The Influence of Cardiorespiratory Fitness on Firefighter Cardiovascular Health Under Exercise Conditions

Sudden cardiac death (SCD) is the number one cause of on-duty firefighter death. It is most likely to occur in adults who are not physically fit that engage in sudden vigorous exercise. Cardiorespiratory physical fitness (also known as aerobic fitness) is a major heart disease risk factor. In FIT and FIRED UP, the study investigators looked at the influence of cardiorespiratory fitness on blood pressure, heart rate, and other heart markers taken from the blood before and after a vigorous exercise test to maximal effort among firefighters from a local fire department in Connecticut. In addition, the investigators also looked at how lifestyle habits including physical activity, nutrition, stress, and sleep may influence our findings. It was hypothesized that aerobically fit firefighters would show less stress on their heart than unfit firefighters.

The primary purpose of this study was to examine the influence of cardiorespiratory fitness on the acute release of SCD biomarkers and other cardiovascular disease (CVD) risk factors at rest and in response to a bout of maximal physical exertion among 21 firefighters from a local fire department in Connecticut. The study investigators hypothesized that firefighters that are aerobically fit will have lower levels of biomarkers of SCD and a more favorable CVD risk factor profile at rest and in response to a maximal physical effort than firefighters that are not aerobically fit.

FIT and FIRED UP is based on the theoretical foundation of the health belief and social cognitive models of health behavior change which have been shown effective in improving diet and exercise behaviors in firefighters. Specifically, the investigators sought to identify job-specific risk factors for SCD and CVD in firefighters in order to better tailor an intervention that focuses on providing information, reducing barriers to changing unhealthy behaviors, reducing stress, and increasing firefighter efficacy to engage in healthier behaviors.

All eligible members of the fire department were invited to participate in the study. Visit 1 included an orientation health education session at the fire department in which the study investigators delivered a lecture on physical activity and "heart healthy" habits. Interested subjects were able to review the informed consent and questionnaires.

Subjects completed and signed the informed consent at the beginning of Visit 2. This visit consisted of 4 health-related fitness assessments, including sit-up, push-up, flexibility and handgrip tests. Visits 3 and 4 consisted of measures of cardiovascular health at Hartford Hospital and the control visit. The cardiovascular health measures included body mass index (BMI), waist circumference, exhaled carbon monoxide (CO), vascular health (i.e., carotid intimal medial thickness and arterial stiffness), heart rate variability (HRV), resting BP, the maximum graded cardiopulmonary exercise stress test (GEST), and blood draws pre- and post-GEST to obtain SCD and CVD biomarkers. Firefighters were then attached to an ambulatory blood pressure (ABP) monitor and heart rate monitor for 24hr to assess ambulatory BP and HRV, respectively. Of note is that Visits 3 and 4 were conducted in random order so that study investigators could isolate the influence of the GEST on the ambulatory BP response to exercise from the control rest day. Randomization was performed using www.randomization.com. The control visit included measures of resting and ambulatory BP. In addition, subjects completed paper and pencil questionnaires on the topics of physical activity, nutrition, sleep, and mental health at this visit.

Eligibility Criteria:
Inclusion Criteria:

* Subjects had to be full active duty firefighters employed by the local fire department in central Connecticut (CT).
* Subjects confirmed that they were taking the same medication for four weeks prior to Visit 1 and continued taking that medication throughout the duration of the study.

Exclusion Criteria:

* Subjects were excluded from the study if they were not able to comply with all study procedures as described in Visit 1, or in the event of injury or illness that would not enable them to participate.
* If subjects had resting blood pressure readings that were \> 160 for systolic blood pressure and/or ≥ 100 mmHg for diastolic blood pressure, they were excluded from the study and referred to their primary care physician for follow up.
* Subjects that were excluded from the study were not penalized in any way by the researchers or the administrators of the local fire department.