Individualized hydration plans improve performance outcomes for collegiate athletes engaging in in-season training

This study investigated whether an individually tailored hydration plan improves performance outcomes for collegiate athletes engaged in seasonal sports. Participants were recruited from three sports (ice hockey, lacrosse, and track & field) as these sports were currently in season and the athletes were engaged in consistent and standardized training sessions. All athletes in this study had practice in the afternoon or evening with the NHP and PHP sessions occurring at the same time of day for each individual. A prescription hydration plan (PHP) was created for each participant that was based on both fluid and sodium losses incurred during moderate to hard training sessions lasting at least 45 min in duration. Athletes were instructed to drink at 15 min intervals at a volume of fluid that prevents a 2% bodyweight loss as well as any weight gain. A maximum fluid consumption level for each PHP was established as a precaution, given that overhydration is a well-known risk factor for exercise-induced hyponatremia [27]. However, the likelihood of this occurring in this study was low given that the athlete cohort in this study engaged in training sessions lasting no more than 120 min [28]. The fluid itself was isotonic relative to the athlete’s specific sweat sodium concentration and was based off of fluids readily available to him or her. The results indicate that this approach was effective in improving heart rate recovery, attention and awareness, and mitigating the loss in anaerobic power that occurred from the training session. Compliance was high with the prescribed volume of fluid well tolerated by the participants. While some athletes did remark that they could taste the extra sodium, this did not appear to affect the compliance to their prescribed hydration protocol, even among those who required the most salt added to their beverage.

To our knowledge, this is the first investigation to look at whether an individually tailored hydration plan improves athletic performance for collegiate athletes engaged in a variety of sports. Previous work has shown that hydration plans based purely on fluid loss hold promise [13]. Bardis et al., examined whether consuming water at regular intervals to offset fluid losses as compared with ad libitum fluid consumption improved the performance of cyclists [13]. The researchers found that power output was maintained throughout a training session consisting of three 5-km hill repeats, whereas when these cyclists consumed water ad libitum, their power output dropped with each successive repeat [13]. Other studies have examined the effects of isotonic beverages on sports performance, yet often compare such beverages to water [2931]. This presents the obvious issue of accounting for any carbohydrate effect as most commercially available sports drinks are 6–10% carbohydrate solutions mixed with several electrolytes, among them sodium. In this study, because the specific beverage consumed by each participant was held consistent between the NHP and PHP training sessions, the results are not confounded by factors such as the carbohydrate composition of a beverage. The PHP intervention manipulated only the fluid quantity and sodium consumed immediately before and during exercise.

In all cases, the final [Na+] of the PHP beverages were higher than any of the sports drinks available to our athletes (though most habitually consumed water during training). With the notable exception of endurance-focused sports drinks, many commercially available beverages do not match the sodium loss rate of many individuals. This is understandable as it is commercially untenable to create a sports drink unique to every individual’s sweat composition. For the majority of individuals engaged in recreational physical activity these drinks are more than sufficient. For elite and amateur athletes looking for every possible safe method to improve performance, the results of this study support commercial sweat testing in order to develop optimal hydration strategies. This may hold especially true for athletes engaged in longer sporting events such as a marathon or Ironman triathlon, where the loss of fluid through sweat is substantial [32]. Supplementation with higher sodium sports drinks or salt capsules may be advisable for athletes engaged in prolonged exercise of 3 h or more in order to maintain serum electrolyte concentrations [33, 34]. Based on these studies and others, the longer an event, the more critical it appears to be to have an adequate hydration plan in place that considers sweat rate and composition [1, 34]. In our study, most of the participants engaged in training sessions lasting between 70 min to two hours and the benefits were apparent.

