Biological rhythms, chronodisruption and chrono-enhancement: The role of physical activity as synchronizer in correcting steroids circadian rhythm in metabolic dysfunctions and cancer.

Rhythms can be observed at all levels of the biologic integration in humans. The observation that a biological or physiological variable shows a circadian rhythm can be explained by several multifactorial systems including external (exogenous), internal (endogenous) and psychobiological (lifestyle) mechanisms. Our body clock can be synchronized with the environment by external factors, called "synchronizers", i.e. the light-dark cycle, but it is also negatively influenced by some pathological conditions or factors, called "chronodisruptors," i.e. aging or low physical activity (PA). The desynchronization of a 24-h rhythm in a chronic manner has been recently defined "chronodisruption" or "circadian disruption." A very large number of hormonal variables, such as adrenal and gonadal stress steroids, are governed by circadian rhythmicity. Such hormones, in normal conditions, show a peak in the first part of the day, while their typical diurnal fluctuations are totally out of sync in subjects affected by cancer or metabolic diseases, such as obesity, diabetes and metabolic syndrome. In general, a flatter slope with altered peaks in cortisol and testosterone circadian rhythms has been observed in pathological individuals. PA, specifically chronic exercise, seems to play a key role as synchronizer for the whole circadian system in such pathologies even if specific data on steroids circadian pattern are still sparse and contradictory. Recently, it has been proposed that low-intensity chronic PA could be an effective intervention to decrease morning cortisol levels in pathological subjects. The standardization of all confounding factors is needed to reach more clear evidence-based results.

Health challenges in long-distance dog sled racing: A systematic review of literature.

Long-distance dog sled races, e.g. Iditarod (Alaska) and Finnmarksløpet (Northern Norway), are extremely demanding sporting events that might expose mushers, handlers and a large number of organisers and volunteers to risks for their health. The purpose of this systematic literature review (PROSPERO registration n. CRD42017069136) was to identify and summarise all available scientific literature relative to health issues connected to participating in these races. Using a literature search strategy in line with PRISMA guidelines, 117 scientific studies, sought through databases (Google Scholar and PubMed, between 2nd and 9th May 2017) and scrutiny of reference lists, were screened. Studies published in English treating any health issues assessed during or after a long-distance dog sled race were included, with no restriction in relation to their study design or the characteristics of participants studied. The quality of the studies was assessed using a standardised checklist. Ten studies met the criteria for being included in a qualitative analysis. The data synthesis showed that participants underwent strenuous psychophysical load, with insufficient sleep/rest and inadequate energy intake. Findings on hydrations are mixed. The risk of incurring in life-threatening injuries or infections was low, although injuries and infections of minor severity were common. No alterations of blood markers were observed from before to after the races. These findings will help planning prevention and treatment strategies in long-distance dog sled races. However, more research is needed in this field in the future.

Chronotype and response to training during the polar night: a pilot study.

BACKGROUND: An individual's chronotype influences his or her physiological rhythms. Some studies have looked at the effect of time of day on the responses to exercise, but studies on the effect of long-term training are lacking. OBJECTIVE: To report the effects of an 8-week training period during the polar night in non-athletes of different chronotypes living at 70°N. DESIGN: In all, 10 morning (M), 10 neither (N) and 10 evening (E) types were recruited, and their aerobic capacity (VO2max), strength, flexibility and balance before and after the training period were tested. RESULTS: 3 E-types, 5 N-types and 6 M-types completed the protocol. An increase in VO2max and strength was observed for the whole group. The best negative correlation (r=-0.5287) was found between the Morningness-Eveningness Questionnaire (MEQ) score and the increase in VO2max, and the best positive correlation (r=0.4395) was found between MEQ and the increase in strength. Changes in balance and flexibility did not show any clear trends. CONCLUSION: In an environment with no outdoor daylight, it seems that the response to 8 weeks of aerobic training is larger in the E- than in the M-types, although the M-types showed a larger improvement in strength.

Chronotype, Physical Activity, and Sport Performance: A Systematic Review.

