When you sweat, you are losing much more than water. You are also losing electrolytes. Sodium and chloride are the most abundant electrolytes in sweat with potassium, magnesium, and calcium present in lower amounts.
The typical understanding amongst athletes is that you need to replace electrolytes during exercise alongside fluids to maintain performance.
However, the research done in this space is sorely lacking. Currently, there is only one randomised control trial from 2018 that shows an increase in performance with sodium replacement during exercise. But these results have not been replicated since.
Despite this, many athletes will drink sports drinks and use other electrolyte products like Hydralyte.
And there is absolutely a place for these products for some athletes. It is just that the importance of replacing electrolytes is likely not as great as many would think.
Beliefs About Replacing Sodium Losses Amongst Athletes
An interesting study was published in 2018 looking at the beliefs around sodium intake amongst a group of endurance athletes.
Respondents generally believed that sodium intake during exercise prevented hyponatremia and exercise-induced cramps.
Seventy-nine percent consciously replaced sodium during exercise and competition, though only 29% had a specific plan. Most likely, they simply ensured they were using sports products such as drinks and gels containing sodium and electrolytes.
Unlike the intake of carbohydrates and fluid during endurance events, there is little evidence to support sodium replacement.
That isn’t to say it is useless. But from an evidence perspective, we don’t have a lot to back up this practice.
Hydration & Performance
The concern around sodium loss through sweat is mostly related to endurance sports. Stop-and-go sports that involve high-intensity intermittent exercise lasting more than an hour also experience this though.
How much sodium an athlete will lose during a session or an event depends on a range of factors including:
- Sweat rate
- The individual composition of their sweat
- Environmental conditions
- Heat acclimatisation
- Training status
Athletes can lose as much as 5000mg of sodium through sweating in a single high-intensity workout. So in the case where sodium losses are high, sodium ingestion may play an important role in minimising dehydration. This is by assisting with fluid and electrolyte balance.
It makes sense to replace sodium and fluid during a long-distance event or a long period of intermittent high-intensity activity.
But as previously mentioned, the research behind sodium ingestion during exercise and its actual impacts on performance doesn’t look very promising.
The Research
A 2018 systematic review found just five studies looking at the association between sodium ingestion and endurance performance.
Only one of the five studies suggested that sodium intake benefited endurance performance. This study was a randomised control trial. It provided athletes with either sodium capsules or a placebo during a half ironman triathlon.
They found that athletes provided with the sodium capsules had finishing times that were 8% faster than those given placebo.
Eight percent is huge when it comes to nutrition interventions. The performance benefit of caffeine supplementation, adequate fluid intake, and carbohydrates typically show less than half of the benefit found in this study.
Although these findings have not been replicated since and other studies investigating the same thing found next to no performance benefit. Therefore, it’s highly likely that sodium replacement does not have this big of an impact on performance. This one study is a bit of an outlier.
It is generally felt that this finding may have been confounded by other variables. This included the triathlon transitions and other competitors in the event which cannot be controlled. As is the nature of any research not done in lab conditions.
Effects On Thirst
For a lot of athletes, drinking to thirst is a key way to avoid dehydration during exercise. For most, it can be quite an effective one.
However, thirst sensation is highly sensitive to changes in sodium. If you are losing lots of sodium through sweat and not replacing it, you’re less likely to feel thirsty despite also losing fluids.
This is because the body has many ways to maintain a balance between sodium and fluids, including changes to thirst.
Sodium ingestion during or following exercise will actually help to stimulate thirst. It also stimulates fluid retention by the kidney.
So theoretically, if you were to replace some of your sodium losses during exercise, you would have a greater thirst sensation. This would then help you to drink more fluids. Plus your body will be able to retain more of that fluid.
Therefore, sodium ingestion could assist with efforts to maintain hydration.
We know that losing >2% of your weight due to fluid loss during exercise has a significant impact on performance. If sodium intake assists with avoiding dehydration, it would be worth using as a tool in training and during events.
How much sodium you should be replacing though is highly debatable.
Sodium & Cramps
Exercise-induced muscle cramps (EAMC) typically occur in muscles when contracting in a shortened state.
Although some cramps do not affect athletic performance, other times, they can be completely debilitating.
One of the original theories behind the cause of cramps was the dehydration–electrolyte imbalance theory.
This theory suggests that this depletion, namely of sodium and potassium, results in the sensitisation of select nerve terminals.
