13). Body mass losses may be further amplified in hot environments by elite athletes (13). The negative impact of inadequate hydration is well founded for aerobic exercise but the effect it has on anaerobic performance is not well understood.
Hypohydration of a ≥2% reduction in body mass has been shown to impair aerobic performance, especially in the heat (7). However, studies examining dehydration on anaerobic exercise have shown mixed results with a significant decrease (3,21,22), no effect (11,31), or even a significant increase in performance being reported (1). Such discrepancies among studies have made it difficult to understand the impact of dehydration on anaerobic performance. Kraft et al. (22) outlined factors that may contribute to mixed results among studies including the various levels of dehydration, various modes of decreasing body mass, and a variety of exercise tests performed (i.e., sprints, vertical jump, resistance training).
Studies involving a single bout of anaerobic work have typically shown minimal decrements in performance with dehydration (5,17,18,42). Comparatively, few studies have examined the effects of dehydration on repeated bouts of anaerobic exercise. When intermittent bouts have been used, a significant decrease in performance has occurred for basketball skills (3,9), peak power (22), repetitions to fatigue for resistance training (19,21), and repeated sprint performance (29,30).
The majority of research on dehydration and intermittent anaerobic exercise has primarily induced dehydration and examined performance within the same day (21,22,29,30). Judelson et al. (19) recently noted potential confounders of this approach such as elevated core temperature or fatigue from the dehydration protocol. Such confounders may impair exercise performance independent of dehydration. Commonly, athletes will participate in a practice session and have time to reduce core temperature and rest before the next practice the next day. Therefore, there is a need to understand what impact dehydration has on repeated sprint performance within this paradigm while trying to reduce potential confounders. The purpose of this study was to identify if decrements in performance occur during intermittent sprint activity as a result of hypohydration and the magnitude of impairment, fatigue, and perceptual responses regarding feelings of effort and recovery.
Experimental Approach to the Problem
To examine the effects of dehydration on intermittent sprint performance, participants completed 2 identical exercise protocols to induce dehydration in a warm environment (38–39° C). Participants then completed 2 identical intermittent sprint bouts in 2 different treatments of hydration states. A similar protocol to Judelson et al. (19) for dehydrating and rehydrating participants was used for this study. Treatments included euhydrated (EU) and dehydration of 3% of body mass (DEHY). Euhydrated and DEHY were conducted in a counterbalanced order. All intermittent sprint bouts were performed in a temperature-controlled environment (22° C) and occurred at the same time of the day to minimize variation of circadian rhythms. All trials were separated by 1 week. The participants were asked to refrain from heavy exercise for 48 hours, and refrain from caffeine, tea, and alcohol for 48 hours before each trial and also to arrive well rested. Participants continued their regular exercise regimen with the baseball team throughout the week with the exception of 48 hours before each trial.
Eight male collegiate NCAA Division II baseball players volunteered for this study. Participants were not using medications during the time of the study (assessed by questionnaire), and all athletes had been medically cleared to participate in NCAA athletics.
Before participation, the details and risks associated with the experimental protocol were explained, and written informed consent was obtained for each individual in accordance with the local Institutional Review Board policy for use of human subjects. Age (yr) was recorded, along with height (cm) and body mass (kg) measured using a calibrated Scale (Detecto-Medic; Detecto Scales Inc., Brooklyn, NY, USA). Body fat percentage was estimated using skinfold calipers (Lange, Cambridge, MD, USA) and a three-site method (chest, abdomen, thigh) (34), which was completed by the same investigator for all participants. Descriptive data were computed for participants as follows: age (21.2 ± 1.1 years), height (181.9 ± 7.9 cm), body mass (90.3 ± 8.5 kg), and percent body fat (10.5 ± 3.5%).
