COLUMNS: Research Digest
Scott Riewald, PhD, CSCS, NSCA-CPT
What impact does dehydration or hypohydration have on an athlete in the weight room? A great deal of information has been published in the literature on hypohydration and the effects it has on endurance exercise performance. Similarly, there are a number of studies in which the authors have demonstrated that dehydration limits or has no effect on strength variables such as peak strength, power, and high-intensity endurance. Yet, a careful review of the literature will show that few of these studies have been able to isolate the effects of the hypohydration from other potentially confounding variables-things such as increased core temperature, body weight, or caloric restrictions. Additionally, most of the studies conducted to date have used single repetition/maximal efforts or isometric fatigue trials to evaluate strength and power deficits. But how does that relate to what is typically seen in a strength training workout that involves multiple sets and multiple repetitions of isotonic exercises? Recently, Judelson and colleagues (1) were able to examine the effects of hypohydration on strength, power, and resistance training while also controlling for many of seemingly confounding variables. In addition to simply looking at strength and power measures, the researchers used electromyography to examine the central nervous system's ability to activate working muscles in a dehydrated state. The results from this study show the importance of proper hydration and how hypohydration can negatively impact performance in the weight room.
WHAT METHODOLOGY WAS USED?
Seven healthy men (age 23 ± 4 years) with a background in resistance training participated in a randomized study design that controlled hydration status as well as other performance-affecting variables. All participants had at least 6 months of experience performing back squats and underwent a baseline resistance challenge test set, i.e., 6 sets of 10 back squats, using loads representing 80% of their 1RM, at the start of the study. During this test, if subjects were unable to complete a full set of 10 repetitions, they continued to exhaustion, but they still attempted to complete all 6 sets. The total number of repetitions performed was recorded. This resistance challenge was repeated later, with the athletes in different hydration states: euhydrated, hypohydrated by 2.5% of their body mass, and hypohydrated by 5% body mass. Test sessions lasted approximately 28 hours and started with each athlete walking on a treadmill in a heated environmental chamber until he lost 5% off his body mass (or in some cases they were stopped early if other criteria were met). Subjects then were given a high-carbohydrate meal and were rehydrated orally and with an intravenous saline solution so that the next morning they were hypohydrated by 0%, 2.5%, or 5%. After a night's sleep, subjects completed several peak power and performance tests followed by the resistance exercise challenge (10-12 hours after rehydration). The number of repetitions in these tests was kept constant with what was performed during the baseline test to ensure equal work production among test scenarios. Test sessions were separated by 1 week to allow for recovery.
WHAT DID THE RESULTS SHOW?
Test results were as follows:
- Urine-specific gravity, an indicator of dehydration, was significantly greater before the hypohydrated tests compared with the euhydrated trials. However, there was no significant difference in body mass in subjects among trials.
- No significant differences were noted between hydrated and hypohydrated groups in any of the power or performance tests, which included a vertical jump, peak lower body power (measured via a 3-repetition jump squat test), peak lower body force (measured via an isometric squat), and alterations to the central nervous system drive (although a nonsignificant decrease in neural drive to the leg muscles was noted in each of the hypohydrated states).
- Subjects completed significantly greater work during the first three sets of the resistance exercise challenge when properly hydrated compared with either the 2.5% or the 5% hypohydrated test cases. On average, the athletes were able to complete 3-5 fewer repetitions through the first three sets when hypohydrated.
- Subjects completed significantly greater work over the first 5 sets in the euhydrated condition compared with the 5% hypohydrated test scenario.
- Hypohydration resulted in an increased pre-exercise core temperature.
WHAT DO THESE RESULTS MEAN TO THE STRENGTH AND CONDITIONING COACH?
Although the results indicate that dehydration only has a limited impact on single repetition maximal strength and power efforts, it does impact the ability to engage in multiple-set resistance training programs-the type of training commonly implemented in many strength and conditioning programs. The more severe the hypohydration, the greater the impact on performance. Performance through 3 sets was affected when subjects were hypohydrated 2.5% and 5 sets when they were hypohydrated by 5%. Exercising in a hypohydrated state clearly would have an acute effect by reducing the quality of an individual training session. However, taken over the long haul, regularly training in a hypohydrated state will have an impact on the overall training volume. Although this may seem inconsequential or unrealistic, the fact is, “chronic” dehydration is quite common: many athletes (especially those who train in the morning) come to the training session already dehydrated.
Additionally, although the decrease in neural drive to the muscles was not shown to be significant, there are likely changes along the neuromuscular pathway (central or peripheral nervous system or even at the level of the muscle) that could result in altered recruitment patterns during training. Again, this could modify the desired training effect and adaptations one hopes to produce with a given workout. The bottom line is that proper hydration should be emphasized with the athletes you train to achieve peak performance. Not only is it important on the playing field, but it should be a focus in the weight room as well.▪
1. Judelson, DA, Maresh, CM, Farrell, MJ, Yamamoto, LM, Armstrong, LE, Kraemer, WJ, Volek, JS, Spiering, BA, Casa, DS, and Anderson, JM. Effect of hydration state on strength, power and resistance exercise performance. Med Sci Sports Exerc
39: 1817-1824, 2007.