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        <title>Frontiers in Physiology | Chronobiology section | New and Recent Articles</title>
        <link>https://www.frontiersin.org/journals/physiology/sections/chronobiology</link>
        <description>RSS Feed for Chronobiology section in the Frontiers in Physiology journal | New and Recent Articles</description>
        <language>en-us</language>
        <generator>Frontiers Feed Generator,version:1</generator>
        <pubDate>2026-05-13T13:23:07.799+00:00</pubDate>
        <ttl>60</ttl>
        <item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2026.1858443</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2026.1858443</link>
        <title><![CDATA[Correction: Circadian system functional status and sleep in blind subjects with and without conscious light perception]]></title>
        <pubdate>2026-04-27T00:00:00Z</pubdate>
        <category>Correction</category>
        <author>David Martínez-Martínez</author><author>Pedro González-Romero</author><author>Beatriz Rodríguez-Morilla</author><author>María Ángeles Bonmatí-Carrión</author><author>María Ángeles Rol</author><author>Pedro Francisco Almaida-Pagán</author>
        <description></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2026.1787735</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2026.1787735</link>
        <title><![CDATA[Circadian system functional status and sleep in blind subjects with and without conscious light perception]]></title>
        <pubdate>2026-04-13T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>David Martínez-Martínez</author><author>Pedro González-Romero</author><author>Beatriz Rodríguez-Morilla</author><author>María Ángeles Bonmatí-Carrión</author><author>María Ángeles Rol</author><author>Pedro Francisco Almaida-Pagán</author>
        <description><![CDATA[To understand circadian rhythms and sleep in an understudied population, which is particularly prone to suffer chronodisruption (CD), eighteen blind volunteers of 51.5 ± 3.6 years (Mean ± SEM) and 26 volunteers (51.8 ± 1.2) with no visual impairments wore the ambulatory circadian monitoring (ACM) device Kronowise® for seven consecutive days in real-life conditions. Nine of the blind participants declared to have some sort of light perception while the other nine declared to lack conscious light perception. ACM combines measurements of distal skin temperature; motor activity, light exposure and feeding schedules, providing information about lifestyle and the bidirectional crosstalk between internal time and external synchronisers, which is paramount to determine a subject’s CD degree. We found a extraordinarily diverse population in terms of blindness aetiology and thus, in the degree of affectation of the participants visual and circadian systems. Our results pointed to poorer circadian health and sleep in the blind participants, which could be directly related to the impact of disease over circadian photoreception but also to disruption of daily habits. Compared to controls, blind participants showed significantly lower light exposure and physical activity values during the day and higher time of movement during the night. Besides, we analysed feeding schedules in the blind participants for the first time and found that their last meal of the day happened later than in controls, thus blind participants’ night fasting was shorter. Altogether, our results indicated substantial behavioural circadian alterations associated with the disease.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2026.1797489</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2026.1797489</link>
        <title><![CDATA[The role of circadian rhythms in the pathogenesis of myopia]]></title>
        <pubdate>2026-04-01T00:00:00Z</pubdate>
        <category>Review</category>
        <author>Ning Zhang</author><author>Guoge Han</author><author>Rui Hao</author>
        <description><![CDATA[Myopia is a complex ocular disorder arising from the interaction of genetic predisposition and environmental cues that regulate eye growth. Increasing evidence indicates that the circadian timing system plays a critical role in ocular development and refractive homeostasis. The retina, choroid, and sclera possess intrinsic molecular clocks that generate rhythmic oscillations in gene expression, neurotransmitter release, and tissue physiology. Disruption of these ocular circadian rhythms has been implicated in abnormal axial elongation through pathways involving dopamine and melatonin signaling, light-dependent retinal pathways, and diurnal fluctuations in intraocular pressure. In this review, we summarize current knowledge of the molecular mechanisms underlying circadian regulation in ocular tissues and discuss how environmental light exposure and sleep–wake cycles modulate these processes. We further integrate evidence linking rhythmic alterations in retinal, choroidal, and scleral function to myopia development. Finally, we propose mechanistic frameworks through which circadian dysregulation may contribute to myopia onset and progression, highlighting potential molecular targets for rhythm-based intervention strategies.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2025.1732257</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2025.1732257</link>
