Hydration for riding

Staying hydrated properly during rides can be a challenge on longer rides - especially if you're not riding with a pack and you have limited water water bottle capacity on your bike. A key part of staying hydrated is knowing how much fluid you're losing - your sweat rate. A number of factors can affect your sweat rate such as weather conditions and training intensity. To figure out your sweat rate do some testing for a few days. Before you go for a ride, weigh yourself naked or in some light weight clothing and use the same clothing to weigh yourself in after your ride. If you need to, hit the bathroom before you weigh yourself to help get an accurate measurement. You also need to keep track of how much fluid you drink during/after your ride before you weigh yourself the second time. Your fluid loss is your before weight minus your weight after plus the weight of any fluids you took in during the ride. Once you know your sweat rate then you know how much fluid you should ideally be taking in while you are riding. During the testing days, drink/eat as you normally would, but don't pre-hydrate just before your ride as you want to get an accurate measurement of your fluid loss. to figure it out use the following formula. Note that 1L of water weights 1kg.

Bodyweight before - Bodyweight after + Fluid intake weight = Net fluid loss weight

Net fluid loss / Ride duration in hours = hourly sweat rate.

90kg - 89kg + 2kg = 3kg

3L / 2hrs = 1.5L per hour

So, ideally you should be drinking 1.5L of fluid per hour

In terms of pre-hydration, it's worthwhile to consider it for rides lasting longer than an hour. While pre-hydration has it's benefits, you don't want to gulp a large volume of water just before a ride though as that could negatively affect performance. The ACSM recommends drinking about 5-7ml/kg of bodyweight at least 4hrs before training, and possibly another 3-5ml/kg about 2hrs before training.

4hr window = 90kg x 6ml = 540ml of fluid

2hr window = 90kg x 4ml = 360ml of fluid

Source: Nutrient Timing for Peak Performance, Skolnik, Heidi

I thought after years of science we were back to "drink when you're thirsty". Even for a certain person the fluid requirements change with ambient temperature, exertion level, etc. 

There was an article from a sports medicine professional who had never seen someone die of dehydration post-race, but they had seen people die of over hydration (gulping too much too fast). Basically dilutes your blood I think?

Posted by: Squint

I thought after years of science we were back to "drink when you're thirsty". Even for a certain person the fluid requirements change with ambient temperature, exertion level, etc. 

There was an article from a sports medicine professional who had never seen someone die of dehydration post-race, but they had seen people die of over hydration (gulping too much too fast). Basically dilutes your blood I think?

That's called hyponatremia, when the sodium content in your blood is too low. It happens due to taking in too much water. That's part of the science behind things like sports hydration drinks, is that they have the right balance of water, glucose and salts to keep you hydrated properly. The info I shared is about maintaining proper hydration for peak performance, and figuring out your sweat rate is a key part of it, including adjusting for variables like weather. The problem with drinking when you're thirsty is that you're already getting dehydrated. That's what thirst is, a sign that you're low on fluids.

This reminded me of this youtube video that pops up on my feed every once in a while:

https://www.youtube.com/watch?v=7UhT6-GntcY

hahahaha - that's hilarious

Posted by: Squint

I thought after years of science we were back to "drink when you're thirsty". Even for a certain person the fluid requirements change with ambient temperature, exertion level, etc. 

There was an article from a sports medicine professional who had never seen someone die of dehydration post-race, but they had seen people die of over hydration (gulping too much too fast). Basically dilutes your blood I think?

Believe your referring to the 2012 article by Dr Timothy Noakes. 

https://www.outsideonline.com/running/tim-noakes-serious-problem-overhydration-endurance-sports/

Also has a book that goes more in depth on it.  Though if you can find Natural Born Heroes by Christopher McDougall has a couple off chapters dedicated to him as well as Dr Phil Maffetone. mentions this whole marketed idea that our bodies are broken and therefore cannot tell one they are thirsty.

Since you mention dilutes the blood. Well that brings up another aspect of this. Reality is that the whole "Hydrate or die" marketing dogma all it does is focus on drinking fluids during the event or ride. All that does really is replace water in the blood. It is hard to explain so in simple terms hydration marketing talks about things like muscle performance and so on. Here is the thing muscle cell or cellular hydration is a slow process  and happens over numerous days before that big ride or event. 

It is late and am tired. Give me a day or two to dig out the book and will take a photo of the specific pages around that.

The whole point of figuring out one's sweat rate is so that you are replacing fluids at the proper rate. You not only want to make sure you're drinking enough, but also not drinking too much. It's not about our bodies "being broken" or marketing schtick to sell a product, but understanding what our needs are so we can perform at our best. An athlete's performance can drop from as little as a 1% weight loss due to fluid loss. For every 1% weight fluid loss, our heart rate can increase by 5-8 bpm and core body temp can increase by about .2 to .3 degrees Celsius. The increase in HR is due to the blood getting thicker from fluid loss, so it becomes harder for the heart to pump blood through the body. This also means that it's harder for muscles to get enough of the fuel and nutrients they need to function. 

For shorter rides/workouts of about an hour or less, hydration typically isn't a huge concern, but as the duration of the ride increases, proper hydration and fueling becomes more of a factor. Remember that sweat isn't just water, it's also contains sodium, chloride, potassium, calcium and magnesium, so drinking only water and/or too much water on longer duration events hours can throw off your electrolyte balance. Sodium and chloride are the most abundant electrolytes in sweat, and while the amount lost can vary a fair bit, on avg there will be about a 1000mg of each lost in a litre of sweat. This is more of a concern for 4+ hour events like century rides or ultra marathons and is when hyponatremia can become a serious issue as the the risk of taking in too much water and not enough electrolytes, particularly sodium, is higher. Sodium is important because it regulates fluid balance in the body, and the combo of heavy or extended sweating, taking in too much water and not enough sodium will pull sodium out of the bloodstream and have negative health effects. In terms of fluid intake, if people are feeling bloated or have gained weight after a race they know they've taken in too many fluids and could be at risk of hyponatremia. Having a salty food or some salty water could help bring things back into balance. Besides the physiological effects of hyponatremia, I think the biggest danger is that the symptoms of dehydration and hyponatremia are similar. A person in a state of hyponatremia could make things worse by taking in excess fluids because they feel they are dehydrated. I would guess that this is probably a significant factor in cases where people die from hyponatremia. So in the search for proper hydration awareness of your fluid loss and intake is key. Don't get overly distracted with the idea of hyponatremia and allow it to negatively affect your need for fluid intake or your performance. 

While we can use thirst as a rough guide, it's not always accurate and it may not account for electrolyte loss. Taking a little bit of time to understand your own rate of fluid and electrolyte loss can help you perform and feel better. It's pretty easy to figure out your sweat rate at different times of the year to account for temp and humidity. In terms of sodium loss, if your sweat tastes very salty or you notice white lines or discolouration on your shirt after it's dried from a longer ride then you could be a heavy sweater and need to replace sodium at a higher rate than the avg. Sports drinks can be a viable option as they provide, water, fuel (glucose) and electrolytes. One product that I've found works well for me is something called Carbion+, but there are many available.  If you're a heavy sweater, read the labels to see what level of electrolytes exist per litre. Another option is to go with some fruit juice and add maybe half a teaspoon of salt - there are 2300mg of sodium in one teaspoon of table salt. Pair that knowledge with your sweat rate to get a solid idea of how much fluid and electrolytes you should be taking in.