Dehydration has long been shown to reduce motor performance, cognitive function, and alertness in a range of athletic and nonathletic populations (6,8,19,22,23,33). Studies deploying cognitive-motor tasks to measure perceptual discrimination, target accuracy, visual tracking, choice reaction time, attentional focus, concentration, and fatigue perception (19) concur that the effects of mild dehydration (−1 to 3% body mass change [ΔBM]) result in cognitive-motor dysfunction (33). D'Anci et al. (9) reported that a −1.7% ΔBM significantly increased errors during a continuous cognitive-motor performance task, whereas Szinnai et al. (31) found that at a −1.8% ΔBM increased tiredness was accompanied by a significant impairment in subjective cognitive-motor functioning, measured as alertness and concentration. Gopinathan et al. (18) noted that a −2 to 4%, but not −1% ΔBM, impaired cognitive functioning, suggesting a proportionate relationship between dehydration status and mental performance.
In an attempt to replicate more complex sport-specific performance tasks, requiring gross movement coordination, control, and accuracy, Epstein et al. (16) found that a −2.4% ΔBM significantly impaired speed and accuracy during a simulated target shooting task. In support of these findings, Devlin et al. (12) recorded significant deterioration in cricket bowling accuracy (i.e., line and length) when undertaken in a dehydrated state (−2.8% ΔBM). Furthermore, McGregor et al. (24) and Edwards et al. (14) found performance decrements during complex soccer-skill tasks when BM loss was 2.4% of the initial pretrial mass.
Methods of dehydration attenuation, induced by exercise (7), environment modification (7,16), fluid restriction (1,26,28,31), or a combination (18), have been previously used to augment total body fluid loss. During sport-specific activity, such as golf, which requires a low metabolic energy cost and is performed over extended periods (>4 hours), both voluntary fluid intake and climate alterations are the main contributors to modifications in an individual's hydration status (29). Given the importance of effective cognitive-motor functioning to swing execution and perceptual environmental judgment (29), acute mild dehydration, as a consequence of poor fluid management, may impact cognitive-motor ability (i.e., shot distance, shot accuracy, and shot judgment). It was therefore the purpose of this investigation to quantify the likely impact acute mild dehydration, augmented through noninvasive fluid restriction may have on the golf-specific motor-cognitive performance in low-handicap players.
Experimental Approach to the Problem
A repeated-measures counterbalanced design was applied to assess the participants in 2 conditions (euhydrated and dehydrated). The conditions were separated by a 7-day period. The participants were randomly assigned to 1 of the 2 conditions and reported to the institution's performance center between 10 and 12 AM on the morning of the assessment with each visit lasting approximately 90 minutes. All data collection took place within an indoor golf performance suite (temperature: 20 6 0.3 C; humidity: 53 6 3%) that comprised a netted hitting area and a performance feedback area with video projector and screen. The hitting area was sufficiently designed to replicate conditions similar to that experienced outdoors. All urine collections and assessments were supervised by an investigator throughout. On arrival at the center, each participant's BM and stature (without footwear) were recorded before data collection. The BM (Seca, 770 digital platform scale, Cranlea, United Kingdom), with the participants wearing underwear only and stature (stadiometer, Cranlea), were recorded to within 0.1 kg and 0.01 m, respectively. Before the research period, all the participants reported to the center on 3 consecutive days for baseline BM measurements.
Each experimental condition (i.e., euhydrated and dehydrated) involved regulated intake of fluids over the 12-hour period before testing as previously implemented (1). Dehydration was induced once for each participant during the study using a basic, noninvasive, fluid restriction approach (1,27). This involved fluid abstinence and overnight fasting with a standardized breakfast the morning of the test (i.e., 2 lightly buttered slices of toast). Euhydration was ensured by consumption of approximately 1.5–2.0 L of water during the day before assessment and especially in the 12-hour period before testing. After overnight fasting, the participants consumed a standardized breakfast (i.e., 2 lightly buttered slices of toast) with an additional intake of 500 ml of water 2 hours before assessment.
The participants were asked to refrain from urination during the 30-minute period before the arrival at the center and were instructed to collect urine samples upon arrival (2–4 oz). The samples were collected in inert plastic containers, stored at room temperature, and were not left for 15-20 minutes before analysis. The hydration status of the participant was quantified by measuring BM (change from baseline measure) and urine color. The use of urine color and associated charts has been previously shown to be both reliable and effective in establishing hydration status (3,4). Urine color was assessed by holding each sample container next to a color scale in front of a white background in a well-lighted room (5).