BACKGROUND: Many variables related to sport have been shown to have circadian rhythms. Chronotype is the expression of circadian rhythmicity in an individual, and three categories of chronotype are defined: morning types (M-types), evening types (E-types), and neither types (N-types). M-types show earlier peaks of several psychophysiological variables during the day than E-types. The effect of chronotype on athletic performance has not been extensively investigated. OBJECTIVE: The objective of the present review was to study the effect of chronotype on athletic performance and the psychophysiological responses to physical activity. METHODS: The present review adheres to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) reporting guidelines. We searched PubMed, Scopus, and Web of Science for scientific papers using the keywords "chronotype", "circadian typology", "morningness", and "eveningness" in combination with each of the words "sport", "performance", and "athletic." Relevant reference lists were inspected. We limited the search results to peer-reviewed papers published in English from 1985 to 2015. RESULTS: Ten papers met our inclusion criteria. Rating of perceived exertion and fatigue scores in relation to athletic performances are influenced by chronotype: M-types perceived less effort when performing a submaximal physical task in the morning than did N- and E-types. In addition, M-types generally showed better athletic performances, as measured by race times, in the morning than did N- and E-types. Other results concerning chronotype effect on physiological responses to physical activity were not always consistent: heterogeneous samples and different kinds of physical activity could partially explain these discrepancies. CONCLUSIONS: Sports trainers and coaches should take into account the influence of both the time of day and chronotype effect when scheduling training sessions into specific time periods.

Sleep recovery in participants after racing in the Finnmarkslop - Europe's longest dog­sled race.

BACKGROUND: During the dog-sled race, the Finnmarkslop (FL), which lasts up to 7 days, participants get little sleep and what they get is fragmented; concerns have been raised about proper sleep recovery. The aim of this study was to examine awareness of sleep deprivation by FL participants and post-race sleep recovery after completion of the race. METHODS: A total of 55 participants responded to an online survey 1 week and 1 month after the race; this measured the following factors: their awareness of sleep loss and possible strategies for recovery; their sleep-wake patterns using a Pittsburgh Sleep Questionnaire Index; and possible changes in respondents' sleep-wake patterns compared with their regular routines. RESULTS: During the FL, participants slept about 3-4 hours a day. Many were not aware of the accumulated sleep debt and did not engage in strategies to make up the loss. Insufficient levels of sleep and impoverished sleep quality were observed after the race, especially among those who were engaged in the FL for a longer period. Alertness levels were affected 1 week after the race. CONCLUSIONS: Among participants in the FL, the lack of awareness of sleep debt and insufficient sleep recovery could lead to health consequences. Those engaged in the race for longer should be more cautious during the recovery process because of possible sleep problems occurring after the race. Educational campaigns and easy access to professional support should be provided for participants in this type of sporting event.

THE EFFECT OF CHRONOTYPE ON PSYCHOPHYSIOLOGICAL RESPONSES DURING AEROBIC SELF-PACED EXERCISES.

It was hypothesized that an individual's chronotype might influence the response to physical activity at a given time of day. This study aimed to analyze the psychophysiological responses during a walking task at different times of day in individuals with different chronotypes. 46 students (M age=24.8 yr., SD=7.2) filled in the Morningness-Eveningness Questionnaire to determine chronotypes. Heart rate, walking time, and the rating of perceived exertion (RPE) were measured during two self-paced walking sessions: one in the morning (08:30) and one in the afternoon (15:30). A multivariate analysis of variance found a significant interaction between chronotype and time of day. The post hoc analysis showed a significant difference for RPE in the morning session, with evening types reporing a higher RPE compared with the morning types. The chronotype and the time of day when a physical task is undertaken can influence the RPE response, although it might not influence physiological or performance parameters. This has to be taken into account, because it can affect test reliability as well as possibly have a negative influence on the affective responses to a given task.

Green exercise as a workplace intervention to reduce job stress. Results from a pilot study.

