Progressive Dehydration Causes a Progressive Decline in Basketball Skill Performance

Abstract

Purpose: 

To determine the effect of 1, 2, 3, and 4% dehydration (DEH) versus euhydration (EUH) on basketball performance in adult male players.

Methods: 

Seventeen 17- to 28-yr-old male basketball players completed 3 h of interval treadmill walking (40°C and 20% relative humidity) with or without fluid replacement. Subjects completed six trials in random order: 1) EUH with a carbohydrate-electrolyte solution (CES), 2) EUH control (flavored water with 0% carbohydrate and 18 mM sodium), 3) 1% DEH, 4) 2% DEH, 5) 3% DEH, and 6) 4% DEH. After a 70-min recovery period, subjects performed a sequence of continuous basketball drills designed to simulate a fast-paced game. Measures of overall skill performance during the 80-min game included 1) total time to complete basketball-specific movement drills (sprinting, defensive slides, sprinting-defensive slides combination, and repetitive jumping drills) and 2) total number of shots (foul-line and baseline jump shots, layups, three-point, 15-ft, free throws) made per game.

Results: 

Performance during all timed and shooting drills declined progressively as % DEH increased. Total time to complete basketball-specific movement drills was slower (1%: + 7 ± 6; 2%: + 20 ± 5 (P < 0.05); 3%: + 26 ± 7 (P < 0.005); 4%: + 57 ± 9 (P < 0.0001) s), and fewer shots were made during DEH versus EUH control (1%: −5 ± 1; 2%: −6 ± 2 (P < 0.05); 3%: −8 ± 2 (P < 0.005); 4%: −10 ± 1 (P < 0.0001) shots made). There were no significant differences in performance between CES and EUH control.

Conclusion: 

Basketball players experienced a progressive deterioration in performance as DEH progressed from 1 to 4%. The threshold, or % DEH at which the performance decrement reached statistical significance, was 2% for combined timed and shooting drills.

Recent field research with players of the National Basketball Association (NBA) indicates that inadequate hydration practices are common in this group of athletes. In 2004-2005, Osterberg et al. (^21,22) showed that NBA players were inadequately hydrated prior to and during NBA preseason practices and NBA summer league games. Specific gravity measurements of urine samples collected from NBA players before competition indicated that approximately half of the players were ≥ 1% hypohydrated (⁷) before the practice or game commenced. During competition, only about 40% of sweat losses were replaced; thus, players accrued an additional 1-3% dehydration (DEH) throughout the course of practices and games (^21,22). These field study results suggest that a combination of inadequate pregame and in-game hydration practices can lead to up to 4% DEH by the end of competition. Considering that the outcome of most basketball games is decided in the final minutes of play, the effect of 1-4% DEH on basketball performance merits study in a more controlled setting.

DEH has been implicated in impaired performance in many prolonged aerobic exercise tasks (^2,8,17,23). For example, compared with euhydration (EUH, enough fluid consumed to maintain initial body mass), cycling time to exhaustion was significantly shorter (¹⁷) and total work completed in a 30-min cycling time trial was significantly less (⁸) when subjects were 3.2 and 3.0% DEH, respectively. In addition, compared with EUH, running velocity decreased by 6-7% during 5000- and 10,000-m outdoor track races when runners were 1.6 and 2.1% DEH, respectively (²).

The impact of DEH on performance of various short-duration, high-intensity activities has also been tested previously. University and semiprofessional soccer players' performance in a soccer skill test after intermittent high-intensity shuttle running was significantly impaired during 2.4% DEH trials compared with ad libitum fluid intake (which led to 1.4% DEH) trials (¹⁸). Conversely, compared with a control condition (0.6-0.7% DEH), 2.2 and 2.5% DEH were not detrimental to competitive sprint (50, 200, and 400 m) or power (vertical jump) performance in high school and collegiate track athletes (²⁶).

The game of basketball is characterized by intermittent bouts of high-intensity activity repeated over a prolonged period of time and requires the execution of complex sport-specific skills. Only two studies have tested the effects of DEH on basketball-specific skills. Dougherty et al. (¹¹) have shown that shooting percentage and on-court sprinting and lateral movement times within a simulated game context were significantly impaired by prior 2% DEH relative to placebo EUH in 12- to 15-yr-old male basketball players. Conversely, Hoffman et al. (¹⁵) found no difference in basketball shooting performance in 17-yr-old boys playing a simulated two-on-two full-court basketball game when no fluid was given (causing progressive 1.9% DEH) versus EUH.