An athletic group of low-handicap experienced male golfers (n = 7; age: 21 ± 1.1 years; mass: 76.1 ± 11.8 kg; stature: 1.77 ± 0.07 m; handicap: 3.0 ± 1.2; playing experience: 6.2 ± 1.9 years) volunteered to take part in this study. For the purposes of this investigation, all the individuals were expected to be playing golf competitively at least once a week, while undertaking golf-specific training on 3 further occasions during the same week. Having gained institutional ethical approval for this study, all the participants gave written informed consent and were made aware of the nature, purpose, and risks of the research. Before study commencement, all participants underwent a medical screen to ensure that they had no known history of cardiovascular, respiratory, or renal disorders. All the participants were requested to refrain from strenuous physical activity, caffeine, and alcohol during the 24-hour period before testing. All were instructed to follow their normal dietary patterns 7 days leading to their study involvement. Verbal advice was provided to ensure that all were euhydrated during this period. This ensured that baseline assessments reflected normalized status before hydration manipulation.
Motor Performance Task
The participants were required to hit 30 golf balls within a laboratory-based netted, enclosed swing area. Upon arrival and before the start of the first trial, the participants were instructed to perform a minimum of 10 warm-up practice golf swings to familiarize themselves with the experimental setup. Along with any additional stretching, the total number of swings was recorded during the first visit and repeated at their second.
Golf ball launch data were collected for each trial with a GolfAchiever (Focaltron Corp., Sunnydale, CA, USA) golf swing and ball launch condition analyzer connected to a laptop computer. Previously used by Doan et al. (13), the GolfAchiever uses solid-state semiconductor laser technology to capture ball and club information in detail. Variables collected for this investigation were ‘ball carry’ distance (meters) and off-target accuracy (distance [meters] perpendicular to the target line). Before each trial, and following the manufacturer's guidelines, the GolfAchiever was calibrated to ensure accuracy in data capture. Previous research has shown that the use of indoor golf launch monitors, as a means of evaluating ball and club information, has been shown to provide reliable data (21). The ball was hit while it was located on an artificial grass surface. For each shot, the ball rested on a rubber tee, located within the GolfAchiever plate, which raised the bottom of the ball approximately 0.5 cm above the plate surface.
In a random order, the participants were given a 9, 7, or 5-iron and instructed to set up and hit the ball as if they were making a full shot or swing to a set target point set at 110 m (9-iron), 125 m (7-iron), and 140 m (5-iron), respectively. The target was projected, via a floor mounted unit, onto the back of the netting using a golf-specific software package (GolfAchiever, Focaltron Corp., Sunnydale, CA, USA). Each club was used a total of 10 times.
Cognitive Performance Task
Golf-specific cognitive ability was assessed in the form of distance judgment, a key cognitive task performed during target-related activities (27,29). Incorporating depth perception, attentional focus, and contrast analysis (27), the trial replicated in a controlled manner the requirements a golfer would normally undertake when making executive decision-making choices on-course. Each participant was shown, in a random order, 30 golf location images, which were taken from a real on-course setting. Each image was taken using a high-quality digital camera from 30 different locations around an unfamiliar golf course to replicate the ‘approach’ view a golfer would normally encounter on a golf course. Each location was selected based on the high level of visibility to each flag. The actual distance (meters) from the point where each image was taken to the flag position was measured for accuracy. Each image, projected onto a 5 × 3-ft screen, was presented to the player. They were then asked to provide an estimated distance, in yards, to the flag position. Their responses were recorded, and converted to meters, on a preformatted monitoring sheet. For each hole, an error score was derived by calculating the estimated distance from the actual measured distance.
All descriptive results are reported as mean ± SD. The assumption of normality was verified using a Shaprio-wilk test. For analysis of motor performance task data, a 2 × 3 repeated measures analysis of variance was used to determine significant differences between the 2 hydration conditions (euhydrated vs. dehydrated) and the different club selections (9, 7, and 5-iron on average shot distance [meters] and off-target accuracy [meters]). Follow-up paired comparisons were used in conjunction with a Holm's Bonferroni procedure for controlling type 1 errors when significant F values were determined (p ≤ 0.05). For analysis of the cognitive performance task data, a related-samples Wilcoxon test was used to evaluate the influence of the condition (2 levels) on error score (actual distance − estimated distance). Statistical significance was set at the p ≤ 0.05 level of confidence. All analyses were performed via SPSS (version 14.0; SPSS, Inc, Chicago, IL, USA).
