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Background: Wrist-worn heart rate monitors have not been extensively validated for heart rate variability analysis. The purpose of this study was to compare time-domain variability of heart interval series (R-Ri) recorded by the Polar S810 monitor (Polar Electro Oy, Kempele, Finland) 02). The SDNN, CV, and pNN50 indices did not show differences (P = 0.12 to 0.73). Conclusions: The Polar S810 monitor was feasible and reliable for recording short-term R-R interval series, showing excellent agreement with the ECG in providing the time-domain indexes of heart inter-val variability with differences functionally not relevant. The CV showed the higher agreement in both postures, and the SDNN and pNN50 in the standing posture. (PACE 2009; 32:43-51) wrist-worn heart rate monitor, Polar monitor, exercise practice, heart rate variability, cardiac autonomic function Introduction Time-and frequency-domain variability analysis of spontaneous short-or long-term heart interval series is a recently introduced tool widely employed for simple, noninvasive, and sensitive evaluation of cardiac autonomic modulation in different functional and clinical conditions.

Firefighting is associated with high-level physical demands and requires appropriate physical fitness. Considering that obesity has been correlated with decreased cardiorespiratory fitness (CRF) and that the prevalence of obesity may also be elevated within firefighters (FF), we analyzed the association between CRF and body composition (BC) in Brazilian military FF. We assessed 4,237 male FF (18-49 years) who performed a physical fitness test that included BC and CRF. Body composition was assessed by body mass index (BMI), body adiposity index (BAI), body fat percentage (BF%), and waist circumference (WC). CRF was assessed by the 12-minute Cooper test. Comparisons of VO2max between the BC categories were analyzed using the Mann-Whitney test, and the analysis was adjusted for age using the General Linear Model. The Spearman test was used for correlation analysis and the odds ratio (OR) was calculated to assess the odds of the unfit group (≤ 12 metabolic equivalents [METs]) for poor BC. Statistically significant differences were considered when p ≤ 0.05. Considering the BMI categories, 8 volunteers (0.2%) were underweight, 1,306 (30.8%) were normal weight, 2,301 (54.3%) were overweight, and 622 (14.7%) were obese. The VO2max was negatively correlated with age (rs = -0.21), BMI (rs = -0.45), WC (rs = -0.50), and BAI (rs = -0.35) (p < 0.001). Cardiorespiratory fitness was lower in the obese compared with the nonobese for all age categories (-3.8 ml · kg(-1) · min(-1); p < 0.001) and for all BC indices (-4.5 ml · kg(-1) · min(-1); p < 0.001). The OR of the unfit group having poor BC in all indices varied from 2.9 to 8.1 (p < 0.001). Despite the metabolically healthy obesity phenomenon, we found a strong association between CRF and BC irrespective of age and the BC method (BMI, BAI, WC, or BF%). These findings may aid in improving FF training programs with a focus on health and performance.

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HRR from the 1st to 5th min post-exercise negatively correlated with parasympathetic modulation in resting orthostatic, but showed no correlation in supine position. At the 3rd and 5th min, a positive correlation with combined sympathetic-parasympathetic modulation in both positions was observed.