Sodium is an essential component to many aspects of human performance. Sodium is readily available to the body through the consumption and digestion of the salt, the mineral composed of sodium and chloride. Salt is expressed as the chemical equation NaCl, of which sodium is 40% of the composition.
The usual concern regarding sodium and its impact on health is the consumption of excess sodium, given the dietary practices prevalent throughout many parts of the world. Most commercially prepared foods have salt or a similar sodium compound in their formulation. Elevated levels of sodium place significant stresses on the body's fluid and blood volume balance. Sodium is the major underlying cause of transient high blood pressure and chronic hypertension present in a significant proportion of the adult population of most Western countries. As the body does not store water-soluble sodium for lengthy periods, the sodium must be disposed of and excreted through the production of urine in the renal system. The kidneys are placed under additional stress to process and excrete the additional sodium.
Sodium's properties as an electrolyte (a substance capable of carrying an electric charge) make it invaluable to the ability of the body to transmit nerve impulses to its muscles; sodium and potassium operate in a form of chemical partnership at the cellular level to facilitate the transmissions. The level of sodium within the bloodstream, which is the body's measure in the regulation of fluid levels, is maintained at a constant proportion of water versus sodium. The sodium level is maintained by the regulation provided to the body by the autonomic nervous system, an involuntary control mechanism centered in the hypothalamus region of the brain.
For an inactive person, a sodium deficit is not likely to be noticed immediately; for an athlete, any significant deficit in sodium levels will have an embedded and pronounced and negative impact on the body's performance both in muscle function and with respect to the ability of the athlete to maintain a healthy fluid level.
A deficit is a pronounced reduction in the optimal amount of a substance within the body, a gap between ideal and actual that is not capable of compensation by any other process. A sodium deficit, which often occurs in a gradual and cumulative fashion as a training session or a competition progresses, will most profoundly impact various aspects of athletic performance, including insufficient or incomplete rehydration, which occurs when sodium levels are below optimum. The body will not absorb all of the required water to bring fluid levels to the desired level, because the body will not absorb water into the bloodstream to create a ratio of sodium to fluid that is much below the recommended operating range. This incomplete rehydration will have its greater impact on performance the day following the creation of the sodium deficit, as the fluid level to support activity the next day will be inadequate, which often leads to dehydration at a far earlier point than would otherwise be expected.
Muscle cramps tend to occur in the larger working muscles of the body, particularly in the gastrocnemius and soleus (calf) muscles, and the quadriceps. Muscle cramps are a direct result of reduced sodium levels, as the nerve impulses that direct the muscles to function during sport are not transmitted to the muscle. The transmission of the impulse is facilitated through the sodium/potassium pump, an electrochemical reaction involving the electrolytes sodium and potassium, which alternate in an ebb and flow through the cells of the muscle, a part of the electrical current that carries the impulse to its intended cellular target. When sodium is deficient, the pump is not in balance and the transmission of the impulse cannot be completed. The end result for the athlete is a painful, often disabling muscle cramp. Unless sodium is absorbed into the body, proportionate to additional fluid as the body loses sodium through perspiration, cramping will persist.
The condition of hyponatremia is the most serious of the consequences of sodium deficit. When sodium levels become reduced through the perspiration created through athletic activity, the body may block the absorption of any additional fluids to preserve the existing sodium balance. Water may remain in the stomach, or, if it is passed through the small intestine, the water is stored in the cells of the body. Known as water intoxication, hyponatremia can quickly lead to significant neurological dysfunction, including drowsiness, a lack of coordination, and ultimately to unconsciousness. The solution to the sodium deficit is often an intravenous injection of a hypertonic saline solution with 3% sodium chloride, administered in regular intervals over a 24- to 48-hour period. Poorly treated, hyponatremia is fatal.