Before the initiation of the experimental protocol, 3 familiarization sessions were used. The first 2 familiarization sessions consisted of eight 30-m sprints with 45 seconds of rest between each sprint. These first 2 sessions served to introduce participants to the equipment, timing of the sprints, and perceptual variables that would be asked during the trials. The last familiarization sessions consisted of 24 sprints broken into 3 bouts of 8 sprints. Each sprint was separated by 45 seconds of rest, and each bout was separated by a 3-minute rest period. The final familiarization session provided an exact replication of what participants would perform during EU and DEHY. An electronic timing system was triggered by the release of a hand touch pad (TC timing system; Power-Systems Inc., Knoxville, TN, USA), which has been validated by Haugen et al. (15). Infrared timing lights were set at hip height, as instructed by the manufacturer, and were used to record the time of each sprint. All participants started sprints in a standing position. The touch pad was adjusted to hip height for participants on an adjustable table. This was done to minimize participants having to perform sprints from a 3-point stance to which they were unaccustomed. How participants' feet were positioned during the first familiarization session was recorded and used throughout the trials, as suggested by Duthie et al. (10).
During the familiarization trials, euhydrated weight was established by urine specific gravity (Usg) of ≤1.020 (4). The following indexes of hydration status were used for Usg: well hydrated <1.010, minimal dehydration 1.010–1.020, significant dehydration 1.021–1.030, and serious dehydration >1.030 in accordance with the National Athletic Trainers' Association (4). Urine was analyzed for all familiarization sessions and experimental trials. Usg was analyzed by refractometry (A300CL; Atage Co., Spartan, Tokyo, Japan) and calibrated with distilled water before each trial for the dehydration session and intermittent sprint protocol (26,32). Urine was analyzed in duplicate, with the average recorded for Usg. Before reporting, participants were instructed to consume 1 L of water, at approximately 21:00 hours, the night before the trial and additional 1 L of water, at 06:00 hours, the morning of the familiarization sessions. Participants were instructed to perform this procedure of fluid consumption for each familiarization session to establish pretrial body mass (19). All participants reported to the laboratory at 07:00 hours for each familiarization session. On arrival to the laboratory, participants were asked to empty their bladder into a clear container for the examination of Usg with body mass being recorded during this period. Euhydrated weight was calculated from the average body mass during the familiarization trials as suggested by Cheuvront et al. (6). Participants were also required to record all food and fluids consumed in a 24-hour period before the establishment of the first pretrial body mass. Food and fluids were replicated for the additional preliminary trials and all exercise trials. Participants verbally verified before each trial that they had adhered to food and fluid consumption. If participants did not comply with previous food and fluid consumption, the trial was rescheduled.
During the experimental trials, participants arrived at 15:00 hours to the Human Performance laboratory. Participants were also instructed to arrive in a 90-minute postprandial state. Participants were then asked to empty their bladder in a container to analyze urine and were weighed nude before each trial. If participants Usg was >1.020, the trial was rescheduled. Participants self-inserted a rectal thermocouple (Trec) (Physitemp Ret-1 rectal thermocouple; Physitemp Instruments, Inc., Clifton, NJ, USA) 8 cm beyond their anal sphincter. The rectal thermocouple has been used extensively in other studies (8,14,21,22). Participants were instructed to sit quietly for 15 minutes while baseline measurements of heart rate (HR) and Trec were examined. An HR monitor was worn throughout the test (Polar, Lake Success, NY, USA).
Participants wore a long-sleeve shirt and ankle-length athletic pants during the dehydration portion of the trial. Clothing composed of 100% cotton was provided to participants by investigators. Underneath the long-sleeve shirt and pants, participants wore a short-sleeve t-shirt and shorts composed of 100% cotton fabric, as well as socks and running shoes.
During the dehydration sessions, participants walked on a motor driven treadmill at 6.1 km·h−1 with no incline until 3% dehydration of body mass was achieved. Participant's body mass was examined in 30-minute increments, and as participants approached the desired body mass loss, weight was measured more frequently. Participants exited the heat chamber, dried off with a towel, and nude body mass was reexamined each time.
If Trec reached 39.2° C, participants were required to reduce the intensity of the exercise or stop exercising and sit in the environmental chamber until Trec decreased or until 30 minutes of time had elapsed. Also, trials were terminated if participants asked to stop exercising or displayed signs and symptoms of heat illness. Heart rate and Trec were recorded every 5 minutes during the dehydration portion of the trial.