The impact of DEH on basketball performance in adult players has not been investigated. Additionally, in most previous DEH-related research, investigators have studied the impact of a single level of DEH (e.g., 2% DEH) versus EUH on exercise/sport performance. Few investigators have tested progressive levels of DEH in a dose-response manner to determine whether a critical level of water deficit exists at which performance is impaired compared with that of EUH. Therefore, the aim of the present study was to determine the effect of 1 to 4% DEH versus EUH on performance of basketball-specific shooting and movement drills during a simulated game in highly skilled 17- to 28-yr-old male players. DEH levels of 1, 2, 3, and 4% were tested (on separate days) and compared with EUH control (flavored water with 0% carbohydrate and 18.0 mM sodium) to determine whether there is a DEH threshold at which performance is significantly impaired. Additionally, EUH with a 6% carbohydrate-electrolyte solution (CES) was compared with EUH control to determine whether addition of carbohydrate enhances basketball performance over EUH with a carbohydrate-free solution.

METHODS

Subjects.

Seventeen highly skilled male basketball players (17-28 yr) volunteered to participate in this study (Table 1). The players' highest level of competitive basketball experience ranged from high school (N = 9) to college (Division III, N = 4; Division I, N = 4). Each was a first-team member and standout player (assessed by self-reported basketball game statistics) for their respective teams. Participants were informed of the experimental procedures and associated risks before providing written informed consent. This study was approved by the institutional review board for the protection of human subjects of the Pennsylvania State University. Preliminary screening included a resting 12-lead electrocardiogram, skinfold measurement to determine adiposity, blood analysis (CHEM-24), a graded exercise test on a treadmill to determine maximal oxygen uptake (V˙O_2max), a physical exam, and maximal vertical jump measurement.

TABLE 1: Subject characteristics.

Experimental procedure.

Seventeen subjects completed six experimental trials: 1) EUH with a commercially available lemon/lime-flavored CES (6% carbohydrate and 18.0 mM Na), 2) EUH control (lemon/lime-flavored water with 0% carbohydrate and 18.0 mM sodium included to enhance palatability), 3) 1% DEH, 4) 2% DEH, 5) 3% DEH, and 6) 4% DEH. Experimental trials were scheduled at least 1 wk apart and were assigned in a randomized, counterbalanced order.

Subjects reported to the laboratory on the morning of each test day after having swallowed a disposable temperature sensor the night before and fasting overnight. Immediately on arrival they voided and then were weighed (all body mass measurements were taken with the subject wearing shorts and heart monitor only). Next, the subject ate a low-carbohydrate standardized breakfast (550 kcal total: 50 g (36%) carbohydrate, 16 g (25%) fat, and 56 g (39%) protein) and drank 5 mL of water per kilogram of body weight. After breakfast the subject had an 18-gauge Teflon catheter placed in an antecubital vein in one arm. After emptying his bladder, the subject entered an environmental chamber set at 40°C and 20% relative humidity. Next, the subject was weighed (initial body mass) and was then asked to stand quietly on a treadmill for 10 min before the baseline blood sample, heart rate (HR), blood pressure (BP), and core temperature (T_c) were obtained. Next, the subject walked (in shorts, socks, shoes, and heart rate monitor only) for nine 15-min bouts (50% V˙O_2max) separated by 5 min of rest. Ten minutes into each walking bout, a blood sample, T_c, HR, BP, and rating of perceived exertion (RPE) were obtained. At the end of the 3-h interval-walking protocol, the subject exited the chamber and was asked to complete the Fatigue Survey, a visual analog rating scale with questions pertaining to physical well-being (described later), and then to empty his bladder.

EUH/DEH protocol.

Subjects were weighed during each rest period to determine periodic sweat loss. During the EUH trials, subjects drank enough CES or flavored water with sodium during rest periods to fully replace sweat and urine losses and maintain their initial body mass. During the DEH trials, fluid was restricted until the subjects reached their target body mass (i.e., body mass that corresponds with the desired % DEH). If a subject's body mass fell below his target body mass, he ingested distilled water to maintain the desired % DEH.

Recovery period.

After the catheter was removed from the subject's arm, he sat in a thermoneutral room (ambient temperature = 23°C) for a 70-min recovery period. During this time, body mass, T_c, HR, and BP were measured at 15-min intervals. The subject drank water, CES, or flavored water with sodium as needed to maintain the desired hydration state. A urine sample was collected at the end of recovery.

