Search Results (58)

Assessing task workload during military En Route Critical Care (ERCC) and other high-risk clinical operations remains challenging. This study evaluated heart rate variability (HRV) and body motion as digital biomarkers of task workload among Critical Care Air Transport (CCAT) teams during simulated ERCC missions. Seventy-two U.S. Air Force clinicians participated in 26 high-fidelity simulations. HRV and body motion were continuously captured via a chest-strap wearable sensor, and the NASA Task Load Index (NASA-TLX) was used to assess self-reported workload. Results demonstrated high feasibility (>90% HRV, 100% motion retention) with high wearable comfort ratings. Both HRV and Motion metrics showed strong construct validity, significantly differentiating resting baseline from active simulation (all p < 0.001, effect sizes d = 0.54–1.22 for HRV, r = 0.92–1.00 for motion). Convergent validity was selective: only baseline-adjusted root mean square of successive differences (RMSSD) demonstrated significant associations with NASA-TLX mental demand (β = −0.250, p = 0.005) and temporal demand (β = −0.233, p = 0.003). Baseline-adjusted RMSSD effectively indexes perceived workload, while Motion metrics provide complementary information about physical task demands. These findings support multimodal approaches integrating physiological reactivity, motion patterns, and self-reported ratings for comprehensive workload assessment in complex operational settings. Full article

This study aims to determine the validity of the short-term scaling exponent of detrended fluctuation analysis (DFA-a1), respiration rate, and the ratio between respiration rate and the DFA-a1 (RRa1) in the estimation of the load associated with the first and second ventilatory thresholds (VT1, VT2) during running in a sample of adolescents. Twenty-two adolescents (11 males and 11 females) performed an incremental graded exercise test, monitored through the Polar H10 chest strap, synchronized with the Garmin Forerunner 965 equipped with the alphaHRV app. In the estimation of the load associated with the VT1, there was no significant HRV indices effect (F_(2,36) = 1.528; p = 0.231), nor a HRV indices and sex interaction effect (F_(2,36) = 0.319; p = 0.729). In the estimation of the VT2, there was a significant HRV indices effect (F_(2,36) = 20.3; p ≤ 0.001). Specifically, DFA-a1 displayed a moderate overestimation of the speed associated with the VT2 (0.41 [0.14 to 0.68] km/h); meanwhile, the respiration rate (−0.56 [−1.03 to −0.09] km/h) and RRa1 (−0.87 [−1.38 to −0.36] km/h) displayed a small and large underestimation, respectively. No significant HRV indices and sex interaction effect was observed (F_(2,36) = 1.626; p = 0.211). In conclusion, DFA-a1, respiration rate and RRa1 are valid HRV indices to estimate the load associated with the VT1. However, DFA-a1 displayed a moderate overestimation of the load associated with the VT2, while the respiration rate and RRa1 displayed a small and large underestimation, respectively. Full article

Objective: Rapid vertical manoeuvres and intermittent vibration in autonomous electric vertical take-off and landing (eVTOL) aircraft can provoke pronounced psychological anxiety in passengers. To address this, we propose a closed-loop adaptive system that integrates an in-ear wearable sensor with dynamic regulation of the cabin microenvironment, enabling real-time monitoring of each passenger’s autonomic state and delivering individualised mitigation through a continuous sense–analyse–intervene–feedback loop. Methods: The system is built around a pair of custom in-ear modules that integrate dual-wavelength photoplethysmography (PPG; 525 nm green and 940 nm infrared), galvanic skin response (GSR), and a six-axis inertial measurement unit (IMU) sampled at 200 Hz. To suppress the 20–80 Hz vibration generated by the distributed electric propulsion system, a compliant silicone damping sleeve attenuates high-frequency components at the hardware level, while a Kalman filter fuses the IMU and PPG streams and an adaptive notch filter removes residual rotor harmonics. The pipeline raises the heart-rate-variability (HRV) signal-to-noise ratio (SNR) to 24.1 dB, with a Pearson correlation of 0.96 against a medical-grade chest strap. A hybrid CNN–LSTM network—two convolutional layers (32 filters each) followed by two LSTM layers (128 hidden units)—predicts impending anxiety from HRV time-domain features (RMSSD, pNN50) and frequency-domain features (LF/HF ratio), triggering intervention 8.2 s in advance on average. According to the predicted anxiety level (mild/moderate/severe), a fuzzy controller modulates transcutaneous auricular vagus nerve stimulation (1–5 mA), the binaural-beat frequency (4–8 Hz, theta band), and the cabin lighting colour temperature (2700–6500 K) in real time. The intervention parameters are continuously refined by SPSA-based stochastic optimisation of the HRV recovery rate (step size 0.01; updated every 30 s). Results: In a randomised controlled experiment conducted in a simulated flight environment (N = 50; aged 22–45 years; 1:1 sex ratio), the active group reached physiological recovery in 52.3 s on average, compared with 98.6 s for the sham-controlled group—a 47% reduction (Cohen’s d = 1.24, p < 0.001). User acceptance reached 94%. Conclusions: The proposed in-ear platform enables closed-loop adaptive regulation of anxiety in the eVTOL cabin and overcomes the limitations of conventional passive mitigation strategies. By combining vibration-tolerant physiological sensing with multimodal environmental control, the work offers a practical pathway for improving passenger experience in urban air mobility and provides a useful reference for human-factors standards governing autonomous aircraft. Full article