        <title><![CDATA[The effects of total sleep deprivation on the circadian rhythms and psychophysiological factors in military cadets; a comparison between wakefulness in light and darkness]]></title>
        <pubdate>2026-01-16T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Kateřina Skálová</author><author>Jan Maleček</author><author>David Kolář</author><author>Kateřina Červená</author><author>Jana Kopřivová</author><author>James Tufano</author><author>Dan Omcirk</author><author>Jan Padecký</author><author>Tomas Vetrovsky</author><author>Zdeňka Bendová</author>
        <description><![CDATA[ObjectivesBoth sleep deprivation (SD) and light at night have negative effects on human health and performance. The aim of our work was to compare the intermediate effects of total SD under two lighting conditions: full indoor lighting and darkness mimicking natural nocturnal wakefulness.MethodsWe examined melatonin levels during SD nights, locomotor activity and peripheral temperature rhythms, cognitive performance, mood, hunger, glycaemia and food preference after SD and recovery sleep. Statistical evaluation included ANOVA with FDR correction and confidence intervals.ResultsSD transiently altered peripheral temperature rhythm and post-SD activity, with faster resynchronisation after SD in darkness. Subjective sleepiness increased after SD, with light at night alleviating morning sleepiness. Positive affect decreased after SD but normalised after recovery sleep in both groups. Negative affect worsened in the morning after SD in darkness. Cognitive performance declined after SD, but this effect was higher after SD in darkness. Preprandial glycaemia was higher after recovery sleep following SD in darkness, and sweet taste preference was significantly higher after SD in darkness.ConclusionLight exposure during SD may lead to lower subjective sleepiness and better cognitive performance the next morning compared to SD in darkness. However, light during SD also causes more pronounced and persistent disruptions to circadian rhythms of temperature and activity. This underscores the trade-off between the short-term benefits of nocturnal light exposure and its potential long-term impacts on circadian health.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2025.1686942</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2025.1686942</link>
        <title><![CDATA[Chronic circadian misalignment accelerates sarcopenia progression in mice]]></title>
        <pubdate>2025-11-13T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Takashi Seya</author><author>Nobuya Koike</author><author>Naoki Okubo</author><author>Yasuhiro Umemura</author><author>Yoshiki Tsuchiya</author><author>Kazuya Yabumoto</author><author>Yasuhiro Endo</author><author>Kanako Iinuma</author><author>Akiyo Kakibuchi</author><author>Akira Sugimoto</author><author>Kenji Takahashi</author><author>Seung-Hee Yoo</author><author>Zheng Chen</author><author>Kazuhiro Yagita</author>
        <description><![CDATA[IntroductionIn today’s 24/7 society, circadian misalignment caused by environmental and lifestyle factors is associated with various adverse health consequences. Understanding tissue-specific pathology is required to counter this growing public health challenge. A potential association of environmental circadian misalignment with sarcopenia, or accelerated loss of skeletal muscle strength and mass, is poorly documented.Methods14-week-old wild-type C57BL/6J male mice were exposed to a chronic jet lag (CJL) paradigm consisting of an 8-h phase advance every 4 days (the ADV group) or a fixed light-dark cycle (the LD group) for 64 weeks. Grip strength was measured during the experiment, and hindlimb muscle weight was assessed after the 64-week CJL. In addition, transcriptomic and histological analysis of the hindlimb muscles were performed in all animals.ResultsADV mice exhibited significant reductions in grip strength and muscle weight relative to LD mice. Transcriptomic and histological analyses showed activation of TWEAK/Fn14 signaling and reduced myofiber cross-sectional area, hallmark features of sarcopenia, in the ADV group. Somewhat surprisingly, ADV mice showed increased centrally nucleated fibers, myosin heavy chain co-expressing fibers, and myogenic gene expression, suggesting that compensatory muscle regeneration and remodeling processes are activated but remain insufficient to counter muscle atrophy.ConclusionThese findings demonstrate that circadian misalignment is a potential risk factor for sarcopenia, underscoring circadian rhythms as a key regulator and actionable target for sarcopenia prevention.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2025.1591728</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2025.1591728</link>
        <title><![CDATA[Maximizing performance in child footballers: chronotype and time of day study]]></title>
        <pubdate>2025-10-17T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Ilknur Kaba</author><author>Baha Engin Çelikel</author><author>Oğuzhan Adanur</author><author>Coşkun Yılmaz</author><author>Süreyya Yonca Sezer</author><author>Çetin Tan</author><author>Tebessüm Ayyıldız Durhan</author><author>Uğur Özer</author><author>Tülay Ceylan</author>
