Heart Rate Variability in Sport Performance: Do Time of Day and Chronotype Play A Role?

Test-retest reliability of exercise blood pressure and the workload-indexed systolic blood pressure slope in healthy males and females

The reliability of blood pressure (BP) measured during submaximal and maximal exercise, and confounding effects of biological sex, remain to be fully established but have implications for using exercise BP as a cardiovascular risk factor. We hypothesize that exercise BP test-retest reliability will not differ between sexes but will be higher during submaximal compared to maximal exercise. Eighty-four participants (22 ± 5 yr; 36 females) completed two maximal treadmill tests (modified Bruce protocol) separated by ≥2 days. Exercise BP was measured every 90 s using automated auscultation (Tango M2 monitor). Breath-by-breath oxygen uptake was analyzed. Test-retest reliability was assessed using two-way, mixed-effects, consistency, single-rater intraclass correlation coefficient (ICC) analysis on the total group and separated by sex at submaximal and maximal exercise. Systolic BP during submaximal (ICC = 0.65 [0.49-0.76], P < 0.01) and maximal (ICC = 0.66 [0.52-0.77], P < 0.01) exercise both displayed substantial reliability between visits. In contrast, the SBP/MET slope showed poor submaximal (ICC = 0.12 [-0.09-0.33], P = 0.13) but substantial maximal (ICC = 0.63 [0.48-0.75], P < 0.01) exercise reliability. Females showed substantial reliability in submaximal systolic BP (ICC = 0.73 [0.53-0.85], P < 0.01) and peak systolic BP (ICC = 0.74 [0.54-0.87], P < 0.01) and SBP/MET slope (ICC = 0.78 [0.60-0.88], P < 0.01); the submaximal SBP/MET slope had fair reliability (ICC = 0.28 [-0.06-0.56], P = 0.05). Males showed moderate reliability in submaximal systolic BP (ICC = 0.53 [0.26-0.72], P < 0.01) and peak systolic BP (ICC = 0.41 [0.15-0.62], P < 0.01) and SBP/MET slope (ICC = 0.48 [0.22-0.67], P < 0.01); the submaximal SBP/MET slope had poor reliability (ICC = 0.06 [-0.18-0.31], P = 0.32). Systolic BP showed similar reliability during submaximal and maximal exercise, with females demonstrating higher reliability in exercise systolic BP compared to males.NEW & NOTEWORTHY Limited work has assessed the reliability of exercise blood pressure (BP) in young healthy males and females. Our results demonstrate that systolic BP test-retest reliability did not differ between submaximal and maximal exercise. Sex-specific analysis found that females had higher reliability in exercise systolic BP than males. Despite the acceptable average reliability, exercise BP measured using automated auscultation possesses wide confidence intervals, which impact sample size requirements in future trials.

The relationship between cardiac activity, behaviour and endogenous oxytocin and vasopressin in Prader-Willi Syndrome: An exploratory study

This study aimed to increase our understanding of cardiac activity abnormalities in Prader-Willi Syndrome (PWS) and the relationship between cardiac activity, PWS behaviours thought to be associated with cardiac vagal tone and endogenous oxytocin and vasopressin levels. We compared cardiac activity (respiratory sinus arrhythmia (RSA), low-frequency heart rate variability (LF-HRV), heart period) in 30 adolescents and adults with PWS to 30 typically developing age-matched controls. RSA, LF-HRV, and heart period were lower in individuals with PWS than in the control group. In the control group, RSA was higher for females than males. However, for those with PWS, there was no difference between the sexes. Individuals with the mUPD genetic subtype had lower RSA and LF-HRV than participants with the PWS deletion subtype and compared to typically developing controls, no difference was found between the latter two groups. Heart period was also lower for those with mUPD compared to controls. Higher RSA reduced the odds of having temper outbursts and skin-picking. RSA was lower in those with PWS and psychosis compared to those with PWS without psychosis. Finally, we found RSA correlated with vasopressin for those with mUPD but not deletion. There was no relationship between RSA and oxytocin plasma or saliva levels. Our findings suggest autonomic dysfunction in PWS that is more marked in mUPD than deletion and potentially due to greater loss of parasympathetic activity in mUPD.

Relevance of high glycaemic index breakfast for heart rate variability among collegiate students with early and late chronotypes

Plasma glucose spikes affect cardiac autonomic modulation resulting in a decrease of heart rate variability (HRV). We hypothesize that a later chronotype or a higher morning plasma melatonin level is associated with larger decreases of HRV following an early high glycaemic index (GI) breakfast. In persons with an early (n = 21) or a late (n = 15) chronotype who consumed a high GI breakfast at 7 a.m. glucose data were continuously monitored. Time domain HRV parameters were calculated from blood volume pulses derived by wireless wrist worn multisensor. HRV changes (values after minus values before breakfast) were associated with chronotype by multivariable linear regression adjusted for age, sex and baseline levels. Morning plasma melatonin levels were determined from samples drawn on the run-in day. Time domain parameters indicate a higher HRV before high GI breakfast in both chronotypes. A later chronotype tended to be associated with smaller decreases of mean interbeat intervals (p = 0.08) only; no associations were seen with morning melatonin levels. This exploratory analysis in a small sample provides a first indication that in young healthy adults later chronotype might be associated with reduced ANS activation following a high GI breakfast. Future studies should elucidate whether this indicates parasympathetic or sympathetic inhibition.

Combined effects of a Mediterranean diet and respiratory muscle training on higher education woodwind musicians: A randomized controlled trial

A two-factor within subjects and randomized controlled was conducted with three groups (two experimental and one control) to explore the effects of the Mediterranean diet and respiratory muscle training on ventilatory fatigue, stress, and emotional performance of woodwind musicians. 70 students from the Valencia Conservatory of Music were recruited and randomized into three groups: respiratory training group + nutrition program (RTG; n = 17), control group (CG; n = 35) and nutrition program group (NPG; n = 18). The nutritional program was based on Mediterranean a diet. Body composition, emotional intelligence, physiological stress and ventilatory response were assessed for all groups before and after intervention. Mixed ANOVA showed main effects of diet and training interventions on emotional attention (F = 8.042; p = 0.006), clarity (F = 9.306; p = 0.003), repair (F = 5.527; p = 0.022), Forced-Expiratory-Volume (F = 30.196; p < 0.000) and Forced-Vital-Capacity (F = 21.052; p < 0.000), with both interventions improving emotional intelligence and ventilatory variables. Bonferroni post-hoc analysis revealed significant differences of RTG and CG for emotional attention (MD = 4.60; p = 0.023), comprehension (MD = 5.734; p = 0.005), repair (MD = 8.576; p < 0.000), FEV1 (MD = 0.862; p = 0.005), and FCV (MD = 1.608; p < 0.001); with similar results when comparing NTG and CG: emotional attention (MD = 4.156; p = 0.041), comprehension (MD = 4.473; p = 0.033), repair (MD = 6.511; p = 0.001), Forced-Expiratory-Volume (MD = 1.608; p < 0.001), and Forced-Vital-Capacity (MD = 1.183; p < 0.001). No significant effects of experimental groups were observed for physiological stress variables (p > 0.05). This results suggests that respiratory training enhances emotional intelligence and lessens respiratory fatigue in musicians, and a combination of a Mediterranean diet and respiratory muscle training further boosts emotional intelligence, albeit with limited impact on physiological stress. This study represents a novel investigation into the approach by dietary interventions and respiratory muscle training in wind musicians since there are no studies that analyze it.

Heart rate variability measurement and influencing factors: Towards the standardization of methodology

Heart rate variability (HRV) is widely recognized as an effective and valuable tool for evaluating cardiac autonomic modulation. However, various factors can influence HRV before and during assessment, complicating the interpretation and comparability of results. This review outlines the different factors affecting HRV and underscores the importance of considering them to ensure consistent and reliable HRV outcomes. Key influencing factors are categorized into physiological (e.g., age, gender, genetics), lifestyle (e.g., physical activity, alcohol use, smoking, drugs, diet), environmental (e.g., time of day, temperature, noise), and methodological (e.g., body position, recording duration, and respiration) domains. Knowing these factors can help researchers and physicians gain a better understanding of HRV and improve the interpretation of their findings. Consequently, this can lead to the development of standardized methods for consistently assessing and interpreting HRV measures in clinical practice.

Effects of chronotype on sleep, mood and cardiovascular circadian rhythms in rotating night shift medical workers

PURPOSE

Whether chronotype affects the health outcomes of night shift work populations is unknown. This study aimed to assess the influence of different chronotypes in the rotating night shift population on sleep status, mood, blood pressure (BP), and heart rate variability (HRV), as well as the circadian rhythm of BP and HRV.

