Hydration for Indoor Rowing: A Plan You Test, Not a Rule You Follow

The old version of this article told you that hydration is a planned input and that thirst is a late signal. Read the papers it leaned on and the answer is narrower and more useful.

For most indoor rows — half an hour to an hour, in a room you can control, at an intensity you chose — drinking to thirst is the better guide. The sessions where it is not are the long ones, the hot ones, and the ones where the result matters.

The premise needs narrowing

The strongest statement on the drink-to-thirst question is a review written specifically to settle it. It found that no study has shown that drinking more than you want to produces any biological advantage, and that doing so can cause exercise-associated hyponatremia [4] Noakes 2010. That was the argument against the old advice, which by 1996 was telling every athlete to drink enough to stay ahead of thirst and lose no weight at all [4] Noakes 2010.

The counter-argument, written later, is not that planned drinking is always better but that it is better in identifiable situations. Planned drinking is optimal for activities longer than 90 minutes, particularly in the heat, for higher-intensity exercise with high sweat rates, for exercise where performance is a concern, and when you want carbohydrate at about 1 g a minute [2] Kenefick 2018. Drinking to thirst may well be sufficient for short sessions of under an hour to 90 minutes, for exercise in cooler conditions, and at lower intensity [2] Kenefick 2018.

That is the whole of it, and it is more useful than a slogan. An indoor row training twice a week for 45 minutes is in the first group. The rower doing a 90-minute piece in July with the radiator on is in the second.

The review also draws the line in a way worth memorising: never drink so much that you gain weight during the session [2] Kenefick 2018. Weight gain means you have taken in more fluid than you lost, which is the mechanism behind dilutional hyponatremia.

The number that matters, and what it does and does not mean

Two per cent of body mass is the threshold most often quoted, and it is genuinely important — but it is important for a narrower reason than the old article claimed.

The position stand's goal during exercise is to prevent excessive dehydration, defined as more than 2 per cent body-weight loss from water deficit, and excessive changes in electrolyte balance, in order to avert compromised performance [1] American College 2007. The later review puts the mechanism more precisely: dehydration of 2 per cent or more is associated with impaired thermoregulatory function and elevated cardiovascular strain, and in many conditions — warmer, longer, more intense — impaired aerobic performance [2] Kenefick 2018.

That "in many conditions" is doing real work. It is a conditional cost, not a price list.

What the meta-analysis actually found

The old article cited a meta-analysis of dehydration and time-trial performance as the evidence that dehydration costs you. Read it, and it says something close to the opposite.

Five studies, all cycling time trials, thirteen effect estimates, 39 subjects. Mean ambient temperature 26.0 °C, mean intensity 68 per cent of VO₂max, mean duration 86 minutes. The dehydration averaged a body-mass loss of 2.20 per cent, against 0.44 per cent in the euhydrated trials. The effect on performance was a non-significant change of 0.06 per cent [3] Goulet 2011. The conclusion: body-mass loss of up to 4 per cent did not alter outdoor cycling time-trial performance, and exercise intensity and duration moved performance far more than dehydration did [3] Goulet 2011.

The same meta-analysis reports that drinking to thirst was associated with better performance than drinking at a rate below thirst (+5.2 per cent) or above it (+2.4 per cent) [3] Goulet 2011.

Two caveats, because this is one sport in one set of conditions. The participants were not elite rowers in a hot room. The finding is that dehydration up to 4 per cent did not cost outdoor cycling performance; it is not a licence to ignore thermoregulation in a room at 28 °C, where the strain effect of 2 per cent is the part that bites [2] Kenefick 2018.

Before the session: start euhydrated, several hours out

The position stand's instruction is that pre-hydration with drinks, on top of normal meals and fluid intake, should be begun at least several hours before the activity, so that fluid is absorbed and urine output can return to normal levels [1] American College 2007. The goal is to start the activity euhydrated, with normal plasma electrolyte levels [1] American College 2007.

Note what that is and is not. It is not "arrive super-hydrated". It is "give your kidneys time". The old article gave a specific 5–7 mL per kilogram figure for a two-to-three-hour window and attributed it to this position stand; the stand says several hours, and the per-kilogram number in the literature belongs to the earlier guidance. Drink the way you drink on an ordinary morning, and start early enough that you will have had a chance to urinate before you get on the machine.

There is a second, less obvious pre-session point about sodium, and it comes from the fluid review rather than the position stand: in hot-weather conditions, active athletes can lose 4 to 10 litres of water and 3500 to 7000 mg of sodium a day [5] Shirreffs 2011. That is a recovery problem — how you replace it after a hot session — not a pre-session instruction.

During the session: the only number worth measuring

Everything above is a population statement. The one number that belongs to you is your own sweat rate, and the simplest way to get it is to measure your body weight before and after and treat the difference as your fluid loss [1] American College 2007. A kilogram is very close to a litre.

The review of sweat-testing methodology is blunt about the rest. Body-mass change is the simplest and most accurate way to assess whole-body sweat rate, but you have to exclude non-sweat sources of mass change and account for sweat trapped in your clothing [6] Baker 2017. Sweat sodium concentration varies with the collection method, the timing, skin cleaning, sample storage and the analytical technique, so a number from a study is a starting point at best [6] Baker 2017.

