Primary Reference
Gann, J. J., Green, J. M., OʼNeal, E. K., Renfroe, L. G., & Andre, T. L. (2016). Effects of Hypohydration on Repeated 40-yd Sprint Performance. Journal of Strength and Conditioning Research, 30(4), 901-909. doi:10.1519/jsc.0000000000001177
Introduction: Athletes often participate in sports and practice in a hypohydrated state. Research has even demonstrated some athletes perform in a chronic hypohydrated status. Hypohydration impairs performance in training and competition. Most research supports a negative influence of hypohydration on performance. The few studies which have not demonstrated a performance loss with hypohydration may have not achieved the level of body mass loss associated with impairment (~>3%). Other possibilities include differing modes of exercise and testing, nutrition, and training experience. The use of single repetition testing such as one repetition maximum and vertical jumping may not require the amount of energy contribution from aerobic processes to effect performance in a hypohydrated state. Therefore, it is more likely that repeated efforts of anaerobic performance will increasingly demonstrate performance loss as greater body mass is lost through sweat. Repeat sprint performance is an important component of many sports, including football, soccer, and rugby. Athletes participating in these sports may be subject to chronic states of hypohydration secondary to practices, competition, and extreme weather. Therefore, the purpose of this study was to examine the effects of significant hypohydration (3% body mass loss) on 40-yd sprint performance, heart rate (HR), agility test (AT), and perceptual measures.
Purpose: The purpose of this study was to examine the effects of significant hypohydration (3% body mass loss) on 40-yd sprint performance, heart rate (HR), agility test (AT), and perceptual measures.
The authors did a good job of explaining the reasoning many studies have not demonstrated performance loss during anaerobic testing. It appears there is a critical point in which hypohydration begins impairing performance. This critical point appears to be around 3% body mass loss. I also think the authors made a good point in it is less likely hypohydration impacts single repetition testing because the energy demands are not high enough. It is more likely hypohydration will impact repeated measures, such as sprinting.
Subject Description: Twelve anaerobically fit (3 times a week for at least 3 weeks) current/former Division II male athletes participated in this study. The age of the subjects ranged from 19-25 years. An initial health screening was performed and subjects completed a physical activity readiness questionnaire. Height (cm) and body mass were recorded (kg). Body fat was estimated using skin calipers.
Methods: A baseline trial (BT) was performed to familiarize subjects with the testing procedure. Subjects were educated on hydrating themselves throughout the day prior to the initial baseline session to ensure euhydration. A standardized breakfast was provided which consisted of a protein bar and sports drink. Prior to BT, urine specific gravity (USG) was assessed with a manual refractometer to assess hydration. Subjective ratings of sleep quality and thirst were taken using a visual analog scale. A 5 minute standardized warm-up was performed. Afterwards, 10 x 40-yd sprints were performed. A 60-second active recovery period was performed which consisted of subjects walking back to the starting line. Upon completion, a 5 minute recovery period was administered. A second 10 x 40-yd sprint protocol was performed. Sprints were performed in a controlled environment and a photogate timing system was used to record sprint times. Sprint times were recorded at the 10-yd line and 40-yd line. Another 5 minute recovery period was provided after which the subjects completed two trials of the agility test (AT). AT consisted of a modified T-test, which substitutes shuffling between cones with sprinting. Times were recorded to the nearest hundredth with the photogate sensor. HR was recorded continuously via Polar team 2 heart rate monitoring system. Ratings of perceived exertion (RPE) were recorded 3 minutes after the final sprint. Session RPE (SRPE) was assessed 10 minutes after completion. RPE was assess on a 0-10 scale.
Following BT, subjects returned for the experimental trials which was performed in a cross-over design separated by a minimum of 3 days.
Hydrated Trial: Subjects were educated on avoiding alcohol and caffeine 24 hours prior to the laboratory, hydration, and consumption of 500 ml of water prior to arrival. Subjects were instructed to consume a light meal 2-3 hours prior to the trial which was to be replicated on the subsequent trial. Dehydration was achieved via submersion in a 39° water bath to produce a 3.5% loss in body mass. Core temperature was monitored using a Physitemp rectal thermocouple. Subjects were toweled off and weighed every 30 minutes. Subjects were replaced 75% of fluid losses after each 30 minute segment. After treatment, subjects were given additional volume of water to result in a total of 125% fluid replacement of sweat loss. A prepackaged standardized evening meal was provided. Subjects were educated on consuming fluid in a metered fashion before returning to the lab the following morning. Urine was collected between the evening and morning session. Upon return, hydration status was assessed via body mass and USG. Subjects then completed performance trials identical to the BT.
