Resilience to stress integrates cognitive, physiological, and behavioral adaptations to sustain performance under adversity. Genetic variation in catechol-O-methyltransferase (COMT, rs4680) and angiotensin-converting enzyme (ACE, rs1799752) modulates dopaminergic and renin-angiotensin signaling, influencing tissue oxygenation and fatigue resistance. We examined COMT- and ACE-promoter methylation and genotypes in relation to resilience traits in Swiss tactical athletes (24.6 years) with a maximal power output of 534 W and 21,656 W, respectively, during cardiopulmonary exercise and elbow strike testing. At a 5% false-discovery rate, COMT genotype/methylation explained ~12% of the variance in cognitive performance and metabolic resilience, while ACE explained ~6-7% in strength-endurance and muscle resistance. Antidromic linear associations between COMT genotype and methylation with visual reaction time under reactive stress indicate opposing regulatory influences, best captured by regression models incorporating (epi)genetic covariates. The strongest methylation effects involved COMT promoter associations with muscle hemoglobin content across cardiopulmonary exercise zones (r = 0.43-0.58) and sport-specific strain (r = -0.46). COMT- and ACE-promoter methylation, correlated with time spent in the first aerobic training zone (r = 0.55 and 0.32), indicating environmentally responsive epigenetic modulation. These findings highlight neurovascular-metabolic coupling via dopaminergic and renin-angiotensin pathways as a key mechanism in stress adaptation. System-level adaptations in these pathways align with COMT and ACE (epi)genetic blood profiles, positioning them as candidate resilience biomarkers. Larger, preregistered studies with site-specific CpG analyses and mechanistic assays are needed to establish causal relevance and translational utility for resilience-informed performance optimization in high-stakes professionals.
Wearable body-attached multi-sensor systems enable detailed analysis of human motion and physiological signals in sports, rehabilitation, and movement research. While wireless synchronization techniques can reliably align sensor data streams, interpreting and validating complex or unconstrained activities often requires an additional, objective visual reference. Existing laboratory-grade reference systems provide high accuracy but are impractical for outdoor or field deployments. In contrast, commercial video timecode solutions typically rely on local device-to-device synchronization, which increases the power required to maintain synchronization. This is not desirable in many application scenarios. This paper presents a lightweight Timecode Generator (TCG) that converts Global Navigation Satellite System (GNSS)-derived time directly into a Linear Timecode (LTC) signal that is injected into the recording via a camera audio channel. The approach eliminates continuous handshaking, allowing the system to be activated immediately before the action of interest, thus reducing power consumption and enabling smaller batteries and unobtrusive hardware designs of body-attached sensor nodes. The TCG supports common video frame rates of 24, 25, and 30 frames per second (fps). Experimental evaluation confirms that accurate time alignment is maintained for several minutes without GNSS updates. At 30 fps, the alignment duration is 543 s before a potential frame-level shift occurs. With an average power consumption of 35.37 mW, the system achieves an operating time of up to 75 h when powered by two standard AAA alkaline batteries.
Anterior cruciate ligament (ACL) injuries are common in competitive alpine skiing and pose significant challenges for return-to-performance (RTP) pathways. The aim of this scoping review was to map the current state of research, identify key factors for recovery, highlight knowledge gaps and synthesize evidence- and expert-informed practice recommendations for RTP after ACL injury. A search was conducted in four electronic databases using a set of pre-defined search terms. Studies that examined relevant aspects of RTP in competitive alpine skiers (not competitive para alpine skiers or recreational alpine skiers) who had suffered an ACL injury were included. Two assessors independently screened titles, abstracts and full-text sources to determine eligibility. Of the 622 double-removed hits from the literature search and the two studies added manually, 35 studies were included in this scoping review based on the eligibility criteria. The entities extracted included study characteristics such as general descriptors, injury patterns, surgical details, rehabilitation/training activities, testing/monitoring metrics, and key outcomes. The extracted data were then narratively/descriptively synthesized across several key domains. Most studies identified focus on epidemiology, secondary risks and early rehabilitation, with limited research on later recovery phases, such as returning to competition and returning to performance. There is also little evidence regarding the psychological and social factors that influence RTP. While further research is needed to fill these knowledge gaps, we propose a sport-specific, criteria-based and multi-domain RTP framework with stepwise progression on snow. Finally, we provide insights into practical implementation and present a comprehensive and jointly created RTP protocol for competitive alpine skiers to serve as a guideline for evidence- and expert-informed practice.
