Are you unable to maintain your energy levels or feeling fatigued? Is your pee always a darker yellow? Are you now exercising over longer distances or harder session in the gym than previously?
Dehydration is prevalent in athletes, non-athletes and office workers alike. It is certainly a factor to consider both for athletes and amateurs who exercise in the heat. Hydration is also relevant for many of us going about our daily affairs and might not be drinking enough H2O for our own wellbeing.
How can we tell if we are hydrated or dehydrated? When properly hydrated our pee should be not darker than a light, straw yellow colour. Anything darker than this and we are dehydrated and potentially setting ourselves up for failure. Understanding our hydration properly can make a real difference in exercise performance and recovery, even for amateur athletes - runners, cyclists, sports practitioners and exercisers.
At 2% loss of bodyweight minor impairments in cognitive (affecting decision making e.g. team sports or martial arts) and physical performance commence.
4% loss of bodyweight can lead to marked decrease in performance, cognitive impairment , nausea, cramping, and (dangerously) heat exhaustion.
>7% dehydration may require intravenous rehydration.
Sweat Rate Calculation
Everyone sweats at a different rate and if you exercise your water requirements increase. There is little value in comparing one person to the next, nor following standard guidelines of 'drink 8 glasses of water per day'. There is, however, a simple way to put some science into personal hydration strategy, you can measure your sweat rate. You will require:
a set of bathroom scales
a notepad & pen
a calculator
To get an accurate result work out for 45 to 60 minutes. Longer than that duration the calculations might be off as bodyweight changes due to increasing loss of glycogen.
Prior to exercise and after your last drink:
Weigh yourself naked (in kg), note your weight e.g. 70.0kg
Work out
Record, in hours, your workout duration e.g. 1hour 15mins (1.25hrs)
After your workout, strip and weigh yourself. Calculate your weight loss e.g. 1.8kg loss. If you drank (i.e. added) fluids during the workout you need to subtract this amount from your post exercise weight.
Sweat Rate Formula: Weight Loss (kg) / Time (hours)
A 70kg person who sweats 1.8 litres in 1hr 15mins has a Sweat Rate of 1.4 Litres per Hour. This is 2.6% loss of body weight
Measure yourself over a few workouts, see how the numbers compare under similar or different conditions.
What to do with the Information?
It is impossible to fully rehydrate during the course of a sweaty session. The aim is to slow down the rate of dehydration so that one can continue to function. Understanding sweat rate allows us to plan how much water to carry for longer training sessions and to rehydrate.
Rehydrate fully. We need drink about 1.5x the sweat loss amount to rehydrate. Our 70kg person losing 1.8kg (running, say, around MacRitchie Reservoir in 1 hour or doing a hybrid or functional workout) needs to drink 2.7 litres of water to rehydrate, during AND post exercise.
Never drink more water than you lose - you should not gain weight from your water intake. This can lead to a dangerous sodium imbalance condition hyponatremia. Symptoms of this condition include: muscular weakness and/or twitching, dizziness, lightheadedness, headache, nausea and/or vomiting, body weight gain from baseline, swelling of hands and/or feet.
Post workout session, rehydrate gradually.
Drinking plain water is not always suitable for sports hydration during longer duration events, you should consider a hydration (not energy) beverage. We discuss the options, store bought and homemade, here.
What I Have Learnt
I enjoy running and working out, mostly outdoors. Compared to others I sweat a lot when I exercise. I never knew the facts until I measured myself, I was surprised!
I now know that if I am properly hydrated I can 'run easy' up to 8, maybe, 10km without carrying water. If I am dehydrated, run harder or longer, I now always carry a hydration pack, especially if I am trail running or rucking. Remember, if you start your workout dehydrated you cannot make up the deficit once you start.
Awareness. I drink sufficient water throughout the day. I also eat plenty of fruit and vegetables, a source of hydration and nutritionally beneficial for exercise and recovery.
Being aware of my hydration has improved my running, recovery and, I feel, my general energy levels. I no longer get really thirsty after my runs, I get back to full hydration sooner.
There are some good online resources that discuss this topic in depth, especially for endurance sport athletes whose needs are specific.
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Related Studies
López-Torres, O.; Rodríguez-Longobardo, C.; Escribano-Tabernero, R.; Fernández-Elías, V.E. Hydration, Hyperthermia, Glycogen, and Recovery: Crucial Factors in Exercise Performance— A Systematic Review and Meta-Analysis. Nutrients 2023, 15, 4442. https://doi.org/10.3390/nu15204442
Adrogué HJ, Tucker BM, Madias NE. Diagnosis and Management of Hyponatremia: A Review. JAMA. 2022 Jul 19;328(3):280-291. doi: 10.1001/jama.2022.11176. PMID: 35852524.
Bhasin-Chhabra B, Veitla V, Weinberg S, Koratala A. Demystifying hyponatremia: A clinical guide to evaluation and management. Nutr Clin Pract. 2022 Oct;37(5):1023-1032. doi: 10.1002/ncp.10907. Epub 2022 Aug 29. PMID: 36036229.
Surapongchai J, Saengsirisuwan V, Rollo I, Randell RK, Nithitsuttibuta K, Sainiyom P, Leow CHW, Lee JKW. Hydration Status, Fluid Intake, Sweat Rate, and Sweat Sodium Concentration in Recreational Tropical Native Runners. Nutrients. 2021 Apr 20;13(4):1374. doi: 10.3390/nu13041374. PMID: 33923890; PMCID: PMC8072971.
Wardenaar, F.C.; Thompsett, D.; Vento, K.A.; Pesek, K.; Bacalzo, D. Athletes’ Self-Assessment of Urine Color Using Two Color Charts to Determine Urine Concentration. Int. J. Environ. Res. Public Health 2021, 18, 4126. https://doi.org/10.3390/ijerph18084126
Ayotte, D., Corcoran, M.P. Individualized hydration plans improve performance outcomes for collegiate athletes engaging in in-season training. J Int Soc Sports Nutr 15, 27 (2018). https://doi.org/10.1186/s12970-018-0230-2
Casa DJ, DeMartini JK, Bergeron MF, Csillan D, Eichner ER, Lopez RM, Ferrara MS, Miller KC, O'Connor F, Sawka MN, Yeargin SW. National Athletic Trainers' Association Position Statement: Exertional Heat Illnesses. J Athl Train. 2015 Sep;50(9):986-1000. doi: 10.4085/1062-6050-50.9.07. Erratum in: J Athl Train. 2017 Apr;52(4):401. PMID: 26381473; PMCID: PMC4639891.
Adan A. Cognitive performance and dehydration. J Am Coll Nutr. 2012 Apr;31(2):71-8. doi: 10.1080/07315724.2012.10720011. PMID: 22855911.
Additional studies here: Studies on Hyponatremia, Sweat Rate and Exercise in Singapore and Tropical Climates
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