Curr Rev Musculoskelet Med (2008) 1:131–136 DOI 10.1007/s12178-008-9020-9 Musculoskeletal performance and hydration status Joseph A. Rothenberg Æ Andre´ Panagos Published online: 4 March 2008 Humana Press 2008 Abstract Maximal performance during competition is the drive many competitors use to train harder. However, there are several variables that contribute to impair a competitor’s performance. These variables work by alter- ing the homeostatic mechanisms within the body. Once homeostasis is altered the competitor’s body is no longer optimized to face the stresses of the athletic competition. The environment works as an all encompassing variable that will affect sweat rate. During increased environmental heat strain, one must adjust for critical variables, such as temperature regulation, hydration status, and electrolyte levels, as they can contribute to impaired performance. Acclimatization through training and competition will reduce or slow down the effects of these stress factors. Ever evolving recommendations are produced to aid competitors in maintaining homeostasis. Despite all the generic rec- ommendations that are made, however, every athlete needs to individualize their training and competition regimens to optimize personal performance. Keywords Dehydration Hydration status Hyponatremia Introduction Athletes continuously look for ways to improve perfor- mance. This drive goes from the elite athlete to the weekend warrior. Whether it is to run faster, longer, or simply take their body further than they have before, there J. A. Rothenberg (&) A. Panagos Physical Medicine & Rehabilitation, New York Presbyterian Hospital, New York, NY, USA e-mail: jr872-60@mindspring.com are always some goals to be met and surpassed. Most ergogenic aids are designed to help the competitor maintain homeostasis the longest, as when normal metabolism becomes disturbed that performance declines. The muscles are the tools we use to perform these tasks, and it is the ﬂuid in the body that carries needed nutrients, which act as catalysts to keep us moving. Therefore, hydration status and maintenance of homeostasis are critical factors before, during, and after competition. The typical person is composed of approximately 60% water, with highly trained athletes approaching 70% water content throughout their bodies [1]. This increased total body water (TBW) content in athletes is typically com- mensurate to their relative lean body mass compared to the general population. Approximately 65% of TBW is intra- cellular, while 35% is extracellular (comprising plasma and interstitial ﬂuid) [2]. Euhydration is deﬁned as the normal state of water content in the absence of relative dehydration [3]. Dehy- dration is deﬁned as the condition that results from the loss of excessive body water, with amounts greater than 2% being considered signiﬁcant [4]. Dehydration reduces endurance exercise performance, impairs exercise toler- ance, and can result in hyperthermia [5]. Dehydration of *2% results in symptoms of thirst, ﬂushing, dark-colored urine, dry mouth, fatigue, and weakness. After 5% dehy- dration sweating decreases and core temperature rises. A 10% loss of body water is considered an emergency with symptoms including muscle spasms, confusion, and potential loss of consciousness [6]. In conjunction, thermoregulation is also important as it can be drastically affected by hydration status. Thermo- regulation is affected by metabolism, radiation, conduction, convection, and evaporation [7]. Radiation is the loss/gain of heat in the form of infrared energy. Conduction is the