After the dehydration procedure, participants exited the environmental chamber into the laboratory at ambient temperature of 21° C. Participants were instructed to dry off and change clothes. Thereafter, participants were instructed to sit quietly and remain seated and rest while they were rehydrated by investigators to achieve either an EU or 3% DEHY state for the next morning. During the EU portion of the trial, participants were provided with fluid volumes greater than the amount of sweat loss that occurred during the dehydration process (150% fluid replacement) (36,37) and were given additional fluids to replace overnight fluids lost (1 L). Fluids consisted of an oral ingestion of water only with 60 mmol·L−1 of Na+ added to aide in fluid retention (36). The water was also flavored with a solution that contained no calories. Fluids were consumed in metered increments during the recovery period at a rate of 1 L·h−1 consisting of 250 ml every 15 minutes. On the third hour into the rehydration period, participants were instructed to purchase dinner from the nearby cafe at the university. Participants were given several food options to choose from by investigators, which consisted of similar calorie, macronutrient content, and sodium levels. The food item participants selected during the first dehydration trial was replicated for the next trial. Participants then returned to the laboratory and consumed the food while continuing the rehydration process. For the 3% DEHY portion of the trial, participants were given 500 ml of fluid (water only) flavored with a solution that contained no calories along with food after the dehydration procedure. Once the hydration process was complete, for either EU or DEHY, participants were instructed not to consume any additional food or water thereafter.
The next morning, participants arrived to the laboratory at 06:30 hours to perform the intermittent sprints. Participants were asked to empty their bladders to examine Usg before body mass was recorded. All testing took place indoors in a gymnasium on a level hardwood floor. Before the start of the intermittent sprints, each participant completed a 400-m general warm-up followed by 5 minutes of standardized dynamic warm-up (e.g., high-knee, carioca) and 4 practice sprints at 20, 30, 35, and 40 m. Participants were instructed to perform the first 2 practice sprints at 50% of max and the last 2 sprints at maximal intensity. After the warm-up, each session consisted of an intermittent sprint protocol used by Laurent et al. (24,25) to examine fatigue and recovery. Participants preformed twenty-four 30-m sprints divided into 3 bouts with 8 sprints performed per bout (total, 24 sprints). There was 45 seconds of rest between each sprint and 3 minutes between bouts. The participants performed 8 sprints per bout as to minimize the occurrence of pacing throughout the trial (24,25). Participants were instructed to approach the line with 10 seconds left before the next sprint and were provided a 5-second countdown before the start of each sprint. Participants were not informed of the number of sprints they had completed during the intermittent trial. Verbal encouragement was consistently given to each participant throughout every sprint.
Before the start of each trial, participants were asked to rate how recovered and prepared they felt for the intermittent sprints using the perceived recovery status scale (PRS, Table 1) adapted from Laurent et al. (25). At the conclusion of each sprint, HR, ratings of perceived exertion (RPE) using the OMNI scale, and perceived readiness (PR) scale (Table 2) were recorded. The OMNI RPE pictorial 0–10 scale (35,41) was introduced to participants before the intermittent sprint trials. Before each session, participants were instructed regarding RPE with “0” anchored to seated rest and “9-10” to feeling of maximal exertion. The PR scale by Laurent et al. (25) was also verbally anchored before each session (Table 2), and a session RPE (SRPE) was recorded 20 minutes after the completion of the exercise using the OMNI scale to rate the global difficulty of the entire exercise session (12).
To determine fatigue, a decrement score, which is calculated as a percent, was calculated for each sprint bout in accordance with that of Oliver (33). The decrement score is calculated by dividing the difference between the average sprint time of the bout by the fastest sprint time of the bout and multiplying by 100.
A 2 × 3 within-subjects repeated-measures ANOVA was used to identify significant main effects or interactions between hydration status and bout of sprints on mean sprint times, fatigue, HR, PR, and RPE. When appropriate, univariate follow-ups, including Fisher's LSD, were used to determine where significant differences occurred. If violations of sphericity occurred, data are presented using the Greenhouse-Geisser correction factor. Paired t-tests were used to compare the differences in SRPE and PRS between EU and DEHY. Power is presented as N-β, and effect sizes for main effects are reported as partial eta squared (η2), whereas post hoc effect sizes are presented as Cohen's d. Between condition, effect sizes were classified as a small effect size (d = 0.20), medium effect size (d = 0.50), and large effect size (d = 0.80). Statistical significance was determined a priori at ≤0.05. All data were analyzed using Statistical Package for Social Sciences (SPSS Inc., 19th edition, Chicago, IL, USA) and are presented as mean ± SD.