The list of what makes two people sweat differently is long, and it is worth reading as a list of reasons not to copy anyone else's fluid plan: exercise intensity, environmental conditions, heat acclimatisation, aerobic capacity, body size and composition, protective equipment, sex, maturation, aging, diet and hydration status [6] Baker 2017.

A sensible indoor session is short enough that you can simply drink when you are thirsty and stop. The sessions that need a number are the long, hot ones [2] Kenefick 2018.

Sodium: a limit, not a prescription

The old article told you to add 300–500 mg of sodium for sessions over about an hour. The trial it leaned on says something different, and it is worth reading because it is one of the cleaner null results in the literature.

Nine well-trained cyclists, five men and four women, a randomised double-blind cross-over trial of a 72 km road time trial at 13.8 °C. They took either a 700 mg an hour salt capsule or a placebo, and drank water as they wanted. The salt made no difference to the time: 171 minutes against 172, p = 0.46. It made no difference to the change in plasma sodium either [7] Cosgrove 2013.

What the salt did do was change plasma volume measurably, and that change came with increased thirst [7] Cosgrove 2013. So the honest reading of this paper is a boundary, not a dose: in cool conditions, over about three hours, sodium neither helped nor hurt, and taking it made you feel like you needed more water.

Sodium earns its place in two situations. It is worth adding when you are sweating heavily for a long time and losing a lot of it in the sweat, and it is worth adding when the risk of drinking too much is on the table, because sodium in the drink slows the rate at which you can over-drink [2] Kenefick 2018. It is not a routine addition to a forty-minute row.

Carbohydrate is not hydration, but the long session needs both

The old article ran hydration and fuelling together. They are different things, but the long session does need both, and the thresholds are worth knowing separately.

For sustained high-intensity sport lasting about an hour, small amounts of carbohydrate, including even mouth-rinsing, enhance performance through central nervous system effects [8] Burke 2011. For longer-duration sports, 30 to 60 g an hour is the appropriate target, and events beyond two and a half hours may benefit from up to 90 g an hour [8] Burke 2011.

Carbohydrate availability is built by what you eat in the hours or days before a session, what you take during it, and what you refuel with during recovery between sessions [8] Burke 2011. For the indoor rower the practical version is simple: the long Saturday piece needs carbohydrate in the bottle and food after it, and the short Tuesday row does not need either.

If you want this individualised rather than general, the joint position statement's advice is that personalised nutrition plans belong with a registered dietitian [9] Thomas 2016.

The room is the variable

Here is the part that makes indoor rowing its own problem, and the old article had it right even where its numbers were wrong.

Outdoor rowing in summer has weather. Indoor rowing has a room: a controlled temperature, an optional fan, and a radiator that comes on in October. A rowing room at 28 °C with no air movement is a heat challenge that has nothing to do with the weather outside, and the body responds the same way to it.

The consensus on training and competing in the heat is blunt about what works: heat acclimatisation should comprise repeated exercise-heat exposures over one to two weeks, and athletes should start training and competition euhydrated and minimise dehydration while they are in it [10] Racinais 2015.

What acclimatisation buys is not just comfort. It improves sweating, improves skin blood flow, lowers body temperature, reduces cardiovascular strain, improves fluid balance, alters metabolism and enhances cellular protection [11] Periard 2015. The size of the change depends on the intensity, duration, frequency and number of the heat exposures and on whether the heat is dry or humid [11] Periard 2015.

So the plan for a hot room is a plan made a week or two in advance, not a bottle you fill on the day.

What to actually do

1. Weigh in and out, once. Same machine, same clothing, dry before you start. The difference is your sweat rate, and it is the only number here that belongs to you [1] American College 2007. Do it on a hard session in a warm room, because that is the session you will need it for.
2. Drink to thirst for short, cool rows. Under about 90 minutes at lower intensity, that is the better guide, and the meta-analysis found it maximised outdoor time-trial performance [2] Kenefick 2018.
3. Plan your drinking for the other cases — over 90 minutes, in the heat, at high intensity with high sweat rates, or when the result matters [2] Kenefick 2018.
4. Never let your weight go up during a session [2] Kenefick 2018.
5. Pre-hydrate from several hours out, and give yourself time to urinate before you start [1] American College 2007.
6. Take sodium when you are losing a lot of it in sweat over a long session, or when you want the brake on over-drinking — not as a routine addition [2] Kenefick 2018. The one measured trial found it made no difference to performance in cool conditions and made you thirstier [7] Cosgrove 2013.
7. Put carbohydrate in the bottle for sessions over about an hour, at 30–60 g an hour [8] Burke 2011.
8. Acclimatise to a hot room over one to two weeks before you plan anything hard in it [10] Racinais 2015.
9. Replace what you lost. In hot conditions that can be 4–10 litres of water and 3500–7000 mg of sodium in a day [5] Shirreffs 2011. When you need to recover fast — a second session within a few hours, or a race the next morning — drink and eat to replace it deliberately rather than waiting [5] Shirreffs 2011.

And the last thing, which no paper settles: if drinking has become something you do because you are supposed to rather than because you are thirsty, that is a conversation to have with a doctor or a registered dietitian, not a plan to tighten [9] Thomas 2016.