        <description><![CDATA[BackgroundA limited number of studies have investigated the effects of circadian rhythm-based running exercise interventions on physical fitness in child athletes. This study aimed to investigate the effects of an eight-week morning and evening running program on lower extremity strength, agility and respiratory function in 10–12-year-old male footballers.MethodsParticipants visited the laboratory three times, with one-day intervals before and after the training program. The assessments included maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP), forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and the FEV1/FVC ratio. Additionally, agility and functional performance tests (FPTs) were conducted for both the dominant and non-dominant legs.ResultsThe findings indicated that morning running was more effective than evening running in enhancing respiratory function. Morning running also showed superior results in lower extremity strength tests, particularly in the single-leg (SL) and triple-leg (THD) crossover hop for distance tests (CHDs) and the 6-m timed-hop test (6 m THT). Furthermore, the agility performance of the morning running group was significantly better than that of the evening and control groups.ConclusionConsequently, morning running interventions had a positive impact on key physical fitness parameters, including respiratory muscle strength, respiratory function, agility, and lower extremity strength in child footballers.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2025.1638819</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2025.1638819</link>
        <title><![CDATA[Sleep behaviors modify the association between hemoglobin concentration and respiratory infection: a prospective cohort analysis]]></title>
        <pubdate>2025-09-30T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Yongkui Zhu</author><author>Qian Chen</author><author>Mengying Wang</author><author>Huan Qian</author><author>Qiying Song</author><author>Bofei Liu</author>
        <description><![CDATA[InterpretationHb and respiratory infection showed a nonlinear U-shaped association; such a relation is modified by the chronotype sleep behavior.ObjectiveTo examine the association between Hb and the incidence of hospitalized respiratory infection, and to explore potential modification effects of sleep behaviors.MethodsIncluded were 292,568 individuals without respiratory disease, cancer, or anemia diagnosis in the United Kingdom Biobank . Hb (g/dL) was measured at baseline. The interaction between Hb and sleep behaviors, including sleep duration, insomnia, chronotype, and daytime sleepiness with respiratory infection, was tested.ResultsThe cohort was followed up at a median 12.6 years, and 16,669 incident respiratory infections (9,334 in men, 7,335 in women) were identified. There was a nonlinear U-shaped association between Hb and respiratory infection in both men and women, where the risk increased markedly with Hb above 15.0 g/dL for men and 13.5 g/dL for women. In men, compared with the third quintile group, the hazard ratio (HR; 95% confidence interval [CI]) of respiratory infection in the Q1, Q2, Q4, and Q5 quintile groups was 1.28 (1.21–1.37), 1.07 (1.00–1.14), 1.06 (0.99–1.13), and 1.09 (1.02–1.17), respectively. In women, the HR (95% CI) was 1.20 (1.12–1.29), 1.09 (1.01–1.17), 1.01 (0.94–1.09), and 1.05 (0.98–1.13) in the Q1, Q2, Q4, and Q5 quintile groups of Hb, respectively, compared with the third quintile group. There was a significant interaction between Hb concentration and chronotype on the risk of respiratory infection (P for interaction = 0.005). The elevated risk of respiratory infection associated with Hb was more pronounced among participants with late chronotype.ConclusionThe study suggests that Hb and respiratory infection have a nonlinear U-shaped association and that such a relation is modified by chronotype.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2025.1642386</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2025.1642386</link>
        <title><![CDATA[Knockdown of Mct1 in the arcuate nucleus increases food-anticipatory activity in mice]]></title>
        <pubdate>2025-09-26T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Tomaz Martini</author><author>Urs Albrecht</author>
        <description><![CDATA[Animals rely on internal time-keeping mechanisms to anticipate regular events such as feeding, allowing preemptive gene expression which enables timely physiological responses. A manifestation of anticipatory mechanisms is also a rise in body temperature and activity before a predictable mealtime. The activity, which resembles food seeking, depends on the communication between peripheral organs and the brain. The liver plays a central role by producing metabolic signals, including beta-hydroxybutyrate, which is released into the blood in anticipation of feeding. This release is controlled by the transporter MCT1, and its hepatic ablation in mice impairs food-anticipatory activity (FAA). However, in parallel, loss of MCT1 in the arcuate nucleus, a brain nucleus that orchestrates feeding behaviour, was implicated in increased food intake, creating a paradox. Here, we demonstrate that MCT1’s role in feeding behavior is tissue dependent, and that while hepatic and systemic disruption of Mct1 impair FAA, arcuate nucleus Mct1 knockdown increases FAA. This underscores the complexity of small molecule signalling in metabolism, of which MCT1 is merely a transporter, and whose actions are ligand, and hence context and tissue dependent.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2025.1610790</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2025.1610790</link>
