The main roles played by sodium in the body include fluid balance, nerve transmission, and muscle contraction. Basically, without salt your body can't rehydrate quickly and its functions slow. (Think about how lethargic you sometimes feel after a long workout. Part of the feeling comes from lack of sodium.) Since endurance athletes are almost always working to minimize fluid loss during exercise, one can see how this mineral can be important to a sound training/race-day nutrition plan. We also know that as little as a 2% decrease in body weight from dehydration can impair performance, so consuming adequate amounts of sodium during exercise will help your body retain the liquids you drink and prolong your best performance.

According to The Institute of Medicine, the Adequate Intake (AI) for sodium is roughly 1.5g/day for people up to 50 years of age, and experts believe this amount should be sufficient for physically active people. But there's "active" in terms of the general population, and then there's "active" in terms of CTS. For those athletes engaged in higher intensity and/or longer duration events in hot or humid conditions, you may need substantially more sodium during and right after your training.

Moreover, there are many factors that go into figuring out the right amount of sodium intake during exercise. Among those factors, here are the big ones:

• Sodium intake in the overall diet. If you chow through bags of chips, canned soups, and French fries, you probably have plenty of salt in your diet. But if you make fresh fruits and vegetables a staple at every meal, you might need to pay more attention to sodium intake during exercise by adding small—the key word being small—amounts of salt to foods throughout the day.
• Personal sweat rate. Some people perspire more than others. The more you perspire, the more salt you can lose through your skin. Find out yours by weighing yourself naked before and after a workout. Each pound of weight loss is equal to 16 ounces of fluids.
• Hydration status. If you're topped up on sports beverages such as PowerBar's Endurance, you're probably in good shape salt-wise. If you haven't had to urinate in the last hour or your urine is yellow, you're dehydrated. To fill up, you'll need some sodium during exercise since sodium helps to increase our drive to drink; otherwise, your body will work to shed that water until it reaches its optimal water/sodium balance.
• Degree of acclimatization. It takes about 10 days for the body to acclimate to hot and humid temperatures. Until then, it sheds moisture (and salt) like a faucet to keep cool. If you jump from a relatively cool clime to a hot one like the cool mountains to the steamy flats of Florida, you're going to need more salt to keep things functioning until you acclimatize.
• Equipment or clothing. A study found that football players lost more fluids during a three-hour practice than a marathon runner running for the same amount of time. While the runner was undoubtedly doing more exercise, the football players' equipment, plus the fact that they were standing around most of the time with no self-created breeze to evaporate their sweat (which would cool them down), caused them to lose buckets of fluids from their bodies.

Best Ways to Stay Salted
The research available on sodium supplementation appears to support the additional intake of sodium in general for athletes in heavier training, but it is best consumed in a sports drink or gel with adequate fluids and a balance of other nutrients.

The one supplement that is not recommended is the salt tablet. Using salt tablets may actually lead to over-consumption of sodium and subsequent gastrointestinal distress. The few studies that have examined supplementation with salt tables do not support their use and do not show improvements beyond the usual consumption of a balanced sports drink or gel.

Ingesting adequate sodium (not usually a problem in the typical Western diet) and consuming between 0.5-0.7g of sodium per liter of fluids for exercise lasting greater than 1 hour is a great place to start, but always keep in mind the factors that can affect sodium loss and be prepared to adjust your intake accordingly. Done right, you'll not only keep your central nervous system firing your muscles in tune, you'll also ensure that your hydration status is set to Thrive, not simply Survive.