Summer is just around the corner and as the temperature heats up, now is the perfect time to visit hydration and its effects on exercise performance.
Our body is over 60% water making hydration essential for everyone, all the time. Water plays many important roles in our body including maintaining blood volume, transporting nutrients, getting rid of waste products and importantly, regulating our body temperature.
During exercise, our body cools itself by sweating to lose heat. Sweat loss varies depending on the intensity and duration of exercise and by the ambient temperature and humidity. It is also highly individual – some people sweat no more than 500ml/hour, where others (and you’ll know who you are), sweat upwards of 3.5L/hour.
It’s important to know what sort of sweater you are and develop a personalised hydration plan to prevent dehydration, as we know dehydration affects performance. It increases your heart rate, impairs heat regulation, reduces mental function, affects skill level, decision-making and increases the perception of effort – not ideal! Sweat losses of approximately 2-3% of body weight can negatively impact performance.
It’s possible to estimate your own sweat rate by measuring changes in body weight during exercise. A simple way to do this is to weigh yourself nude before and after a training session, ensuring you towel dry off to remove the sweat. Subtract your post-exercise weight from your pre-exercise weight and divide by the total time (hours) to calculate your hourly sweat rate. If you drink during the session, you will also need to factor this in…
Sweat rate (L/hour) = (Pre-exercise weight – Post-exercise weight) + Fluid consumed (L)
Keep in mind, this is an estimate – it doesn’t take into account substrate oxidation (using up your stored fuel during exercise) or respiratory water losses (evaporation of fluid from breathing), or your margin of error 😉.
Most triathletes finish a race having lost more fluid than they have consumed. However, it is possible to over drink and this can lead to hyponatraemia (low blood sodium concentration). You shouldn’t gain weight during a session. It’s also not necessary to replace 100% of fluid lost to match your sweat rates completely during exercise, just enough to minimise the damage.
An Accredited Sports Dietitian can assist you with calculating your sweat rate during training and racing across of range of environmental conditions to develop an individualised hydration plan.
When we sweat, we also lose electrolytes from the body such as sodium, chloride, potassium, magnesium and calcium. You can determine your individual electrolyte losses by sweat testing. This involves wearing a patch on your forearm during a run or ride and analysing it in the lab for sodium concentration (See a Sports Dietitian for this). This is particularly important for the longer events (half Ironman, Ironman, marathons etc.) where replacing sweat electrolytes is crucial.
Sweat sodium concentrations vary widely between individuals and aren’t correlated to sweat rate. Large electrolyte losses may cause muscle cramping. If you frequently notice white marks on your exercise clothes when they dry off, chances are you are probably a salty sweater as these white marks are crusted salt deposits. If this is you, it may be beneficial to replace some of the sodium lost in sweat during exercise.
Fluid needs are highly individual – work with an Accredited Sports Dietitian to develop a hydration plan specific to you to minimise the risk of dehydration and consequent performance limitations – practice this in training so you know what works for you.
Stay cool 🙂
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