Table 2.
Data extraction and summary of selected studies.
| References/Title | Participants | HRV analysis | Performance measurement | Results | CASP Score |
|---|---|---|---|---|---|
| Gamble et al. (27) Different profiles of decision making and physiology under varying levels of stress in trained military personnel |
Male US infantry soldiers/SRT operators (n = 26) Age: 30.73 ± 7.71 yrs |
Low Frequency domain (LF) High Frequency domain (HF) LF/HF Ratio |
Threat identification simulation: accuracy, sensitivity Low stress and high stress shoot conditions |
Basal HF-Accuracy: positive relationship, p = 0.0379 Basal HF-sensitivity: positive relationship, p = 0.0379 LF/HF-stress condition: negative relationship, p = 0.0379 |
10/11 Quasi-Experimental |
| Marcel-Millet et al. (28) Physiological responses and parasympathetic reactivation in rescue interventions: The effect of the breathing apparatus |
French Firefighters (n = 28 males) Age: 37 ± 7 yrs Height: 179 ± 6 cm Weight: 76 ± 9 kg BMI: 24 ± 2 (n = 6 females) Age: 29 ± 3 yrs Height: 171 ± 4 cm Weight: 64 ± 3 kg BMI: 22 ± 1 |
SDNN LnRMSSD |
Three load conditions: personal protective clothing only (PPC); PPC and the full self-contained breathing apparatus (SCBA); and with PPC and only the cylinder of the SCBA (SCBAc) One baseline unloaded condition: Intermittent Fitness Test (IFT) VO2max: 54.3 ± 4.9 ml/kg/min |
PPC-SCBA, SDNN: 27.8 ± 14.1-21.4 ± 9.2 (p <0.05) IFT-PPC, LnRMSSD: 2.4 ± 0.5-2.1 ± 0.5 ms p <0.01 IFT-SCBAc, LnRMSSD: 2.4 ± 0.5-2.0 ± 0.5 p <0.01 IFT-SCBA, Ln RMSSD: 2.4 ± 0.5-2.0 ± 0.5 p <0.01 |
10/11 Quasi-Experimental |
| Sanchez-Molina et al. (29) Effect of Parachute Jump in the Psychophysiological Response of Soldiers in Urban Combat |
Male Spanish Army Soldiers (n = 19) Age: 31.9 ± 6.2 yrs Height: 173.6 ± 5.3 cm Weight: 73.8 ± 8.3 kg BMI: 24.2 ± 2.3 Experience: 12.8 ± 7 yrs |
RMSSD LF HF ΔHF power |
Simulated Parachute infiltration or ground infiltration into urban combat simulation Blood lactate Blood oxygen saturation (BOS) Rate of perceived exertion (RPE) |
Blood Lactate increased significantly at the end of the simulation regardless of infiltration method (p <0.05) RMSSD and HF domain decreased while LF increased regardless of infiltration method (p <0.05) RMSSD-ΔLactate: r = −0.504 (p = 0.039) LFpost-ΔLactate: 0.589(p = 0.013) HFpost-ΔLactate: r = −0.589 (p = 0.013) ΔHF-BOS: r = 0.493 (p = 0.044) |
9/11 Quasi-Experimental |
| Porto et al. (30) Firefighters' basal cardiac autonomic function and its associations with cardiorespiratory fitness |
Two groups of Male Brazilian Firefighters (n = 38, on-duty) Age: 41 ± 11 yrs BMI: 26.1 ± 7.8 (n = 26, off-duty) Age: 40 ± 12 yrs BMI: 26 ± 13 |
pNN50: CRF <12METs: 1.3 CRF>12METs: 3.6 RMSSD: CRF <12METs: 18.3 CRF>12METs 23.8 LF/HF ratio: CRF <12METs: 5.2 CRF>12METs: 3.3 |
Maximal metabolic equivalent capacity (METs): VO2max (on-duty): 42.4 VO2max (off-duty): 40.0 Groups divided into <12METs or >12METs On duty status |
Significant differences between those with METs <12 and >12: PNN50 (p = 0.07) RMSSD (p = 0.03) LF/HF Ratio (p = 0.01) No difference between duty status |
11/11 Case-Control |
| Sanchez-Molina et al. (31) Assessment of Psychophysiological Response and Specific Fine Motor Skills in Combat Units |
Two groups of male Spanish Army Soldiers (n = 19 Light Infantry) Age: 30.2 ± 5.25 yrs Height: 176.15 ± 8.31 cm Weight: 77.93 ± 10.25 kg |