        <title><![CDATA[The effect of time of day on anaerobic performance and blood lactate response in trained men: assessment in relation to chronotype]]></title>
        <pubdate>2025-08-20T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Yakup Köse</author><author>Mehmet Ulaş</author><author>Emrah Atay</author><author>Hilal Ertürk Yaşar</author>
        <description><![CDATA[This study examined the effects of the time of day on anaerobic performance and blood lactate levels in 20 trained male athletes with intermediate type (IT) and close to evening type (CET) chronotypes. The athletes completed vertical jump and repeated sprint ability (6 × 20 m) tests at three different times (07:00-08:00 h, 13:00-14:00 h, and 18:00-19:00 h). Blood lactate levels were measured at baseline, post-RSA (3 min), and post-RSA (33 min). Results showed that peak power [F (2,36) = 18.437, p = 0.001, η2p = 0.506] and average power [F (2,36) = 25.677, p = 0.001, η2p = 0.588] for vertical jumps -hands on hips- [F (2,36) = 15.683, p = 0.001, η2p = 0.466] and hands-free [F (2, 36) = 11.200, p = 0.001, η2p = 0.427] and repeated sprint ability (6 × 20 mt) tests were significantly higher in the evening and afternoon compared to the morning, consistent with previous findings on circadian effects on neuromuscular function. Additionally, regardless of chronotype, significantly higher lactate accumulation was reported in the afternoon and evening hours compared to the morning hours at peak lactate levels at 3 min post-RSA [F (2,38) = 16.62, p = 0.001, η2p = 0.474]. Regarding recovery (33rd m) lactate levels, CET individuals showed significantly better lactate clearance in the evening compared to the morning and afternoon hours [F (2,36) = 7.125, p = 0.002, η2p = 0.284]. In contrast, IT individuals did not show time-dependent differences in recovery. These findings highlight the role of circadian rhythms in anaerobic performance and metabolic responses. Differences in lactate accumulation and clearance suggest that time of day and chronotype should be considered when designing training and recovery strategies.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2025.1619673</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2025.1619673</link>
        <title><![CDATA[Prokineticin 2 neurons form diverse subpopulations in the suprachiasmatic nucleus and rely on VPAC2-signaling for diurnal rhythmicity]]></title>
        <pubdate>2025-07-15T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Ida Stangerup</author><author>Birgitte Georg</author><author>Jens Hannibal</author>
        <description><![CDATA[IntroductionProkineticin 2 (PK2) is believed to function as an output molecule, relaying circadian rhythms of behavior and physiology from the suprachiasmatic nucleus (SCN). The expression of PK2 in the SCN is primarily driven by the molecular clock, oscillating with high levels early-mid day and low levels during night. Furthermore, light at night induces the expression of PK2. Until recently, the absence of a reliable PK2 antibody has hindered characterization of PK2 neurons in the SCN, including whether they constitute a phenotypically homogeneous population or comprise distinct subtypes, some potentially light-responsive. Hence, the aim of this study was to characterize PK2 neurons in relations to light-responsiveness and neuropeptidergic markers of the core-shell division.MethodsDouble and triple immunohistochemistry of PK2 together with phenotypical neuropeptide/receptor markers of the core-shell division was performed at zeitgeber time (ZT) 8. Light-responsiveness of PK2 SCN neurons was evaluated using FOS and EGR1 ZT18, 2 h following a 30-min light-pulse stimulation. Data were visualized and processed using confocal microscopy. Moreover, PK2 mRNA was evaluated over a 12:12 light-dark cycle in both wildtype and VIP type 2 receptor (VPAC2) knockouts mice, using qPCR.ResultsThe majority of PK2 neurons were located in the shell, constituting a subpopulation of vasopressin (AVP) and neuromedin S (NMS) neurons. Few PK2 neurons were found in the ventral core, constituting a subpopulation of vasoactive intestinal polypeptide (VIP) and NMS neurons. PK2 shell neurons expressed the VPAC2 receptor, and in its absence, diurnal rhythmicity of PK2 mRNA was abolished. In addition, the PAC1 receptor—specific for pituitary adenylate cyclase-activating polypeptide (PACAP), one of two neurotransmitters of the retinohypothalamic tract—was found on some PK2 neurons. Moreover, nighttime light-pulse stimulation broadly induced FOS and EGR1 immunoreactivity throughout the SCN but only in few PK2 neurons.ConclusionPK2 SCN neurons are heterogeneous yet highly dependent on intact VIP-VPAC2 signaling to maintain a coherent diurnal expression pattern. A neuroanatomical and functional basis suggest two potential pathways for regulating PK2 expression: a diurnal mechanism involving VIP signaling through the VPAC2 receptor and a direct light-mediated pathway via retinal innervation through the PAC1 receptor.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2025.1595057</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2025.1595057</link>