Basketball drill session.

After recovery, the subject was moved to a nearby gymnasium where he completed an orchestrated sequence of continuous basketball drills designed to simulate a fast-paced basketball game. The drill session commenced 20 min after the recovery period. Basketball drills were 80 min in duration and consisted of four 15-min quarters with 5-min breaks between quarters and a 10-min break at halftime. The drill session was designed in consultation with coaches from NCAA Division I, II, and III basketball programs and incorporated most aspects of the game of basketball including: speed (sprinting drills), agility/lateral movement (defensive slide drills), explosiveness (vertical jump drills), shooting (off the dribble and off the pass), and a combination of two or more of these basketball-specific tasks. The simulated basketball game was designed to include drills that were relatively simple and routine to experienced basketball players. In addition, the subjects were familiarized with the drills before their first experimental trial, to avoid a learning effect.

The first quarter of the simulated basketball game consisted of seven drills: 1) baseline jump shots: start at half court, sprint to cone at baseline area, receive pass from investigator standing on foul line, shoot a 15-ft baseline jump shot, sprint to opposite sideline at half court, repeat (number made in 2 min); 2) layup shooting: start at elbow, dribble in, shoot a layup, then get own rebound, dribble to opposite elbow, dribble in, shoot a layup, repeat (number made in 2 min); 3) ladder suicide sprints: start at baseline, sprint to foul line, sprint back to baseline, sprint to half court, sprint back to baseline, sprint to opposite foul line, sprint back to baseline, sprint to opposite end line, sprint back to baseline, sprint to opposite foul line, sprint back to baseline, sprint to half court, sprint back to baseline, sprint to foul line, sprint back to baseline (time to completion); 4) 30 vertical jumps: the subject was asked to repeatedly touch a mark set at 70% of his maximum vertical jump 30 times as quickly as possible (time to completion); 5) zigzags: defensive slides to each cone set in a zigzag pattern from baseline to baseline on one side of the basketball court, performed over four lengths of the court total (time to completion); 6) around-the-world shooting: continuous 15-ft shooting from seven spots (number made in 2 min); and 7) full-court combination: start at corner, sprint forward to half court, defensive slides across midline, sprint forward to opposite corner, defensive slides across opposite baseline, backpedal to half court, defensive slides across midline, backpedal to baseline, defensive slides across baseline (time to completion). The second quarter consisted of seven drills: 8) foul-line jump shots: start at corner, zigzag defensive slides to half court, sprint to center court, pickup basketball, dribble to foul line, shoot a foul-line jump shot, sprint to opposite corner, repeat (number made in 3 min); 9) three-point shooting: continuous three-point shooting from seven spots (number made in 2 min); 10) 20 court-width sprints (time to completion); 11) maximum vertical jump: subject allowed one step and then must jump off two feet (best height of three attempts); 12) 30 lane slides: defensive slides across width of key (time to completion); 13) key combination: start on baseline at corner of key, sprint forward to top corner of key, diagonal defensive slides to opposite corner of key on baseline, sprint forward to top of key corner, diagonal defensive slides to opposite corner of key (time to complete five); and 14) free-throw shooting (number made in 20 attempts). The drills performed in the third quarter were the same as that of the first quarter and the drills performed in the fourth quarter were the same as that of the second quarter.

Performance measures included single and total number of stationary shots made (15-ft, three-point, and free-throw shots), single and total number of shots "on the move" (i.e., subject required to sprint, defensive slide, and/or dribble between shot attempts) made (layups, baseline jump shots, and foul-line jump shots), single maximum vertical jump, single repetitive vertical jumps, single and total sprint times (ladder suicide and 20 court widths), single and total defensive slide times (zigzags and 30 lane slides), and single and total times for the sprinting-defensive slide combination drills (full-court and key combinations). Additionally, a total score was calculated for all timed drills (total time to complete ladder suicide, 30 vertical jumps, zigzags, full-court combination, 20 court widths, 30 lane slides, and key combination) and all shooting drills (total number of baseline jump shots, layups, 15-ft shots, foul-line jump shots, three-point, and free-throw shots made) to represent overall skill performance over the entire course of the simulated basketball game.

The desired hydration state was maintained throughout the basketball drill session by weighing the athlete at the end of each quarter and having him drink the appropriate volume of fluid during the rest periods. The subject's T_c, HR, and RPE were obtained immediately after he completed the full-court combination drill in the first and second quarters and after the key combination drill near the end (i.e., before free-throw shooting) of the second and fourth quarters. At the end of the second and fourth quarters, the subject was asked to void his bladder and complete the Fatigue Survey.

