Originally Posted by
big john
I agree with most of your post with a couple of exceptions. First, I think hyponatremia is extremely rare with cyclists. I've heard of it, once with a friend who was part way through RAAM and had to be hospitalized and another time with a guy who was doing a 150 mile climbing ride on a hot day and he wasn't eating. I think if a cyclist is eating or at least taking electrolytes the risk is minimal. I know people have died from it during marathons, but these are people who spend 6+ hours running with nothing but water.
The other thing is the "drink only when thirsty" idea. This may work for some but certainly not everyone every time. When I do a hot climbing ride I cannot keep up with the fluid loss and have to start forcing water early in the ride. I typically come home from a hot ride (6 hours, more or less) 5 or 6 pounds lighter. I tried to ration water once, still drank a bunch, and was 11 pounds lighter after the ride. To me, thirst doesn't enter it and I must make a conscious effort to drink.
My wife got hyponatremia on one of our 10-day backpacks. The weather was cool and showery. We hiked maybe 6 hours. After we made camp, she was obviously not OK, pale, nauseous, confused. It was a bit terrifying. We talked and I finally figured it out: she'd been drinking to the timing pattern she used on long bike rides, except that it was cool and she wasn't sweating. I'd only drunk about 1 pt. all day and felt fine. I gave her 2 Endurolytes with a little water and she was fine in 1/2 hour. Drink to thirst.
If you're not thirsty and are hammering water, you are definitely at risk. No matter how much water you're drinking, and about a liter per hour is all that's possible, you need to take enough electrolytes that you're slightly thirsty because that indicates proper balance and should produce slightly better performance and recovery. Definitely don't ration water. Why would one do that? We should all know that water does more good in the body than it does in the bottle. If you're low on water and worried, drink it.
I have a little heat exhaustion story which might be helpful to someone. My wife and I were on our honeymoon hike, long ago, in the Olympic National Park. It was sunny, amazing. About 5 miles up the trail, we came upon a fellow with all the symptoms of a divorced lawyer and heat exhaustion. He had his ~12 y.o. kid for the weekend. They had ~$1000 worth of new REI gear. He was wearing a down parka, pale and sweating. We were in shorts and T-shirts. He was not OK. Actually the first person we met was his son, who told us about his dad, up the trail. He'd been sent back down the trail to look for water. We asked the dad if he had water and yes he did but he was afraid to drink it because that was all they had. We gave him some electrolytes, talked him into drinking the water, gave him some more, and walked up the trail with them for an hour. He was fine, so we dropped them and took off. The trail we were on had stream crossings every mile or so, typical of the Olympics. Back in the day, I never carried water in the Park, just a handy cup.
Feeling cold and yet sweaty on a warm day is not what one expects from heat exhaustion, but there it is. Untreated heat exhaustion becomes heat stroke, which becomes a medical emergency.