        <title><![CDATA[The modulatory role of short-chain fatty acids on peripheral circadian gene expression: a systematic review]]></title>
        <pubdate>2025-07-14T00:00:00Z</pubdate>
        <category>Systematic Review</category>
        <author>Adriano dos Santos</author><author>Andrii Vasylyshyn</author>
        <description><![CDATA[Circadian rhythm disruption significantly impacts health and causes a wide range of metabolic, cardiovascular, and psychiatric disorders. Changes in peripheral circadian clock expression are associated with the gut microbiome, particularly via the activity of short-chain fatty acids (SCFAs). The objective of this review is to explore the association between SCFA levels and peripheral circadian gene expression. This review was performed according to PRISMA guidelines. In total, eight studies were included after the PubMed database search and screening process based on inclusion and exclusion criteria. Risk of bias assessment was conducted using the SYRCLE and RoB 2 tools for animal and human studies, respectively. The results showed that propionate, acetate, and butyrate levels correlated with the expression of PER1, PER2, BMAL1, CRY1, and CRY2 in peripheral tissues, including the submandibular gland, liver, kidney, and blood serum. These findings suggest that SCFA supplementation may offer therapeutic potential for individuals with circadian misalignment, such as shift workers or patients with metabolic disorders. Although there was methodological variability among the included studies, it did not significantly compromise the overall quality of the review. The limited availability of human studies (n = 1) represents a significant constraint. Nevertheless, the findings support that SCFA supplementation may serve as a potential strategy for peripheral clock modulation. However, further human trials are needed to validate these findings in clinical settings.Systematic Review Registration:https://osf.io/6kd5q.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2025.1622236</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2025.1622236</link>
        <title><![CDATA[Circadian influences on central nervous system barriers and the glymphatic system]]></title>
        <pubdate>2025-06-23T00:00:00Z</pubdate>
        <category>Review</category>
        <author>Brittany D. Elliott</author><author>Claire O. Kisamore</author><author>Randy J. Nelson</author><author>A. Courtney DeVries</author><author>William H. Walker</author>
        <description><![CDATA[The central nervous system (CNS), comprising the brain and spinal cord, is fortified by complex barriers that protect the underlying organs and maintain homeostasis. The importance of proper fortification and homeostatic regulation provided by these systems has broad implications for many physiological processes and several pathological conditions are associated with their disruption. Recent studies support the notion that CNS barriers and fluids are regulated by circadian rhythms. Whereas reciprocal associations between the structural and functional integrity of neural barriers and disease states are well-established, the role of circadian rhythms in mediating these relationships remains unspecified. The goals of this review are to provide a general overview of three primary systems responsible for maintaining CNS homeostasis, namely the blood-brain barrier, blood-cerebrospinal fluid barrier, and glymphatic system, and to synthesize recent evidence highlighting the role of circadian rhythms as a critical regulator of CNS fluid and barrier function.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2025.1574757</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2025.1574757</link>
        <title><![CDATA[Morning vs. evening: the role of exercise timing in enhancing fat oxidation in young men]]></title>
        <pubdate>2025-04-23T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Hao Lan</author><author>Kaibin Wu</author><author>Chunyun Deng</author><author>Songtao Wang</author>
        <description><![CDATA[ObjectiveThis study aimed to investigate the acute effects of exercise timing (morning vs. evening) on fat oxidation and energy expenditure in young men, with a focus on interactions between exercise and meal timing.MethodsEighteen male college students (23.47 ± 2.11 years) completed a randomized crossover trial under five conditions: sedentary control (SC), exercise before breakfast (EBB), exercise after breakfast (EAB), exercise before dinner (EBD), and exercise after dinner (EAD). Indirect calorimetry (COSMED K5) measured substrate utilization during exercise, post-exercise recovery (0–4 h), and the following morning. Total exercise volume (running distance) was standardized, and energy expenditure was normalized to body weight (kcal/kg).ResultsDuring the sedentary control test, participants showed similar trends in total energy expenditure. Dring exercise, the EBB group demonstrated significantly higher fat expenditure compared to EAB (P < 0.05), EBD (P < 0.01), and EAD (P < 0.01). Morning exercise overall exhibited superior fat oxidation (P < 0.01). Post-exercise (0–4 h), EBB sustained elevated fat utilization (P < 0.01 vs. EBD/EAD), while EAD showed enhanced fat oxidation the following morning (P < 0.01 vs. EAB).ConclusionThe findings suggest that exercise timing may influence temporal patterns of fat oxidation, with morning fasting potentially favoring acute lipid utilization, while evening exercise appears to correlate with delayed metabolic adjustments. Although total energy expenditure remained comparable across conditions, the observed shifts in substrate allocation imply a possible circadian-sensitive modulation of energy partitioning. These preliminary observations underscore the need for further investigation to clarify the long-term physiological relevance of such timing-dependent metabolic responses.