BACKGROUND: Stress and mental fatigue are major health threats to employees in office-based occupations. Physical activity is widely used as a stress-management intervention for employees. Moreover, experiences in contact with nature have been shown to provide stress-reduction and restoration from mental fatigue. OBJECTIVES: In a pilot study designed as a randomized controlled trial we investigated the impact of a green-exercise intervention on psychological and physiological indicators of stress in municipality employees. METHODS: Fourteen employees (7 females and 7 males, 49±8 yrs) volunteered in an exercise-based intervention in workplace either outdoors in a green/nature area or in an indoor exercise-setting. The intervention consisted of an information meeting and two exercise sessions, each including a biking bout and a circuit-strength sequence using elastic rubber bands (45-minutes, at about 55% of HR reserve, overall). Main outcomes were perceived environmental potential for restoration, affective state, blood pressure (BP) and cortisol awakening response (CAR AUC(G) and CAR AUC(I)) and cortisol levels in serum. Measurements were taken at baseline and in concomitance with the exercise sessions. Furthermore, affective state and self-reported physical activity levels were measured over a 10-weeks follow-up period. RESULTS: Compared with the indoor group, the nature group reported higher environmental potential for restoration (p <  0.001) and Positive Affect (p <  0.01), along with improved CAR AUC(I) (p = 0.04) and, marginally, diastolic BP (p = 0.05). The nature group also reported higher ratings of Positive Affect at follow-up (p = 0.02). Differences at post-exercise were not found for any of the other components of affective state, systolic BP, CAR AUC(G) and cortisol levels measured in serum. CONCLUSIONS: Green-exercise at the workplace could be a profitable way to manage stress and induce restoration among employees. Further studies on larger samples are needed in order to improve the generalizability of the results.

THE POTENTIAL OF USING EXERCISE IN NATURE AS AN INTERVENTION TO ENHANCE EXERCISE BEHAVIOR: RESULTS FROM A PILOT STUDY.

According to attention-restoration theory (ART), natural environments can provide restorative experiences. In this pilot study, a mixed-methods approach was used to examine the potential of using exercise in a natural environment to enhance exercise behaviors. The study included an assessment study and an intervention study (overall n = 19). The participants underwent a standardized exercise program including biking and circuit strength training, either indoors or outdoors in nature. Measurements included connectedness to nature, perceived exertion, perceived environmental restorativeness, enjoyment, affect, future exercise intention, and self-reported exercise behavior. The participants also wrote a brief text describing the way in which the environment influenced their feelings while exercising. Quantitative data were analyzed using the Spearman rank correlation and linear mixed-effects modeling. The qualitative information was analyzed thematically. The integrated results indicated that, in accordance with ART, exercising in nature was associated with a greater potential for restoration and affective responses, which in some participants led to enhanced intention to exercise and increased exercise behavior. However, some perceived that the indoor exercise provided a more effective workout. Further studies on larger samples are needed.

Exercise Intensity and Pacing Strategy of Cross-country Skiers during a 10 km Skating Simulated Race.

The aim of this study was to observe the cardiovascular demands by monitoring the heart rate (HR) and the pacing strategy by evaluating the speed during a simulated cross-country skiing race. Eleven skiers (16.45 ± 1.67 yrs; 21.32 ± 2.03 kg m(-2); 72.35 ± 4.69 mL min(-1) kg(-1)) competed in a 10 km event divided into four laps. The HR profile was classified into four intensity zones. The skiers spent 66.84 ± 23.64% and 31.82 ± 23.77% of the total time above 90% and at 80-90% of the HRmax respectively, whereas the lower zones were negligible. During the event, a progressive increase in intensity was observed: HRmean raised by 2.42% in the last versus the first lap (p < 0.001). The skiers decreased their speed in the second (p = 0.017) and the third laps (p < 0.001) compared to with the first lap. In the fourth lap the skiers increased the speed slightly but without statistical difference. The speed maintained by the skiers resulted in the adoption of a reverse J-shaped pacing strategy.

Chronotype influences activity circadian rhythm and sleep: differences in sleep quality between weekdays and weekend.