This study examined the within-session (same-day) test–retest reliability of heart rate (HR) and parasympathetic modulation, assessed using the root mean square of successive differences (RMSSD), across exercise and recovery phases in trained soccer players. Twenty-seven male soccer players (age: 24.9 ± 3.7 years) completed a standardized soccer training session. HR and RMSSD were recorded using an ECG-based chest-strap monitor at rest, pre-exercise, and at ~10–20 min, 1 h, and 3 h post-exercise. At each time point, two consecutive 5 min seated recordings were obtained under identical conditions. Test–retest reliability was evaluated using intraclass correlation coefficients (ICC_(3,1)), standard error of measurement (SEM), coefficient of variation (CV%), minimal detectable change (MDC₉₅), paired-samples t-tests, and Hedges’ g effect sizes. HR demonstrated excellent reliability across all time points (ICC = 0.980–0.994; SEM = 0.87–1.25 bpm; CV% = 1.33–3.70%). RMSSD showed excellent reliability at rest (ICC = 0.944) and pre-exercise (ICC = 0.918), moderate reliability during early recovery (~10–20 min; ICC = 0.551), and good reliability at 1 h (ICC = 0.826) and 3 h post-exercise (ICC = 0.873). No significant systematic differences were observed between test and retest measurements (all p > 0.05), and effect sizes were trivial. These findings indicate that within-session reliability of HR remains consistently high across exercise and recovery phases, whereas RMSSD reliability varies according to measurement timing, particularly during early recovery. Full article

Heart rate recovery (HRR) is an important indicator of cardiovascular autonomic function, yet evidence in women with breast cancer remains limited. This study aimed to analyze heart rate recovery during the first two minutes following a maximal exercise test and to examine its association with age, weekly physical activity, and oncological treatment duration using wearable technology. A cross-sectional design was applied in 22 women with breast cancer enrolled in an oncological exercise program. Participants performed a maximal treadmill test using the Modified Bruce Protocol, after which the mean heart rate was recorded across eight 15 s recovery intervals using a wearable chest-strap heart rate sensor integrated with an inertial device (WIMU PRO). Results showed a progressive and significant decrease in heart rate during recovery, with the first statistically significant pairwise difference emerging at 45–60 s post-exercise compared to the initial recovery interval (p < 0.05), within the context of a continuous HR decline. Regression analysis identified weekly physical activity hours (β = −0.281, p = 0.013) and oncological treatment duration (β = −0.245, p = 0.038) as significant predictors of mean heart rate recovery, explaining 4.8% of the variance, while age was not significantly associated (β = 0.049, p = 0.622). In conclusion, a differentiated recovery pattern emerged at approximately 45–60 s post-exercise, with weekly physical activity and oncological treatment duration as determinants. These findings support the use of wearable-based monitoring to inform individualized exercise prescription in women with breast cancer. Full article

Understanding how anthropometric characteristics influence internal load during boxing remains limited, despite heart rate (HR) being a key indicator of exercise intensity. This study examined the relationship between anthropometry and HR responses during three boxing-specific exercises—shadowboxing, pad work, and heavy bag work—in 39 male practitioners (29.0 ± 2.3 years). Body height (BH), body mass (BM), and body mass index (BMI) were assessed. HR_peak and HR_mean were recorded using a validated chest-strap monitor (Polar H10). Significant positive correlations were observed between BH, BM, BMI, and HR responses across all modalities, with the strongest associations during heavy bag work (e.g., HR_peak: BH r = 0.658, BM r = 0.681, BMI r = 0.677; all p < 0.001). Regression analyses indicated that BH explained 23–36% of HR variance during shadowboxing and pad work, whereas BM and BMI showed greater predictive capacity during heavy bag work, explaining up to 46% of HR_peak variance. Repeated-measures ANOVA revealed significant differences between modalities, with heavy bag work eliciting the highest intensities (p < 0.001). These findings demonstrate that greater anthropometric dimensions are associated with higher cardiovascular responses, supporting individualized training prescriptions based on morphological characteristics. Full article