Levels of Hydration
Hydration status in this study was reflected by the assessment of BM (ΔBM) and urine color assessment (UCOL). Across conditions, the BM was significantly different (p = 0.01) (Euhydrated; 75.9 ± 11.7 kg vs. Dehydrated; 75.0 ± 11.4 kg). When each was compared with mean baseline BM measurement (76.1 ± 11.8 kg), euhydrated BM reduced on average by 0.2 kg (−0.3 ± 0.6%), whereas dehydrated BM was reduced on average by 1.1 kg (−1.45 ± 0.53%). The BM before the dehydrated condition was significantly different from baseline BM measurement (p = 0.01); however, the euhydrated condition was not (p = 0.40). Measurement of UCOL revealed a significant increase (p = 0.02) from 2 ± 0.9 (range: 1–3) to 4 ± 0.5 (range: 4–5) across the euhydrated and dehydration conditions.
Motor Performance Measures
For the overall distance, differences between condition (euhydrated vs. dehydrated) and club selection (9, 7, and 5-iron) are presented in Figure 1A. The main effect for condition revealed that performance in the dehydrated state was significantly impaired (114.6 ± 12.9 m; p = 0.04) when compared with the euhydrated state (128.6 ± 8.8 m). No significant interaction (p = 0.20) (condition × club selection) was found; however, differences were found to increase when distance for each club was compared across the euhydrated and dehydrated conditions (Table 1).
For off-target accuracy, differences between condition and club selection are presented in Figure 1B. The main effect for condition revealed that performance in the dehydrated state was significantly impaired (7.9 ± 2.0 m; p = 0.001) when compared with the euhydrated state (4.1 ± 0.8 m). No significant interaction (p = 0.17) (condition × club selection) was found; however, differences were found to increase when off-target accuracy for each club was compared across the euhydrated and dehydrated conditions (Table 1).
Cognitive Performance Measures
Accumulated total distance for the 30 golf location images was 2,588 m (average: 86 m, range: 19–183 m). In the euhydrated condition, the estimated total distance was 2,600 ± 81 m (range: 2,455–2,684 m), incurring an accumulated distance error of 12 m (range: −133–96 m). For the dehydrated condition, estimated total distance increased to 2,677 ± 209 m (range: 2,287–2,895 m), incurring an accumulated distance error of 87 m (range: −321–307 m). Analysis of mean error scores across the 2 conditions revealed a significantly higher misjudgment of distance in the dehydrated state (8.8 ± 4.7 m; p < 0.001) when compared with the euhydrated state (4.1 ± 3.0 m).
The principal finding of this study was that acute mild dehydration (mean: −1.5% ΔBM), measured by way of a golf-related task performance replicable of that experienced during on-course play, resulted in a significant impairment of both motor and cognitive abilities. Both distance and accuracy were affected by mild dehydration, confirming previous research findings (12,16). Cognitive performance, as measured through distance judgment, was also significantly impaired when mildly dehydrated. This supports evidence that has shown cognitive ability, expressed as attention function, perceptual function, execution function, and psychomotor function is impaired by mild dehydration (8,18,19,28). It is widely recognized that mild dehydration is associated with a number of negative performance effects (20). To our knowledge, this is the first study to have measured the likely impact acute mild dehydration (−1 to 3% ΔBM), augmented through 12-hour noninvasive fluid restriction approach has on the golf-specific motor-cognitive performance.
The degree to which cognitive-motor performance is decreased by ΔBM has been shown to be proportional to dehydration level (18). At levels equating to a −1% ΔBM, mental performance, expressed as arithmetic ability, short-term memory, and visuomotor functioning has remained unaffected. Szinnai et al. (31) found no significant change in a range of abstract objective cognitive-motor measures when participants were mildly dehydrated over a 24-hour period (−1.77% ΔBM). What was noted, however, was that subjective estimation of concentration, tiredness, alertness, and sense of effort were significantly higher during the dehydrated state. After 13 hours of fluid restriction that resulted in a ΔBM of around 1%, Shirreffs et al. (28) observed heightened (p < 0.05) feelings of thirst, reduced concentration levels, and an impaired overall feeling of wellness when compared with a euhydrated state. However, Patel et al. (25) found self-reported ratings of fatigue increased when dehydrated.
