PH 2015 logo on black copyGetting your hydration right, both fluid and electrolytes, is critical to race success, particularly in longer events or those in hotter conditions than you are used to. To help you put together your race hydration plan, I’ve asked Andy Blow, founder of Precision Hydration ( and an expert in this area, a few questions. Andy is a former elite short course triathlete, X Terra age group champion, and top 10 Ironman and 70.3 finisher. He’s also a sports scientist who worked with Formula One teams. After discovering, through trial and error, the difference that getting his fluid and sodium intake right made to his own race results, he launched Precision Hydration back in 2011, working with athletes to measure their sweat and sodium losses and put together individualised hydration plans, using innovative technology. There followed the launch of a range of electrolyte products with varying sodium content and an online test to enable more athletes to choose the right products for them. Click here to access the test:. Use the code JSD10 for 10% off your initial product order. Precision Hydration has recently launched a new range of four different strngth electrolyte powders, with natural sugars and fruit flavours in place of artificial sweeteners. The sugar helps to improve absorption, making the product even better for hydration, while also contributing to your carbohydrate requirements at 15g per 500ml. The sachets are also really convenient to use. Click here here for more information.

Q: How does inadequate hydration during training or racing affect performance?

A: The classic response to why inadequate hydration negatively affects performance in endurance activities centres on the effect that reduced body fluid levels have on your blood volume and consequently the level of cardiovascular strain you’re under when exercising. In a nutshell, the theory says that as dehydration sets in you have less and less blood to pump to the skin (for cooling) as well as to supply the working muscles, and because of this your work rate is reduced.

For a long time it was widely believed that a 2% body weight drop (in terms of sweat loss) was the magic level at which dehydration started to significantly impede performance in this way.

This ‘2%’ idea has been challenged in recent years as the nuances around how dehydration has been studied in the lab (such as forced fluid loss using diuretics or by not allowing people to drink even when thirsty) and data from actual events ‘in the real world’ don’t always correlate. For example, athletes in actual sporting events have demonstrated in many circumstances that they seem be able to tolerate a much greater than 2% loss in body fluids before performance starts to decline. It therefore seems highly likely that there is no hard and fast rule, or easily definable single threshold, beyond which dehydration impacts performance for everyone.

Furthermore, although a decrease in blood volume is undoubtedly a big part of the issue that dehydration creates in the body, it’s not the only factor in play. Theories like the ‘Central Governor’ model of how fatigue works point to the idea that low body fluid levels might also be registered at a subconscious level in the brain and prompt an involuntary reduction in work rate in order to protect the body from damage. For this reason there is likely much more to it than the simple “less blood / more cardiovascular strain” concept can adequately represent.

All that said, the bottom line is that there there is basically universal agreement that dehydration beyond a certain point – that point being very individual to the athlete and situation in question – hampers exercise performance significantly, so getting to this point needs to be avoided if you want to perform at your best.

Q: How important is it to include electrolytes such as sodium when hydrating? What role do they play in staying hydrated?

A: Sodium is the main electrolyte in your extra cellular fluid (ECF) and therefore the one that is lost in the greatest amount in sweat because sweat is drawn from the ECF. The concentration of sodium in ECF, particularly in the blood plasma, is very tightly regulated by the body and so putting sodium back in along with fluids to replace that lost in sweat helps maintain ECF and blood volume better than drinking water or low sodium fluids alone. Adding sodium to drinks or taking it in alongside fluids is not a big deal for short bouts of exercise of less than 60-90 minutes but, depending on your individual rate of sodium loss, it can start to be extremely helpful once you get beyond that time frame, especially in hot conditions or at any other time when total sweat output is high.

Q: In your experience, how much do sweat rates vary between individuals, both fluid loss and sodium loss?

A: Sweat rates vary a lot from person to person because of genetics, body size, environmental conditions, work rate, clothing, exercise mode and a host of other factors. We’ve seen sweat rates of less than 500ml/hr for some smaller athletes, even when they’re working really hard in hot conditions, and rates of 3+ litre/hr for others in the same circumstances. Over several hours of training or racing this can add up to massively different levels of total sweat volume loss.

Sodium concentration also varies a great deal between individuals, but tends to be very stable within an individual athlete. We’ve seen around a 10 fold variation (200mg/l at the low end, 2000mg/l at the high end) with an average of around 950mg/l.

When you add the differences in sweat rate to the possible differences in sodium content, the net fluid and net sodium loss variation can be incredible. We’ve seen athletes losing less than an estimated 3g of sodium during an ironman event, with others losing over 45g in the same conditions.

Q: How can you tell if you are becoming deficient in sodium and other electrolytes during training or racing?

A: If you are becoming deficient in sodium, symptoms are not always easy to spot but include:

  • Feelings of low blood pressure (i.e. dizziness when you stand up quickly)
  • Lethargy/malaise/fatigue
  • Muscle cramps
  • Mild confusion / reduced coordination and reactions
  • Headaches

It is also likely that you might either crave salty foods or that salt will taste really good as your body is crying out for it.

During long endurance races many athletes report either twitching muscles or muscle cramps, headaches and reduced coordination as signs that they are getting low on sodium. If sodium depletion is indeed the cause then these symptoms go away pretty quickly if you ingest some salt/sodium supplements, and with time and practice you can become better at reading the early signs of problems in order to increase your intake earlier and keep serious issues at bay.

More chronic sodium depletion in athletes has also been linked to overtraining type symptoms as well.

Q: How do you assess how much fluid and sodium you require for a race?

A: Working out sodium and fluid requirements for racing is definitely something that is both an art and a science. The science bit comes from having an understanding of your range of rate of fluid and electrolyte losses in different conditions. You can do this by weighing yourself before and after a few key training sessions in simulated race conditions (1kg of weight loss = approx. 1 litre of sweat) to have an idea of your sweat rate.  To understand your sweat sodium content you can get an advanced sweat test done to analyse the sodium content, or use our online estimator if you’re unable to do a full test. The ‘art’ bit then comes from you using these figures to test and refine the actual levels of intake that work best for you in the field by doing some ‘trial and error’ type testing in training and competition. There is definitely no ‘one size fits all’ recommendation that can be made here, and even your own strategy needs to be flexible enough to take into account differing conditions that occur in the environment and in your body from day to day. That said, if you’re organised in how you approach the ‘trial and error’ in a short amount of time, you will dial in the upper and lower end of fluid volume and sodium that seem to work for you and become adept at listening to your body to tweak your plan on any given day.

Q: Is it necessary to ‘sodium load’ the day before a race?

A: It’s not ‘necessary’ but it can be very helpful, especially before longer, hotter and more intense races because it helps to ensure you start with ‘full tanks’ in terms of blood volume and sodium levels being topped up. We recommend taking in around 500-750ml of a strong electrolyte solution (such as our 1500mg drink) the night before and morning of a big event. This displaces a similar amount of plain water you’d normally have take in at that time and the additional sodium helps your body to retain some extra fluid and ensure you’re not diluting your electrolyte levels in the process.

Thanks, Andy! For more information, follow Precision Hydration on Twitter @thesweatexperts and visit their website where readers of this blog can get 10% off their initial order by using the code JSD10.

Jo Scott-Dalgleish BSc (Hons) is a BANT Registered Nutritionist, writing and giving talks about nutrition for endurance sportBased in London, she also works as a Registered Nutritional Therapist, conducting onetoone consultations with triathletes, distance runners and cyclists to help them eat well, be healthy and perform better through the creation of an individual nutritional plan. To learn more about these consultations, please visit