Dehydration Procedure and Urine Specific Gravity
All participants lost the entire 3% body mass during the trials. No participant was stopped because of signs or symptoms of heat ailments, and no participant requested to stop the dehydration process. One participant did report feeling light-headed immediately after the dehydration process for 1 trial.
The exercise duration for the dehydration process only varied slightly between sessions (EU 90 ± 12 minutes vs. DEHY 87 ± 9 minutes) and was not significantly different (p = 0.94). Mean environmental conditions for the dehydration process were 38.6 ± 0.5° C and 30–40% humidity. The next morning in the gymnasium during the intermittent sprint protocols, the environment was 22 ± 2.1° C and 25–32% humidity. Trec (EU 38.2 ± 0.4° C vs. DEHY 38.2 ± 0.3° C; p = 0.68) and HR (EU 143 ± 19 b·min−1 vs. DEHY 138 ± 18 b·min−1; p = 0.47) showed no significant difference throughout the dehydration process. There was no significant difference (p > 0.05) in calories (EU 970 ± 104 kcal vs. DEHY 957 ± 89 kcal), or sodium (EU 2530 ± 26 mg vs. DEHY 2420 ± 17 mg) consumed after the dehydration procedure during the establishment of body mass for the next morning. Mean percentage change in body mass before the start of the intermittent sprints was EU −0.32 ± 0.34% vs. DEHY −3.28 ± 0.41%. Usg was ≤1.020 for all familiarization trials, before the dehydration process (EU 1.004 ± 0.004 vs. DEHY 1.005 ± 0.003), and before the intermittent sprints for EU (1.011 ± 0.004) with the exception of the DEHY intermittent sprint trial (1.024 ± 0.004).
All participants completed all 24 sprints with no injury. The repeated-measures ANOVA revealed a significant main effect of condition on sprint times (p = 0.03; η2 = 0.51; N-β = 0.65) between conditions but not bout of sprints (p = 0.32) and no significant interaction (p = 0.06). Post hoc measures comparing mean sprint times between conditions are shown in Figure 1. There was no significant difference between EU and DEHY mean sprint times during the first bout (p = 0.18) but significantly higher mean sprint times in the DEHY vs. EU condition during the second bout (4.87 ± 0.29 vs. 5.03 ± 0.33 seconds; p = 0.01; d = 0.94) and the third bout (4.91 ± 0.29 vs. 5.12 ± 0.44 seconds; p = 0.02; d = 0.98).
Data revealed no significant main effect between DEHY vs. EU condition (3.0 ± 1.6% vs. 3.5 ± 2.0%; p = 0.10, d = 0.26) or between bouts 1, 2, and 3 of repeated sprint work (3.0 ± 1.8%; 3.5 ± 2.9%; and 3.3 ± 1.8%, respectively, p = 0.65) suggesting similar rate of fatigue during the sessions.
Data analysis revealed a significant main effect of condition (p = 0.01; η2 = 0.64; N-β = 0.86) and bout (p < 0.01; η2 = 0.62; N-β = 0.90) on HR during repeated sprints but no significant interaction (p = 0.99). Post hoc analyses revealing significant differences are shown in Figure 2. Results show no significant difference in mean HR response between conditions during the first bout; however, participants demonstrate significantly lower HR during the second bout (p = 0.05; d = 1.45) and the third bout (p = 0.01; d = 1.3) for the EU vs. DEHY condition.