METHODS

A total of 208 rotating night shift workers were included. All participants completed structured questionnaires to assess chronotype, mood and sleep status. During their daily lives outside of the night shift, they underwent 24-hour Holter electrocardiogram monitoring and 24-hour ambulatory blood pressure monitoring. Day-time and night-time BP and BP dipping were obtained. Day-time and night-time HRV values (SDNN, RMSSD, LF, HF, LF nu, SD1, SD2 and SD2/SD1) were calculated and fitted to the cosine period curve. Three circandian parameters (mesor, amplitude and acrophase) were extracted to quantify the circadian rhythm of the HRV indices.

RESULTS

Among all three groups, E-type showed more fatigue and sleepiness. In addition, E-type showed blunted diastolic BP dipping. Notably, E-type showed association with higher RMSSD, LF, HF and SD1 in the night time, and higher mesors of RMSSD and LF and amplitude of SD2/SD1 in circadian analysis.

CONCLUSION

Chronotype is a factor affecting fatigue, sleepiness and cardiovascular circadian rhythms of rotating night shift workers. Chronotype should be taken into consideration for managing night-shift rotation to promote occupational health.

High-intensity interval training (HIIT) and slow breathing interventions alleviate premature ejaculation (PE) symptoms

Background

Physical exercise may alleviate premature ejaculation symptoms, a prevalent male sexual dysfunction linked to a series of negative outcomes for men and their partners.

Objective

We investigated the effectiveness of high-intensity interval training (HIIT) and slow breathing interventions on premature ejaculation symptoms and their relation to autonomic activity and attention regulation.

Method

Chinese adult men (N = 76, M = 21.89, SD = 3.32) with premature ejaculation completed one of the two-week interventions in their homes or as participants in a normal breathing control group; they reported their age, height, weight, physical activity level, premature ejaculation symptoms, and attention regulation. In the HIIT group, 26 participants engaged in a 7-minute HIIT each day. In the slow breathing group, 25 participants performed 7-minute slow breathing exercises per day while the 25 participants in the normal breathing group similarly performed normal breathing exercises. All participants measured their heart rate once before and five times (with one-minute intervals) after the intervention. When participants had penile-vaginal sex with their partners, they measured their heart rate once after ejaculation.

Results

Time × Intervention interaction was significant with lower levels of premature ejaculation symptoms on Days 12, 13, and 14 in the HIIT group (M ± SD = 16.19 ± 3.45, 15.96 ± 3.43, and 15.15 ± 3.62) compared to the normal breathing group (M ± SD = 17.68 ± 3.06, 17.68 ± 3.15, and 17.44 ± 3.25). Higher levels of attention regulation were associated with fewer premature ejaculation symptoms. We also found that a larger increase in heart rate from resting to after sex was associated with fewer premature ejaculation symptoms.

Conclusion

Compared to the control group, the efficacy of two weeks of HIIT exercise in mitigating PE symptoms suggests its potential as a novel treatment for PE.

Cerebral Hemodynamics and Vagally Mediated HRV Associated with High- and Low-frequency Yoga Breathing: An Exploratory, Randomized, Crossover Study

Background

Volitionally modifying respiration leads to changes in middle cerebral arterial (MCA) blood flow. The effect of changes in breath rate on MCA blood flow has not been reported.

Aims and Objectives

To determine the effect of slow (bumblebee yoga breathing) and fast (high frequency yoga breathing) yoga breathing techniques on MCA blood flow and vagally mediated heart rate variability.

Materials and Methods

Thirty participants (mean age ± standard deviation, 27.3 ± 4.2 years) were assessed on 2 separate days practicing either high frequency yoga breathing (HFYB, breath frequency 54.2/min) or slow frequency bumblebee yoga breathing (BBYB, breath frequency 3.8/min) in random order to determine the effects of changes in breath frequency on MCA hemodynamics. Assessments included transcranial Doppler sonography, vagally mediated heart rate variability (VmHRV), and respiration.

Results

Both HFYB and BBYB (i) reduced MCA flow velocities, i.e., peak systolic, end diastolic, and mean flow velocities, and (ii) increased MCA pulsatility indices. There was an increase in VmHRV during BBYB based on increased power in high frequency (HF) and low frequency (LF). LF reflects VmHRV for slow breath frequencies. In BBYB the average breath rate was 3.8 breaths/min. In contrast, VmHRV decreased during HFYB (based on reduced HF power; repeated measures analysis of variance, P < 0.05, all cases).

Conclusion

Hence, irrespective of the differences in breath frequency, both HFYB and BBYB appear to reduce MCA flow velocities and increase the resistance to blood flow bilaterally, although the VmHRV changed in opposite directions. MCA velocity and pulsatility changes are speculated to be associated with low global neural activity during yoga breathing.

A 2-week high-intensity interval training intervention improves ejaculation control among men with premature ejaculation

BACKGROUND

Premature ejaculation (PE), which leads to substantial distress in men and their partners, is a common male sexual dysfunction worldwide. However, there is still a lack of effective treatments without side effects.

OBJECTIVES

We investigated the effect of high-intensity interval training (HIIT) on PE symptoms.

MATERIALS AND METHODS

We recruited 92 Chinese men aged 18-36 to complete the experiment. There were 22 (13 in the control group; 9 in the HIIT group) men diagnosed with PE and 70 (41 in the control group; 29 in the HIIT group) men with normal ejaculatory function. In the HIIT group, participants completed HIIT exercises every morning for 14 days. Participants also completed surveys inquiring about demographic information, erectile function, PE symptoms, body image (including sexual body image), physical activity, and sexual desire. The heart rate was measured before and after each HIIT. In the control group, participants were instructed not to do HIIT, but other procedures were the same as in the HIIT group.

RESULTS

Results indicated that the HIIT intervention alleviated PE symptoms in men with PE. In addition, in the HIIT group, men with PE who had a higher heart-rate increase during the HIIT intervention reported the greatest overall decrements in PE symptoms. In men with normal ejaculatory function, HIIT did not decrease PE symptoms. In addition, increments in the heart rate during the intervention were associated with more pronounced PE symptoms post-intervention in this group. Analyses of secondary outcome measures suggested that the HIIT intervention improved general and sexual body image satisfaction of men with PE compared to before the intervention.

DISCUSSION AND CONCLUSION

In summary, HIIT intervention may reduce PE symptoms in men with PE. The heart-rate increase during the intervention may be a key factor influencing the effect of the HIIT intervention on PE symptoms.

Effects of physical exercise interventions on ejaculation control

INTRODUCTION

Premature ejaculation is a prevalent male sexual dysfunction that causes significant distress for men and their partners on a global scale. Despite its widespread impact, effective treatment options without undesirable side effects remain limited.

OBJECTIVES

The present review aimed to provide an overview of experimental studies that analyzed the effects of physical exercise interventions on premature ejaculation.

METHODS

The inclusion criteria for the review included: Population: Adult men. Intervention: An intervention designed to increase physical exercise was delivered in the study. Comparison: Before versus after intervention with or without a comparison group receiving a drug treatment or an active or no control intervention. Outcomes: Self-reported or clinician-rated premature ejaculation or its symptoms. Study type: Experimental designs. We conducted the search process in 9 databases: APA PsycNET, PubMed, Scopus, SPORTDiscus, JSTOR, ScienceDirect, Web of Science, Embase, and CAB Direct. This review included six intervention studies that included 433 participants (307 men with premature ejaculation) ranging from 18 to 50 years of age. All participants had a stable female sexual partner and had not any other physical or mental problems.

RESULTS

The synthesized results indicated that yoga, running, and high-intensity interval training alleviate premature ejaculation symptoms in men with premature ejaculation after varying intervention duration times. The effectiveness of physical exercise for premature ejaculation symptoms was similar to that of drug treatments.

CONCLUSION

Physical exercise can be one of the potential treatment modalities for premature ejaculation. The intensity of physical exercise and the effort of participants during exercise are key factors affecting improvements in ejaculation control. A potential limitation was that the review did not include any literature written in non-English languages.

