Training Tips from the Master: Hydration

Note from Martin: This week we’re starting a series of training tips from Jonathan, our resident PhD, published author, lover of all things Australia and captain of the team’s small yet vicious Masters squad. To start things off, he takes aim at hydration. I’ve given this one a close read, since not enough water and salt left me cramping towards the end of the Cat 4 Murad Road Race a few weeks back.

waterThe hot weather is now here with a vengeance, so I wanted to lead off the first of an episodic new series here at the DVR site on the mercurial art of training, preparing, and executing your stuff on Race Day. Today is all about hydration.

Too little can badly impair athletic performance by inducing dizziness, raising core body temperature, and increasing heart rate. This all adds up to less than optimal performance. Drinking too much, a condition known as hyponatremia, is also possible but for practical purposes less a concern on the bike – how many water bottles can you carry? – than it is for runners tempted by all those handy water stations. So let’s focus on the big picture: How much water do you need?

Each rider is different, so the best approach is to perform a few “sweat tests” under varying conditions. I recommend separate tests for trainer sessions and outdoor workouts, with periodic retesting as the outdoor temperatures rise and fall. Simply weigh yourself before the workout, keep track of the liquid you consume throughout, then weigh yourself afterwards (be sure to jettison those heavy sweaty clothes first). Note the duration of exercise. Oh yeah, try not to pee throughout; you don’t want to have to measure that, now do you?

Subtract your post-ride weight from your pre-ride weight to get water weight lost. Multiple this by 20 [the training literature can be a bit vague here, with suggestions of 16 – 24 ounces, so I split the difference] to get the approximate number of ounces needed to close that gap. Add in the amount of liquid consumed during the workout and divide by the number of hours spent exercising. Now you’ve got a useful rule of thumb of ounces per hour for similar conditions.

NB – Total weight loss of 1.5% or so is OK but anything over that should be addressed in future training sessions.

Here’s an example from a few weeks ago on the trainer:

  • Pre-ride weight: 151
  • Post-ride weight: 149
  • Fluid consumed during exercise: 3 large bottles, or 72 ounces
  • Duration: 2 hours

Here goes:

  • 151 – 149 = 2 pounds lost to water weight, or 40 ounces of liquid
  • Water consumed = 72 ounces, rough equivalent of 3.6 pounds
  • Total recommended consumption = 72 ounces (consumed) + 40 ounces (to close gap) = 112 ounces
  • Divided by 2 hours yields 56 ounces per hour, the equivalent of 2 1/3 bottles per hour.

Now that we know our liquid requirements, we can start to think about the age-old cycling question: So what should we put in those bottles anyway? Stay tuned.


  1. But in your example, you only lost 2 pounds, which is less than 1.5% of your starting weight, so I think your 3 large bottles was fine and you shouldn’t consumer more. It’s not ideal to end a ride at the pre-ride weight; that’s what the 1.5% ROT is for.

  2. Good point, Joe. I should have used a more extreme example, such as a July outdoor session, when the discrepancy between start and finish is likely to be much greater

    That said, I still aim to end a training session at or near my pre-training weight, with the 1.5% as a cushion. Thanks.

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