Several studies have shown the differences among chronotypes in the circadian rhythm of different physiological variables. Individuals show variation in their preference for the daily timing of activity; additionally, there is an association between chronotype and sleep duration/sleep complaints. Few studies have investigated sleep quality during the week days and weekends in relation to the circadian typology using self-assessment questionnaires or actigraphy. The purpose of this study was to use actigraphy to assess the relationship between the three chronotypes and the circadian rhythm of activity levels and to determine whether sleep parameters respond differently with respect to time (weekdays versus the weekend) in Morning-types (M-types), Neither-types (N-types) and Evening-types (E-types). The morningness-eveningness questionnaire (MEQ) was administered to 502 college students to determine their chronotypes. Fifty subjects (16 M-types, 15 N-types and 19 E-types) were recruited to undergo a 7-days monitoring period with an actigraph (Actiwacth® actometers, CNT, Cambridge, UK) to evaluate their sleep parameters and the circadian rhythm of their activity levels. To compare the amplitude and the acrophase among the three chronotypes, we used a one-way ANOVA followed by the Tukey-Kramer post-hoc test. To compare the Midline Estimating Statistic of Rhythm (MESOR) among the three chronotypes, we used a Kruskal-Wallis non-parametric test followed by pairwise comparisons that were performed using Dunn's procedure with a Bonferroni correction for multiple comparisons. The analysis of each sleep parameter was conducted using the mixed ANOVA procedure. The results showed that the chronotype was influenced by sex (χ(2) with p = 0.011) and the photoperiod at birth (χ(2) with p < 0.05). Though the MESOR and amplitude of the activity levels were not different among the three chronotypes, the acrophases compared by the ANOVA post-hoc test were significantly different (p < 0.001). The ANOVA post-hoc test revealed the presence of a significant difference (p < 0.001) between the M-types (14:32 h) and E-types (16:53 h). There was also a significant interaction between the chronotype and four sleep parameters: Sleep end, Assumed Sleep, Immobility Time and Sleep Efficiency. Sleep Efficiency showed the same patterns as did Assumed Sleep and Immobility Time: the Sleep Efficiency of the E-types was poorer than that of the M- and N-types during weekdays (77.9% ± 7.0 versus 84.1% ± 4.9 and 84.1% ± 5.2) but was similar to that measured in the M- and N-types during the weekend. Sleep Latency and Movement and Fragmentation Index were not different among the three chronotypes and did not change on the weekend compared with weekdays. This study highlights two key findings: first, we observed that the circadian rhythm of activity levels was influenced by the chronotype; second, the chronotype had a significant effect on sleep parameters: the E-types had a reduced sleep quality and quantity compared with the M- and N-types during weekdays, whereas the E-types reached the same levels as the other chronotypes during the weekends. These findings suggest that E-types accumulate a sleep deficit during weekdays due to social and academic commitments and that they recover from this deficit during "free days" on the weekend.

Hydration in female drivers in a 1044 km dog sled race in Finnmark.

OBJECTIVE: Drinking strategies during long dog sled competitions are important to avoid dehydration. Most of the studies involving dog sled racers (mushers) refer to male subjects. The purpose of this study was to study female mushers participating in a dog sled race of 1044 km, with a focus on hydration and drinking behavior. METHODS: Two female mushers (aged 50 and 23 years), of the 6 who signed up for participation in the dog sled 1044 km race, volunteered for the study. Before the race, maximum oxygen uptake and maximum heart rate (HR) were determined. Body compositions was measured before and shortly after the race. Heart rate was continuously measured by a HR monitor in the first 2 legs of the race, and urine samples were collected during the race. Urine osmolality and urine specific gravity were determined using freezing point depression and handheld refractometer. Values of urine osmolality greater than 900 mOsm · L(-1) and specific gravity greater than 1.030 were used as signs of dehydration. RESULTS: The older musher had a mean HR of 65%, and the younger musher had a mean HR of 57% of the predicted maximum HR. The mushers reached a peak HR of 91% of their predicted maximum; they worked at an average HR of 55% (average of all legs). The younger woman had urine osmolality values above the dehydration limits in most of the samples. Only small changes in the before and after race anthropometric measurements were found. CONCLUSIONS: Dog sled racing is a strenuous activity and drinking strategies are important to avoid dehydration. It seems that the drinking strategy of our subjects was adequate to supplement the hydration loss; yet, emotional arousals occurring during the race may affect drinking behavior. The attentive assistance of the mushers' handlers is therefore important.

