Paige Schaa, Jeremy Gross, Clayton Nicks, Brian Tyo, Kate Early. Columbus State University, Columbus, GA.

BACKGROUND: Cardiovascular health and physical activity in emergency responders has declined, putting them at greater risk of a myriad of conditions, especially when performing strenuous occupational tasks. Heart rate variability (HRV) provides indices of autonomic system activity, which has shown a relationship to cardiovascular disease and physical activity in middle-ages adults. The purpose of this study was to assess the relationship of HRV and physical activity indices in firefighters and police officers. METHODS: Emergency responders (12 police officers and 9 firefighters) participated in two separate laboratory sessions with physical activity measured for 6 days between visits using ActivPal3. Physical activity (steps per day, active time, standing time, sedentary time and car time) was averaged for the working days (3-5 days). Body composition was assessed in visit one and the second visit consisted of a resting heart rate, (HRV) and blood pressure measures in a ten-minute seated position. HRV included a 5-min assessment of standard deviations of all the NN intervals (SDNN), root mean square successive difference (RMSSD), high- (HF) and low- (LF) frequency, LF/HF ratio indices. Pearson correlations were used to examine relationships between HRV and physical activity indices. RESULTS: First responders’ average age (40.8± 9.4y), height (1.7±0.6m), and weight (84.1± 18.7kg) were obtained prior to testing. Mean HR was reported as 72±12bpm, RMSSD 28.1±15.1ms, LF 828.7±953.6ms2, HF 328.1±320.1ms2, and LF/HF 3.8±3.4. Emergency responders’ average physical activity on working days was follows: steps per day 9793±3992steps, active time 2.1±1.9hr, sedentary time 8.0 ±0.7hr, and car time 2.2±0.8hr. Car time was related to RMSSD (r=-0.48, p=0.02) and HF (r=-0.53, p=0.01). No other relationships were found between PA and HRV (p>0.05). CONCLUSIONS: Overall, HRV indices suggest lower parasympathetic activity. A lower HRV for emergency responders was also observed in relationship to time spent sitting in a car, suggesting potential negative consequences of prolonged sitting on cardiovascular health. Combining HRV with accelerometer-based physical activity measurements may enhance monitoring cardiovascular health and fitness unobtrusively in this population.

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