New research co-led by Brock explores the dynamics and treatment of post-exercise hypotension, a decrease in resting blood pressure that can last up to a few hours following intense exercise.Those who feel faint after a strenuous workout can take heart: that queasy, slightly dizzy sensation isn’t necessarily a sign of being out of shape.
In fact, a glass or two of one’s favourite drink post-workout may be all that is needed to perk back up.
This is one of the main conclusions of new research, co-led by Brock University Professor of Kinesiology Toby Mündel, published earlier this month.
Conducted by an international research team, the study aimed to better understand the dynamics and treatment of post-exercise hypotension — a decrease in resting blood pressure that can last up to a few hours following intense exercise.
While this blood pressure reduction is positive for health overall, Mündel says the downside is that the sudden drop can cause fainting.
The Canada Research Chair in Extreme Human Environments says previous studies have been inconclusive as to whether “your hydration status — whether you’ve had enough to drink, or not — makes that worse.”
Some researchers have attributed post-workout fainting to a reduction in blood volume. This is caused when there is less water in the blood due to dehydration, which has the effect of thickening the blood.
“The research is mixed, with some studies saying hydration has an impact on post-exercise hypotension and others saying it does not,” says Mündel, adding the team was driven to find a clear answer.
The study saw 12 men first undergo 10 minutes of high-intensity exercise following their regular pre-exercise intake of fluids. After finishing the exercise, they recovered for one hour while their blood pressure was checked.
The next time the men came in, they were banned from drinking anything in the 12 hours before the workout. Participants reported feeling weaker, dehydrated and had lower blood pressure than when they’d kept up their usual fluid intake.
Participants again went through 10 minutes of intense exercise after going 12 hours without fluid. Afterward, they chose to consume either 1.2 litres of a sports drink within five minutes or 1.1 litres whenever they wanted to, over the course of an hour.
Both approaches fixed the problem of weakness, dehydration and low blood pressure after the exercise, says Mündel.
“However, if you chug water after exercise, there might be other benefits,” he says. “Having a big volume of liquid afterwards brought your heart rate and body temperature down quickly.”
Mündel says the research findings come at a time when many people are fasting as part of religious observances. Some of this fasting includes abstaining from liquids, as well as food, for long periods of time.
“If people go a day without drinking or eating anything, and then they go to the gym or play soccer, they might want to have some fluids afterwards to stop them from fainting,” he says.
The research findings also apply to firefighters and military personnel, who may not always get the hydration and nutrition they need to perform their physically demanding jobs, says Mündel.
Although the researchers used a sports drink in the study, water or any other liquids will have the same impacts, he says.
Mündel recommends that, ideally, people be well-hydrated before undergoing intensive exercise. Drinking something afterwards, however, can make up for being dehydrated beforehand, he says.
The study, “The effect of hypohydration before and different rehydration strategies after severe intensity exercise on post-exercise hypotension in men,” was published on March 4 in the European Journal of Applied Physiology. The 13-member research team was co-led by Mündel and Tze-Huan Lei, from the Xi’an University of Science and Technology in China.
Supporting the research was funding from the federal government’s Natural Sciences and Engineering Research Council of Canada and the Canada Research Chairs Program.
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