Introduction: This study investigated heart rate variability (HRV) and perceived recovery status (PRS) in relation to sprint performance in competitive athletes involved in sprint events. A secondary aim was to explore potential gender-based differences in these relationships. Methods: Fifty-six sprint-trained athletes (21 males, 35 females; age 16–21) participated in a 5-day in-season microcycle. Daily morning HRV was measured using Polar H10 chest straps and the HRV4Training app, with the root mean square of successive differences (LnRMSSD) used as the primary HRV marker. Perceived recovery was assessed each morning using the PRS scale. On each day, athletes completed 20 m maximal sprint tests. Linear mixed-effects models were used to examine the relationships between LnRMSSD, PRS, gender, and sprint performance while accounting for repeated measurements within athletes. Results: Linear mixed-effects modeling revealed that LnRMSSD was a significant negative predictor of sprint time (β = −0.019, p = 0.003), indicating that higher parasympathetic activity was associated with faster sprint performance. PRS was also a significant negative predictor of sprint performance (β = −0.014, p = 0.008). Conclusions: Daily recovery markers were associated with sprint performance in competitive sprint athletes, with potential gender-specific patterns that should be interpreted cautiously. Both LnRMSSD and PRS were significantly associated with sprint performance, highlighting the relevance of combining physiological and subjective recovery markers in athlete monitoring. Full article

Background: Athletes may experience paroxysmal arrhythmias that occur during exercise and are difficult to document using standard diagnostic modalities. Such arrhythmias are often unpredictable, transient, and cannot be reproduced during routine exercise testing or ambulatory electrocardiographic monitoring, leading to prolonged diagnostic pathways and uncertainty regarding management. Methods: This case series presents ten athletes in whom clinically relevant paroxysmal arrhythmias were initially detected using commercially available wearable digital devices, primarily chest-strap heart rate monitors and smartwatches. Results: In most cases, arrhythmias could not be documented using conventional diagnostic methods despite repeated investigations. Most presented athletes were referred for invasive electrophysiological study, which confirmed supraventricular arrhythmias and enabled curative catheter ablation based solely on data obtained from wearable devices. The use of digital devices substantially shortened the time to diagnosis and treatment, reduced diagnostic burden, and allowed definitive therapy in symptomatic athletes. Conclusions: Wearable technology, particularly chest-strap heart rate monitors, may play an important role in the diagnostic evaluation of exercise-induced paroxysmal arrhythmias when standard methods fail. Full article

Background: The purpose was to determine the ventilatory and metabolic demands in percentage-based heart rate (HR) zones in active-duty firefighters. Methods: Male career firefighters (n = 48, 38.17 ± 9.02 years, 1.79 ± 0.05 m, 88.27 ± 12.50 kg) completed a maximal treadmill test while wearing chest strap monitors to measure physiological responses corresponding to Zone 1 (50–59%), Zone 2 (60–69%), Zone 3 (70–79%), Zone 4 (80–89%), and Zone 5 (90–100%) based on age-predicted maximal HR. Aerobic capacity (VO_2PEAK, mL·kg⁻¹·min⁻¹), average minute ventilation (V_E, L·min⁻¹), and respiratory exchange ratio (RER) in each zone was measured via indirect calorimetry. Linear mixed models determined significant differences in V_E, RER, and time in zone (min). Results: Significant relationships emerged between VO_2PEAK and average RER in Zone 5 (r = −0.33) and time in Zone 3 (r = 0.45), Zone 4 (r = 0.41), and Zone 5 (r = 0.41). A significant HR zone effect emerged in V_E (F = 516.01, p < 0.001) indicating that V_E increased as zone intensity increased. After controlling for VO_2PEAK, a significant HR zone effect emerged in RER (F = 11.90, p < 0.001), indicating that average RER increased as zone intensity increased. No HR zone effect was found for time in zone (F = 1.18 p = 0.332) after controlling for VO_2PEAK. Conclusions: A practical cardiovascular workload measure, such as percentage-based HR zones determined from treadmill testing, have distinct ventilatory and metabolic responses. Higher aerobic capacity is related to greater time spent working in higher HR zones. Full article

