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Hydration Calculator

Enter your pre-run weight   kg
Enter your post-run weight kg
Enter your running time mins
Enter any fluid consumed on run lts
 
Fluid (sweat) loss  lts
De-Hydration %
Post run fluid required (within 4 hours) lts
Sweat Rate lts/hr

Also see the Lucozade Sport Hydration Calculator

A big thank you to Emma Kingzett, the Lucozade Sports Scientist and her team for their visit on 2 February 2010.

She took urine samples and weighed us before our 45 minute training session and again afterwards (see results below).

   Grantham AC Hydration Results Sheet

RUNNERS NAME

 PRE USG (g/ml) PRE WEIGHT (kg) POST WEIGHT (Kg) LOSS GAIN (Kg) FLUID INTAKE (kg) SWEAT LOSS (L) DEHY. % EXERCISE DURATION (Hr) SWEAT RATE (L/H) Recommended Fluid Intake lts
Emma Kingzett 1.015 62 61 1 0 1 1.61 0.75 1.33 1.5
Neil D 1.005 62.8 62.3 0.5 0 0.5 0.80 0.75 0.67 0.75
Gavin D 1.01 64.9 64.5 0.4 0 0.4 0.62 0.75 0.53 0.6
Martin 1.016 93.3 92.6 0.7 0 0.7 0.75 0.75 0.93 1.05
Keith C 1.01 74.9 74.4 0.5 0 0.5 0.67 0.75 0.67 0.75
Feena 1.005 61.7 61.6 0.1 0 0.1 0.16 0.75 0.13 0.15
Catherine 1.001 61.3 60.9 0.4 0 0.4 0.65 0.75 0.53 0.6
Karen 1.017 64.7 64.4 0.3 0 0.3 0.46 0.75 0.40 0.45
Keith M 1.023 76.4 75.9 0.5 0 0.5 0.65 0.75 0.67 0.75
Jan 1.01 57 56.7 0.3 0 0.3 0.53 0.75 0.40 0.45
Robert 1.02 87.2 86.6 0.6 0 0.6 0.69 0.75 0.80 0.9
Paul 1.005 71.5 70.9 0.6 0 0.6 0.84 0.75 0.80 0.9
John 1.003 88 87.6 0.4 0 0.4 0.45 0.75 0.53 0.6
Helen 1.021 58.9 58.6 0.3 0 0.3 0.51 0.75 0.40 0.45
Hannah 1.007 49.7 49.5 0.2 0 0.2 0.40 0.75 0.27 0.3
Key:
Pre USG: This is the Specific Gravity of the urine sample before training. The lower the better.
Pre Weight: Your weight before training
Post Weight: Your weight after training (wearing exactly the same clothes as for the pre weight measure)
Loss/Gain: The difference between your pre run weight and your post run weight.
Sweat Loss: The net amount of fluid loss (1kg = 1lt)
Dehy %: The amount you are dehydrated ie for Emma: 1/62 x 100 = 1.61 (loss/gain divided by pre weight times 100)
Exercise Duration: Time spent exercising in hours ie 45 minutes = 0.75 hours
Sweat rate: The amount of fluid lost per hour (sweat loss divided by exercise duration)
Recommended Fluid Intake: The amount of fluid that should be consumed within a couple of hours of training (1.5 times the sweat loss)
What does it all mean: Once you know your sweat rate in lts/hr you know how much you should be drinking after any run ie Fluid required = sweat rate x time (hrs) x 1.5
Remember to start your run in a well hydrated state ie clear urine. The Dehy % value calculated in the table above is the value attributed to the run only. If you are starting at a point not fully hydrated then you could be getting seriously dehydrated on longer runs. Did you know being just 2% de-hydrated can equate to a 10% reduction in performance.

For comprehensive information on hydration, nutrition and much more visit the excellent Lucozade website

 

With a reasonable set of scales and using the calculator above you can keep a log similar to the one below. You can compare winter/summer training conditions and the different amount of effort you put in and it's effect on your dehydration level and sweat rate. The values in the shaded columns are obtained from the calculator above.

Date Distance Time run mins Temp deg C Run effort % Kit Pre run weight kg Post run weight kg Fluid consumed lts Fluid loss lts De-hy % Sweat rate lts/hr Recc fluid intake after run lts
02/02/10 hard pyramid 3,4,5,6,5,4,3 min 45 3 100% FW 71.5 70.9 0 0.6 0.84 0.8 0.9
07/02/10 13M 94 4.3 90% FW 71 70.5 0.5 1 0.7 0.64 1.5
11/04/10 13M 90 11 95% ST 69.5 69 0.5 1 0.72 0.67 1.5
09/07/10 9M 65 24.7 90% SV 70 69 0.5 1.5 1.43 1.38 2.25

Notes

Kit
FW - Full winter ie weather top, leggings, hat and gloves
W - Winter ie weather top and leggings
SP - Spring ie Weather top
ST - Shorts and T shirt
SV - Summer ie Vest
Run effort
100% - Race pace for distance run
90% - Fast training run
80% - Steady training run