It seems so simple. We ride, get sweaty, get thirsty, and drink something. So why is hydration presented as a complex science, a problem requiring a deep understanding of human physiology, advanced testing, and an array of ‘scientifically formulated’ solutions? Does it really need to be this complicated?
Is “drink when you’re thirsty” an oversimplification? Why is there so much controversy around this topic? And how can there be so many solutions that are so different, yet supposedly based on the same scientific evidence?
Welcome to the simple-yet-complex, scientific-yet-controversial world of hydration for athletes. In this multi-part series, we’ll unpack what we know about hydration and electrolytes for cyclists. We’ll look at why these topics have been so hotly debated over the years; where there’s common ground among the various protagonists; where opinions differ and why; and the more recent scientific work that’s been quietly carried out, often out of sight of those fanning the flames of controversy.
Parts one and two cover water ins and outs from the body and hydration, while part three will dive into the role of electrolytes. What I hope you take away from these stories is that hydration and electrolytes (especially sodium) are intricately connected – you shouldn’t think about them in isolation. This is also the subject of the latest Performance Process podcast, where I sat down with Ronan Mc Laughlin to cover this important topic. If you prefer an audio format, look for it wherever you get your podcasts or simply scroll down.
Getting into hydration
As both a practitioner and researcher, I’ve had an interesting journey with hydration and electrolytes. I entered the profession as a practitioner in the mid-2000s, at a time when the debate around when, how, and how much to drink, and whether electrolytes were important or not, was often framed as a David vs Goliath battle between the sports and electrolyte drink industry, and those who sought to oppose their messaging.
Just as McDonald’s is the poster boy for fast food due its dominance, Gatorade had become the unofficial symbol of ‘big hydration’. Not only was it the dominant market player, but it had also conducted much of the research in the area through the Gatorade Sports Science Institute (GSSI). The GSSI also rolled out methods and equipment that allowed practitioners to collect sweat samples and analyse sodium losses, via their sports science and commercial partners across the Western world.
The opposing side of this debate was led by several research academics, but none more so than the now-retired but still controversial, Professor Tim Noakes. While Tim is better known these days for his views around low-carb, high-fat diets, before this it was hydration and electrolytes he focussed much of his work on, culminating in the publication of his 2012 book ‘Waterlogged’.
My own move into research came later on, and as a scientist who entered the field a generation after those debating its merits, I was in the fortunate position of not being pulled strongly in either direction. I was able to observe both sides of the argument without being pushed to take a side myself. I could see that both sides were actually doing some great science, but their differing interpretations arose largely because they were approaching the area from radically different perspectives.
Much of the focus of the GSSI was on pro-level athletes, in shorter, high-intensity sports where sweat losses are high and the access, ability, and opportunities to drink are limited. Noakes, on the other hand, approached hydration from his role providing medical support to the Comrades ultramarathon in South Africa, a race where he encountered cases of overhydration resulting from the long-duration, lower-intensity event where access, ability, and opportunities to drink can exceed the actual need for fluid. It wasn’t surprising to me that they formed very different views of what hydration strategies should look like. It also wasn’t surprising that applying one strategy or the other to both situations may not be the best way to go.
What I’ve done below is try to take both of these viewpoints into account. With another decade or so of research in the books, as well as a moving-on in how we conceptualise exercise intensity and the needs of different events, what I hope to do is take what we know and apply it in a more nuanced fashion. We need solutions that can be adapted to optimise health and performance whether you’re smashing out a criterium in the heat of the Aussie summer, or grinding out an ultra-distance event like Race Across America or a 24-hour MTB event in a cooler environment.
Defining our terms
Before we get too deep into the science, we need to define a few terms:
Total body water: The amount of water in the human body, usually expressed in litres. This varies a bit between people depending on how much body fat you have, but is typically 50-55% of the individual’s bodyweight for females, and 55-60% for males (slightly higher for very lean individuals like pro cyclists).
Intracellular fluid: The fluid that exists inside the cells of our body. This is typically about two-thirds of our total body water.
Extracellular fluid: The fluid that exists outside the cells of our body. This is around one-third of total body water and can be further divided into intravascular fluid (or plasma volume) – the fluid in our blood vessels – and interstitial fluid – the fluid that surrounds the outside of our cells.
Euhydration: The state of being normally hydrated. Essentially what the body is trying to achieve by manipulating the fluid ins and outs from the body.
Hypohydration: The state of having lower-than-normal total body water, due to fluid losses that haven’t been adequately replaced. These losses mostly come from sweat in an exercise scenario, but can come from unreplaced urine losses, or in the case of illness, vomiting and diarrhoea.
Dehydration: The process of losing total body water. People frequently confuse dehydration and hypohydration. The technical difference is that dehydration is the process of losing water, whereas hypohydration is the outcome, or state of being in a fluid deficit.
Hyperhydration: The state of having higher-than-normal total body water, due to the retention of excess fluid in the body, rather than the normal process of peeing it out to maintain euhydration.
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