Effects of sleep loss on the rest-activity circadian rhythm of helpers participating in continuous dogsled races.

OBJECTIVE: The Finnmarksløpet dogsled race lasts up to 7 days. Helpers, who keep time, coach, and transport equipment, have to be alert though they have little and fragmented sleep. This study investigated disruptions of the rest-activity rhythm among helpers. METHODS: 10 helpers were monitored by actigraph a week before, during, and after the race. Sleep logs, sleepiness rate, and self-reported quality of sleep were collected. RESULTS: Nonparametric circadian rhythm analysis showed significant differences between the pre- and postrace interdaily stability and amplitude of rhythm. Compared to prerace, sleepiness at bedtime was increased and number of nocturnal awakenings was reduced postrace, although the actigraphic outputs showed no improvement in sleep quality. Helpers who were engaged in the race for a longer span (5-6 days) had more difficulty recovering from the sleep loss accumulated during the race than those engaged for a shorter time (2-3 days). CONCLUSION: Poor sleep combined with prolonged and demanding mental focus for 2 days or more has a negative influence upon the rest-activity cycle, though complete restoration of the cycle occurs over 1 week or more. Being in such a condition for ≥ 5 days leads to disruptions of the circadian component of the sleep-wake cycle that hampers the sleep recovery process. Disrupted sleep and demanding mental requirements are common in long-distance sporting events as well as among shift workers. Follow-up intervention should be made in such cases to ensure the return of a healthy rest-activity rhythm and sleep quality.

Influence of chronotype on responses to a standardized, self-paced walking task in the morning vs afternoon: a pilot study.

The response to sub-maximal physical activity performed in the morning and late afternoon by individuals with different chronotypes was investigated. 22 participants filled out the Morningness-Eveningness Questionnaire and underwent a self-paced walking task that consisted of walking from the top to the bottom of a hill and back three times (1,836 meters, with a slope of 14.16%). The task was repeated twice: late afternoon (16:30) and early morning (08:30). Walking speed (time for completion in seconds), heart rate, and perceived exertion were measured during each task, with overall results given as a general descriptive analysis. Preliminary findings suggest that chronotype is likely to influence the responses to exercise, mostly with evening-types seeming at a disadvantage when performing a physical task in the morning. Individuals can be classified by circadian typology or chronotype, which is the propensity to be a morning-type, evening-type, or neither-type. The circadian typology, commonly referred to as being a morning person or an evening person or somewhere in between, is involved not only in the expression of physiological rhythms, but also in habits and lifestyles, such as sleeping patterns (Park, Matsumoto, Seo, & Shinkoda, 1999) that emerge especially during adolescence (Park, Matsumoto, Seo, Kang, & Nagashima, 2002) and remain throughout adult life (Koukkari & Sothern, 2006).

Methodological issues for studying the rest-activity cycle and sleep disturbances: a chronobiological approach using actigraphy data.

Shift work schedules, intensive physical exercise late in the day, psychological stress, or a busy lifestyle might induce disorders of the circadian structure, which can affect health on both the physiological and neurobehavioral levels. Rest-activity rhythm is strongly connected with an organism's circadian structure, and irregular sleep-wake patterns can lead to a disruption of entrainment, resulting in physiological and neurobehavioral dysfunction. Shift nurses are often subject to disturbances in the quality and duration of their sleep, raising the possibility of negative impacts on their health and their patients' safety. Researchers have used actigraphy in a number of studies to assess sleep patterns. Because of the close connection between sleep and circadian structure, it may be useful to extend the evaluation of actigraphy data to the analysis of the rest-activity rhythm with rhythmometric procedures to provide a better understanding of possible sleep disorders in relation to entrainment. Actigraphy is an easy and reliable way to study these rhythms and identify possible circadian-rhythm disorders. In this article, the authors discuss methodological issues concerning the evaluation of the rest-activity rhythm, with a focus on actigraphy.

