Modern wearable devices report several heart rate‐based nocturnal health metrics, including resting heart rate (RHR) and heart rate variability (HRV). The purpose of this study was to assess the validity of nocturnal RHR and HRV from five wearable devices (Garmin Fenix 6, Oura Generation 3, Oura Generation 4, Polar Grit X Pro, & Whoop 4.0) against an electrocardiogram (ECG) reference. Thirteen healthy adults (6 females) wore an ECG reference and multiple wearables simultaneously during sleep, totaling 536 nights. Interdevice accuracy varied significantly (p < 0.05). For RHR, Oura Gen 3 (Lin's Concordance [CCC] = 0.97, mean absolute percentage error [MAPE] = 1.67 ± 1.54%) and Gen 4 (CCC = 0.98, MAPE = 1.94 ± 2.51%) demonstrated the highest accuracy, outperforming Polar's poor (CCC = 0.86, MAPE = 2.71 ± 2.75%) and WHOOP's moderate agreement (CCC = 0.91, MAPE = 3.00 ± 2.15%). Garmin was excluded from RHR analyses due to methodological inconsistencies. For HRV, Oura devices provided the highest accuracy; Oura Gen 4 (CCC = 0.99, MAPE = 5.96 ± 5.12%), Oura Gen 3 (CCC = 0.97, MAPE = 7.15 ± 5.48%). WHOOP showed moderate accuracy (CCC = 0.94, MAPE = 8.17 ± 10.49%), followed by poor agreement from both Garmin (CCC = 0.87, MAPE = 10.52 ± 8.63%) and Polar (CCC = 0.82, MAPE = 16.32 ± 24.39%). Oura devices showed the highest agreement for RHR and HRV, and WHOOP showed acceptable agreement, whereas Garmin Fenix and Polar demonstrated lower concordance, highlighting the importance of continuous validation and providing valuable benchmarks for clinicians, researchers, and consumers.

Sleep and circadian rhythms are critically important for optimal physical performance and maintaining health during training. Chronotype and altered sleep may modulate the response to exercise training, especially when performed at specific times/days, which may contribute to musculoskeletal injury. The purpose of this study was to determine if cadet characteristics (chronotype, sleep duration, and social jetlag) were associated with injury incidence and inflammation during physical training. Reserve Officers’ Training Corps (ROTC) cadets (n = 42) completed the Morningness/Eveningness Questionnaire to determine chronotype, and 1-week sleep logs to determine sleep duration and social jetlag. Salivary IL-6 was measured before and after the first and fourth exercise sessions during training. Prospective injury incidence was monitored over 14 weeks of training, and Army Physical Fitness Test scores were recorded at the conclusion. Chronotype, sleep duration, and social jetlag were assessed as independent factors impacting IL-6, injury incidence, and APFT scores using ANOVAs, chi-squared tests, and the t-test where appropriate, with significance accepted at p < 0.05. Evening chronotypes performed worse on the APFT (evening = 103.8 ± 59.8 vs. intermediate = 221.9 ± 40.3 vs. morning = 216.6 ± 43.6; p < 0.05), with no difference in injury incidence. Sleep duration did not significantly impact APFT score or injury incidence. Social jetlag was significantly higher in injured vs. uninjured cadets (2:40 ± 1:03 vs. 1:32 ± 55, p < 0.05). Exercise increased salivary IL-6, with no significant effects of chronotype, sleep duration, or social jetlag. Evening chronotypes and cadets with social jetlag display hampered performance during morning APFT. Social jetlag may be a behavioral biomarker for musculoskeletal injury risk, which requires further investigation.

Vatne, EA, Cencer, D, Vatne, M, Pulvermacher, K, Saenz, C, Kraemer, WJ, Robinson, B, Jones, P, Quebedeaux, N, Sprague, R, Dial, M, Carpenter, T, and Hagen, J. Relationship between objective measures of sleep and nocturnal cardiovascular physiology and swimming performance in collegiate female athletes: A Bayesian analysis. J Strength Cond Res XX(X): 000–000, 2026—There is substantial evidence that sleep influences athletic performance; however, relationships with real-world competition outcomes remain unclear. Therefore, the purpose of this study was to explore the associations between objectively measured sleep, nocturnal cardiovascular physiology on the night before competition, and swim performance in female collegiate athletes. Female swimmers ( n = 11) who wore a sleep monitoring device the night before competition, competed in the 200-yard freestyle (short course yard), and had ≥21 of 28 prior nights of valid data were included. Sleep metrics included total sleep time (TST), time in bed (TiB), and sleep efficiency (SE), whereas nocturnal cardiovascular metrics included heart rate variability (HRV) and resting heart rate (RHR) standardized as individualized z -scores. Race times were obtained from a publicly available database. Bayesian linear mixed-effects models estimated posterior probabilities of performance improvement. Results indicated a high probability that greater TST and TiB were associated with faster race times, with substantial support for improvements of at least 1 second per additional hour of sleep. In contrast, SE, HRV, and RHR showed low posterior evidence of meaningful associations with performance. These findings extend prior sleep and performance literature that has been confined to proxy assessments of athletic performance in controlled settings to real-world competition that should inform athlete education, emphasizing the importance of sufficient sleep opportunity and duration before competition.

Objective: The aim of the study was to evaluate the combined effects of sleep deprivation and simulated wildland firefighting on systemic inflammation and oxidative stress. Methods: Ten participants performed two exercise trials while exposed to woodsmoke following one night of normal sleep or sleep deprivation (4 hours) in a crossover design. Blood biomarkers of oxidative stress and inflammation were quantified through ELISAs. Results: Interleukin-6 significantly increased after simulated wildland firefighting ( P < 0.001, ηp ² = 0.74), with no effect of sleep deprivation. Oxidative stress markers (8-isoprostanes, 3-nitrotyrosine, myeloperoxidase) showed no significant changes or interactions. Conclusions: Simulated wildland firefighting elicits an inflammatory response but does not alter oxidative stress markers. Acute sleep deprivation did not to modulate these responses. Future research should explore the cumulative effects of prolonged sleep restriction and repeated woodsmoke exposure to better understand their impact on inflammation and oxidative stress.

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