RMSSD LF HF |
Simulated Urban Combat Competitive State Anxiety Inventory (CSAI-2R) |
RMSSD, LF and HF values were significantly different between the light and heavy infantry groups (p <0.001): RMSSDpre: Light: 38.26 ± 40.69 Heavy: 164.89 ± 73.16 LFpre: |
10/11 Case-Control |
| BMI: 25.00 ± 3.11 Experience: 9.95 ± 5.17 yrs (n = 12 Heavy Infantry) Age: 34.5 ± 4.85 yrs Height: 177.42 ± 7.28 cm Weight: 79.21 ± 9.57 kg BMI: 25.10 ± 1.8 Experience: 14.58 ± 4.87 yrs |
Light:76.60 ± 10.75 Heavy: 19.25 ± 13.11 HFpre: Light: 35.10 ± 25.51 Heavy: 80.59 ± 13.41 RMSSDpost: Light: 7.62 ± 5.62 Heavy: 88.68 ± 4.45 CSAI-2R correlated with all HRV measures: HFpre: r = 0.382(p = 0.034) LFpre: r = 0.406 (p = 0.24) RMSSDpre: r = 0.416 (p = 0.022) HFpost: r = −0.487 (p = 0.006) LFpost: r = 0.424(p = 0.020) RMSSDpost: r = 0.433 (p = 0.017) |
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| Andrew et al. (32) Adiposity, muscle and physical activity: Predictors of perturbations in hear rate variability |
Buffalo, NY (USA) Police Officers (n = 360) Age: 42.1 ± 7.66 yrs BMI: 29.0 ± 4.40 Resting HR: 64.0 ± 8.82 bpm |
Low Frequency domain natural log (LnLF): 5.31 ± 0.91 High frequency domain natural log (LnHF): 4.96 ± 1.13 |
Physical Activity Recall Questionnaire (Ln Physical Activity Index): 2.66 ± 1.04 |
Significant (p <0.05) correlation between LnPA and HRV: LnLF: r = 0.071 LnHF: r = −0.035 |
11/12 Cohort |
| Andrew et al. (33) Police work stressors and cardiac vagal control |
Buffalo, NY (USA) Police Officers (n = 259 males) Age: 41.2 ± 6.8 yrs (n = 87 females) Age: 40.7 ± 5.5 yrs |
Low Frequency domain natural log (LnLF) High frequency domain natural log (LnHF) |
Spielberger Police Stress Survey | No significant correlations for men Significant (p = 0.024) inverse relationship between the “lack of support” stressor and LnHF for females |
10/12 Cohort |
| Delgado-Moreno et al. (34) Combat Stress Decreases Memory of Warfighters in Action |
Male Spanish Army Soldiers (n = 20) Age: 35.4 ± 6.2 yrs Height: 179.9 ± 7.0 cm Weight: 82.38 ± 10.5 kg BMI: 25.7 ± 2.6) |
Low Frequency domain (LF), Pre: 48.3 ± 4.2, Post: 74.8 ± 14.4 High Frequency domain (HF), Pre: 51.7 ± 3.1 Post: 25.1 ± 14.3 All values in normalized units (n.u.) |
Urban Combat simulation Post-mission event recall questionnaire Body Temperature, Pre: 37.8 ± 1.2°C, Post: 37.5 ± 1.3°C |
Significant correlations between the following: LFpost, temp post: p = 0.035, r = 0.473 LFpost, correct sound recall: p = 0.020, r = −0.516 HFpost, temp post: p = 0.035, r = −0.474 HFpost, correct sound recall: p = 0.019, r = 0.517 |
10/12 Cohort |
| Diaz-Manzano et al. (35) Higher Use of Techniques Studied and performance in melee combat produce a higher psychophysiological stress response |
Male Spanish Army Soldiers (n = 19) Age: 28.8 ± 4.9 yrs Height: 176.2 ± 5.3 cm Weight: 75.1 ± 5.3 kg BMI: 24.2 ± 1.3 |
RMSSD pNN50 HF (nu) LF (nu) HF/LF Ratio SD1 SD2 |
Hand-to-hand combat training drill Analyses divided by higher performing half vs. lower performing half (HPG, LPG) |
Significant pre-post differences for all HRV measures in the HPG Significant differences for all HRV measures in the LPG, except HF (p = 0.880), LF (p = 0.164) and HF/LF ratio (p = -.140) |
10/12 Cohort |
| Duarte et al. (36) Efforts of Patrol Operation on Hydration Status and Autonomic Modulation of Heart Rate of Brazilian Peacekeepers in Haiti |