Heart rate (HR), a non-invasive indicator of physiological arousal and autonomic nervous system engagement, is widely used in cognitive and affective sciences to monitor individual responses and interpersonal synchrony in dynamic emotional and social contexts. Recent advances in wearable sensors have enabled researchers to assess HR synchrony in ecologically valid settings. In this study, we replicate prior validations of the Polar H10 chest strap for individual HR measurement and extend these findings by evaluating its validity for measuring HR synchrony between individuals. Dyads completed a previously validated experimental task designed to elicit HR fluctuations while jointly attending to emotionally evocative, 5-min audiovisual stimuli. First, we observed high correspondence (Pearson’s r > 0.99) between the Polar H10 and a gold-standard ECG system in measuring individuals’ HR, both at the aggregate and moment-to-moment levels, thus confirming and extending prior findings. Second, we found high correspondence (Pearson’s r > 0.95) between the two systems in quantifying dyadic HR synchrony using multiple analytical approaches. These results support the use of the Polar H10 as a low-cost, easy-to-use, and reliable tool for both individual and dyadic HR measurement. This represents an important step toward establishing its applicability in real-world settings where traditional ECG systems are impractical. Full article

Purpose: This study evaluated the accuracy of arm-based photoplethysmography (PPG) wearable heart rate (HR) monitors in comparison to a validated chest strap reference across various activity levels. Methods: Twenty-eight healthy adults (14 males, 14 females; aged 23.8 ± 1.1 years) wore six HR monitors: Polar H10 chest strap, Polar Verity Sense on the forearm, Garmin Forerunner on the wrist, and three identical Whoop 4.0 devices placed on the left wrist, forearm, and upper arm. Participants completed rest, warm-up, high-intensity burpees, and graded treadmill exercise. HR data were analyzed using mean absolute percentage error (MAPE), Bland–Altman analysis, concordance correlation coefficient (CCC), and Deming regression. Results: Accuracy was highest at rest and gradually decreased as movement intensity increased. During rest, all devices showed minimal bias and high agreement (CCC > 0.99), with Verity Sense recording the lowest MAPE. In warm-up, Whoop-upper arm and Verity Sense outperformed wrist and Garmin positions, while the Whoop-forearm showed proportional and systematic bias. Burpees resulted in the lowest accuracy across devices (CCC < 0.50), but Whoop-upper arm performed better than other placements. During the Modified Bruce protocol, Verity Sense and Whoop-upper arm had the strongest agreement with the chest strap. Placement of identical Whoop units affected accuracy, with the upper arm outperforming forearm and wrist positions. Conclusions: PPG wearables provided accurate HR monitoring at rest, during warm-up, and during steady-state graded exercise, particularly when positioned proximally (forearm or upper arm). Accuracy declined during short, high-intensity, full-body activities due to motion artifacts. Both the forearm-mounted Verity Sense and the upper-arm Whoop demonstrated the closest agreement with the chest-strap reference. The intra-device comparison of identical Whoop units confirmed that anatomical placement alone significantly affects accuracy. Full article

The validity and accuracy of photoplethysmography (PPG)-based wearable heart rate (HR) monitors remain debatable. This study aimed to determine the concurrent validity of HR records from a wide range of contemporary PPG monitors across the full spectrum of exercise intensities and running conditions. Ten well-trained male endurance athletes performed several incremental maximal aerobic (IMA) tests and high-intensity interval training (HIIT) sessions while wearing a Polar H9 chest strap, as the reference criterion; 16 PPG-based heart rate monitors were tested (Amazfit Fit5; Apple Ultra and SE; Garmin 35, 45, 235, and 935; Polar M200, M430, OH1, Vantage M, Vantage V, Vantage V3, and Verity Sense; Galaxy Watch 5, Suunto 3 Fitness). The results showed excellent ICC (>0.90) versus the reference device across IMA and HIIT tests. Overall, the ICC decreased, and magnitudes of error increased (BIAS, SEM, and CV) as the intensity increased. Moreover, lower ICC values and greater BIAS, SEM, and CV were observed during the HIIT compared to the IMA test. Nevertheless, notable differences between devices were observed in magnitude of errors, accuracy, data loss, and read failures. In conclusion, PPG-based HR monitor validity is device-dependent and therefore exercise data from running training and competitions should be interpreted with caution. Full article