In complex kinetic chain movements, such as the golf swing, reduced sensations of effort may have a negative effect on motor drive and subsequent neuromuscular function (20). Upper extremity muscle groups have been shown to reorganize muscle activity patterns during the onset of fatigue (32) thereby combating deleterious effects of neurophysiological homeostatic imbalance, as seen during states of mild dehydration (33). Such reorganization of multiple joint angles or muscle firing patterns may therefore compensate for cognitive-motor dysfunction throughout the movement. Considering the small margins of error involved in precise impact achievement during the golf swing, even slight alterations however may compromise outcome success (i.e., shot distance and accuracy). Such notion is supported by evidence highlighting the effect fatigue, induced by dynamic motor movements, similar to that encountered during golf, has had on skilled movement performance (10).
Davey et al. (10) noted that after repetitive movement that resulted in peripheral motor impairment, the ability to perform a dynamic tennis shot was diminished. The authors postulated that with the increased sense of fatigue comes an accompanying decline in skill, manifesting itself through poor timing, body alignment, and dysfunctional segment coordination. Combined with the findings that postural instability diminishes when mildly dehydrated (−2.7% ΔBM) (11,17), observations from this study support the consensus that mild hypohydration (−1 to 2% ΔBM) impairs motor performance.
Any onset of cognitive-motor dysfunction during golf will impact first on the ability to select the right shot type (i.e., visual acuity and ability to perceptively contextualize differences, such as shades of green, gradient changes, flag distances) and second the execution of the swing. Low level fatigue, similar to that which might be encountered during a round of golf, has been shown to impact negatively on decision-making accuracy (27). During a decision-making test, which involved selecting the correct performance outcome from a range of scenarios, accuracy scores after mild fatigue was significantly lower when compared with pretest and high exertion performances. In light of these observations, decrements in performance, as a consequence of perceptual alterations (i.e., increased sense of effort) may have contributed to the decrements in decision-making accuracy within the dehydrated state.
Edwards and Noakes (15) recognize that it still remains unclear whether such cognitive-motor dysfunction, attenuated by mild dehydration, is a consequence of physiological homeostatic imbalance, such as hormonal or cellular effects, as outlined by Wilson and Morley (33), or central motor behavior changes attributable to increased sensations, such as thirst (18,30). Suggestive of a signaling mechanism that promotes greater conscious perception of effort, thereby evoking behavioral change, Edwards and Noakes (15) propose that impaired cognitive-motor performance may be linked to a centrally mediated mechanism of thirst perception, rather that absolute levels of dehydration (i.e., loss of total body water). Continued research is needed to further elucidate the role such central regulatory processes play in augmenting perceptual changes when in states of mild dehydration.
Participation in outdoor activity exposes individuals to a variety of factors that influence sweat loss and can lead to a dehydrated state. Establishing the impact of acute dehydration on motor-cognitive performance offers an insight into the effects on physical activity during recreational and competitive golf. These results demonstrate that even a small reduction in BM, attributed to acute mild dehydration (mean: −1.5% ΔBM), augmented through 12-hour noninvasive fluid restriction, attenuates golf performance. Given that players are on-course for periods of around 4 hours, often with limited fluid purchasing opportunities (i.e., ninth hole), maintaining hydration can be compromised. Exacerbated in warm conditions, the 90-kg player would only have to lose on average 1.4 kg (−1.5 ΔBM), equating to 350 g (∼350 ml·h−1) fluid depletion per hour to impact on performance capacity during the final, often crucial holes of a round. With predicted sweat rates in temperate conditions of around 400 ml·h−1 when traveling at 5–6 km·h−1 (2) not dissimilar to locomotor speeds while playing golf (29), management of fluid intake for the player must ensure maintenance of a hydrated state throughout the round. Players should therefore be encouraged to develop customized fluid replacement programs that prevent excessive (>1% BM reductions from baseline BM) dehydration. The routine measurement of preround and postround BM is practically useful (2) for determining sweat rates and customized fluid replacement programs. To ensure the player arrives on the first tee in a dehydrated state, the individual should slowly drink beverages to the volume of between 5–7 ml·kg−1, so for a 90-kg player between 450 and 630 ml, at least 4 hours before a round (2). Throughout the course of play, the consumption of beverages containing electrolytes and carbohydrates should ensure adequate hydration (0.4–0.8 ml.kg.h−1) thereby reducing the impact on cognitive-motor performance.
No sources of funding were used to support this research investigation. The authors have no conflict of interests relevant to the content of this research article.
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