Measurements.

Heart rate was measured using a Polar® heart rate monitor, and blood pressure was measured by brachial auscultation (sphygmomanometry). Rating of perceived exertion was assessed using the Borg scale (⁴). Body mass was measured to the nearest 0.05 kg using a Seca 770 scale. A CorTemp Disposable Temperature Sensor (COR-100) and CorTemp Recorder (CT-2000) were used to measure T_c. The vertical jump drills were performed using a Vertec.

Blood and urine analysis.

Venous blood samples (9.5 mL each) were drawn without stasis. A 2-mL aliquot was transferred into an EDTA-treated test tube and immediately analyzed for hematocrit (microhematocrit centrifugation) and hemoglobin (Hemacue Hb 201⁺) in triplicate. The remaining 7.5-mL aliquot was transferred into a serum separator tube, allowed 30-60 min to clot, and then centrifuged at 4°C for 15 min. Serum was analyzed for glucose concentration (S_gluc; hexokinase UV method, Olympus Model AU5200), sodium concentration (S_Na; ion-specific electrode method, Olympus Model AU5200), total protein concentration (S_prot; biuret method, Olympus Model AU5200), and osmolality (S_osmol; freezing point depression, Advanced DigiMatic Osmometer Model 3D2) in triplicate. Urine samples were analyzed for specific gravity (U_sg; Refractometer, Atago A300CL), osmolality (U_osmol), volume (U_vol), and color (U_col). Urine color was determined by holding each specimen container next to a validated color scale (¹) in a well-lit room. The eight-color scale ranges from 1 (very pale yellow) to 8 (brownish green).

Calculations.

Mean arterial pressure (MAP) was calculated as MAP = (1/3) pulse pressure + diastolic BP. Sweat loss (SL) was calculated from Δ body mass corrected for fluid consumed and urine excreted. The percent change in plasma volume from baseline (ΔPV) was calculated from hematocrit and hemoglobin (¹⁰).

Subjective ratings.

The Fatigue Survey was administered to the subject after the heat chamber exercise (minute 180), at halftime (minute 305), and at the end of the simulated basketball game (minute 350). The survey consisted of a 100-point visual analog rating scales (ranging from "none" (0) to "very" or "severe" (100)) which assessed subjective feelings of lightheadness, windedness, hotness, side stitch/ache, muscle cramping, total-body fatigue, upper-body fatigue, and leg fatigue.

Statistical analysis.

The two distinct hypotheses tested were 1) 1 to 4% DEH will progressively impair basketball performance compared with EUH control, and 2) CES EUH will improve basketball performance measures compared with EUH control. To present the comparison of skill performance results for 1 to 4% DEH versus EUH control and CES versus EUH control trials, data from the EUH control trial were subtracted from 1 to 4% DEH and CES trials because the data are paired data from the same subject. Taking the difference from EUH control better reflects each hypothesis directly, removes the subject effect, and provides an effective comparison of the treatments.

To determine the DEH threshold (% DEH at which results are significantly different from EUH control) for basketball performance, subjective ratings, physiological, and RPE variables, a repeated-measures analysis of variance (ANOVA) was conducted. The data were analyzed with a linear mixed model by using PROC MIXED in SAS 9.1. The covariance structure was chosen by the Akaike information criterion (AIC). Treatment groups (hydration status) were treated as fixed effects and subjects were treated as random effects. The P values were adjusted for multiple comparisons between the treatment groups using Dunnett's post hoc test. Similarly, a linear mixed model was used to compare basketball performance, subjective ratings, physiological, and RPE variables between CES EUH and EUH control. The significance level for all statistical tests was set at alpha = 0.05. All data are presented as means ± SD, unless otherwise indicated.

RESULTS

There were no statistically significant differences between CES EUH and EUH control in the basketball performance scores, subjective ratings, RPE, or physiological variables (except that S_gluc was higher in CES trials at the end of heat chamber exercise); thus, CES EUH was excluded from the presentation for simplification. All subsequent comparisons of 1-4% DEH versus EUH refer to EUH with the lemon/lime-flavored water containing 0% carbohydrate and 18 mmol sodium.

Physiological and RPE variables.

