Sweat Testing for Race Day Hydration

How to calculate your sweat rate

1.      not to beat around the bush… go to the toilet make sure you pee and then record your body weight afterwards, ideally with no clothes on (that’s A).

2. Do your training session and record exactly how much you drank. 

This is easy if you drink from a single bottle or two; simply weigh your bottles before you ride (that’s X) and after (that’s Y) and record the difference (that’s Z). 1 gram = 1 millilitre.*

*Make sure all units are in kg/litres

3. After the session, towel yourself dry and then record your weight (that’s B). Again no clothes on is best, as your clothes will hold some sweat.

4. Now subtract your post-exercise weight (B) from your pre-exercise weight (A) to get the weight you lost during the session.

Weight lost (C) = A-B

  5. Subtract the weight of the bottle(s) before (X) and after (Y) to obtain the amount you consumed (Z).

Volume consumed (Z) = X-Y

6. You can now calculate your sweat rate with the below calculation.

(C+Z) / time.

Note: It’s best to try not to pee during the sessions, as this can skew the results. However if you do have to go, a good estimate of fluid loss is ~0.3l (300ml). You then just need to subtract 300ml (0.3kg) from your estimated sweat rate at the end.

Recommended session 

1 hour bike - race pace. Try to sustain the intensity through the whole hour. (do not go out too hard).

Tom Payne at Mallory Park