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2025.1589740</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2025.1589740</link>
        <title><![CDATA[The effect of time of day on visual reaction time performance in boxers: evaluation in terms of chronotype]]></title>
        <pubdate>2025-04-16T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Kemal Kurak</author><author>İsmail İlbak</author><author>Stefan Stojanović</author><author>Ramazan Bayer</author><author>Yunus Emre İlbak</author><author>Krzysztof Kasicki</author><author>Tadeusz Ambroży</author><author>Łukasz Rydzik</author><author>Wojciech Czarny</author>
        <description><![CDATA[IntroductionConsidering the impact of individual differences on athletes’ performance, chronotype emerges as a crucial variable in training program design. Chronotype influences an individual’s ability to achieve peak physical and cognitive performance at different times of the day based on their biological rhythms. While numerous studies have explored the relationship between chronotype and physical performance, its effect on reaction time performance remains insufficiently investigated. In sports, where reaction time is a key determinant—such as in boxing—understanding this relationship could contribute to the personalization of training programs. Therefore, the aim of this cross-sectional study was to examine how the visual reaction performance of active boxers varies at different times of the day based on their chronotypes.MethodsTwenty-four active boxers participated in the study. Their chronotypes were determined using the Morningness-Eveningness Questionnaire, categorizing them as either morning type (M-type) or evening type (E-type). The participants were divided into two groups: M-type (n = 12) and E-type (n = 12). Each participant completed a visual reaction time (VRT) performance test at three different times of the day: morning (09:00 h), afternoon (13:00 h), and evening (17:00 h).ResultsThe findings revealed a statistically significant group × time interaction effect on VRT performance (p < 0.01). M-type athletes showed a significant decline in VRT performance during the evening compared to the morning and afternoon. In contrast, E-type athletes demonstrated significantly better performance in the evening compared to the morning.ConclusionsBoxers’ visual reaction time performance varies throughout the day depending on their chronotype. These results suggest that coaches and exercise specialists should consider athletes’ chronotypes when designing training programs focused on reaction time enhancement. To optimize performance, it is recommended that M-type athletes conduct such training sessions in the morning, while E-type athletes should train in the evening, when their reaction time performance tends to peak.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2025.1535331</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2025.1535331</link>
        <title><![CDATA[Heart rate variability with circadian rhythm removed achieved high accuracy for stress assessment across all times throughout the day]]></title>
        <pubdate>2025-04-14T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Yafei Shen</author><author>Zihan Fang</author><author>Tao Zhang</author><author>Feng Yu</author><author>Ying Xu</author><author>Ling Yang</author>
        <description><![CDATA[BackgroundAssessing real-time stress in individuals to prevent the accumulation of stress is necessary due to the adverse effects of excessive psychological stress on health. Since both stress and circadian rhythms affect the excitability of the nervous system, the influence of circadian rhythms needs to be considered during stress assessment. Most studies train classifiers using physiological data collected during fixed short time periods, overlooking the assessment of stress levels at other times.MethodsIn this work, we propose a method for training a classifier capable of identifying stress and resting states throughout the day, based on 10 short-term heart rate variability (HRV) feature data obtained from morning, noon, and evening. To characterize the circadian rhythms of HRV features, heartbeat interval data were collected and analyzed from 50 volunteers over three consecutive days. The circadian rhythm trends in the HRV features were then removed using the Smoothness Priors Approach (SPA), and XGBoost models were trained to assess stress.ResultsThe results show that all HRV features exhibit 12-h and 24-h circadian rhythms, and the circadian rhythm differences across different days for individuals are relatively small. Furthermore, training classifiers on detrended data can improve the overall accuracy of stress assessment across all time periods. Specifically, when combining data from different time periods as the training dataset, the accuracy of the classifier trained on detrended data increases by 13.67%.DiscussionThese findings indicate that using HRV features with circadian rhythm trends removed is an effective method for assessing stress at all times throughout the day.]]></description>
