By Adam St. Pierre,
CTS Ultrarunning Coach
For a few years now, I’ve been fairly critical of sweat sodium concentration testing. In my own personal experience, I’ve suffered more in races when I’ve taken in too much salt, rather than not enough. I’ve also seen, in both races and training, that the amount of salt residue on my shirt/pack/hat at the end of a run seems to correlate directly with the amount of sodium I take in while running. I thought this (along with some bad experiences taking in too much sodium at Western States 100 in 2011) was sufficient evidence to support the idea that sodium supplementation was “bunk”- a marketing ploy.
I planned my races and counseled athletes to: “Know your sweat rate in a variety of conditions, and ensure that you have sufficient fluids to prevent a large amount of dehydration as measured by body mass loss during training and racing. You will consume sufficient sodium in your running foods and sports drinks to replace enough of what you lose, so don’t worry about taking in any more or really tracking your sodium intake.”
This is the biggest problem with N=1 evidence, generalizing my experience to others.
I recently attended the TrainingPeaks Endurance Coaching Summit in Boulder, CO. Andy Blow, a former elite triathlete and Team Sports Scientist for Benetton and Renault F1 teams, gave one of the most useful talks I attended. I went to his talk, titled ‘Drink to Thirst or Drink to a Plan?’ expecting Andy – now the founder of Precision Hydration – to try to sell product or push drinking to a plan at all times. Instead, I was treated to a balanced discussion of the times/conditions when drinking to thirst is adequate and where having a plan is necessary, and the spectrum that exists between the 2 extreme positions.
When to Drink to Plan and When to Drink to Thirst
In general, the hotter/more humid the conditions, the longer the event, and the less experienced the athlete – the more necessary it is to have a plan. Shorter races, cooler conditions, and more experienced athletes can “wing it” with less chance for negative repercussions – these athletes can drink to thirst. Of course, the caveat here is that heat/humidity/duration/experience level are all relative based on what an athlete is accustomed to.
Sweat Sodium Testing
Andy and the crew were offering free sweat sodium testing to all Summit attendees, so I got tested. (Disclaimer: I have no financial or endorsement relationship with Andy Blow or his company.) The test starts with 15 minutes of relaxing while an electrode placed on the forearm stimulates sweat glands. Then a small disc is placed on the sweaty spot to absorb sweat via capillary action. When the capillary tube is full enough, the tester takes the sweat out and injects it into a sodium analyzer. The analyzer measures the concentration of sodium in mmols/L, which can be converted to mg/L for ease of planning.
It turns out I have a pretty low sweat rate and a moderate sweat sodium concentration. With this combination, I’ve been able to get through ultras without an extreme need to replenish sodium stores. My n=1 experiences made sense… for me and the way I sweat. If I was a heavier sweater OR had a higher sweat sodium concentration, then I likely would not have been successful in those events, as my sodium losses would have been too large for my minimal intake to cover for.
I’ve had some reasonable success as an ultrarunner, despite not intentionally supplementing sodium while running. However, another factor in my experiences is that I have done most of my ultras in moderate conditions. I’ve never raced a super hot or humid event. If any of my races had been on a hotter/more humid day, I may have had worse results from my method of planning fluid intake but not planning sodium intake.
Sweat Concentration and Pre-Test Sodium Intake
In the past I’ve been reluctant to have my sweat sodium concentration tested, or to recommend testing to my athletes. My contention was that your sweat sodium concentration is impacted by the amount of sodium you take in; take in a lot, sweat out a lot; take in a little, sweat out a little. This view isn’t supported by anything more than anecdotal evidence, but also isn’t disproved by any available evidence.
Being a bit of a skeptic… I did a second sweat sodium test later in the day… after consuming about 5000mg of sodium over the course of 2 hours. I thought for sure that I would sweat out more sodium in the second test because of the large dose. When I tested again, my sweat sodium concentration was about the same. I’d be interested in additional tests, during exercise, day to day… but for now I’m content that my own personal sweat sodium concentration is around 1000mg/L and will utilize this information for a more scientific approach to my sodium intake during training and racing.
- Measure your sweat rate. Weigh yourself nude before a run. Go for a 1-2 hour run. Don’t drink anything on the run, don’t urinate either. Weigh yourself nude after the run. Each pound of weight you lost is equivalent to 16oz of fluid (.47L). If you eat/drink or urinate while running you would have to factor that in, so it’s simpler not to.
- Have your sweat sodium concentration tested. It is painless and simple and may be a beneficial starting point for dialing in your race day hydration plan (otherwise you may suffer a bit during trial and error). Knowing your sweat rate (the amount of sweat you lose) per hour in a variety of conditions is also crucial.
- If you know that you lose 1000mg of Sodium per liter of fluid and that you lose about 1L of fluid per hour… then you should plan on consuming around 1000mg of Sodium per hour! You can get sodium from sports drinks, foods, and supplements as needed.
- Use the above information to create a plan for training and racing to ensure that you stay within about 3-5% of your “normal” body weight and replace most of your sodium losses. It’s important to stick more closely to your plan during longer training sessions or events, hotter/more humid conditions, and when aid points are farther apart or infrequent. Less experienced athletes (or athletes who are inexperienced running in the conditions they will see on race day) may benefit from being more “to plan” while experienced athletes running in conditions they are accustomed to may be able to “wing it” successfully.