Originally Posted by
DougRNS
I recently added a 10 minute cool down ( or until heart rate drops to a bit above resting rate) after hard rides. I had a scary incident where I blacked out after a 25 mile max effort in very dry/hot conditions..
Apparently I have been lucky the past 29 years of riding and avoided the combination of dehydration and little/no cool down. I always knew that you were supposed to cool down to flush out lactic acid and recover better but it never seemed to matter much and I would be lazy and not always do it.
What happens is all the blood will stay in your legs if you sit down or stand in place and low blood sugar from improper eating before/during the ride and dehydration,thickening the blood, can knock you out. When you are fit your heart rate can drop pretty fast and the heart will not be able to circulate the blood to your head. The bottom line is eat right, stay hydrated and Cool down so the blood can flow back out of your legs to the rest of your body. As long as you do those three things you should not have problem. Please google something like "blacking out after a hard workout" to make sure you get the facts right. Apparently this is fairly common.
I now build in a 2-3 mile cool down on hard efforts. I usually do out and backs so I will go out 14 and back 11 and cool down for 3 or something similar.
When you work out your veins and arteries while dilate to allow more blood to circulate in your system as your heart pumps more blood (otherwise your blood pressure would increase too much). When you stop your workout, for most people, the veins and arteries will contract as the heart slows down, but for some, they stay dilated as the heart slows down. This drops the blood pressure and can lead you to pass out. The "passing out" is the way your system tells you to lie down so the blood can go back to your brain.
I'm the lucky type that his veins and arteries constrict is synchronized with hear rate drop. Had my blood pressure checked as I was doing a stationary bike work out until I maxed out last Winter. My BP stayed at around 140 until I went all out, where it climbed to 180 and HR at 177. My HR dropped nicely with my BP.
I'm 54, I personally never do cool downs, warm ups or stretching. I ride twice daily 20 km which takes me about 45-50 minutes each time, depending on winds.