Time of Day Effects on Anaerobic Performance Using a Nonmotorized Treadmill

ABSTRACT

Renziehausen, JM, Bergquist, AM, Park, J-H, Hill, EC, Wells, AJ, Stout, JR, and Fukuda, DH. Time of day effects on anaerobic performance using a nonmotorized treadmill. J Strength Cond Res 37(10): 2002-2007, 2023-The purpose of this study was to determine the effects of time of day on performance during a maximal effort sprinting assessment (30nmt) and determine potential differences based on chronotype and sex. Twenty-six recreationally active men (n = 12) and women (n = 14) between the ages of 18 and 35 years old (21.5 ± 2.4 years) completed the 30nmt at 9:00 am, 2:00 pm, and 7:00 pm in a randomized order over a 24-hour period. Resting heart rate and temperature assessments were taken at each visit. A dietary recall and the Morningness-Eveningness Questionnaire were used to assess kilocalories (kcals) and chronotype, respectively. Two-way (time x sex) repeated measures analyses of variance were conducted to determine differences in peak/mean power, peak/mean velocity, distance, resting heart rate, temperature, and kcals at each time point. Paired sample t tests were used to assess peak and nadir of each performance variable. A significance level was set at p < 0.05. There was a significant main effect for temperature (p < 0.001), resting heart rate (p = 0.007), and pre-exercise caloric intake (p = 0.021) throughout the day. No significant main effects for time were found for peak power (p = 0.766), mean power (p = 0.094), peak velocity (p = 0.497), mean velocity (p = 0.193), or distance (p = 0.262). There were no significant time × sex interactions for any dependent performance variables (p > 0.05). Significant differences were shown between the peak and nadir of each performance variable (p < 0.001). There were no significant differences in performance during maximal effort anaerobic assessments shown throughout the day; however, peak/nadir of performance times may be individualized and differ between morning types and intermediate types.

Effects of Acute Exercise on Cardiac Autonomic Response and Recovery in Non-Dialysis Chronic Kidney Disease Patients

Purpose: Heart rate variability (HRV) has gained acceptance as a key marker of cardiovascular health. We compared HRV responses after continuous moderate-intensity exercise (CMIE) and high-intensity interval exercise (HIIE) matched for intensity and duration in individuals with midspectrum chronic kidney disease (CKD). Methods: Twenty men and women (age 62.0 ± 10 yrs.) diagnosed with CKD stages G3a and G3b participated in a 2 (condition) x 4 (time point) repeated cross-over measures design study. HRV time-domain indices were based on the standard deviation of all NN intervals (SDNN) and the square root of the mean of the sum of the squares of differences between adjacent NN intervals (RMSSD) and frequency domain. High-frequency (HF), low-frequency (LF), total power (TP) were examined. CMIE consisted of treadmill walking for 30 minutes at a 2% incline and speed corresponding to 60%-65% of reserve volume of oxygen (VO2R). HIIE included five intervals of 3 minutes at 90% of VO2R and 2 minutes at 20% VO2R intervals. Conditions were designed to be of the same average intensity (60% to 65% of VO2R) and caloric expenditure (~144 kcal). Results: Immediately following exercise SDNN, RMSSD, HF, LF, and TP were significantly lower compared to before exercise (p <.05). HRV responses were not different between conditions and conditions X time (p >.05). Conclusions: Thirty minutes of either CMIE or HIIE decreased HRV indices, pointing to an autonomic imbalance favoring vagal mediation. HRV's responses regarding HIIE were no different from CMIE, therefore, from an autonomic function point of view this similarity may be useful for CKD exercise prescription and programming.

Heart rate variability behavior in athletes after a sports concussion: A systematic review

OBJECTIVE

This systematic review aims to investigate the adaptations of the autonomic nervous system (ANS) after a concussion by measuring HRV in athletes over the age of 16 after injury.

METHODS

This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). Web of Science, Pubmed, SCOPUS, and Sport Discus were searched using predefined search terms to identify relevant original cross-sectional, longitudinal, and cohort epidemiological studies published before December 2021.

RESULTS

After screening 1737 potential articles, four studies met the inclusion criteria. Studies included participants with concussion (n = 63) and healthy control athletes (n = 140) who practised different sports. Two studies describe a decrease in HRV following a sports concussion, and one proposed that the resolution of symptoms does not necessarily reflect ANS recovery. Lastly, one study concluded that submaximal exercise induces alteration in ANS, not seen in rest after an injury.

CONCLUSIONS

In the frequency domain, a decrease in high frequency power and an increase of low frequency/high frequency ratio is expected, as the activity of the sympathetic nervous system increases, and the parasympathetic nervous system decreases after injury. In the frequency domain, heart rate variability (HRV) may help monitor the activity of ANS evaluating signals of somatic tissue distress and early identification of other types of musculoskeletal injuries. Further research should investigate the relationship between HRV and other musculoskeletal injuries.

How our hearts beat together: a study on physiological synchronization based on a self-paced joint motor task

Cardiac physiological synchrony is regarded as an important component of social interaction due to its putative role in prosocial behaviour. Yet, the processes underlying physiological synchrony remain unclear. We aim to investigate these processes. 20 dyads (19 men, 21 women, age range 18-35) engaged in a self-paced interpersonal tapping synchronization task under different levels of tapping synchrony due to blocking of sensory communication channels. Applying wavelet transform coherence analysis, significant increases in heart rate synchronization from baseline to task execution were found with no statistically significant difference across conditions. Furthermore, the control analysis, which assessed synchrony between randomly combined dyads of participants showed no difference from the original dyads' synchrony. We showed that interindividual cardiac physiological synchrony during self-paced synchronized finger tapping resulted from a task-related stimulus equally shared by all individuals. We hypothesize that by applying mental effort to the task, individuals changed into a similar mental state, altering their cardiac regulation. This so-called psychophysiological mode provoked more uniform, less variable fluctuation patterns across all individuals leading to similar heart rate coherence independent of subsequent pairings. With this study, we provide new insights into cardiac physiological synchrony and highlight the importance of appropriate study design and control analysis.

Time of Day and Chronotype-Dependent Synchrony Effects Exercise-Induced Reduction in Migraine Load: A Pilot Cross-Over Randomized Trial

Migraines are the most common cause of chronic pain. Effective, non-pharmacological strategies to reduce migraine load, like exercise, are needed, but it is unclear how exercise timing and chronotype modulate the effects. We sought to determine the effects of time-of-day of exercise, and synchrony with one's chronotype, on migraine load. We performed a pilot cross-over randomized trial where participants with chronic migraine completed two one-month exercise interventions, consisting of either morning exercise (before 09:00 a.m.) or evening exercise (after 7:00 p.m.) in a randomized repeated measures cross-over design (Clinical Trial #NCT04553445). Synchrony was determined by exercise time and chronotype (i.e., a morning type participant exercising in the morning is 'in-sync,' while an evening type participant exercising in the morning is 'out-of-sync'). Migraine burden, and anthropometric assessment occurred before and after each month of exercise. Data was analyzed using repeated measures ANOVA with significance accepted at p < 0.05. When comparing morning and evening exercise, there was no significant improvements in any migraine-related parameters. However, when comparing in-sync and out-of-sync exercise, we found that migraine burden was only improved following in-sync exercise, while no benefits were seen in out-of-sync exercise. Our data suggests that exercise timing has limited impact, but synchrony with chronotype may be essential to decrease migraine load in chronic migraineurs.

Effects of neuromodulation on cognitive and emotional responses to psychosocial stressors in healthy humans

Physiological and psychological stressors can exert wide-ranging effects on the human brain and behavior. Research has improved understanding of how the sympatho-adreno-medullary (SAM) and hypothalamic-pituitary-adrenocortical (HPA) axes respond to stressors and the differential responses that occur depending on stressor type. Although the physiological function of SAM and HPA responses is to promote survival and safety, exaggerated psychobiological reactivity can occur in psychiatric disorders. Exaggerated reactivity may occur more for certain types of stressors, specifically, psychosocial stressors. Understanding stressor effects and how the body regulates these responses can provide insight into ways that psychobiological reactivity can be modulated. Non-invasive neuromodulation is one way that responding to stressors may be altered; research into these interventions may provide further insights into the brain circuits that modulate stress reactivity. This review focuses on the effects of acute psychosocial stressors and how neuromodulation might be effective in altering stress reactivity. Although considerable research into stress interventions focuses on treating pathology, it is imperative to first understand these mechanisms in non-clinical populations; therefore, this review will emphasize populations with no known pathology and consider how these results may translate to those with psychiatric pathologies.

Closed-loop acoustic stimulation during an afternoon nap to modulate subsequent encoding

Sleep is able to contribute not only to memory consolidation, but also to post-sleep learning. The notion exists that either synaptic downscaling or another process during sleep increase post-sleep learning capacity. A correlation between augmentation of the sleep slow oscillation and hippocampal activation at encoding support the contribution of sleep to encoding of declarative memories. In the present study, the effect of closed-loop acoustic stimulation during an afternoon nap on post-sleep encoding of two verbal (word pairs, verbal learning and memory test) and non-verbal (figural pairs) tasks and on electroencephalogram during sleep and learning were investigated in young healthy adults (N = 16). Closed-loop acoustic stimulation enhanced slow oscillatory and spindle activity, but did not affect encoding at the group level. Subgroup analyses and comparisons with similar studies lead us to the tentative conclusion that further parameters such as time of day and subjects' cognitive ability influenced responses to closed-loop acoustic stimulation.