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        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2025.1553736</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2025.1553736</link>
        <title><![CDATA[Circadian system coordination: new perspectives beyond classical models]]></title>
        <pubdate>2025-03-12T00:00:00Z</pubdate>
        <category>Review</category>
        <author>Ovidiu Constantin Baltatu</author><author>Luciana Aparecida Campos</author><author>José Cipolla-Neto</author>
        <description><![CDATA[BackgroundThis review examines novel interaction mechanisms contributing to the robustness of circadian rhythms, focusing on enhanced communication between the suprachiasmatic nucleus (SCN) and peripheral clocks. While classical models explain biological clocks through molecular interactions and biochemical signaling, they incompletely account for several key features: precision maintenance despite cellular noise, rapid system-wide synchronization, and temperature compensation. We propose that the SCN, acting as a central hub, may utilize non-classical mechanisms to maintain robust synchronization of peripheral clocks, contributing to biological timekeeping stability. The clinical implications of this model are significant, potentially offering new approaches for treating circadian-related disorders through quantum-based interventions. Recent advances in quantum biosensors and diagnostic tools show promise for early detection and monitoring of circadian disruptions, while quantum-based therapeutic strategies may provide novel treatments for conditions ranging from sleep disorders to metabolic syndromes.Aim of reviewTo evaluate classical models of circadian rhythm robustness and propose a novel synchronization model incorporating quantum mechanical principles, supported by recent advances in quantum biology and chronobiology, with emphasis on potential clinical applications.Key scientific conceptsRecent research in quantum biology suggests potential mechanisms for enhanced circadian system coordination. The proposed model explores how quantum effects, including entanglement and coherence, may facilitate rapid system-wide synchronization and temporal coherence across tissues. These mechanisms could explain features not fully addressed by classical models: precision maintenance in noisy cellular environments, rapid resynchronization following environmental changes, temperature compensation of circadian periods, and sensitivity to weak electromagnetic fields. The framework integrates established chronobiology with quantum biological principles to explain system-wide temporal coordination and suggests new therapeutic approaches for circadian-related disorders.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2024.1504879</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2024.1504879</link>
        <title><![CDATA[Re-scoping ultradian rhythms in the context of metabolism]]></title>
        <pubdate>2024-12-12T00:00:00Z</pubdate>
        <category>Opinion</category>
        <author>Daan R. van der Veen</author><author>Menno P. Gerkema</author>
        <description><![CDATA[Rapid, ultradian biological rhythms are only partly comparable to circadian (24-h) rhythms. Often, the ensuing expectations from this comparison are that 1) ultradian rhythms should be driven by discrete oscillators, 2) they are biochemically buffered, and 3) they must be functionally linked to extrinsic events and cycles. These three expectations are not always met, but perhaps there is an adaptive benefit to ultradian rhythms not meeting these expectations, which sets them functionally apart from circadian rhythms. In view of the extensive descriptions of the manifold types of ultradian rhythms across all biological levels (e.g., see papers in this research topic), it seems important to ask whether we should actively create a new set of definitions and expectations. To make a start, we here lay out some important questions we need to ask about ultradian rhythms. We then illustrate how these questions highlight one key area of exploration: the linked expression of ultradian rhythms in metabolism and behaviour and the role this plays in addressing a negative energy balance.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2024.1323127</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2024.1323127</link>
        <title><![CDATA[The interplay among sleep patterns, social habits, and environmental cues: insights from the Spanish population and implications for aligning daily rhythms]]></title>
        <pubdate>2024-10-25T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>María-Ángeles Bonmatí-Carrión</author><author>Jesús Vicente-Martínez</author><author>Juan Antonio Madrid</author><author>Maria Angeles Rol</author>
