In this study, scientists analysed the blood, saliva and urine of 11 firefighters who had just completed a rigorous training exercise.
After a 45 minute training exercise in the California sun, whereby they had to carry 40lbs worth of gear over hilly terrain (all whilst wearing fire-resistant clothing!), firefighters immediately gave samples of their blood, saliva, and urine for analysis
From each of the samples, the proteins, lipids, and metabolites were analysed, to try to gain an understanding of what happens when the body undergoes intense physical exercise.
“Heat stress can be life threatening,” said Kristin Burnum-Johnson, a corresponding author of the study. “We wanted to take an in-depth look at what’s happening in the body and see if we’re able to detect danger from exhaustion in its earliest stages. Perhaps we can reduce the risk of strenuous exercise for first responders, athletes, and members of the military.”
The team detected hundreds of molecular changes in the firefighters.
The differences before and after exercise underscored the body’s efforts at tissue damage and repair, maintenance of fluid balance, efforts to keep up with increased energy and oxygen demand, and the body’s attempts to repair and regenerate its proteins and other important substances.
Interestingly, the team found some unexpected results in the saliva. There was a change in the the oral microbiome of the mouth, showing that the body was increasingly on the lookout for bacterial invaders. Scientists also saw a decrease in signalling molecules important for inflammation and for fighting off viral infections. Having fewer inflammatory signals in the respiratory system helps the body improve respiration and blood flow; less inflammation allows people to breathe in air more quickly, meeting the body’s eager demand for more oxygen.
But less inflammation leaves the body more vulnerable to viral respiratory infection – which is exactly what other scientists have noted in elite athletes and others who exercise vigorously. Some studies have shown that a person is up to twice as likely to come down with a viral respiratory infection in the days after an especially energetic workout.
“People who are very fit might be more prone to viral respiratory infection immediately after vigorous exercise. Having less inflammatory activity to fight off an infection could be one cause,” said Ernesto Nakayasu, a corresponding author of the paper.
He notes that the work provides a molecular basis for what clinicians have noticed in their patients who do strenuous workouts.