HR, T_c, MAP, RPE, sweat loss, U_vol, U_col, U_sg, and U_osmol data are presented in Table 2. There were no significant differences in the physiological variables among trials at baseline. At the end of the heat chamber exercise, HR was significantly and progressively higher during 1-4% DEH and T_c was significantly and progressively higher during 2-4% DEH compared with the EUH control trial. At the end of the 70-min recovery period, HR and T_c only remained significantly elevated above that of EUH control in the 4% DEH trial. At halftime (end of the second quarter) of the 4% DEH trial the subjects' T_c remained elevated above that of EUH control. During 3-4% DEH the subjects' sweat loss was significantly less than that of EUH control throughout the entire basketball "game" (end of second and fourth quarters).

TABLE 2: Physiological and rating of perceived exertion (RPE) variables.

Blood variables.

S_gluc, S_Na, S_osmol, S_prot, and ΔPV at baseline and the end of the heat chamber exercise are presented in Table 3. There were no significant differences in the blood variables among trials at baseline. Compared with the EUH control trial, S_osmol and ΔPV (% decrease) were significantly and progressively higher during 1-4% DEH, S_Na was significantly higher during 2-4% DEH, and S_prot was significantly higher during 3-4% DEH at the end of the heat chamber exercise.

TABLE 3: Blood variables.

Subjective ratings.

Responses to the subjective questionnaires are presented in Figure 1. At the end of the heat chamber exercise (Fig. 1A), subjects rated their feelings of lightheadedness, windedness, overheatedness, muscle cramping, total-body fatigue, upper-body fatigue, and leg fatigue significantly higher during 3-4% DEH versus EUH control. Compared with EUH control, subjects reported feeling significantly more lightheaded and having greater leg fatigue during 3-4% DEH, and they felt greater upper- and total-body fatigue during 4% DEH at the end of the basketball "game" (Fig. 1B).

FIGURE 1: Responses to subjective 100-point visual analog rating scales (ranging from "none" (0) to "very" or "severe" (100)) at the end of the heat chamber exercise (A) and at the end of the basketball "game" (B). Only scales yielding significant effects at these time points are presented. Data presented as means ± SE. DEH, 1-4% dehydration trials; EUH C, euhydration control trial; * P < 0.05 vs EUH C.

Fluid intake.

During the EUH trials subjects consumed 486 ± 189, 641 ± 123, and 501 ± 152 mL of CES or 443 ±251, 575 ± 192, and 430 ± 191 mL of flavored water with sodium, at the end of quarters 1, 2, and 3 of the drill session, respectively. During the DEH trials, the volume of distilled water consumed at the end of each quarter (in chronological order from quarter 1 to 3) was 437 ± 171, 597 ± 201, and 493 ± 163 mL for 1% DEH; 465 ±173, 512 ± 223, and 361 ± 167 mL for 2% DEH; 315 ± 208, 408 ± 155, and 320 ± 153 for 3% DEH; and 216 ± 92, 388 ± 180, and 299 ± 173 for 4% DEH. Fluid volumes seemed to be well tolerated by the athletes in terms of gastrointestinal comfort, as their subjective ratings of side stitch or ache were relatively low, even during the EUH trials (e.g., 11 ± 15 on a 100-point scale, at the end of drills during CES trials).

Basketball performance.

Each individual basketball drill was performed twice per drill session (i.e., once per half). Within trials, there were no statistically significant differences in individual drill performance scores between half 1 and half 2; therefore, scores for each individual drill were calculated as the average of the two halves. Then, total performance scores were calculated as the sum of all individual drill performance scores within the same drill category.

There were no statistically significant differences in overall basketball performance between CES and EUH control. The total number of shots made (sum of baseline jump shots, layups, around-the-world shots, foul-line jump shots, three-point shots, and free-throw single performance scores) was 83 ± 3 shots for CES and 86 ± 3 shots for EUH control trials. The total time to complete basketball-specific movement drills (sum of ladder suicide, 30 vertical jumps, zigzags, full-court combination, 20 court-width sprints, 30 lane slides, and key combination single performance scores) was 370 ± 13 s for CES and 386 ± 11 s for EUH control trials.

Figure 2 illustrates the single drill and total results relative to EUH control for shots "on the move." The threshold for significantly impaired performance for baseline jump shots and layups was 4 and 3% DEH, respectively. Single performance scores for foul-line jump shots were not affected by any level of DEH. When the results from all three drills were combined, the total number of shots "on the move" made was significantly impaired by 3-4% DEH. Thus, the DEH threshold for significantly impairing this type of basketball shooting performance was 3% DEH.