        <description><![CDATA[IntroductionThe interplay among sleep patterns, social habits and environmental cues is becoming increasingly more important for public health and wellbeing due to its connection to circadian desynchronization. This paper explores said connections in Spain (which has an official and solar time mismatch), introducing the “Three Times Score” ‒which is based on questions widely used in the field‒ as a complementary tool for exploring the interplay of daily rhythms.MethodsThe questionnaire covers sleep-related habits, social time, and environmental time. The study includes 9,947 participants (34.89 ± 12.15 y/o, mean ± SD; 5,561 women) from different Spanish regions. Sleep parameters were obtained for work and free days, as well as a modified version of the sleep-corrected midsleep on free days (MBFbc) and a parameter similar to social jet lag, both derived from bed time rather than sleep time. A number of indexes were computed to compare bed and work-related habits, together with natural light/dark cycle, along with the Three Times Score. Mixed-effect regression analysis was used to test whether the biological, social and environmental factors included in the study significantly predicted the sleep-related parameters: bedtime, wake-up time, time in bed and mid-bedtime.Results and discussionTemporal differences were found between work and free days, with waking-up occurring 2 h earlier on work days (7:10 ± 0:01) than on free days (9:15 ± 0:01). Bed times were 1 h earlier on work days (23:46 ± 0:01) than on free days (00:45 ± 0:01), whereas time in bed was over 1 h shorter on work (7 h 23 min) versus free (8 h 29 min) days. Strong correlations were found between work starting time and waking-up and bedtimes on workdays. Women went to bed earlier and woke up later, spending more time in bed. Differences in sleep habits were observed between work and free days across all age groups. The group of younger adults (18–30) reported going to bed later than older and younger groups, especially on free days. Adolescents and young adults also woke-up later than other age groups, especially on free days. Social jet lag (relative to bed time) and desynchronization indexes also varied with age, with younger adult participants exhibiting higher levels. Seasonal differences were limited, with minor variations between winter and summer. According to the multiple regression analysis, social (day type, work start time, alarm clock usage), biological (age, gender, in most cases related to sex) and environmental (sunset time) factors significantly contribute to predicting sleep/bed related schedules. This study provides insights into sleep habits in the Spanish population, introducing the Three Times Score as a complementary tool for exploring the interactions between sleep/bed-related habits, natural darkness and work-related schedules. Understanding this interplay is crucial for developing tailored interventions to improve sleep and wellbeing.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2024.1435848</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2024.1435848</link>
        <title><![CDATA[Effect of circadian clock disruption on type 2 diabetes]]></title>
        <pubdate>2024-08-06T00:00:00Z</pubdate>
        <category>Mini Review</category>
        <author>Hong Thuan Tran</author><author>Takeru Kondo</author><author>Amal Ashry</author><author>Yunyu Fu</author><author>Hiroko Okawa</author><author>Chenphop Sawangmake</author><author>Hiroshi Egusa</author>
        <description><![CDATA[IntroductionType 2 diabetes (T2D) is the predominant form of diabetes mellitus and is among the leading causes of death with an increasing prevalence worldwide. However, the pathological mechanism underlying T2D remains complex and unclear. An increasing number of studies have suggested an association between circadian clock disruption and high T2D prevalence.MethodThis review explores the physiological and genetic evidence underlying T2D symptoms associated with circadian clock disturbances, including insulin secretion and glucose metabolism.Results and DiscussionNotably, circadian clock disruption reduces insulin secretion and insulin sensitivity and negatively affects glucose homeostasis. The circadian clock regulates the hypothalamic–pituitary–adrenal axis, an important factor that regulates glucose metabolism and influences T2D progression. Therefore, circadian clock regulation is an attractive, novel therapeutic approach for T2D, and various circadian clock stabilizers play therapeutic roles in T2D. Lastly, this review suggests novel therapeutic and preventive approaches using circadian clock regulators for T2D.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/fphys.2024.1466152</guid>
        <link>https://www.frontiersin.org/articles/10.3389/fphys.2024.1466152</link>
        <title><![CDATA[Editorial: Circadian rhythm, athletic performance, and physical activity]]></title>
        <pubdate>2024-07-31T00:00:00Z</pubdate>
        <category>Editorial</category>
        <author>Lucia Castelli</author><author>Jamie Hugo Macdonald</author><author>Pasquale Fabio Innominato</author><author>Letizia Galasso</author>
        <description></description>
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