Effects of Interrupted Daily Routine Due to COVID-19 on Circadian Chronotype and Leisure Time Physical Activity

Circadian chronotype is dependent on many factors including age, physical activity participation, eating and sleeping patterns, and typical schedule. Recently, the COVID-19 pandemic resulted in schedule changes for most individuals. Therefore, the purpose of this study is to examine whether sport participation influences circadian chronotype and physical activity and whether COVID-19 restrictions have impacted chronotype scores. Briefly, 128 physically active males (n = 62) and females (n = 66) between 18 and 55 years old (24.7 ± 7.1) completed a survey consisting of demographics information, the Morningness−Eveningness Questionnaire (MEQ), and the Godin Leisure Time Physical Activity Scale (LTPA). Participants were asked to answer relevant questions about their habits/preferences before and after COVID-19-related restrictions were implemented. MEQ scores categorized individuals into morning (MT), intermediate (IT), and evening (ET) chronotypes. Three-way (pre-COVID-19 chronotype x sport participation x time) repeated measures ANOVA was conducted to evaluate differences in MEQ and LTPA. A significant main effect of time was found for MEQ (p = 0.018) and LTPA (p = 0.002), indicating changes following COVID-19. A significant time x chronotype interaction was shown for MEQ (p < 0.001) with MT (p < 0.001), IT (p = 0.044), and ET (p = 0.044) individuals indicating chronotype-specific changes following COVID-19. LTPA was decreased and MEQ scores changed following COVID-19, with shifts toward IT scores.

Neurobehavioral Symptoms and Heart Rate Variability: Feasibility of Remote Collection Using Mobile Health Technology

OBJECTIVES

To determine the covariance of heart rate variability (HRV) and self-reported neurobehavioral symptoms after traumatic brain injury (TBI) collected using mobile health (mHealth) technology.

SETTING

Community.

PARTICIPANTS

Adults with lifetime history of TBI (n = 52) and adults with no history of brain injury (n = 12).

DESIGN

Two-week prospective ecological momentary assessment study.

MAIN MEASURES

Behavioral Assessment Screening Tool (BASTmHealth) subscales (Negative Affect, Fatigue, Executive Dysfunction, Substance Abuse, and Impulsivity) measured frequency of neurobehavioral symptoms via a RedCap link sent by text message. Resting HRV (root mean square of successive R-R interval differences) was measured for 5 minutes every morning upon waking using a commercially available heart rate monitor (Polar H10, paired with Elite HRV app).

RESULTS

Data for n = 48 (n = 38 with TBI; n = 10 without TBI) participants were included in covariance analyses, with average cross-correlation coefficients (0-day lag) varying greatly across participants. We found that the presence and direction of the relationship between HRV and neurobehavioral symptoms varied from person to person. Cross-correlation coefficients r ≤ -0.30, observed in 27.1% to 29.2% of participants for Negative Affect, Executive Dysfunction, and Fatigue, 22.9% of participants for Impulsivity, and only 10.4% of participants for Substance Abuse, supported our hypothesis that lower HRV would covary with more frequent symptoms. However, we also found 2.0% to 20.8% of participants had positive cross-correlations (r ≥ 0.30) across all subscales, indicating that higher HRV may sometimes correlate with more neurobehavioral symptoms, and 54.2% to 87.5% had no significant cross-correlations.

CONCLUSIONS

It is generally feasible for community-dwelling adults with and without TBI to use a commercially available wearable device to capture daily HRV measures and to complete a short, electronic self-reported neurobehavioral symptom measure for a 2-week period. The covariance of HRV and neurobehavioral symptoms over time suggests that HRV could be used as a relevant physiological biomarker of neurobehavioral symptoms, though how it would be interpreted and used in practice would vary on a person-by-person and symptom domain basis and requires further study.

Effects of Acute Partial Sleep Deprivation and High-Intensity Interval Exercise on Postprandial Network Interactions

Introduction: High-intensity interval exercise (HIIE) is deemed effective for cardiovascular and autonomic nervous system (ANS) health-related benefits, while ANS disturbance increases the risk for cardiovascular disease (CVD). Postprandial lipemia and acute-partial sleep deprivation (APSD) are considered as CVD risk factors due to their respective changes in ANS. Exercising in the morning hours after APSD and have a high-fat breakfast afterwards may alter the interactions of the cardiovascular, autonomic regulation, and postprandial lipemic systems threatening individuals' health. This study examined postprandial network interactions between autonomic regulation through heart rate variability (HRV) and lipemia via low-density lipoprotein (LDL) cholesterol in response to APSD and HIIE. Methods: Fifteen apparently healthy and habitually good sleepers (age 31 ± 5.2 SD yrs) completed an acute bout of an isocaloric HIIE (in form of 3:2 work-to-rest ratio at 90 and 40% of VO2 reserve) after both a reference sleep (RSX) and 3-3.5 h of acute-partial sleep deprivation (SSX) conditions. HRV time and frequency domains and LDL were evaluated in six and seven time points surrounding sleep and exercise, respectively. To identify postprandial network interactions, we constructed one correlation analysis and one physiological network for each experimental condition. To quantify the interactions within the physiological networks, we also computed the number of links (i.e., number of significant correlations). Results: We observed an irruption of negative links (i.e., negative correlations) between HRV and LDL in the SSX physiological network compared to RSX. Discussion: We recognize that a correlation analysis does not constitute a true network analysis due to the absence of analysis of a time series of the original examined physiological variables. Nonetheless, the presence of negative links in SSX reflected the impact of sleep deprivation on the autonomic regulation and lipemia and, thus, revealed the inability of HIIE to remain cardioprotective under APSD. These findings underlie the need to further investigate the effects of APSD and HIIE on the interactions among physiological systems.

Can Acute Exercise Lower Cardiovascular Stress Reactivity? Findings from a Scoping Review

Exaggerated cardiovascular reactivity to and delayed recovery from stress increase the risk of cardiovascular diseases in the future. While exercise training has been shown to attenuate stress-induced cardiovascular reactivity and enhance recovery from stress, the effects with acute exercise are less characterized. The aim of this scoping review was to explore the range and characteristics of published evidence regarding acute exercise on cardiovascular reactivity and stress recovery. The secondary objective was to highlight research gaps and implications for future research. A total of 36 articles met the review inclusion/exclusion criteria, involving 1200 participants from various age groups, fitness and health status. Blood pressure (BP) reactivity was the most measured outcome, followed by heart rate (HR) reactivity, and to some extent, heart rate variability. Overall, acute exercise particularly of the moderate-intensity aerobic type effectively reduced stress-induced BP reactivity in the general population. The effects on HR reactivity and cardiovascular recovery were inconclusive. Further research would be recommended to establish if other forms of exercise intensity or type are equally beneficial to lower exaggerated cardiovascular responses to stress. Despite methodological differences and limitations, the available evidence supports the therapeutic potential of acute exercise in addressing the ill effects of stress on cardiovascular health.

Effect of Weather and Game Factors on Injury Rates in Professional Baseball Players

BACKGROUND

Injury rates in baseball players of all ages are increasing. Identifying modifiable risk factors is paramount to implementing injury prevention programs.

PURPOSE/HYPOTHESIS

The purpose was to evaluate the influence of weather (temperature, humidity, atmospheric pressure, and heat index) and game factors (start time, duration, single vs doubleheader) on injury rates in professional baseball players. We hypothesized that colder temperatures would be associated with significantly more injuries per game.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

This was a retrospective database study. Two data sets were combined: 1 containing all injuries in Major and Minor League Baseball between 2011 and 2017 and 1 containing all games played in Major and Minor League Baseball during the same period to determine the number of injuries per game. Temperature, humidity, atmospheric pressure, and heat index were determined for each game using the data from the US Environmental Protection Agency. Additional game variables included the level of play, the turf type (natural vs artificial grass), the stadium type (open vs dome vs retractable), the game start time, the game duration, and whether the game was a doubleheader. Then, a multivariate analysis was conducted to determine which factors were associated with the number of injuries per game.