FIGURE 2: Box plots of "shots on the move" made during 1-4% DEH relative to EUH control for individual drills (left) and total (sum of baseline jump shots, layups, and foul-line jump shots single performance scores) shots made (right). The top, bottom, and line through the middle of the box correspond to the 75th, 25th and 50th (median) percentiles, respectively. The whiskers extend from the 10th (bottom) to the 90th percentile (top). The black square near the center of each box represents the mean difference from EUH control for each trial. Mean values for the EUH control trial (the basis for each relative comparison) are shown at the right of each panel.

The single drill and total sprint times relative to EUH control are presented in Figure 3. The threshold for impaired performance for the ladder suicide and 20 court-width sprints was 1 and 3%, respectively. When the results from the two drills were combined, the total sprint time was significantly slower during 2-4% DEH. Thus, the DEH threshold for significantly impairing on-court sprinting performance was 2% DEH.

FIGURE 3: Box plots of sprint times during 1-4% DEH relative to EUH control for individual drills (left) and total (sum of the ladder suicide and 20 court-widths single performance scores) sprint times (right). The top, bottom, and line through the middle of the box correspond to the 75th, 25th and 50th (median) percentiles, respectively. The whiskers extend from the 10th (bottom) to the 90th percentile (top). The black square near the center of each box represents the mean difference from EUH control for each trial. Mean values for the EUH control trial (the basis for each relative comparison) are shown at the right of each panel.

A summary of the performance results for the remainder of the drills are presented in Table 4. The DEH threshold for significantly impaired performance for total defensive slide time was 3% DEH (single drills: zigzags = 3% DEH, 30 lane slides = 4% DEH). The DEH threshold for significantly impaired performance for total sprinting-defensive slide combination time was also 3% (single drills: full-court combo = 3% DEH, key combo = 4% DEH). Repeated vertical jump performance was significantly impaired with 4% DEH, while maximum vertical jump was not significantly affected by any level of DEH compared with EUH control. The DEH threshold for significantly impaired performance for total stationary shooting was 4% DEH (single drills: around the world = 2% DEH, three-point shots = not significantly affected, free throws = not significantly affected). Finally, when basketball shooting results are expressed as a percentage, (shots made/shots attempted) performance is only significantly impaired for layup shooting (threshold = 3% DEH).

TABLE 4: Remainder of basketball drills and shooting percentage.

The combined results for all timed drills and all shooting drills are illustrated in Figure 4. These scores represent overall skill performance during the entire 80-min simulated basketball game. Total time to complete all basketball-specific movement drills (sprinting, defensive slides, sprinting-defensive slide combination, and repeated vertical jumps) progressively increased and total number of shots made (stationary shots and shots "on the move") progressively decreased as DEH progressed from 1 to 4%. The threshold, or % DEH at which the performance decrement reached statistical significance, was 2% for all timed drills combined and all shots combined.

FIGURE 4: Box plots of all timed drills (sum of ladder suicide, 30 vertical jumps, zigzags, full-court combination, 20 court-width sprints, 30 lane slides, and key combination single performance scores) and all shots (sum of baseline jump shots, layups, around-the-world shots, foul-line jump shots, three-point shots, and free-throw single performance scores) during 1-4% DEH relative to EUH control. The top, bottom, and line through the middle of the box correspond to the 75th, 25th, and 50th (median) percentiles, respectively. The whiskers extend from the 10th (bottom) to the 90th percentile (top). The black square near the center of each box represents the mean difference from EUH control for each trial. Mean values for the EUH control trial (the basis for each relative comparison) are shown at the right of each panel.

Although the basketball performance results for the DEH trials are presented as differences from the EUH control condition (Figs. 2-4) to better address the specific research hypotheses, it should be noted that the same incidence of statistically significant differences between 1-4% DEH and EUH control was found whether the data were expressed in relative or absolute terms.

DISCUSSION

The main findings from this study were: 1) 17- to 28-yr-old skilled basketball players experienced a progressive deterioration in performance as DEH progressed from 1 to 4%, 2) the threshold, or % DEH at which the overall performance (i.e., combined scores for the entire 80-min simulated game) decrement reached statistical significance, was 2%, and 3) EUH with a CES did not enhance basketball performance over EUH with a carbohydrate-free solution, contrary to previous data in children (¹¹).

