Research Review By Kevin Neeld©

Date Posted:

Aug 2009

Study Title:

Hydration and Muscular Performance: Does Fluid Balance Affect Strength, Power and High-Intensity Endurance?

Authors:

Judelson DA et al.

Author's Affiliations:

Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, CT; Department of Kinesiology, California State University, Fullerton, CA

Publication Information:

Sports Medicine 2007; 37(10): 907-921.

Background Information:

The importance of adequate hydration has been emphasized in research and practice for endurance exercise performance. While athletes generally recognize the association between hydration and performance, many still do not maintain optimal hydration. Furthermore, planned dehydration as a method of temporary weight loss is commonplace in sports such as wrestling and boxing.

Despite the acknowledged endurance performance benefits of adequate hydration, less attention has been paid to the potential negative effects of hypohydration (below optimal) on other measures of athleticism, such as strength, power, and anaerobic performance.

The purpose of this study was to systematically review the literature to determine how hypohydration affects muscular strength, power, and high-intensity endurance.

Pertinent Results:

  • Our knowledge of the true effect of hypohydration on strength, power, and high-intensity endurance is limited due to exacerbating factors (weight loss from caloric restriction in addition to hypohydration, increase in muscle and/or core temperature, and fatigue from exercise-induced hypohydration), masking factors (training status, menstrual status, and a failure to account for a reduction in body weight when using body weight-based measurements of strength) and other factors such as the individuals’ experience of training while hypohydrated.
  • Strength decreased 2.3%, 0.3%, and 3.8% in studies with no factors, masking factors, and exacerbating factors, respectively. The reduction was statistically significant in 15 of 70 (21%) total findings. However, this relationship was strongest in uninfluenced studies (no confounding factors), as more than 2/3 of these studies showed a negative influence of hypohydration such that 3-4% hypohydration resulted in a 2% reduction in strength.
  • Power changed by -3.2%, +1.8%, and -7.7% in studies with no factors, masking factors, and exacerbating factors, respectively. The performance reduction was significant in 9 of 47 (19%) total findings. Taken together, it appears that 3-4% hypohydration results in a 3% reduction in muscular power.
  • High-intensity endurance decreased by 15.0%, 6.7%, and 5.6% in studies with no factors, masking factors, and exacerbating factors, respectively. The performance reduction was statistically significant in 7 of 27 (26%) total findings. 3-4% hypohydration results in a 10% reduction in high-intensity endurance performance.

Clinical Application & Conclusions:

The primary finding of this review was that hypohydration had a considerable negative effect on high-intensity endurance performance. This finding highlights the importance of staying adequately hydrated for all athletes, but also for active members of the general population. The strength and power deficits associated with hypohydration appear to be minimal, but may be worthy of more consideration in elite athletes as the importance of a 2-3% performance decrement is magnified during high level competitions. The authors provide the example of the gold medalist in the 100m dash of the 1996, 2000, and 2004 Olympic Games defeating the 8th place finisher by an average of 3%.

Hypohydration can have a negative effect on performance through:
  1. Cardiovascular mechanisms: Reduced total plasma volume, increased submaximal heart rate, decreased maximal cardiac output, decrease nutrient delivery from the blood, decrease metabolite removal, and altered cellular metabolism.
  2. Metabolic mechanisms: Decreased lactate production secondary to dehydration-induced reductions of glycogen stores.
  3. Neuromuscular mechanisms: A dehydration-induced reduction in motor unit recruitment ability.
Although the majority of the research on the effects of hypohydration on various aspects of performance has notable confounding factors, the evidence generally highlights the importance of maintaining optimal hydration. The one thing the literature completely lacks is any evidence suggesting a downside of proper hydration.

Coaches and trainers should emphasize the importance of proper hydration to their athletes and clients. Two easy ways for people to monitor their hydration status are urine color and body weight. When properly hydrated, urine should be clear/colorless. It may be important to note that consuming a multi-vitamin sometimes results in a neon yellow colored urine, which is not to be confused with a darker yellow color resulting from dehydration.

Another strategy is to have your athletes/clients weigh in and out after each practice or training session. For each pound of weight lost, two cups of water should be consumed. If they have a hard time retaining water, it may be ideal to add some electrolytes (e.g. sodium and potassium) to the drink.

Study Methods:

The authors conducted a systematic review of the literature using Internet databases, references lists from relevant original research articles, book chapters, and review articles.

Study Strengths / Weaknesses:

Not applicable.

Additional References:

  1. Maughan RJ et al. Fluid and electrolyte intake and loss in elite soccer players during training. Int J Sport Nutr Exerc Metab 2004; 14: 333-346.
  2. Shirreffs SM. The importance of good hydration for work and exercise performance. Nutr Rev 2005; 63: S14-S21.
  3. Evetovich TK et al. Effect of moderate dehydration on torque, electromyography, and mechanomyography. Muscle Nerve 2002; 26: 225-231.
  4. Maresh CM et al. Effect of hydration state on testosterone and cortisol responses to training-intensity exercise in collegiate runners. Int J Sports Med 2006; 27: 765-770.