RESULTS

In total, our analysis included 33,587 injuries and 76,747 games. A total of 25,776 (33.6%) games contained an injury, and 41% of injuries occurred as multiples per game, with up to 9 injuries per game. The multivariate analysis identified significant associations between game duration and injuries per game (P < .001; effect size, 0.013) and the level of play and injuries per game (P < .001; effect size, 0.011). There were significant associations between the venue type (P < .001), the game start time (P < .001), humidity (P < .001), the turf type (P = .016), and barometric pressure (P = .031); however, the effect size for each was <0.001, suggesting that these factors are clinically unimportant. Our overall model produced an R² of 0.04, indicating that these variables only predicted 4% of the variance in injury risk.

CONCLUSION

In professional baseball, the weather is not associated with injury risk; however, game duration may contribute to injury risk.

The association between chronotype and sleep quality among female home care workers performing shift work

There is a scarcity of evidence on the association between shift work, sleeping parameters, heart rate variability (HRV), and chronotype, i.e., morningness and eveningness. The aims of this study were to 1) compare participants with different chronotypes (morning (M), evening (E), or neither (N)) in terms of their total sleep time, sleep efficiency, and HRV parameters, taking their age into account, and 2) examine whether self-reported work-related stress, the length of the working career and years performing shift work affect this association. The participants of the study were home care workers working in two shifts in one municipality in Eastern Finland (N = 395). Of these, 52 females (mean age 42.78 y, SD 12.92 y) completed the study questionnaire and participated in physiological measurements. Several sleep-related parameters were assessed (total sleep time, sleep efficiency, number of awakenings, and length of awakening) and indices of autonomic nervous system based on HRV were calculated. The participants worked in two shifts: a morning shift (7:00-15:00 h) and an evening shift (14:00-21:30 h). All these parameters were assessed during the night before the first work shift (N1), the night before the second work shift (N2), the night before the final work shift (N3), and the night before the first day off work (N4). According to the results, 21.2% of the participants were M-types, 17.3% were E-types, and 61.5% were N-types. On average, the participants had been in working life for 18.8 years and performing shift work for 13.7 years. On night N3, E-types had a significantly shorter total sleep time and spent less time in bed compared to M- and N-types. The total sleep time of M-type and N-type participants was on average 66 minutes and 82 minutes longer, respectively, when compared to E-types on night N3. There were no statistically significant differences in actigraphy-based sleep quality parameters between M-, N-, and E-types on nights N1, N2, and N4. Our results together indicate that M- and N-type individuals may have better sleep quality than E-types, which was also reflected in HRV parameters. Further research with longitudinal study design and workplace interventions is needed to determine how the chronotype can be optimally and individually utilized to improve the health and well-being of morning-type and evening-type people. This is particularly important for both younger and older workers entering the workforce to support healthier and longer working lives.

Effects of High-Intensity Interval Exercise and Acute Partial Sleep Deprivation on Cardiac Autonomic Modulation

Sleep deprivation in healthy adults has been associated with disrupted autonomic nervous system function, which in turn has been linked to cardiovascular health. High-intensity interval exercise (HIIE) may affect both sleep and cardiac autonomic modulation. Purpose: To investigate the impact of acute partial sleep deprivation on autonomic cardiac regulation before and after an acute bout of HIIE and the length of time for the autonomic system to return to resting levels. Methods: Fifteen healthy males with body mass index (BMI) of 25.8 ± 2.7 kg·m^-2 and age 31 ± 5 y participated in a reference sleep (~9.5 hr) with no HIIE (RS), a reference sleep with HIIE (RSX), and an acute partial sleep deprivation (~3.5 hr) with HIIE (SDX). HIIE was performed in 3:2 intervals at 90% and 40% of VO₂ reserve. Autonomic regulation through HRV selected time and frequency domain indices were recorded the night before, the morning of the next day, 1 hr-, 2 hr-, 4hr-, and 6-hr post-exercise. Results: HIIE performed in a 3:2 W:R ratio decreased the HRV (p < .05) at 1-hr post exercise and it took up to 4 hr to return to baseline levels. Parasympathetic related HRV indices increased the morning of the next day for SDX (p < .05). Acute partial sleep deprivation and HIIE did not modify the HRV responses compared to reference sleep and HIIE. Conclusion: HRV disturbance typically seen in responses to an acute episode of HIIE is not influenced by acute partial sleep deprivation.

Cortisol Awakening Response and Heart Rate Variability in the Menstrual Cycle of Sportswomen

Purpose: This study aimed to examine the activities of heart rate variability (HRV) and cortisol secretion as markers of the autonomous nervous system (ANS) and the hypothalamic-pituitary-adrenal axis (HPA) during the menstrual cycle in female athletes. Method: Saliva samples of the participants (n = 28) were collected successively at 0, 15, 30, and 60 min after awakening to assess cortisol awakening response (CAR) during each of four phases of the menstrual cycle (the menstruation, ovulation, luteal, and premenstrual phases). Diurnal saliva samples were collected at noon, in the evening (17:00) and 22:00 for cortisol analysis. HRV was measured in the menstrual and premenstrual phases at rest (12:00-14:00). Results: There was no difference between CAR parameters in the menstrual phases. CAR parameters and diurnal cortisol levels were significantly correlated with each other throughout the menstrual cycle. Mean cortisol was a strong predictor of the area under the curve (AUC: S = 0.042; R-Sq = 98.4%). Time-dependent parameters of HRV (standard deviation of the N-N interval [SDNN; P = .049] and the root mean square of the successive R-R differences [rMSSD; P = .038]) were significantly higher in the menstrual phase. There were no correlations between CAR and HRV parameters. Conclusions: We suggest that the hypothalamic-pituitary-adrenal axis activity and the autonomic nervous system work in a separate manner that is not affected by the menstrual phases in sportswomen. The present study contributed to a better understanding of the relationship between the dynamics of cortisol release and the autonomic nervous system in different phases of the menstrual cycle in female athletes.

Heart rate variability improves in 3-5-year-old children following a 6-month physical activity-based intervention: the Active Early Learning (AEL) cluster randomised controlled trial

Heart rate variability (HRV) measurement provides non-invasive assessment of autonomic stability and cardiometabolic disease risk. Insufficient physical activity in early childhood may contribute to negative cardiometabolic health. The Active Early Learning (AEL) study was a 6-month randomised controlled trial investigating the effects of a physical activity-based program incorporating movement within the daily curriculum of preschool children. The current study assessed the effects of the AEL intervention on HRV as a measure of cardiac vagal control. Children aged between 3-5 years and enrolled in a preschool with an attendance of ≥15 children were eligible. Physical activity was recorded using an Actigraph wGT3x accelerometer worn at the waist of participants over 3 consecutive days. A Polar H10 chest strap measured HRV with the HF-band and RMSSD representing cardiac vagal control. After 6 months of the AEL trial, linear mixed model analyses revealed a significant intervention effect for increased HF (p = 0.044). The control group did not demonstrate changes in cardiac vagal control after the intervention ceased. Independent of age, sex, physical activity and BMI, the AEL study elicited significant improvements in the cardiac vagal control of participants who received the intervention. Findings highlight the importance of investigating HRV for assessing the cardiometabolic health in young children. ANZCTR trial registration number: ACTRN12619000638134. Novelty: The AEL curriculum improved child HRV independent of age, sex, physical activity and BMI. Heart rate and RR intervals did not demonstrate changes for the intervention and control groups. Multivariate programs for developing physical competence, confidence, knowledge and motivation may improve child health.

Positive Relationship Between Precompetitive Sympathetic Predominance and Competitive Performance in Elite Extreme Sports Athletes

Elite athletes achieve superior performance under high pressure in competitive situations. Although it is known that such situations affect the precompetitive activity of their autonomic nervous system (ANS), the relationship between precompetitive ANS activity and performance remains controversial. Especially in extreme sports, it has been shown that cardiac sympathetic tone occurs in athletes before competition attempts. However, the relationship between precompetitive sympathetic tone and performance is unclear. To investigate this relationship in extreme sports, we organized a freestyle snowboard jumping competition and examined competitors' physiological states and performance during this event. The electrocardiograms (ECGs) of 20 elite snowboarders were measured 10 min before each jump in different competitive situations: practice, qualifying, and final sessions. The mean heart rate (HR), the low-frequency to high-frequency component ratio (LF/HF ratio), the logarithm of the HF (lnHF) component of the frequency-domain of the heart rate variability (HRV), the ratio of the standard deviation of all R-R intervals to the root mean square of successive differences of R-R intervals (SDNN/rMSSD ratio), and the rMSSD of the time-domain of the HRV were calculated from the ECG data. The results showed a significant increase in the mean HR as well as significant decreases in the lnHF component and rMSSD of the HRV as the sessions progressed. Interestingly, the mean HR, LF/HF ratio and SDNN/rMSSD ratio of the HRV showed significant positive correlations with competitive scores, and the lnHF component and rMSSD of the HRV showed significant negative correlations with the scores. Our results indicate that precompetitive ANS activity becomes predominantly sympathetic in elite extreme athletes, such as freestyle snowboarders, when the competition intensifies, and that this sympathetic predominance is positively related to competitive performance.

