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Excessive intensity during physical physical exercise can weaken your immune system.
This can be a problem for those in physically demanding jobs, such as athletes.
"People who are in very good physical shape may be more prone to viral respiratory infections immediately after intense exercise," suggests Pacific Northwest National Laboratory (PNNL) biomedical scientist Ernesto Nakayasu. "Having less inflammatory activity to fight infection may be one reason."
Although there is strong evidence to suggest that moderate physical activity among healthy individuals can benefit the immune system in the long term, what happens to the immune system directly after intense exercise is controversial.
There is little reliable evidence to support the claim that intense exercise increases the risk of infections, although several previous studies have noted upper respiratory tract infection in athletes, compared to controls, after strenuous activities. Whether these are correlations or causation is unknown.
So Nakayasu and his colleagues tested the blood plasma, urine and saliva of 11 firefighters before and after 45 minutes of intense exercise in which they hauled up to 20 kilograms of gear over hilly terrain.
"We wanted to take a deep look at what's going on in the body and see if we're able to detect the danger of exhaustion at its earliest stages," explains PNNL bioanalytical chemist Christine Barnum-Johnson.
There is no doubt that exercise does wonders for our health, but it turns out that it can also have the opposite effect.
Along with the expected physical changes that help our bodies maintain the increased amount of fluid, energy and oxygen that exercise requires, there is a decrease in molecules involved in the inflammatory process. This is accompanied by an increase in opiorphin, which dilates peripheral blood vessels.
What these changes ultimately mean for the short-term function of the immune system is unclear, but the researchers have a few guesses.
"Opiorphin may increase blood flow to muscles during the exercise regimen to improve oxygen and nutrient delivery," the team wrote in their paper, published by Science news.
"We postulate that the reduction in inflammatory molecules we observe in saliva after exercise may represent an adaptive mechanism to improve gas exchange in response to higher cellular oxygen demand."
There are also changes in the oral microbiome of the participants. Scientists hypothesize that this is due to an increase in antimicrobial peptides found in firefighters' mouths after their intense activity, possibly to compensate for the immune slowdown, although this conclusion is disputed.
Firefighters are exposed to a unique exposure to dirty air during fires, which can also alter their immune responses. What's more, this study only looked at healthy and active men, the researchers cautioned, so more research among a wider community is needed to confirm their findings. /BGNES
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