I’ve been weighing myself before and after rides (both indoor and outdoor), and my sweat rate averages about 42 oz/hr.
Should I aim to replace all that fluid during the ride? Will electrolytes in the water change my sweat rate? At what point does dehydration impact performance? Edit to add: Can I pre-hydrate to help offset the sweat loss?
My typical consumption is 25 oz bottle per hour (with 60 g of carbs and 1200 mg sodium) regardless of ride length.
1 - you don’t need to replace all of it
2 - I don’t think electrolytes will change your sweat rate but it can help with absorption (so you don’t get the sloshing)
3 - There are percentages but I’ve mostly seen it related to running where your performance degrades after a certain percentage of weight loss (mostly water), but keep in mind that basically everyone weighs less at the end of a race and the longer the race the bigger the drop is.
I’ll do some googling and see if I can find how the percentages line up.
@Dr_Alex_Harrison - this has you written all over it!
Get some of these and really dial in your nutrition.
Might be worth a data point, but I’m led to believe that electrolytes don’t really change sweat rate. I’m more curious about the water deficit over multiple hours.
Couldn’t hurt to try to dial in the electrolytes more though!
@pedalpusher174 the patch’s will give you a better idea as to what your sweat rate, fluid loss and sodium loss is so you can dial in your sodium better.
For example using the patchs allowed me to know that on an indoor ride, 75* and medium effort I was expending 22-26oz/hr of sweat rate and 46-60mg/oz of sodium.
so thats an average of 53mg/oz of sodium and an average of 24oz of loss fluid, 24*53= 1272mg of sodium per hour. I try to make and drink 32oz of fluid that contains at-least 1000mg of sodium and for my personal nutrition 80g/carb
Hmm. Follow up question - how much weight lost during exercise is NOT water? I’ md have to assume it’s significant.
On a 2000 kj ride…that’s 500g of fuel (carbs) alone…that’s a pound right there.
Most of the weight of carbs is water. It’s part of molecule that forms glycogen. It’s the main reason you lose weight on a low carb diet. It’s all water.
Mmm. I mean I know there is a lot of water attached to glycogen, but are you actually sure that the water is not above and beyond the weight of the carbs themselves?
For example…500g of table sugar is clearly not wet. I have to believe part of the process of converting it to glycogen involves attaching water to it…meaning 500g of sugar is converted to 1000g of glycogen? Clearly I’m just making up the numbers…
I used a gatorade patch also and it told me something similar. 42 oz or something. It was kind of interesting to me because I had noticed that while indoors, I often drink 1.5 bottles of water an hour, so I think my body intuitively knew that. I don’t drink nearly the same outdoors, probably because I’m more mentally engaged outdoors and don’t think about it. I do think electrolytes is a tool to prevent dehydration. You can pre-hydrate. Drinking a bottle with electrolytes 90 minutes before a ride will start you off well.
For the rides I’ve weighed myself on, there’s been no other intake or exit (pee). I’m also taking in 60+ grams carbs per hour. I have a low FTP (187), so I’m not dumping huge KJs on a ride, but I’ll have to go back to the rides and look.
I’ve heard that for every gram of carbohydrates stored, the body also needs 3? grams of water to store it with? For the water that might be freed up with using stored glycogen, I’m not sure where it goes from there - into the blood stream? Filtered to the bladder? Sweated out?
Does that suggest that I don’t need to replace all that water during the ride? But at what point does dehydration become a factor in performance?
I’m just speculating here…but my guess is that in order to stay at an equal level of hydration, you’d want to replace most, but not all of that weight difference. I’m honestly not sure though.
yes, you are right. I wasn’t actually converting grams to lbs. Mainly because 500 grams is soo much sugar, so wasn’t really thinking about it but yes, 500g is a lb.
I was just using big round numbers. Obviously you wouldnt get there in an hour…but 2000kj is a not uncommon number I see on group rides.
Especially what you say is true, that 3g of water is attached to each gram of sugar…that’s really closer to 2 pounds lost to energy expenditure.
No because your goal is not to end the ride with the same amount of glycogen stores as when you started. Your glycogen stores are already on board before your ride begins and you likely aren’t going to produce much during your ride no matter what you eat or what you drink. When you are exercising the simple sugars you consume can be utilized directly, with no need to form glycogen. Now you may want to replace it by your NEXT ride. I think the goal of staying hydrated is less about creating energy and more about temperature regulation and blood circulation. I think performance will start to degrade between 2% and 5% of body weight. So, not immediately, but I’d say you probably are experiencing performance degradation due to fluid loss on most longer rides. The more you replace, perhaps the easier the recovery, but I don’t think replacing it all is a necessary strategy, or maybe even possible. Absorption may limit that. You also need to understand how salty you sweat. As you probably don’t want to replace all of that either.
Nice! Super good to know sweat rates you might personally see. This will change with conditions outside, of course. But great to know.
No. But the longer your rides are, the closer you need to be to complete replacement. For a 30 minute ride, replacing half would be fine. For a 2 hour ride, replacing 75-80% is probably better. For an 8 hour ride, getting close to 90-95% is wise.
Electrolytes in the water won’t change sweat rate much. They will change sweat concentration. Consuming more will increase sweat sodium concentration. But never to the extent that it completely offsets what you consume. What this means is that it’s helpful to overshoot what you think your sodium needs might be. This is especially true when going very long.
1% dehydration probably impacts performance on the bike. The cooler it is, and the less you need gut absorption, the less you need to worry about hydration. The higher intensity your efforts, the warmer it is, and the more you’ll be consuming carbs on the bike, the closer you need to stay to “euhydrated” (0% loss).
It’s critical to consume sodium with fluids. Do not attempt euhydration without high sodium consumption or you’re guaranteed to approach hyponatremia, which is deadly. 
Yes. With sodium always. An extra 1L before training with 1000-2500mg sodium is a great idea. Drink any extra you like, to thirst, pre-training.
Yep, need more fluid big-time!
Thanks for your perspective and information. I have been boosting my fluid intake on indoor rides and am measuring weight pre- and post-ride for outdoor workouts, but I have fewer data points there.
We haven’t quite hit the hot season in Ohio but I’m hoping to be more on top of hydration this year!