Male Brazilian Army Soldiers (n =20) Age: 23.5 ± 4.7 yrs Height: 175.1 ± 6.8 cm Weight: 74.6 ± 7.9 kg |
AVNN, Pre: 1009.1 ± 119.3 ms Post: 862.7 ± 136.7 ms Low Frequency domain (LF) (nu) Pre: 50.5 ± 17.1 Post: 60.6 ± 13.9 High Frequency domain (HF) (nu) Pre: 49.5 ± 16.9 Post: 39.3 ± 13.8 LF/HF Ratio Pre: 1.49 ± 1.47 Post: 2.12 ± 1.19 |
Estimated Energy Expenditure (EE) Estimated VO2max (Cooper's Test) Estimated Hydration Status (%Body Mass Change) Pre: 74.6 ± 7.9, Post: 72.9 ± 7.6 |
EE-LF/HF ratio: r = 0.49 p = 0.02 VO2max-LF/HF ratio: r = −0.42 p = 0.04 %Body Mass Change: r = 0.53 p = 0.02 |
12/12 Cohort |
| Grant et al. (37) The difference Between Exercise-Induced Autonomic Fitness Changes Measured After 12 and 20 weeks of medium to high intensity military training |
South African Defense Force Recruits (n = 89 males) (n = 65 females) Age: 20.91 ± 1.29 yrs BMI: 22.85 ± 2.78 |
AVNN SDNN RMSSD pNN50 LF (nu) HF (nu) LF/HF ratio SD1 SD2 |
Basic Military training over 12 and 20 weeks VO2max: Basal: 49.54 ± 8.79 12 weeks: 54.14 ± 7.09 20 weeks: 54.15 ± 7.16 |
Significant differences in Mean RRI (p = 0.007), SDNN (p = 0.024), RMSSD (p <0.001) and SD1 (p <0.001) between weeks 12 and 20, but no changes in LF, HF or LF/HF Ratio | 10/12 Cohort |
| Johnsen et al. (38) Heart Rate Variability and cortisol responses during attentional and working memory tasks in naval cadets |
Royal Norwegian Naval Academy Cadets (n = 49) Age: 23.3 ± 8 yrs |
RMSSD | California Computerized Assessment Package (Calcap) Computerized two-back test Background search task Cortisol level |
Basal RMSSD-cortisol: r = −0.35, p <0.04 Basal RMSSD-post calcap: p <0.04 Basal RMSSD-post pop-out attention: p <0.04 Basal RMSSD-recovery: p <0.04 |
10/12 Cohort |
| Jouanin et al. (39) Analysis of heart rate variability after a ranger training course |
Male French Military Academy Students (n = 23) Age: 21.7 ± 0.2 yrs Height: 176.5 ± 1.1 cm Weight: 74.0 ± 1.3 kg |
AVNN Pre: 1008.4 ± 33.1 Post: 1177.5 ± 33.8 SDRR: Pre: 763.1 ± 18.8 ms Post: 837.5 ± 20.5 ms LF (nu) HF (nu) LF/HF ratio Total Power (TP) |
French Ranger Training Course | Pre-Post training: Significant change in Mean RRI (p <0.001), TP (p <0.01), LF, HF and LF/HF ratio, (p <0.05) | 10/12 Cohort |
| Kaikkonen et al. (40) Physiological Load and Psychological Stress During a 24-h Work Shift Among Finnish Firefighters |
Professional Finnish Firefighters (n = 21) Age: 38 ± 7 yrs Height: 178 ± 7 cm Weight: 25 ± 2 kg BMI: 25 ± 2 |
RMSSD (ms): 24 h shift: 42 ± 14 6-h rescue: 38 ± 16 6-h Ambulance: 45 ± 21 |
24-h shift 6-h firefighting shift 6-h ambulance shift |
Significant Difference between shift conditions (p <0.01) | 10/12 Cohort |
| Lyytikäinen et al. (41) Recovery of rescuers from a 24-h shift and its association with aerobic fitness |
Professional Finnish Fire/Rescue personnel (n = 14) Age: 34 ± 9 yrs Height: 178 ± 7 cm Weight: 80.8 ± 11.4 kg |
SDNN RMSSD VLF LF HF |
24-h rescue shift VO2max: 51 ± 9 ml/kg/min |
Significant difference in SDNN: On shift-2nd day: p <0.05 On shift-third day: p <0.001 Significant difference in LF/HF ratio: |
10/12 Cohort |
| LF/HF ratio Total Power |
on shift-2nd day: p <0.05 On shift-third day: p <0.01 No significant effect of VO2max on HRV during recovery |