A Proposal for a Data-Driven Approach to the Influence of Music on Heart Dynamics

Electrocardiographic signals (ECG) and heart rate viability measurements (HRV) provide information in a range of specialist fields, extending to musical perception. The ECG signal records heart electrical activity, while HRV reflects the state or condition of the autonomic nervous system. HRV has been studied as a marker of diverse psychological and physical diseases including coronary heart disease, myocardial infarction, and stroke. HRV has also been used to observe the effects of medicines, the impact of exercise and the analysis of emotional responses and evaluation of effects of various quantifiable elements of sound and music on the human body. Variations in blood pressure, levels of stress or anxiety, subjective sensations and even changes in emotions constitute multiple aspects that may well-react or respond to musical stimuli. Although both ECG and HRV continue to feature extensively in research in health and perception, methodologies vary substantially. This makes it difficult to compare studies, with researchers making recommendations to improve experiment planning and the analysis and reporting of data. The present work provides a methodological framework to examine the effect of sound on ECG and HRV with the aim of associating musical structures and noise to the signals by means of artificial intelligence (AI); it first presents a way to select experimental study subjects in light of the research aims and then offers possibilities for selecting and producing suitable sound stimuli; once sounds have been selected, a guide is proposed for optimal experimental design. Finally, a framework is introduced for analysis of data and signals, based on both conventional as well as data-driven AI tools. AI is able to study big data at a single stroke, can be applied to different types of data, and is capable of generalisation and so is considered the main tool in the analysis.

Applying Heart Rate Variability to Monitor Health and Performance in Tactical Personnel: A Narrative Review

Human performance optimization of tactical personnel requires accurate, meticulous, and effective monitoring of biological adaptations and systemic recovery. Due to an increased understanding of its importance and the commercial availability of assessment tools, the use of heart rate variability (HRV) to address this need is becoming more common in the tactical community. Measuring HRV is a non-invasive, practical method for objectively assessing a performer's readiness, workload, and recovery status; when combined with additional data sources and practitioner input, it provides an affordable and scalable solution for gaining actionable information to support the facilitation and maintenance of operational performance. This narrative review discusses the non-clinical use of HRV for assessing, monitoring, and interpreting autonomic nervous system resource availability, modulation, effectiveness, and efficiency in tactical populations. Broadly, HRV metrics represent a complex series of interactions resulting from internal and external stimuli; therefore, a general overview of HRV applications in tactical personnel is discussed, including the influence of occupational specific demands, interactions between cognitive and physical domains, and recommendations on implementing HRV for training and recovery insights into critical health and performance outcomes.

Can Reactivity of Heart Rate Variability Be a Potential Biomarker and Monitoring Tool to Promote Healthy Aging? A Systematic Review With Meta-Analyses

Background: Monitoring phasic responses of heart rate variability (HRV) in terms of HRV reactivity [i. e., the absolute change from resting state to on-task (i.e., absolute values of HRV measured during exercise)] might provide useful insights into the individual psychophysiological responses of healthy middle-aged to older adults (HOA) to cognitive and physical exercises. Objectives: To summarize the evidence of phasic HRV responses to cognitive and physical exercises, and to evaluate key moderating factors influencing these responses. Methods: A systematic review with meta-analyses was performed. Publications up to May 2020 of the databases Medline (EBSCO), Embase, Cochrane Library, CINAHL, Psycinfo, Web of Science, Scopus, and Pedro were considered. Controlled clinical trials and observational studies measuring phasic HRV responses to cognitive and/or physical exercises in HOA (≥50 years) were included. Results: The initial search identified 6,828 articles, of which 43 were included into the systematic review. Compared to resting state, vagally-mediated HRV indices were significantly reduced during all types of exercises [Hedge's g = -0.608, 95 % CI (-0.999 to -0.218), p = 0.002] indicating a significant parasympathetic withdrawal compared to rest. The key moderating variables of these responses identified included exercise intensity for physical exercises, and participant characteristics (i.e., level of cognitive functioning, physical fitness), task demands (i.e., task complexity and modality) and the individual responses to these cognitive challenges for cognitive exercises. In particular, higher task demands (task complexity and physical exercise intensity) were related to larger HRV reactivities. Better physical fitness and cognition were associated with lower HRV reactivities. Additionally, HRV reactivity appeared to be sensitive to training-induced cognitive and neural changes. Conclusion: HRV reactivity seems to be a promising biomarker for monitoring internal training load and evaluating neurobiological effects of training interventions. Further research is warranted to evaluate the potential of HRV reactivity as a monitoring parameter to guide cognitive-motor training interventions and/or as a biomarker for cognitive impairment. This may facilitate the early detection of cognitive impairment as well as allow individualized training adaptations that, in turn, support the healthy aging process by optimizing individual exercise dose and progression of cognitive-motor training.

Heart rate variability and chronotype - a systematic review

There is a scarcity of evidence on the association between heart rate variability (HRV) and chronotype, i.e., morningness and eveningness. The aim of this systematic review was to examine the association between chronotype, HRV, mood and stress response. We searched PubMed, Web of Science, Scopus, Cinahl, PsycINFO and Google Scholar for peer-reviewed articles published in English between January 2000 and June 2020. A total of 11 articles met the inclusion criteria and were on study population, assessment of HRV and chronotype, main results and study limitations. Seven of the included studies were experimental and four were crossovers. The sample size varied from 9 to 221 participants, and both females and males were included. HRV was assessed using mostly time-domain and frequency-domain parameters; nonlinear parameters were used in only one study. The most used assessments for measuring chronotype were the Horne-Östberg Morningness-Eveningness Questionnaire (MEQ) and the Munich Chronotype Questionnaire (MCTQ). The results showed that chronotype was associated with HRV, but the study designs were situation-specific, focusing, for example, on the effects of shiftwork, stressful situations, exercise, or sleep deprivation on HRV. In addition, some studies showed that evening types (E-type) performed better during evening or nighttime tasks, whereas morning types (M-type) performed better during morning activities. Specifically, E-types showed decreased HRV and HRV recovery in relation to tasks performed during morning or daytime when compared to M-types. As the findings are somewhat contradictory and include some methodological limitations (e.g., small sample sizes, age groups), it is important for future studies to evaluate the association between chronotype and HRV in a longitudinal setting. In addition, further research is needed to determine how chronotype can be optimally and individually utilized to increase the health and well-being of M-type and E-type individuals.

Diurnal and seasonal differences in cardiopulmonary response to exercise in morning and evening chronotypes

Circadian clocks regulate multiple physiological domains from molecular to behavioral levels and adjust bodily physiology to seasonal changes in day length. Circadian regulation of cellular bioenergy and immunity in the cardiovascular and muscle systems may underpin the individual diurnal differences in performance capacity during exercise. Several studies have shown diurnal differences in cardiopulmonary parameters at maximal and submaximal workloads in morning and evening circadian human phenotypes. However, the effect of seasons on these changes was not elucidated. In this study, we recruited subjects with Morningness-Eveningness Questionnaire scores corresponding to morning and evening types. Subjects underwent morning (7:00-9:00) and evening (20:00-22:00) maximal workload spiroergometry in both winter and summer seasons. We analyzed their performance time, anaerobic threshold, heart rate, and respiratory parameters. Our results suggest that evening types manifest diurnal variations in physical performance, particularly in winter. They also have slower heart rate recovery than morning types, irrespective of the time of day or season. Compared to winter, the chronotype effect on the magnitude of morning-evening differences in performance time, maximal heart rate, and anaerobic threshold onset was more significant in summer. Our data are in concordance with previous observations and confirm the difference between morning and evening types in the timing of maximum performance capacity.

Association Between Postoperative Long-Term Heart Rate Variability and Postoperative Delirium in Elderly Patients Undergoing Orthopedic Surgery: A Prospective Cohort Study

Background

Postoperative delirium (POD) is a common complication after orthopedic surgery in elderly patients. The elderly may experience drastic changes in autonomic nervous system (ANS) activity and circadian rhythm disorders after surgery. Therefore, we intend to explore the relationship between postoperative long-term heart rate (HR) variability (HRV), as a measure of ANS activity and circadian rhythm, and occurrence of POD in elderly patients.