Effects of sleep loss and strenuous physical activity on the rest-activity circadian rhythm: a study on 500 km and 1,000 km dogsled racers.

OBJECTIVE: Rest-activity circadian rhythm is strongly linked to an organism's entrainment. Sleep loss and prolonged fatigue could affect the circadian system, inducing neurobehavioral deficits. The Finnmarksløpet is Europe's longest dogsled race. In this competition, lasting up to 7 days, participants (mushers) are physically active most of the time, having little and fragmented rest. Therefore, the race provides an opportunity to investigate the effects of prolonged fatigue and sleep loss. METHODS: Ten mushers, participating in the 500 km and 1,000 km categories, underwent continuous actigraph monitoring (5 days) before and after the race. During the competition, heart rate (HR) was recorded by an HR monitor. RESULTS: There was a reduction in the average activity values during the 24-hr cycle after the race. Although there were signs of a forward phase shift, these were weak and unstable. Nonparametric circadian rhythm analysis (NPCRA) showed reductions in interdaily stability (IS) and relative amplitude (RA). 1,000 km mushers also showed sleep disturbances. CONCLUSION: A period of 3 days of little and fragmented sleep (3-4 hr of total rest per day), in which subjects were engaged in a prolonged physical effort, was enough to significantly affect the rest-activity rhythm. A longer period (5 days) in such a condition induced even more accentuated alterations, with a disturbance in nocturnal sleep. Disrupted sleep is common among hospitalized patients and those working long shifts. This study demonstrates changes in the structure of the rest-activity circadian rhythm that can result and may suggest opportunities for intervention.

Circadian heart rate and blood pressure variability considered for research and patient care.

OBJECTIVES: To review mechanisms of circadian variations in heart rate variability (HRV) and blood pressure variability (BPV) and mortality and morbidity due to cardiovascular diseases (CVD). METHODS: Results from 7-day/24-h HRV and BPV are interpreted by gender and age-specified reference values in the context of a Medline search. RESULTS: Abnormal HRV and BPV measured around the clock for 7 days provides information on the risk of subsequent morbid events in subjects without obvious heart disease and without abnormality outside the conventional (in the sense of chronobiologically unquantified) physiological range. Meditation, beta-blockers, ACE inhibitors, n-3 fatty acids and estrogens may have a beneficial influence on HRV, but there is no definitive outcome-validated therapy. Low HRV has been associated with a risk of arrhythmias and arrhythmic death, unstable angina, myocardial infarction, progression of heart failure and atherosclerosis. BPV may be characterized by treatable circadian-hyper-amplitude-tension (CHAT), which can be transient '24-h CHAT' or '7-day-CHAT', MESOR-hypertension and/or an unusually-timed (odd) circadian acrophase (ecphasia), all associated with an increased risk of stroke, stroke death, myocardial infarction, and kidney disease. CONCLUSIONS: Precise insight into the patho-physiology in time of HRV and BPV is needed with development of a consensus on best measures of HRV for clinical purposes and to determine when a 7-day record interpreted chronobiologically suffices and when it does not, for detection within as well as outside the conventional normal range, for diagnostic clinical practice and to direct therapy of risk greater than that associated with hypertension, smoking or any other risk factor.

Cross-spectrally coherent ~10.5- and 21-year biological and physical cycles, magnetic storms and myocardial infarctions*

Magnetic storms trigger myocardial infarctions with mechanisms relating to heart rate variability. Solar cycle-to-solar cycle differences and solar cycle stage dependence shown herein may resolve prior controversy and serve to advocate coordinated worldwide systematically aligned biological and physical monitoring. * This paper was originally invited by the historian-geophysicist Wilfried SCHRöDER of Bremen, Germany, for his biographical "Encounters," and is to serve as an update on the project on the BIOsphere and the Cosmos (BIOCOS) and its offspring ICEHRV (Dr. Kuniaki Otsuka's International Chronome Ecologic Study of Heart Rate Variability). It is intended for distribution at a NATO conference on space weather hazards, organized by Dr. Ioannis Daglis, June 18-29, 2000.