The No. 1 cause of death in firefighters is a sudden cardiac event that occurs after high-intensity activity. This can be caused by a glitch in the body’s autonomic nervous system that blocks the heart’s return to a normal resting state.

Graduate student David Cornell is researching a physiological indicator of such trouble. His work could help firefighters – and even professional baseball players – rest easier after the unusual physical demands of their jobs.

Cornell studies heart-rate variability, or HRV, which is the change in the time between heartbeats. It’s a measure of physiological stress and can indicate whether the heart is recovering from exertion normally.

“The HRV taken at rest gives us a picture of what’s happening with the autonomic nervous system, which controls the heart rate,” says Cornell, who is working toward dual doctorates in kinesiology and physical therapy. “In fact, it is considered a predictor of mortality.”

In addition to studying strategies to protect cardiac function, he’s developing tools that set optimal training loads for these professionals to improve their performance.

The research extends to starting pitchers, who are some of professional baseball’s most injury-prone athletes. Throwing a baseball may be nothing like fighting fires, but it requires pitchers to regularly go from a state of rest to heavy exertion.

In research he published in 2017, Cornell found that, one day after a pitcher’s regularly scheduled start, his resting heart rate showed an altered functioning of the autonomic nervous system. The HRV returned to normal, however, the next day, knowledge that could improve training and recovery regimens. In 2018, Cornell plans to work as a student physical therapist with the Milwaukee Brewers during spring training.