Methods

The study population of this cohort was elderly patients over 60 years of age who scheduled for orthopedic surgery under spinal anesthesia. Patients were screened for inclusion and exclusion criteria before surgery. Then, participants were invited to wear a Holter monitor on the first postoperative day to collect 24-h electrocardiographic (ECG) data. Parameters in the time domain [the standard deviation of the normal-to-normal (NN) intervals (SDNN), mean of the standard deviations of all the NN intervals for each 5-min segment of a 24-h HRV recording (SDNNI), and the root mean square of successive differences of the NN intervals (RMSSD)] and frequency domain [heart rate (HR), high frequency (HF), low frequency (LF), very low frequency (VLF), ultra low frequency (ULF), and total power (TP)] were calculated. Assessment of delirium was performed daily up to the seventh postoperative day using the Chinese version of the 3-Min Diagnostic Interview for CAM-defined Delirium (3D-CAM). The relationship between HRV and POD, as well as the association between HRV and duration of POD, was assessed.

Results

Of the 294 cases that finally completed the follow-up, 60 cases developed POD. Among the HRV parameters, SDNNI, VLF, and ULF were related to the occurrence of POD. After adjustment for potential confounders, the correlation between HRV indices and POD disappeared. Through stratified analysis, two significant negative correlations emerged: ULF in young-old participants and SDNNI, VLF, and ULF in male patients.

Conclusion

The lower HRV parameters may be related to the occurrence of POD, and this correlation is more significant in young-old and male patients. ANS disorders and rhythm abnormalities reflected by HRV changes may represent a possible mechanism that promotes POD.

Does the chronotype distribution vary between different level football leagues? Insights gained from Czech elite football players

Chronotype refer to individuals' time-of-day preferences for activities, which can be classified as "morning types = (M-types)", "evening types = (E-types)", and "neither types (N-types)". The primary aim of this study was to compare the chronotype distribution of Czech First League (1L) and Czech National Football League (2L) male elite football players, which was divided into two secondary aims: (i) statistically identify and compare the number (presence) of particular chronotypes in 1L, and (ii) statistically identify and compare the number (presence) of particular chronotypes in 2L. The present cross-sectional study employed a self-reported standardized questionnaire, the Composite Scale of Morningness, to study the chronotype distribution among the male elite football players. The chronotype distribution of 139 (85 from 1L with mean age ± S.D. = 25.5 ± 3.7 years and 54 from 2L age = 24.4 ± 4.5 years) players was assessed. Overall, 61 (71.8%) of the participants from 1L were mainly N-types, followed by M- and E-types. Similarly, 40 (74.1%) participants from 2L were mainly N-types, followed by M- and E-types. The statistical analysis of the 1L players showed a significantly higher presence of N-types compared to M- and E-types (χ²₍₂₎ = 57.62, p < .05, V = .58). The same results were detected in 2L, where the N-type was identified in the majority of football players (χ²₍₂₎ = 57.62, p < .05, V = .58). The statistical comparison of the number of presented chronotypes did not show a significant difference (F = 3.29, p > .05, V = .16) between players of the 1L and 2L. Thus, N-types are dominant among Czech elite football players, and the chronotype distribution of male elite football players from the Czech First League and the Czech National Football League does not vary.

Aerobic Continuous and Interval Training under Hypoxia Enhances Endurance Exercise Performance with Hemodynamic and Autonomic Nervous System Function in Amateur Male Swimmers

Hypoxic training is often performed by competitive swimmers to enhance their performance in normoxia. However, the beneficial effects of aerobic continuous and interval training under hypoxia on hemodynamic function, autonomic nervous system (ANS) function, and endurance exercise performance remain controversial. Here we investigated whether six weeks of aerobic continuous and interval training under hypoxia can improve hematological parameters, hemodynamic function, ANS function, and endurance exercise performance versus normoxia in amateur male swimmers. Twenty amateur male swimmers were equally assigned to the hypoxic training group or normoxic training group and evaluated before and after six weeks of training. Aerobic continuous and interval training in the hypoxia showed a more significantly improved hemodynamic function (heart rate, −653.4 vs. −353.7 beats/30 min; oxygen uptake, −62.45 vs. −16.22 mL/kg/30 min; stroke volume index, 197.66 vs. 52.32 mL/30 min) during submaximal exercise, ANS function (root mean square of successive differences, 10.15 vs. 3.32 ms; total power, 0.72 vs. 0.20 ms²; low-frequency/high-frequency ratio, −0.173 vs. 0.054), and endurance exercise performance (maximal oxygen uptake, 5.57 vs. 2.26 mL/kg/min; 400-m time trial record, −20.41 vs. −7.91 s) than in the normoxia. These indicate that hypoxic training composed of aerobic continuous and interval exercise improves the endurance exercise performance of amateur male swimmers with better hemodynamic function and ANS function.

The effect of daily walking exercise on sleep quality in healthy young adults

Purpose

Walking has beneficial effects on sleep quality in elderly population and patients in clinical settings. However, less is known whether walking improves sleep quality among healthy young adults. This study examined the effectiveness of a 12-week walking intervention on sleep quality among sedentary young adults.

Methods

Fifty-four healthy adults aged 19 to 36-years old participated a pedometer based aerobic walking intervention, a cross-over randomized control trial. Participants were assigned into two groups (group A and group B) randomly. The 12-week intervention was divided into three sessions equally. Sleep quality was assessed by Pittsburgh Sleep Quality Index (PSQI) before and after session 1 and session 3. Omron HJ-112 pedometer and daily walking diary facilitated the intervention process. Within group and between group comparisons were made for statistical analysis.

Results

Within group comparison by repeated measures showed that sleep duration (p < 0.01, F-test 22.79), sleep medication (p < 0.05, F-test 5.22), subjective sleep (p < 0.05, F-test 5.51) and global sleep quality (p < 0.01, F-test 12.19) were significantly improved. The comparison between intervention group and control group showed that sleep disturbance was significantly improved (p < 0.05).

Conclusion

Daily walking exercise has a significant effect on facilitating sleep quality and sleep components among young adults. Further studies are suggested to examine the impact of walking intensity on sleep quality.

Changes in Short-Term and Ultra-Short Term Heart Rate, Respiratory Rate, and Time-Domain Heart Rate Variability Parameters during Sympathetic Nervous System Activity Stimulation in Elite Modern Pentathlonists-A Pilot Study

Monitoring of markers reflecting cardiac autonomic activity before and during stressful situations may be useful for identifying the physiological state of an athlete and may have medical or performance implications. The study aimed to determine group and individual changes in short-term (5 min) and ultra-short-term (1 min) heart rate (HR), respiratory rate (RespRate), and time-domain heart rate variability (HRV) parameters during sympathetic nervous system activity (SNSa) stimulation among professional endurance athletes. Electrocardiographic recordings were performed in stable measurement conditions (Baseline) and during SNSa stimulation via isometric handgrip in 12 elite modern pentathlonists. Significant increases in short-term HR and decreases in time-domain HRV parameters with no changes in RespRate were observed during SNSa stimulation. Significant differences were observed between Baseline (all minutes) and the last (i.e., 5th) minute of SNSa stimulation for ultra-short-term parameters. Analysis of intra-individual changes revealed some heterogeneity in responses. The study provides baseline responses of HR, RespRate, and time-domain HRV parameters to SNSa stimulation among elite pentathlonists, which may be useful for identifying abnormal responses among fatigued or injured (e.g., concussed) athletes. More attention to individual analysis seems to be necessary when assessing physiological responses to sympathetic stimuli in professional endurance athletes.