Dehydrated trial: The same dehydration protocol was used to achieve a body mass loss of ~3.5% via hot water submersion. This % loss of body mass was found in previously done pilot work to elicit 3% hypohydration. This approach also allows a certain amount of fluid intake, which is most likely similar to athlete’s intake during competitions.
The methods section was adequate. The authors did a good job explaining the procedures with detail. The method of generating hypohydration is relatively non-specific. In typical game situations, the athletes would be losing water through exercise/movement. In this instance, the athletes were merely sitting in a tank. How much this impacts the results is debatable. It is feasible fatigue plus hypohydration could cause even greater deficits in performance. It is also conceivable that the greater stimulation/motivation from competition could negate the impacts of hypohydration. The authors also failed to justify the sample size, there was not a section devoted to describing power calculations.
Results: Subjects height (178 ± 6 cm), body mass (87.4 ± 11.6 kg), age (21.9 ± 1.8 years), and body fat (7.9 ± 2.6%) were provided. Mean sprint times were included for all participants in a table format, with the change between trials provided. Additionally, mean sprint times were graphed via a line graph. The main effect for the first bout of 10 sprints approached significance (p=0.10) and the main effect for the second bout of 10 sprints was significant (p=0.03). No significant interactions were found for bouts 1 or 2 (p=0.14, p=0.17). T-test for the second bout of 10 sprints found significantly slower times for DT (sprints 2, 5, 6). No significant difference was found for AT (p=0.12). HR for DT was significantly higher than HT (pk1=0.02, avg1 p=0.05, pk2=0.12, avg2 p=0.06). Mean RPE for set 1 (p=0.0001) and follow up t-tests found RPE significantly higher for DT for all 10 sprints. No significant interactions were found for bouts 1 or 2. DT was significantly higher for sprints 1-2 but not for 3-10. RPE1 and RPE2 were significantly higher for DT (p=0.01, p=0.04). Perceived recovery scale was significantly lower for DT than HT (p=0.004). Thirst sensation was also significantly higher for DT than HT (p=0.0001). Urine specific gravity was significantly higher for DT than HT (p=0.0001). Pre-trial USG for HT was ≤1.020, demonstrating each subject was adequately rehydrated.
The results were posted in both a table and in graphs, making the interruption of individual performances easier. From the results, it can easily be seen hypohydration actually improved performance in some individuals, had no effect on some, and had negative effects on others. The authors did a good job of really sifting through the data, using t-tests to look for significance through each sprint.
Discussion: This is the first study to examine significant hypohydration (~3%) on repeat 40 sprint time. From the data presented, only 3 of 20 sprints were significantly slower in DT than HT. These results are in line with previous research demonstrating hypohydration having little effect of anaerobic performance. There was considerable interindividual variability in this study with some subjects whom sprint capacity was considerably affected, some whom were not affected, and some whom sprint times improved. The results of this study reflect fail to reflect an overwhelming effect of hypohydration on average repeat sprint time. Further evaluation of the data revealed 7 of 12 subjects had a slower mean sprint time for DT in the first or second bout of 10 sprints. 5 of 12 subjects had a slower mean sprint time of ≥ 0.1 seconds for at least 1 of 10 sprints during DT and 4 of 12 had a faster sprint time of ≥0.1 seconds for at least 1 of 10 sprints. Overall, 10 of 12 subjects experienced a change. Further evaluation noted the individual with the lowest level of hypohydration experienced the greatest detrimental effect on sprint time while conversely the individual with the highest level experienced the greatest improvement. It has been proposed hypohydration may improve performance in actions where athletes must accelerate their own body mass. This hypothesis would appear in agreement with some subjects experiencing improvements in sprint times. Another possible explanation for a lack of significance is the subjects “pacing” themselves during repeated sprints to offset fatigue. Future research is required to determine the individual factors which influence tolerance to hypohydration.
Conclusion: In conclusion, hypohydration of 3% body mass had little effect on repeated 40-yd sprint performance when group mean analyses were performed. When individual considerations were analyzed, there is evidence most subjects (83%) experience considered effects (either positive or negative). A limitation to this study was no exercise involved in the dehydration process. It is conceivable exercise-induced hypohydration may influence performance to a greater degree.
My thoughts: I felt the authors did an excellent job really digging into the explanations and individual responses to hypohydration. They also noted their limitations to the study in the conclusions section. They discussed multiple theories and hypotheses as to why some individuals improve while others experience decrements. The point about accelerating body mass was noteworthy. It appears some individual’s improvement in relative strength (strength per body mass) results in enough performance benefits to outweigh possible negative effects of dehydration. It would be interesting to see if muscle fiber type plays a role, with type 2 individuals experiencing a greater decline as they utilize anaerobic energy mechanisms more, specifically muscle glycogen. From this week’s reading it is evident hypohydration increases CHO oxidation.
No comments yet.