Research shows that exercise in hot and humid conditions is more likely to facilitate cramping. Leading experts believe that it was indeed the amount of fluid and electrolytes lost that made cramping more likely.
This has been eagerly supported by the sports drink and supplement industries. They market fluid and electrolyte products aimed at preventing or reducing the severity of cramping.
Despite this, there is very little research that directly links shifts in fluid and electrolytes with the occurrence of cramps.
We do, however, know that overhydration can increase the risk of cramping.
This is due to the fact that plasma sodium and osmolality is reduced. So if fluids are aggressively replaced during exercise without any sodium replacement this may lead to an increase in cramping. But the aggressive overhydration likely has more to do with it than the lack of sodium ingestion.
Furthermore, sodium, potassium, calcium, and/or magnesium intake before and during exercise do not appear to prevent the onset of cramping.
Sodium & Avoiding Exercise-Associated Hyponatremia (EAH)
Exercise Associated Hyponatremia (EAH) is a serious, potentially fatal condition.
From 1980 to the present day, 14 athletes have died from EAH and many more have been hospitalised.
EAH is characterised by low blood sodium concentration. This produces a rapid and dangerous swelling of the brain that can result in seizures, coma, and death.
Whilst EAH is thought to be due to both excessive fluid or acute sodium deficit, it appears only excessive fluid intake leads to the symptoms. This supports the idea that excessive intracellular fluid, rather than sodium concentration alone, is harmful.
Therefore, the best way to avoid EAH is to generally avoid consuming more fluid than what is being lost.
If you finish a session or event weighing more than what you started, you are overdoing it on the fluids. For the most part, you do not want to exceed more than a 2% reduction in body weight from fluid losses. Although it is worth knowing that many elite athletes actually do. You definitely don’t want to gain body weight during exercise though.
The risk of hyponatremia can also be reduced by ingesting sodium alongside fluids to maintain a good fluid and electrolyte balance. However, avoiding excessive fluid consumption is the most important factor.
Athletes who ingest sodium through sports drinks and other food and beverages are still at risk of EAH if their fluid intake is high enough.
Sodium Replacement During Exercise
Currently, there is no consensus or guidelines on sodium replacement during exercise.
The role of sodium replacement in athletic performance remains uncertain. We definitely don’t know the best way to go about it.
Who Should Replace Sodium?
Significant sodium replacement is only required when fluid intake exceeds 80% of sweat losses to reduce the risk of hyponatremia.
However, it is very rare that an athlete would consume 80% or more of their fluid losses. In most endurance sports or stop-and-go sports, the opportunities to drink are limited.
For example, a triathlete relies on aid stations during the final leg of a race. Or a soccer player only has access to fluids during halftime.
In an ultra-endurance sport or a slower-paced sport where fluids are highly available, athletes may find themselves replacing a lot of their fluid losses. They may need to consider replacing sodium as well.
It is also recommended by the American Association of Sports Medicine that athletes who:
- Lose a lot of sweat (and therefore sodium)
- Have particularly salty sweat, or
- Replace a high % of their sweat losses
Make an effort to replace some of their sodium losses during exercise.
How Much Should Be Replaced?
In the past, it was often recommended that 100% of sodium losses be replaced in exercise. Although, as discussed previously, athletes will rarely replace 100% of fluid losses.
So it does not make sense to replace more sodium than fluids. This would likely result in an unnecessary increase in plasma osmolality, and an increased fluid shift from the intracellular to extracellular space.
It is incredibly hard to say how much sodium should be replaced. It likely is very individual depending on a range of factors including:
- Type of exercise, intensity and duration
- Fluid availability
- How much fluid the athlete drinks
- How much the athlete sweats
- The individual composition of that athlete’s sweat
If you feel the need to replace some sodium during exercise, using an electrolyte-containing sports drink or similar product is probably all you need.
Individualising sodium and electrolyte intake would not only be very difficult but likely unnecessary as well.
Key Take-Aways
Based on the current body of research, for many athletes, there may be little reason to focus on sodium intake during exercise.
It will be interesting to see if this changes when sodium replacement in prolonged activity is more rigorously studied.
It makes sense for people who lose a lot of sweat, have very salty sweat, and replace a high percentage of fluid losses, to replace sodium as well during exercise.
This may assist with maintaining hydration, reducing the risk of cramps, and possibly also reducing the risk of hyponatremia.
Athletes can do this by utilising sports drinks, salty snacks, gels, and electrolyte powders.