Bayesian Estimation of Correlation between Measures of Blood Pressure Indices, Aerobic Capacity and Resting Heart Rate Variability Using Markov Chain Monte Carlo Simulation and 95% High Density Interval in Female School Teachers

Background: Several explanations regarding the disparity observed in the literature with regard to heart rate variability (HRV) and its association with performance parameters have been proposed: the time of day when the recording was conducted, the condition (i.e., rest, active, post activity) and the mathematical and physiological relationships that could have influenced the results. A notable observation about early studies is that they all followed the frequentist approach to data analyses. Therefore, in an attempt to explain the disparity observed in the literature, the primary purpose of this study was to estimate the association between measures of HRV indices, aerobic performance parameters and blood pressure indices using the Bayesian estimation of correlation on simulated data using Markov Chain Monte Carlo (MCMC) and the equal probability of the 95% high density interval (95% HDI). Methods: The within-subjects with a one-group pretest experimental design was chosen to investigate the relationship between baseline measures of HRV (rest; independent variable), myocardial work (rate–pressure product (RPP)), mean arterial pressure (MAP) and aerobic performance parameters. The study participants were eight local female schoolteachers aged 54.1 ± 6.5 years (mean ± SD), with a body mass of 70.6 ± 11.5 kg and a height of 164.5 ± 6.5 cm. Their HRV data were analyzed in R package, and the Bayesian estimation of correlation was calculated employing the Bayesian hierarchical model that uses MCMC simulation integrated in the JAGS package. Results: The Bayesian estimation of correlation using MCMC simulation reproduced and supported the findings reported regarding norms and the within-HRV-indices associations. The results of the Bayesian estimation showed a possible association (regardless of the strength) between pNN50% and MAP (rho = 0.671; 95% HDI = 0.928–0.004), MeanRR (ms) and RPP (rho = −0.68; 95% HDI = −0.064–−0.935), SDNN (ms) and RPP (rho = 0.672; 95% HDI = 0.918–0.001), LF (ms²) and RPP (rho = 0.733; 95% HDI = 0.935–0.118) and SD2 and RPP (rho = 0.692; 95% HDI = 0.939–0.055). Conclusions: The Bayesian estimation of correlation with 95% HDI on MCMC simulated data is a new technique for data analysis in sport science and seems to provide a more robust approach to allocating credibility through a meaningful mathematical model. However, the 95% HDI found in this study, accompanied by the theoretical explanations regarding the dynamics between the parasympathetic nervous system and the sympathetic nervous system in relation to different recording conditions (supine, reactivation, rest), recording systems, time of day (morning, evening, sleep etc.) and age of participants, suggests that the association between measures of HRV indices and aerobic performance parameters has yet to be explicated.

The effects of varying doses of caffeine on cardiac parasympathetic reactivation following an acute bout of anaerobic exercise in recreational athletes

BACKGROUND

To examine the effects of varying doses of caffeine on autonomic reactivation following anaerobic exercise.

METHODS

Recreationally active males (N = 20; 24 ± 2y) participated in a randomized, double-blind, placebo-controlled, crossover study where participants ingested: [1] Control (CON; no supplement), [2] a non-caffeinated placebo (PLA), [3] 3-mg∙kg- 1 of caffeine (CAF3) or [4] 6-mg∙kg- 1 of caffeine (CAF6) prior to Wingate testing. Parasympathetic (lnRMSSD, primary outcome) and global HRV (lnSDNN, secondary outcome) were assessed at rest (i.e., pre-ingestion), 45-min post-ingestion, and 5-min and 35-min post-exercise recovery. We used a GLM to assess mean (95% CI) changes from pre-ingestion baseline.

RESULTS

Overall, we observed a significant trend for lnRMSSD and lnSDNN (both, p = 0.001, ηp2 = 0.745). Forty-five minutes after treatment ingestion, we observed a significant increase in lnRMSSD for CAF3 (0.15 ms, 95%CI, 0.07,0.24) and CAF6 (0.16 ms, 95%CI, 0.06,0.25), both being significant (both, p <  0.004) vs. CON (- 0.02 ms, 95%CI, - 0.09,0.04). Five-minutes after exercise, all treatments demonstrated significant declines in lnRMSSD vs. baseline (all, p <  0.001). After 35-min of recovery, lnRMSSD returned to a level not significantly different than baseline for CAF3 (0.03 ms, 95%CI, - 0.05, 0.12) and CAF6 (- 0.03 ms, 95%CI, - 0.17, 0.10), while PLA (- 0.16 ms, 95%CI, - 0.25, - 0.06) and CON (- 0.17 ms, 95%CI, - 0.28, - 0.07) treatments remained significantly depressed. A similar pattern was also observed for SDNN.

CONCLUSION

Caffeine ingestion increases resting cardiac autonomic modulation and accelerates post-exercise autonomic recovery after a bout of anaerobic exercise in recreationally active young men. However, no differences between caffeine doses on cardiac autonomic reactivity were observed.

Role of Type and Volume of Recreational Physical Activity on Heart Rate Variability in Men

The aim of this study was to investigate the effect of recreational aerobic physical activity (PA) type and volume on heart rate variability (HRV) in Arab men. This was a retrospective, cross-sectional study, and included men (n = 75, age = 37.6 ± 7.1 years, body mass index (BMI) = 26.7 ± 3.1 kg/m²) who were members of a walking group, cycling group, or were inactive controls. Monthly distances from the past three months were obtained from walking and cycling groups, and the volume of PA was classified into three subgroups (high, moderate, low). HRV was measured using a computerized electrocardiographic data acquisition device. R–R interval recordings were performed while participants rested in a motionless supine position. RR intervals were recorded for 15 minutes, and a five-minute segment with minimal ectopic beats and artifacts was selected for HRV analysis. Time-domain parameters included the mean R–R interval, standard deviation of the mean R–R interval (SDNN), and root-mean-squared difference of successive RR intervals (RMSSD). The frequency-domain parameters included high-frequency power (HF), low-frequency power (LF), and LF to HF ratio (LF/HF). Results showed that there were no significant differences between walking, cycling, and control groups for all HRV parameters. Time-domain analyses based on PA volume showed that age-adjusted SDNN for the high-active group was greater than the low-active group (P = 0.03), and RMSSD for the moderate-active group was greater than the control group (P = 0.009). For the frequency domain, LF for the high-active group was greater than the low-active and control groups (P = 0.006), and HF for the moderate-active group was greater than the low-active group (P = 0.04). These data indicate that walking >150 km per month, or cycling >100 km per month at a speed >20 km/h may be necessary to derive cardiac autonomic benefits from PA among Arab men.

Dental occlusion and sport performance

INTRODUCTION

In recent years, interest has been given to the relationship between dental occlusion and athletes' performance. A correct occlusion allows for a correct position of the mandible in space and could be reached by wearing a splint made by a dentist. Achieving this condition appears to be an advantage for all athletes, and especially for those who have TMJ dysfunction. The purpose of the study was to investigate the hypothesis and common belief that correcting the occlusion or the use of a splint could improve an athlete's performance.

EVIDENCE ACQUISITION

A search on electronic database has been performed and obtained 141 results; then, following the application of the inclusion criteria, only 11 articles were selected.

EVIDENCE SYNTHESIS

A good occlusion seems to be an advantage for the athletes.

CONCLUSIONS

The use of an occlusal splint should be evaluated in different sports, because the occlusion and TMJ conditions of the athletes are different and the efforts in which they are subjected could not be generalized because the sports have various rules and characteristics that involves the stomatognathic system differently.

Interval Hypoxic Training Enhances Athletic Performance and Does Not Adversely Affect Immune Function in Middle- and Long-Distance Runners

This study evaluated the effects of intermittent interval training in hypoxic conditions for six weeks compared with normoxic conditions, on hemodynamic function, autonomic nervous system (ANS) function, immune function, and athletic performance in middle- and long-distance runners. Twenty athletes were divided into normoxic training (normoxic training group (NTG); n = 10; residing and training at sea level) and hypoxic training (hypoxic training group (HTG); n = 10; residing at sea level but training in 526-mmHg hypobaric hypoxia) groups. All dependent variables were measured before, and after, training. The training frequency was 90 min, 3 d per week for six weeks. Body composition showed no significant difference between the two groups. However, the HTG showed more significantly improved athletic performance (e.g., maximal oxygen uptake). The hemodynamic function (e.g., oxygen uptake, oxygen pulse, and cardiac output) during submaximal exercise and ANS function (e.g., standard deviation and root mean square of successive differences, high frequency, and low/high frequency) improved more in the HTG. Immune function parameters were stable within the normal range before and after training in both groups. Therefore, hypoxic training was more effective in enhancing athletic performance, and improving hemodynamic and ANS function; further, it did not adversely affect immune function in competitive runners.

The Role of the Molecular Clock in Promoting Skeletal Muscle Growth and Protecting against Sarcopenia

The circadian clock has a critical role in many physiological functions of skeletal muscle and is essential to fully understand the precise underlying mechanisms involved in these complex interactions. The importance of circadian expression for structure, function and metabolism of skeletal muscle is clear when observing the muscle phenotype in models of molecular clock disruption. Presently, the maintenance of circadian rhythms is emerging as an important new factor in human health, with disruptions linked to ageing, as well as to the development of many chronic diseases, including sarcopenia. Therefore, the aim of this review is to present the latest findings demonstrating how circadian rhythms in skeletal muscle are important for maintenance of the cellular physiology, metabolism and function of skeletal muscle. Moreover, we will present the current knowledge about the tissue-specific functions of the molecular clock in skeletal muscle.