Ratings of Perceived Exertion
Results show a significant main effect of condition (p = 0.01; N-β = 0.75; η2 = 0.57) and bout (p < 0.01; N-β = 1.0; η2 = 0.90) on mean RPE during repeated sprint exercise. There was no significant interaction of condition and bout (p = 0.13). As shown in Figure 3, RPE response increased significantly with each bout of sprints (p ≤ 0.01–0.03). Additionally, participants in the DEHY vs. EU condition demonstrated significantly higher RPE responses during the second bout (p = 0.02; d = 1.85) and third bout (p = 0.01; d = 2.01).
The statistical analyses showed a significant main effect of condition (p = 0.02; η2 = 0.57; N-β = 0.75) and bout (p < 0.01; η2 = 0.90; N-β = 1.0) on mean readiness to perform repeated sprint work. There is no significant interaction of condition and time (p = 0.75). Figure 4 shows significantly decreased readiness (shown as increased PR scores) with each successive bout of sprints. Also, results reveal significantly lowered readiness to perform sprints during the second and third (p < 0.01; d = 1.44–2.14) bouts of sprint when DEHY vs. EU condition. Results show similar readiness across the first 8 sprints between conditions.
Perceived Recovery Status and Session RPE
Figure 5 shows significantly lower PRS when DEHY vs. EU (p = 0.01; d = −1.79) before performing the session of repeated sprint exercise. Also, DEHY produced significantly higher SRPE values (p < 0.01; d = 2.17) than the EU condition after the entire repeated sprint work session.
This study examined effects of dehydration on intermittent sprint performance. The design of the study intended to mimic a situation in which an athlete practiced in the afternoon and either adequately rehydrated or failed to rehydrate before the next practice in the morning. Other studies investigating dehydration on intermittent anaerobic activity have commonly induced hypohydration and examined exercise performance within the same day (21,22,29,30). Potential factors such as elevated core temperature and being fatigued from the hypohydration protocol could confound results with such a design. This study tried to reduce potential confounders and has practical application to what most athletes will be commonly subjected to with sports-related training. Although not an exact replication of intermittent sports activity, we sought to use a sprint distance similar to anaerobic activity endeavors. The intermittent sprints covered a total distance of 720 m (24 × 30-m sprints) similar to total sprint work performed during most team sport activities (i.e., soccer, hockey, rugby) (40). Results show a significantly faster sprint time, lower HR, and decreased perceptual response with large effect sizes occurring primarily in the second and third bouts of sprints for EU vs. DEHY (Figures 1–5).
This study supports previous work on repetitive bouts of anaerobic exercise showing impaired performance from dehydration (3,22,29,30). The majority of studies have examined performance on a cycle ergometer showing significantly reduced total power (16), peak power (22,39), and mean power (22,39) with a reduction in power ranging from 3.4 to 10.4% when dehydrated by 3–4.5% (16,22,39). Studies examining repeated sprints have also shown decrements in performance (3,29,30). Maxwell et al. (29) showed a significant reduction in time to exhaustion of 3.9% while performing 20 seconds intermittent treadmill sprints when dehydrated by 1.5%. Mohr et al. (30) also reported a 2.6% slower mean sprint time during 3 × 30-m runs after a soccer match when dehydrated by 2% compared with euhydrated before the match. Basketball skills and drills have also been shown to progressively decline as the percentage of dehydration increases (3). Baker et al. (3) showed impairments in performance for ladder suicide drills and full court sprints at 1–3% dehydration. This study showed a decrease in mean sprint time of 3.2 and 4.2% in bouts 2 and 3 of the protocol with DEHY (Figure 1). Although, not all studies examining dehydration and repeated anaerobic work have shown decrements in performance (38,43). Collectively, this study and the others show dehydration from 1 to 3% can have negative impact on repeated intermittent sprint performance. These studies stress the importance of athletes competing in intermittent anaerobic sports to be mindful of daily fluid deficits especially in a hot environment and the impact dehydration has on performance.
Performance varied among participants completing the intermittent sprint bouts while dehydrated. Seven of the 8 participants showed an overall decrease in mean sprint time of 3.3% ranging from 1 to 5.5% when DEHY compared with EU. There was 1 participant, however, who experienced an increase in performance of 0.8% when DEHY compared with EU with his mean sprint time being constant throughout the trials among hydration states. It is unclear why performance improved for this participant during the DEHY trial. Players participated in the same training program and had similar years of experience playing collegiate baseball. It seems some individuals may be more immune to effects of dehydration as compared with others. Therefore, it is important for coaches and athletes to be aware of various responses among individuals while dehydrated. Future studies are warranted to understand the individual variances in performance with dehydration.