In the current investigation, the DEH threshold for impaired performance of the fourteen individual drills varied from 1% DEH to not significant within the 1 to 4% DEH range tested. Compared with EUH control, an impairment in performance occurred in one drill at 1% DEH (ladder suicide sprints), one drill at 2% DEH (around-the-world shooting), four drills at 3% DEH (zigzag slides, court-width sprints, layup shooting, and full-court combination) and four drills at 4% DEH (repeated vertical jumps, key combination, lane slides, and baseline jump shots). Performance of the remaining four individual drills (maximum vertical jump, three-point shooting, free throws, and foul-line jump shots) was not affected by 1 to 4% DEH compared with EUH control. Because basketball is a sport characterized by intermittent bouts of sprinting, lateral movement, and jumping interspersed with the execution of complex sport-specific skills, such as dribbling and shooting the basketball, single drill scores were combined to reflect the players' overall performance during the 80-min basketball drill session. These combined scores provide a reasonable representation of how 1 to 4% DEH might affect the players' performance during an actual basketball game. When performance results were collapsed into two major categories (timed drills and shooting drills) the critical water deficit causing a decrease in basketball skill performance was 2% of initial body mass (Fig. 4).

Only two previous studies have tested the effects of DEH on basketball-specific skills. The current data are in agreement with Dougherty et al. (¹¹), who found that 2% DEH significantly impaired on-court sprinting performance in 12- to 15-yr-old boys, and Hoffman et al. (¹⁵), who found that 1.9% DEH had no detrimental effect on vertical jump height or shooting percentage in 17-yr-old boys. Although in the current study, overall shooting percentage (i.e., shooting accuracy) was not affected by DEH, significantly fewer absolute number of shots were attempted and made when subjects were ≥ 2% DEH compared with EUH control. This is most likely attributable to slower sprinting and lateral movement between shot attempts during the allotted time period (2 or 3 min, depending on the drill). Successful scoring in basketball is highly dependent on a player's speed and agility to create a good shot opportunity. Thus, as the current study indicates, 1-4% DEH may not impact shooting accuracy in 17- to 28-yr-old male players, but would impair their scoring ability (i.e., total points scored) within the context of a fast-paced, competitive basketball game. Accordingly, in the current study, DEH had a greater deleterious impact on the number of shots made when players were shooting "on the move" (i.e., players were required to sprint, defensive slide, and/or dribble between shot attempts; 2% DEH: P = 0.05, 3% DEH: P < 0.0001, 4% DEH: P < 0.0001 vs EUH control, Fig. 2) than when shooting from a stationary position (minimal movement between shot attempts; 4% DEH: P = 0.02 vs EUH control, Table 4).

The current study supports the contention that athletic events do not have to take place in a hot environment for DEH to have a detrimental impact on exercise/sport performance. The basketball drills were conducted indoors (ambient temperature = 23-24°); thus, the current study supports research showing that DEH impairs performance during various types of physical activity performed in thermoneutral conditions, including high-intensity intermittent running (¹⁶), distance track running (²), prolonged cycling (^8,17), and maximal aerobic power (⁵) in young adult athletes, anaerobic power in collegiate wrestlers (^14,27), and basketball skills in 12- to 15-yr-old boys (¹¹).

During the heat chamber exercise (controlled exercise intensity, 50% V˙O_2max), HR and T_c were significantly higher with DEH versus EUH control and progressively increased from 1 to 4% DEH. In the current study, HR increased 7 bpm and T_c increased 0.28°C above that of EUH control for every 1% increase in DEH. Additionally, S_osmol increased by 3.5 mOsm·kg⁻¹ and PV decreased by 2.4% compared with that of EUH control for every 1% increase in DEH. These results are consistent with the extensive literature on the effects of graded DEH on physiological function during exercise in hot environments (^19,23). Conversely, during the basketball "game" (self-selected pace to complete drills), HR and T_c were not significantly higher during DEH compared with EUH control trials. Thus, there are no clear physiological mechanisms to account for the DEH-related impairment of basketball performance in the present study. DEH was not associated with higher T_c and HR during the simulated basketball game most likely because subjects' decreased their exercise intensity when they were DEH; as indicated by the significantly slower sprint times (Fig. 3) and increased feelings of fatigue (Fig. 1B) associated with DEH. Accordingly, the impaired basketball performance in the present study can be partially explained by the subjective measures of physical well being; that is, increased feelings of leg fatigue and lightheadedness associated with DEH (significantly different at 3 and 4% DEH) compared with EUH control. The deleterious effect of fluid restriction on subjective feelings of fatigue and physical well being is consistent with previous investigations. For example, boy basketball players in the study by Dougherty et al. (¹¹) reported feeling more lightheaded and upper-body fatigue during 2% DEH compared with the placebo EUH condition. Because of the complexity and dynamic nature of the game of basketball, optimal cognitive function is necessary for successful sport performance (⁶). DEH has been implicated in impaired performance of various cognitive tasks, including, visuomotor tracking, short-term memory, response time, coordination, and attentional vigilance (^9,13,24). Thus, DEH-induced impairment of cognitive function could also account for some of the basketball performance differences between DEH and EUH control trials in the current study.