Lastly, in line with previous work, we also found that while most athletes in this study felt that their current hydration strategies were effective, the majority of this cohort reported feeling dehydrated after a training session [10, 11, 15, 16]. The disconnect between ad libitum fluid consumption and hydration status during competition is well documented [8, 11, 13, 15]. Studies have consistently shown that it is not uncommon for athletes to show up to a training session already dehydrated and consume inadequate fluid levels despite the ready availability of water or sports drinks [8, 11, 1416]. It cannot be definitively stated whether the athletes in our study were dehydrated at the beginning of practice. In this study, the researchers were present to monitor compliance to the prescribed fluid volume, including the pre-practice consumption of the PHP beverage. While the PHP used in the present work was feasible to create and implement, ensuring compliance in day to day training may be challenging. In a study by Logan-Sprenger et al., a third of all ice hockey players failed to hydrate adequately during a game despite these fluids being readily available [15]. Increasing hydration awareness along with providing pre-marked bottles that state how much fluid should be consumed by set time periods, if feasible, may be one approach to overcoming this issue.

Study limitations

This study has several limitations. First, only one training session was utilized per hydration plan. Based on researcher observations, participant feedback, and input by coaches, there was little difference in the training sessions used for the NHP and PHP assessments with each participant. It was important to control for the training sessions utilized as well as ensuring minimal fitness gains in between NHP and PHP sessions. Hence, we required a “wash out” period of 7 days. The training sessions utilized in this study were already pre-scheduled so as not to interfere with the practice plan that each coach designed for their athletes. For each sport at the college where and when this study occurred, the number of ideal sessions to test the PHP were limited. The fact that multiple sports were used to test the PHP is both a strength (broad applicability) and a limitation (non-specific). Given the team schedules and the timing of this study during the winter/spring seasons in the New England, USA area, it is unclear what affect a warmer, more humid climate may have had on the results. Given that both the NHP and PHP training sessions were similar in duration, intensity, mode of training, and climate, we postulate that these results will hold in warmer conditions. More so, given higher degrees of fluid loss with warmer, more humid climates, the benefits from the PHP observed in this study may even be amplified to a certain degree. This is speculative however and future studies if feasible, should consider testing athletes over multiple training sessions per treatment. Additionally, in this study, sweat sodium concentrations were assessed at the forearm. Previous research has indicated that measuring sodium from multiple body sites such as was done by Dziedzic et al., can lead to higher sweat sodium values [35]. Based on Dziedzic’s report, we determined that this difference translates to adding roughly 200 mg more sodium per a 32-oz sports beverage than what was added to the 32 oz beverages in this study. We are unclear on what impact this additional salt may have made concerning the performance outcomes used in this study. From a practical standpoint, assessing the forearm is often a more feasible approach to determining sweat sodium concentrations than a whole-body approach. Another limitation to this study is that it relied on bodyweight changes and fluid intake monitoring to gauge hydration status. This method is less precise than other methods of hydration status such as a urine specific gravity test (USG) [36]. We were unable to conduct a USG due to equipment limitations. We did note however, the bodyweight trends of all athletes in this study over the two weeks preceding the pre-training bodyweight measurements (data not shown). There was no significant difference in these weights as compared with the pre-training bodyweights (taken during the NHP and/or PHP training sessions), indicating that each athlete was weight-stable. This however does not negate the possibility that an athlete was dehydrated, euhydrated or hyperhydrated going into each training session. Further research should include tests such as USG so that hydration status can be confidently determined.

There are also several potential confounders that need to be addressed. Factors such as sleep quality, personal stress, medication use, menstrual cycle, and diet may have affected the outcomes. We did not assess nor control for the athlete’s environment outside of one hour from the training session. One main advantage of the randomized, cross-over design utilized for this study is that each participant served as his or her own control, which presumably minimized the influence of any potential confounding covariates. Despite the strength of this design, future studies in hydration research may do well to assess diet, stress level, and sleep quality as mentally, these factors can significantly impact athletic performance. Collegiate athletes are not immune to the stresses of balancing both academic and athletic responsibilities in addition to managing personal stressors common to all segments of the population.