There was a similar rate of fatigue during the hydration states with no significant difference occurring in decrement scores. Performance was significantly decreased later in the trial for bouts 2 and 3 when DEHY compared with EU (Figure 1). It is logical that dehydration would have adverse effects on performance at the end of the trial when fatigue is most prevalent. Other studies have shown a significant decrease in power and number of repetitions completed with resistance training occurring later in the exercise period while dehydrated (19,21,22). Kraft et al. (23) proposed a 30-second total work being accomplished either from a single bout or multiple bouts of anaerobic exercise before a decrease in performance occurs with dehydration. This study supports this notion with performance not being affected until the second bout of sprints after 32–40 seconds of work had been accomplished (first bout of sprints: 8 sprints × 4–5 seconds each sprint = 32–40 seconds). As the number of sprints increases a greater production of ATP is produced by aerobic metabolism. Therefore, performance decrements may occur later in the exercise bouts based on a greater reliance of aerobic metabolism as compared with anaerobic pathways being potentially less affected by dehydration. Several reviews and position statements (2,20,36) have stated that anaerobic performance is not impacted by dehydration. However, studies cited showing no impact on performance have primarily been single bouts of work, typically ≤30 seconds in duration (4,17,18). Future research should examine rest time between sprints, amount of work accomplished, and the extent to when performance is affected with various levels of dehydration.
Dehydration has been shown to decrease plasma volume, increase hematocrit, elevate HR, and impair stroke volume and cardiac output. This study showed a large effect size for increased HR in bouts 2 and 3 (d = 1.30–1.45) of the sprints for DEHY (Figure 2). This is in accordance with other studies showing an elevated HR when dehydrated while accomplishing less work during intermittent sprints (29) and resistance training to failure (21). However, not every study has shown a difference in HR when dehydrated to various percentages compared with euhydration during anaerobic paradigms (3,22). It is unclear why various responses in HR have occurred even among similar dehydration percentages and protocols (21,22). Studies examining intermittent anaerobic activity have used various methods of inducing hypohydration, rehydrating participants, examining performance, and rest periods during the exercise protocols, which could play a potential factor in the various HR responses.
Participants reported significantly lower perceptual strain during the exercise bout and for the total session when EU in accordance with faster sprint times (Figures 3–5). Moreover, participants reported feeling more adequately recovered and prepared for the exercise bout when EU vs. DEHY (Figure 5). Other studies have shown equivocal results with perceptual response with various percentages of dehydration (3,21,22). Kraft et al. (21) showed a significantly higher RPE with repetitions to failure for resistance training with 3% dehydration. However, in a similar study, the author showed no difference during repeated sprint bouts on a cycle ergometer while accomplishing less work with dehydration (22). No difference in perceptual strain has also been shown with various dehydration percentages for basketballs skills (3). Relatively few studies have examined perceptual response during intermittent anaerobic activity with dehydration. Future studies should consider using the various methods of examining perceptual strain and more homogenous methods of dehydrating participants to better understand the impact of dehydration with perceptual response.
In conclusion, this study showed a significant decrease in sprint performance, elevated HR, and negative perceptual response with 3% DEHY compared with EU. This contrasts some investigations (38,43) but is in agreement with other studies (3,29,30) examining dehydration on repeated anaerobic exercise performance. Future research should examine the impact dehydration would have on agility drills and the various work-to-rest ratios with an array of dehydration percentages.
Results of this study show impairment in repeated sprint performance when dehydrated by 3% of body mass. Decrements in intermittent sprint performance occurred during a thermoneutral environment when dehydrated, and the potential for further decrements in performance is possible when exercising in a hot and humid environment. Strength and conditioning professionals, athletes, coaches, and athletic personnel should be mindful of the impact dehydration has on intermittent anaerobic activity and should be encouraged to closely monitor hydration status from day to day to optimize performance.
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