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| Oliveira-Silva et al. (42) Physical Fitness and Dehydration Influences on the Cardiac Autonomic Control of Fighter Pilots |
Male Brazilian Fighter Pilots (n = 11) Age: 33.2 ± 3.2 yrs Weight: 76.0 ± 8.5 kg Height: 175 ± 5 cm BMI: 24.8 ± 2.3 |
RMSSD: Pre: 24.2 ± 8.2 ms Post: 20.8 ± 10.7 ms SDNN: Pre: 67.0 ± 29.1 ms Post: 77.3 ± 27.5 ms SD1: 17.5 ± 5.6 ms 16.4 ± 7.8 ms SD2: 79.3 ± 18.3 ms 74.7 ± 28.1 ms Sample Entropy (SampEn): Pre: 0.94 ± 0.22 Post: 0.86 ± 0.28 Alpha1 (fractal scaling) |
Flight training Hydration status (hematocrit) VO2max (Montreal University Track Test): 46.4 ± 5.66 Bench Press: 68.7 ± 10.8 kg Pull-Down: 70.0 ± 8.36 kg Leg Press: 201.3 ± 42.49 |
Flight Training day-rest day: RMSSD (p = 0.036), SDNN (p = 0.001), SD1 (p = 0.031) Significant negative correlation between hematocrit and RMSSD, SD1: r = −0.61-−0.81, p = 0.044-0.002 Significant relationship between VO2max-SampEn: r = 0.777, p = 0.001 |
12/12 Cohort |
| Rodrigues et al. (43) Stress among on-duty firefighters: An ambulatory assessment |
Professional Portuguese Firefighters (n = 15 males) (n = 2 females) Age: 29.35 ± 8.85 yrs Experience: 9.41 ± 7.3 yrs |
AVNN: 792.64 ± 92.29 ms LF/HF ratio: 3.82 ± 1.76 |
Perceived Stress Scale (PSS) Work events Normative ECG values: AVNN: 930 ± 133 ms LF/HF Ratio: 3.33 ± 3.47 |
Significant differences between fire, pre-hospital assistance, and accidents: LF/HF ratio (p <0.01) Significant differences between firefighter and normative ECG values: Mean NNI (82% of firefighters lower) LF/HF ratio (71% of firefighters above) |
11/12 Cohort |
| Rodrigues et al. (44) Wearable biomonitoring platform for the assessment of stress and its impact on cognitive performance of firefighters: An experimental study |
Professional Portuguese Firefighters (n = 19 males) (n = 2 females) Age: 29.90 ± 8.83 yrs Experience: 8.33 ± 8.21 yrs |
AVNN SDNN RMSSD pNN20 pNN50 LF/HF ratio |
Trier Social Stress Test (TSST) 2-choice reaction time task (CRTT) |
CRTT1-Mean NNI: significant decrease, p <0.005 TSST-Mean NNI: significant decrease, p <0.005 TSST-SDNN: significant increase, p <0.001 LF/HF ratio-CRRT2: significant increase, p <0.001 LF/HF ratio-TSST: significant increase, p <0.001 |
12/12 Cohort |
| Shin et al. (45) Factors related to heart rate variability among firefighters |
Professional Male South Korean Firefighters (n = 645) |
SDNN RMSSD LnLF LnHF LF/HF Ratio |
Korean Occupational Stress Scale (yes or no answers to a variety of occupational variables) |
Smoking-RMSSD Yes: 31.96 ± 16.92 No: 28.69 ± 15.31 (p <0.05) Smoking-LnLF Yes: 5.73 ± 0.91 No: 5.54 ± 0.98 (p <0.05) Shift work-RMSSD: |
12/12 Cohort |
| Yes: 30.17 ± 16.54 No: 25.78 ± 11.11 (p <0.05) Job Demand-RMSSD: Low: 30.96 ± 16.41 High: 28.04 ± 14.97 (p <0.05) |
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| Souza et al. (46) Resting vagal control and resilience as predictors of cardiovascular allostasis in peacekeepers |
Male Brazilian Army Soldiers (n = 50) Age: 25.4 ± 5.99 yrs BMI: 23.2 ± 4.34 |
AVNN RMSSD 2 min RMSSD 5 min |
Trier Social Stress Test Ergo Resiliency Scale (ER-89) |
Significant Spearman's Correlations for the following: Basal Mean RRI-speech task: r = 0.50, p = 0.0003 Basal Mean RRI-arithmetic task: r = 0.54, p <0.0001 Basal Mean RRI-recovery (speech): r = 0.45, p = 0.001 Basal Mean RRI-recovery (arithmetic): r = 0.53, p <0.0001 ER-89, RMSSD: r = 0.28, p = 0.05 |
11/12 Cohort |