Electrolytes are minerals like sodium, potassium, chloride, calcium, magnesium, bicarbonate, phosphate and sulfate. Hikers can replenish their electrolytes from the normal hiking food eaten, from specially formulated sports/energy drinks or bars or from pill or powder supplements. Even though I am not an expert (just a person with some expertise), here is a synthesis of research done to date on this subject, relative to heavy exercise.
1. Priorities for heavy exercisers: replace water first, carbohydrates second and electrolytes last. Replacing water and carbs in a timely manner will usually prevent extreme fatigue (“bonking”).
2. If exercising hard for more than an hour and if not stopping to drink and eat on a regular basis, use balanced sports drinks or fruit juices to accomplish all three of the priorities listed in #1.
3. If eating regularly during heavy exercise, you only need water; most tolerated foods contain adequate carbs and electrolytes.
4. Even though eating regular food is sometimes difficult during heavy exercise, at least try to eat salty foods as this will encourage more drinking.
5. There are many factors regarding the need for timely electrolyte replacement during heavy exercise: duration, temperature, acclimatization to heat, conditioning, sweat rate, individual differences regarding loss of electrolytes, age. Because of these factors, there is no one answer for all individuals participating in heavy exercise regarding the best concentration of water and electrolyte replacement; it is individual and situational.
6. Given the current state of knowledge, one generalization that can be made with confidence for heavy exercisers is that electrolytes need to be replaced in some form at some time for optimal performance; a good approximation is to plan on electrolyte replacement if exercising at least 3-5 hours.
7. Regardless of individual differences and the current state of knowledge, there is complete agreement on the need for special attention to mineral and electrolyte replacement when one works up drenching sweats for several consecutive days. In these extreme situations, it is hard to eat enough of the right kinds of food for normal replacement of electrolytes.
8. It is generally agreed that lack of electrolyte/mineral replacement for heavy exercisers can eventually result in medical problems (e.g., heart irregularities, cramps, weakness, nausea).
9. Drinking too much water without replacing the salts will result in a serious medical problem called “hyponatremia” (low blood sodium concentration; water intoxication).
10. One only needs to replace electrolyte salts that are lost; imbibing extra will not enhance performance and will likely reduce it. At the least, too much salt will result in increased effort needed to carry the extra water the body will desire.
11. Assuming all of the above is true, the American College Of Sports Medicine and years of human experience suggest that if you are pushing hard for many hours, or you're hiking through hot and dry conditions, you should pay close attention to both water and electrolyte intake. Sports drinks are only one way to accomplish this.
How does the above fit with your own knowledge of this subject? Consider circling the items above you find questionable (i.e., needing more research). Also, consider prioritizing the top three items to which you need to pay particular attention.