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Hydration - Blog 004

Updated: Apr 16, 2019

This weeks blog is based around hydration. We asked Ian Thomas to write this one as he is a registered dietitian. A lot of people do not understand the importance of drinking water throughout the day and how easily it is to become dehydrated. At the bottom of the page is a link to Ian's website where he works with people to live a healthier lifestyle. Get in touch if you feel he could help you or if you have any further questions!

Keeping hydrated to maximise exercise performance:

How much should I drink in a day?

What should I drink during exercise?

When should I start drinking?

Do I wait until I’m thirsty?

Are all common questions and everyone seems to have their own opinion, so no wonder hydration is such a confusing topic. We’re going to take a look at the research and summarise just exactly what it is you need to know when it comes to how and when to stay hydrated.

Why do we need to drink?

Our bodies are 60% water, making adequate fluid consumption a key component of good health. Not only do all our cells function in a fluid environment but our blood, which is 92% water helps regulate body temperature and delivers nutrients around the body.

The general recommendation for non-active people is to take in 2-2.5L of water, some of which can come from food, a day; this translates to 1.6-2L of drunk water or 8-10 glasses.

When you exercise, especially in a warm environment you lose water as sweat in an attempt to keep your body temperature stable. If you become too warm, hyperthermia, this can double your cardiac output and result in blood being taken away from key organs (Deussen 2007) therefore sweating is a key survival mechanism but if water is not consumed to replace that lost, it can result in new problem.

Research suggests that just 2% dehydration will start to impair exercise performance and cognitive processes; this is just 1% for teens and adolescents (Nernet 2009). The impact on exercise performance is largely dependent on the environment with cycling performance being reduced by up to 23% in 40oC and 3% in 10oC (Trangmar 2019).

As dehydration progresses it will start to impact different systems in the body and produce symptoms, including:

- An increased heart rate

- Increased levels of fatigue

- Gastrointestinal issues such as cramping

- Increased risk of stroke

- Inability to focus and think straight

When to drink to stay hydrated?

Generally speaking, drinking steadily throughout the day will be enough to maintain your hydration levels. The easiest way to check whether you are drinking enough is by the colour of your pee! You should aim to keep it a pale yellow, almost straw like colour; the darker and more orange it gets, the more you need to hydrate (If it becomes brown and thick then this warrants a call to the Doctor).

Throughout the day, relying on thirst for when to drink will get you by, although if you tend to get absorbed in what you are doing this could mean that you are already dehydrated by the time you recognise that thirst signal. This is important for your training sessions as research has found that in young athletes, 50-75% will start their training or competition, already dehydrated (Sexton 2012) and that athletes tend to only rehydrate to 70% after they have exercised meaning that they are in a dehydrated state before, during and after their sessions.

It is generally recognised that you should aim to drink 500ml of fluid about 2 hours before your exercise session and then a further 125-250ml just before your session starts.

To replenish sweat losses and keep your performance levels elevated, aim to drink 250-500ml every hour of exercise (Nazni 2010). Drinking a further 500ml after training will ensure hydration levels return to pre-exercise levels.

Interestingly, although resistance training may not result in sweating in the same way as cardiovascular training, dehydration will still impeded performance and the above recommendations will apply the same (Greenleaf 1965).

What should I drink?

For any exercise session lasting 60 minutes or under then just water will be adequate. Sports drinks provide no benefit when performing these shorter sessions. If you are training for longer than 60 minutes your fluid requirements will vary depending on your desired outcomes of the session and should be personalised. Sports drinks should contain 4-8% carbohydrate and be drunk at a rate of 600-1200ml/h (Convertino 1996), but again, will only provide benefits if sessions exceed 60 minutes and are of a moderate to high intensity.


Planning your hydration, at least for the recreational athlete, does not need to be complicated but is a key component of realising the benefits of your training.

- Keep the colour of your wee pale yellow by drinking throughout the day

- 2 hours before training drink 500ml of water and 125ml more just before training

- Drink 250ml/hour of training and 500ml immediately after

- For the average trainee, sports drinks will provide no benefits

Note: This advice is for recreational, not professional athletes, who would be justified in going in to more depth and complexity with their hydration protocols.


Convertino VA , et al 1996 American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine and Science in Sports and Exercise [01 Jan 1996, 28(1):i-vii

Deussen 2007 Institut für Physiologie, Medizinische Fakultät Carl Gustav Carus, TU Dresden, Fetscherstr. 74, 01307 Dresden.

Greenleaf, J and Sargent F. Voluntary dehydration in man. J Appl Physiol 20: 719-724, 1965.

Nemet D, Eliakim A. Pediatric sports nutrition: an update. Curr Opin Clin Nutr Metab Care. 2009;12(3):304-309.

Nazni P, Vimala S. Nutrition knowledge, attitude and practice of college sportsmen. Asian J Sports Med. 2010;1(2):93-100.

Sexton M. Beat the heat: athletic training prof offers hydration tips. University of South Carolina website. Updated August 31, 2012.

Trangmar, S.J. & González-Alonso, J. Sports Med (2019) 49(Suppl 1): 69.

Ian's Website

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