Introduction & Purpose: Wearable devices using photoplethysmography (PPG) are increasingly used for non-invasive monitoring of physiological responses during daily life and physical activity. However, accuracy can vary with movement and sensor placement, and continuous validation remains essential. Compared with wrist-worn devices, upper-arm placements showed higher-quality PPG signals and are less affected by motion artefacts (Schweizer & Gilgen-Ammann, 2025). This study aimed to validate heart rate (HR) measurements obtained from the Polar 360 upper-arm strap across a wide range of activities and intensities. Methods: Fourteen healthy adults (7 females; 173.4 ± 9.0cm, 71.9 ± 10.2kg, 33.4 ± 9.2years) with fair skin completed six laboratory-based activities, each separated by a two minutes of transition/rest: (1) 2min lying, (2) 5min sitting, (3) treadmill walking–jogging–running–jogging–walking sequence (5×3min), (4) ergometer cycling at low–moderate–high–very high–low intensities (5×3min), (5) 8min strength training circuits, and (6) 8min high-intensity interval training (HIIT) circuits. HR was measured concurrently using the Polar 360 PPG (1Hz) sensor worn on the non-dominant upper arm and the Polar H10 electrocardiogram (ECG, 1Hz) chest strap as criterion. HR data were averaged in 10-s intervals and analyzed for systematic bias (mean difference), mean absolute error (MAE), mean absolute percentage error (MAPE), Lin’s concordance correlation coefficient (CCC) (McBride, 2005), and the percentage of data within ±5bpm of the criterion. Results: Criterion HR values ranged from 69.4 ± 11.9bpm (lying) to 161.1 ± 15.9bpm (HIIT). Overall, the Polar 360 showed substantial agreement with the criterion (bias = −0.65bpm, MAE = 1.93bpm, MAPE = 1.62%, CCC = 0.987), with 92.3% of 10-s HR intervals within ±5bpm of the H10 reference. Activity-specific accuracy varied markedly: cycling showed excellent agreement (bias = −0.02bpm, MAE = 0.62bpm, MAPE = 0.44%, CCC = 0.999, 99.5% within ±5bpm), whereas HIIT produced poorer results (bias = −1.93bpm, MAE = 4.18bpm, MAPE = 2.71%, CCC = 0.828, 81.3% within ±5bpm). Walking demonstrated near-excellent agreement, lying yielded similarly low accuracy as HIIT, and sitting and strength training showed moderate agreement (CCC = 0.904 and 0.910, respectively). Discussion & Conclusion: The Polar 360 demonstrated strong overall validity for HR measurement compared with ECG, though accuracy varied by activity. Consistent with previous findings, PPG-based HR accuracy decreased with greater motion and reduced peripheral blood flow (Schweizer & Gilgen-Ammann, 2025). Nevertheless, the Polar 360 outperformed most commercial wearables across comparable activity conditions. Its combination of accuracy, comfortable upper-arm placement, and long battery life make it a promising alternative to ECG-based chest straps for continuous HR monitoring in both research and applied settings. References McBride, G. B. (2005). A proposal for strength-of-agreement criteria for Lin’s concordance correlation coefficient (NIWA Client Report: HAM2005-062). National Institute of Water & Atmospheric Research. https://www.medcalc.org/download/pdf/McBride2005.pdf Schweizer, T., & Gilgen-Ammann, R. (2025). Wrist-worn and arm-worn wearables for monitoring heart rate during sedentary and light-to-vigorous physical activities: Device validation study. JMIR Cardio, 9, Article e67110. https://doi.org/10.2196/67110