Background/Objectives: Complex emotions in daily life often arise as mixtures of basic emotions, but most emotion-recognition systems still target a small set of discrete states and rely on contact-based sensing. This study aimed (1) to examine whether four compound emotions—Positive Surprise, Negative Surprise, Positive Sadness, and Negative Sadness—defined by valence direction within basic emotion categories can be differentiated using heart rate variability (HRV), and (2) to evaluate the feasibility of a camera-based contactless system (Deep Health Vision System, DHVS) by comparing it with a reference chest-strap device (Polar H10). Methods: Ten healthy adults viewed video clips designed to induce the four complex emotions. HRV was recorded simultaneously using Polar H10 and a webcam-based rPPG implementation of DHVS. Two-minute baseline and during-stimulus segments were extracted, and change rates of standard HRV indices were computed. After each stimulus, participants reported Valence, Arousal, Dominance, and proportional basic-emotion composition. Statistical analyses examined within-condition HRV changes, associations between HRV and self-reports, differences across emotion/valence conditions, and concordance between DHVS and Polar H10. Results: Self-reports confirmed distinct affective profiles for the four compound emotions. Positive and Negative Surprise were associated with heart rate reduction, while Positive Sadness showed reduced total power; Negative Sadness yielded heterogeneous but nonsignificant HRV changes. Specific HRV indices demonstrated condition-dependent correlations with Valence, Arousal, and Dominance. LF/HF changes were more sensitive to emotion category (Surprise vs. Sadness), whereas total power changes were more sensitive to valence (positive vs. negative). DHVS partially reproduced Polar H10 HRV patterns, with clearer concordance under positive-valence conditions. Conclusions: HRV captures distinct autonomic signatures of complex emotions defined by valence direction and shows meaningful links with subjective affective evaluations. LF/HF and total power provide complementary information on emotion category and valence-related autonomic reactivity, supporting indicator-specific modeling strategies. DHVS shows preliminary feasibility as a contactless HRV sensing platform for complex emotion recognition, warranting further validation with larger samples and more robust rPPG processing. Full article

Heart rate variability (HRV) is widely recognized as an indicator of general health, particularly time domain measures like the root mean square of successive differences (RMSSD) between consecutive heartbeats. Consumer wearables measuring HRV have potential for wide accessibility meaning that their broad use to capture HRV as a health biomarker is possible. Our objective was to investigate the validity of HRV measured by wearables as a general health indicator. We examined whether resting HRV assessed by wearables across five studies—two using smartwatches, two using heart rate chest straps, and one using a smartring—exhibited expected associations with diverse health domains, including mental, physical, behavioral, functional, and physiological. We focused on resting HRV measures recorded while in primarily stationary conditions, either upon waking or while sleeping, because such measures would theoretically reduce the effects of potential confounders such as movement artifacts, daytime caffeine intake, and postural changes. Wearables measured resting HRV had small-to-moderate associations with more clinically oriented and trait-like (or slow-changing) health measures like Hba1c (average blood glucose, r = −0.21, p = 0.014), depressive symptoms (r = −0.22, p = 0.024), and sleep difficulty (r = −0.11, p = 0.003). Wearable-measured resting HRV can potentially serve as a health biomarker, but further research is needed. Full article

This study evaluated the accuracy of heart rate (HR) measures of a commercial wearable device on tattooed skin and assessed tattoo characteristics associated with HR accuracy. Participants (n = 25) wore a chest strap HR monitor (criterion) and an armband HR monitor (experimental) during rest and self-paced walking and running. Conditions with the experimental device on tattooed and non-tattooed sections of skin were completed, and HR was collected every second and compared via Lin’s correlation (CCC) and the mean absolute percent error (MAPE). Skin tone and tattoo age and intensity were evaluated with HR accuracy. HR from tattooed skin was not accurate during rest (MAPE = 22.9%; CCC = 0.25), walking (MAPE = 7.5%; CCC = 0.68), or running (MAPE = 5.1%; CCC = 0.83). Measures taken on non-tattooed skin were within acceptable standards for accuracy throughout all three conditions (MAPE < 5%; CCC > 0.90). Skin tone was the only characteristic found to contribute to HR accuracy during rest (p = 0.046) and walking (p = 0.045). No variables loaded for running. The presence of arm tattoos affected HR readings, with the greatest inaccuracy occurring at rest. Specific tattoo characteristics did not statistically contribute to HR accuracy, as shown by the regression analysis. More research is needed to clarify how the varied tattoo characteristics affect HR devices. Full article