In the current study, there were no differences in basketball performance whether EUH was maintained with CES or a carbohydrate-free solution. Interestingly, in a similar study conducted in our lab with 12- to 15-yr-old boy basketball players, performance was significantly enhanced with CES compared with placebo EUH (lemon/lime-flavored water with 0% carbohydrate and 18 mmol sodium) (¹¹). The age-related differences in basketball skill performance with CES versus EUH control may be attributed to cognitive function changes with carbohydrate availability. For example, glucose administration has been shown to improve attention and reaction to frustration in children (³), whereas glucose intake has no effect on variables of attention in adults (¹²). Thus, we speculate that children may be more apt than adults to experience an improvement in performance of complex tasks, such as basketball drills, when exogenous glucose is provided. The inconsistent results between the current study and that with 12- to 15-yr-old boys may also be explained by age-related differences in substrate use during exercise. Timmons et al. (²⁵) have shown that the oxidation rate of exogenous carbohydrate during 60 min of submaximal cycling is significantly higher in early prepubertal boys than in men. A greater metabolic reliance on exogenous carbohydrate in boys than in men may explain why CES consumption improved basketball performance of the 12- to 15-yr-old boys, but had no affect on the performance of the 17- to 28-yr-old men (compared with EUH control).

Limitations

The CES consisted of lemon/lime flavoring, 6% carbohydrate, and 18.0 mM sodium, whereas the EUH control beverage consisted of lemon/lime flavoring, 0% carbohydrate, and 18.0 mM sodium. During the 1-4% DEH trials, distilled water was consumed to maintain the DEH body mass. Sodium was included in the EUH fluids to enhance palatability and provide an osmotic impetus to retain the ingested fluid in the vascular space. Because the EUH control beverage was carbohydrate free, this drink served as an adequate control condition to compare to the effect of carbohydrate intake (via CES) on performance. However, the EUH control drink (flavored water with sodium) was not a true control condition with which to compare 1-4% DEH, because a sodium-free drink (distilled water) was consumed during the DEH trials. Because of this study design, it is possible that some of the performance benefits of EUH control over DEH could be attributed to the ingestion of sodium (and its effects on body fluid distribution) during the EUH control condition versus no sodium intake during the 1-4% DEH trials.

The investigators and subjects were well blinded to the EUH control versus the CES trials because the EUH beverages were coded and were of the same color and flavor. In addition, all attempts were made to blind the subjects to their level of DEH. The volume of fluid consumed during the experiment was not obviously different among successive DEH levels (no more than a 150-mL difference per quarter). It is possible that the subjects could have sensed this small difference in volume consumption among DEH trials; however, it is not likely because: 1) fluid was given to the subjects in an opaque bottle, 2) at least 1 wk elapsed between trials, and 3) the trials were completed in random order. Although it was realistic to disguise successive DEH levels, it was difficult to completely blind subjects to EUH control versus 1-4% DEH, because distilled water was consumed during DEH trials to maintain DEH body mass (compared with the flavored drink ingested during the EUH control trials).

In summary, basketball performance measures of 17- to 28-yr-old, highly skilled, male basketball players were similar when players maintained EUH with CES versus a carbohydrate-free solution, contrary to previous data in children. Players experienced a progressive deterioration in performance, compared with EUH control, as DEH progressed from 1 to 4%. The critical level of water deficit at which overall performance (combined scores for the entire 80-min simulated game) was significantly impaired compared with EUH control was 2% DEH. Therefore, players should be advised to implement adequate pregame and in-game hydration strategies to prevent ≥ 2% DEH and its detrimental impact on basketball performance.

We are grateful to the subjects for their participation in this study. Additionally, we thank Jane Pierzga, Michael Hyduk, Doug Johnson, and Randy McCullough for their technical assistance and the General Clinical Research Center nursing staff for their medical support.

Support for this study was provided by the National Basketball Association, Gatorade Sports Science Institute, and the General Clinical Research Center Grant MO1 RR010732.