Can a first responder's heart show strain before they feel it?
My husband Gary has served as a firefighter for 20 years. First responders are trained to push through: the call, the shift, the next call. That training saves lives. It also means the people closest to them, and often first responders themselves, are the last to see the strain building.
So the question at the center of Promises Recovery is simple to ask and hard to answer: can we see strain earlier, before a person has to raise their hand?
One place researchers are looking is the heartbeat.
What heart rate variability is
Your heart doesn't beat like a metronome. The time between beats speeds up and slows down by fractions of a second, moment to moment. That variation is called heart rate variability, or HRV.
Researchers increasingly see higher HRV as a sign of a well regulated nervous system, one that can rev up for a challenge and settle back down afterward. Under stress, HRV tends to drop. And today it can be measured outside a lab, with a chest strap, a smartwatch, or a smart ring.
What the research in first responders has found
Stress shows up in the heartbeat. A systematic review of 60 studies of first responders and tactical personnel found that stressful events reduced HRV, and bigger stressors kept it lower for longer afterward. Lower resting HRV was also linked to lower situational awareness and poorer decision making in tasks like navigation and marksmanship. (Corrigan et al., BMC Public Health, 2021)
The mind and the heart are connected. In a study of 107 firefighters who wore heart monitors for 24 hours, HRV was significantly lower in those with depression than in those without. The researchers suggested this could be one possible link between depression and sudden cardiac death in firefighters. Possible is the right word: this was a single snapshot in time. (Liao, Al Zaiti and Carey, SAGE Open Medicine, 2014)
Trends over time may matter more than any single day. Nine Dutch police officers wore a smart ring every night for between 15 and 55 weeks. When their HRV became more erratic from day to day, their reported stress and physical symptoms rose over the following weeks. Nine people is a very small study, but it's the kind of signal that's worth testing properly. (de Vries et al., Healthcare, 2022)
Research also links the HRV response to stress with things we can't see on a monitor, like emotional support and how people cope. (Hourani et al., Physiology and Behavior, 2020)
What the research doesn't show yet
This is the part I most want donors to understand, because it's why the work needs funding.
Long term strain is barely studied. The 60 study review found there weren't enough studies to say whether HRV can track the slow buildup of stress over repeated calls, which is exactly what first responders live with.
Cause and effect are unclear. A separate review of 20 studies concluded that HRV is a useful indicator of fitness and performance in tactical jobs, but that measurement methods vary widely and more research is needed to understand causes. (Tomes, Schram and Orr, Frontiers in Public Health, 2020)
The signal is complicated. When 59 firefighters wore smart rings for 15 weeks, they slept more on days off, as you'd expect, yet their HRV was higher on shift days. The researchers said it highlights "the complexity of the readiness and HRV signals." (Luedke et al., Occupational and Environmental Medicine, 2025)
Nobody can honestly say today that a wearable can predict a mental health crisis in a first responder. What the research does say is that the question is real, the early signals are interesting, and the studies that would answer it haven't been done at the scale they need.
The questions we want to fund
One of the ways Promises Recovery wants to help is by funding independent university research on questions like these:
Can changes in HRV, sleep, and recovery, tracked over months and years, show strain building before a crisis?
Do those signals look different for firefighters, police officers, paramedics, and dispatchers, and across a career?
How do you protect first responders' privacy, so the data is theirs and is used to connect them to support, never against them?
University researchers will choose their own tools and methods. We'll share what they find, whatever it shows. If a technology works, independent research is how anyone will know it. If it doesn't, first responders deserve to know that too.
Help fund the research
We haven't funded our first study yet. Every gift now goes toward making that first grant possible, here in Florida.
To support this work, use the Donate button at the top of this page.
Pam RobertsCofounder, Promises Recovery
Sources
Corrigan SL, et al. Monitoring stress and allostatic load in first responders and tactical operators using heart rate variability: a systematic review. BMC Public Health. 2021;21:1701. doi:10.1186/s12889-021-11595-x
Liao LM, Al Zaiti SS, Carey MG. Depression and heart rate variability in firefighters. SAGE Open Med. 2014;2:2050312114545530. doi:10.1177/2050312114545530
de Vries H, et al. Trends in daily heart rate variability fluctuations are associated with longitudinal changes in stress and somatisation in police officers. Healthcare. 2022;10(1):144. doi:10.3390/healthcare10010144
Hourani LL, et al. Mental health, stress, and resilience correlates of heart rate variability among military reservists, guardsmen, and first responders. Physiol Behav. 2020;214:112734. doi:10.1016/j.physbeh.2019.112734
Tomes C, Schram B, Orr R. Relationships between heart rate variability, occupational performance, and fitness for tactical personnel: a systematic review. Front Public Health. 2020;8:583336. doi:10.3389/fpubh.2020.583336
Luedke J, et al. Differences in total sleep time and heart rate variability between shift types in firefighters. Occup Environ Med. 2025;82(8):363 to 369. doi:10.1136/oemed-2025-110197
Promises Recovery has no involvement in any of these studies.
Comments