Last updated: 23-Aug-18
By Renee McGregor
Performance Dietitian and Author of Training Food and The Fast Fuel Books.
Most runners are keen to enhance their performance, regardless of what distance they run or level they are at. They will research kit, training, nutrition and hydration and with so much information now available, it can be a bit of a minefield.
In reality, it is a combination of many factors from running technique, to training sessions and appropriate fuelling that will optimise running performance.
Nutrition for running and ultra running, in particular, is a controversial subject – with many evangilising ketogenic diets and others swearing by a more traditional high-carbohydrate intake. Similarly, when it comes to hydration and fuelling on the run, individuals have their processes and practices that they prefer to adhere to.
However, the one thing that most ultra-runners overlook is their intake of salt, or sodium to be precise. While most of you will understand the importance of taking on electrolytes, there seems to be little understanding of their actual role, purpose and importance.
It is well documented in scientific literature (Von Duvillard et al) that fluid intake and adequate hydration during exercise are essential and, more importantly, critical during prolonged training sessions and competition events.
The key role of fluid intake during ultra running is that it maintains:
- thermoregulation (body temperature)
- adequate plasma (blood) volume.
Ensuring that plasma volume and thermoregulation stay within an optimal range has a direct impact on performance. When core body temperature rises, due to dehydration, plasma volume decreases, resulting in an increased heart rate, which accelerates fatigue.
Just a 1% reduction in body weight through fluid losses can contribute to these negative physiological effects. In addition, dehydration has a marked affect on cognitive function, resulting in your inability to make decisions. During an ultra, this has been shown to cause runners to make navigational mistakes as well as reduce their ability to react to thirst and hunger requirements.
Whilst most runners are very conscientious about meeting their fluid intake, what they may not be aware of is the role of sodium. Sodium encourages and increases the absorption of fluid into the body, helping to maintain hydration.
So How Much is Enough?
Most runners will sweat between 400-2400 ml per hour of exercise, with the average value being around 1200 ml per hour, although this will vary with age, sex, weight, intensity of training and also the environmental temperature. These sweat losses are predominantly water but the main electrolyte lost is sodium.
The sodium content of sweat varies substantially from 115 to greater than 2000 mg per 1000 ml of sweat. A runner who is a “salty sweater” (i.e., has a high amount of sodium in their sweat) may lose well in excess of the recommended intake.
It is obvious, then, that in ultra running events and training, sodium losses may be very high. In temperatures of 20 Celsius, if a runner loses 1200ml of sweat in an hour and 900mg of sodium/L, then in an ultra race lasting five hours, their fluid losses will be in the region of 6000ml and their sodium requirements 5400mg. Therefore, they will require 1080mg of sodium per hour.
Most electrolyte tablets, salt capsules or energy drinks will only provide around 250-300mg of sodium. If you are diluting your electrolytes into 750ml, this will mean having to consume in the region of 2250ml of fluid per hour to meet your sodium needs, which is – practically – very difficult, both from a consumption and transportation point of view.
Is it any wonder, then, why so many runners complain of the common symptoms associated with low sodium intakes and dehydration?
- gastro-intestinal distress
- impaired concentration
- heat stress.
Indeed, the biggest cause of stomach issues during runs is related to sodium imbalance and not to the sports nutrition gel or bar that most runners blame. If your body is dehydrated, and you are consuming glucose, this will become highly concentrated within the gut. As blood flow is being directed away form the stomach to the working muscles, it cannot absorb this quick enough, resulting in stomach upsets.
As a rule of thumb, I generally suggest ultra runners need to take around 700-900mg of sodium an hour during longer training and competition. This can be a mix of salt tablets, electrolytes, energy drinks and even food.
Some good food suggestions include:
- salted peanuts
- mashed potato with cheese or marmite
- cheese straws
- cured meat.
Sodium balance and staying hydrated is not just confined to during running, it is equally important to think about it leading up to an event. I regularly recommend that individuals start drinking electrolytes in the 24 hours prior to race day.
Post race, restoring fluid losses is critical in replenishing glycogen stores. Being dehydrated will delay this process significantly and thus also affect how quickly you recover.
One of the best sources of post-race recovery is milk, as it provides hydration, carbohydrate, protein and also electrolytes in the correct balance for your body to absorb.
About the writer: Renee McGregor is a Performance Dietitian and Author of Training Food and The Fast Fuel Books. There is more information on her website www.reneemcgregor.com
Further reading (click on these titles to download):
- Exercise and Fluid Replacement (American College of Sports Medicine)
- Hydration in Sport and Exercise (British Nutrition Foundation – Nutrition Bulletin)
- Dehydration and Rehydration in Competitive Sport (Scandinavian Journal of Medicine and Science in Sports)
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