Circadian rhythms in competitive sabre fencers: internal desynchronization and performance

Daily, weekly and annual patterns in children's accidental sport injuries

Details of serious injuries to children ≤16 yrs. of age that necessitated urgent surgical intervention by the Department of Pediatric Surgery of the University Hospital of Lausanne, Switzerland were recorded into a database registry. Some 15 110 entries listed the precise time of injury, and 3114 (20.6%) of these resulted from participating in sport-associated activities. Time-of-day, day-of-week and month-of-year differences in the total number of children's accidental sport injuries (CASI) were validated. Time-of-day patterns were substantiated for "All Sports", for both boys and girls 5-16 yrs. of age, with more boys than girls experiencing incidents at almost every clock hour. Moreover, they were substantiated for this age group for each of the six different considered individual and team CASI categories - Physical Exercises at School; Bicycle Riding; Roller Skating and Skateboarding; Snow Skiing, Sledding, and Tobogganing; Soccer; and Basketball - for which sample sizes were sufficiently large (n > 230) to perform statistical assessment by ANOVA, t-test and/or cosinor analyses. CASI happened primarily between 06:00 and 17:00 h and rarely evening or overnight. Features - specific clock-time and number of peaks and troughs - of the CASI daily curve pattern of the individual six sport categories differed somewhat; nonetheless, excess or greatest number of CASI typically happened between 12:00 and 14:00 h, even when summertime and other scheduled school and family vacation periods were taken into account. Time-of-day and day-of-week patterns in the boy/girl sex ratio were also validated, with midday and Friday/Saturday peaks, respectively. We hypothesize the prominent 24 h patterns of CASI of 5-16 yr. olds, in particular, are representative of a combination of several determinants. These include exogenous periodic and cyclic environmental and sociocultural phenomena, genetic sex-related traits, plus endogenous circadian cognitive and physiologic rhythms, with the common midday injury excess of many sport categories, at least in part, the consequence of the well-documented midday dip in attention and vigilance of children.

Do night and around-the-clock firefighters' shift schedules induce deviation in tau from 24 hours of systolic and diastolic blood pressure circadian rhythms?

Systolic (S) and diastolic (D) blood pressures (BP) [SBP and DBP] are circadian rhythmic with period (τ) in healthy persons assumed to be maintained at 24.0h. We tested this assumption in a sample of 30 healthy career (mean >12 yrs) 30-to-46 yr-old male Caucasian French firefighters (FFs) categorized into three groups according to work schedule and duties: Group A - 12 FFs working 12h day, 12h night, and occasionally 24h shifts and whose primary duties are firefighting plus paramedical and road rescue services; Group B - 9 FFs working mostly 12h day and 12h night shifts and whose duties are answering incoming emergency calls and coordinating service vehicle dispatch from fire stations with Group A personnel; Group C - 9 day shift (09:00-17:00h) FFs charged with administrative tasks. SBP and DBP, both in winter and in summer studies of the same FFs, were sampled by ambulatory BP monitoring every 1h between 06:00-23:00h and every 2h between 23:01-05:59h, respectively, their approximate off-duty wake and sleep spans, for 7 consecutive days. Activity (wrist actigraphy) was also sampled at 1-min intervals. Prominent τ of each variable was derived by a power spectrum program written for unequal-interval time series data, and between-group differences in incidence of τ≠24h of FFs were assessed by chi square test. Circadian rhythm disruption (τ≠24h) of either the SBP or DBP rhythm occurred almost exclusively in night and 24h shift FFs of Group A and B, but almost never in day shift FFs of Group C, and it was not associated with altered τ from 24.0h of the circadian activity rhythm. In summer, occurrence of τ≠24 for FFs of Group A and B differed from that for FFs of Group C in SBP (p=0.042) and DBP (p=0.015); no such differences were found in winter (p>0.10). Overall, manifestation of prominent τ≠24h of SBP or DBP time series was greater in summer than winter, 27.6% versus 16.7%, when workload of Group B FFs, i.e. number of incoming emergency telephone calls, and of Group A FFs, i.e. number of dispatches for provision of emergency services, was, respectively, two and fourfold greater and number of 12h night shifts worked by Group B FFs and number of 24h shifts worked by Group A FFs was, respectively, 92% and 25% greater. FFs of the three groups exhibited no winter-summer difference in τ≠24h of SBP or SDP; however, τ≠24h of DBP in Group B FFs was more frequent in summer than winter (p=0.046). Sleep/wake cycle disruption, sleep deprivation, emotional and physical stress, artificial light-at-night, and altered nutrient timings are hypothesized causes of τ≠24h for BP rhythms of affected Groups A and B FFs, but with unknown future health effects.

Concepts in human biological rhythms

Biological rhythms and their temporal organization are adaptive phenomena to periodic changes in environmental factors linked to the earth's rotation on its axis and around the sun. Experimental data from the plant and animal kingdoms have led to many models and concepts related to biological clocks that help describe and understand the mechanisms of these changes. Many of the prevailing concepts apply to all organisms, but most of the experimental data are insufficient to explain the dynamics of human biological clocks. This review presents phenomena thai are mainly characteristic ofand unique to - human chronobiology, and which cannot be fully explained by concepts and models drawn from laboratory experiments. We deal with the functional advantages of the human temporal organization and the problem of desynchronization, with special reference to the period (τ) of the circadian rhythm and its interindividual and intraindividual variability. We describe the differences between right- and left-hand rhythms suggesting the existence of different biological clocks in the right and left cortices, Desynchronization of rhythms is rather frequent (one example is night shift workers). In some individuals, desynchronization causes no clinical symptoms and we propose the concept of "allochronism" to designate a variant of the human temporal organization with no pathological implications. We restrict the term "dyschronism" to changes or alterations in temporal organization associated with a set of symptoms similar to those observed in subjects intolerant to shift work, eg, persisting fatigue and mood and sleep alterations. Many diseases involve chronic deprivation of sleep at night and constitute conditions mimicking thai of night shift workers who are intolerant to desynchronization. We also present a genetic model (the dian-circadian model) to explain interindividual differences in the period of biological rhythms in certain conditions.

Circadian and sleep disorders in Parkinson's disease

Impaired sleep and alertness, initially recognized by James Parkinson in his famous monograph "An Essay on the Shaking Palsy" in 1817, is one of the most common and disabling nonmotor symptoms of Parkinson's disease (PD). It is only recently, however, that sleep disturbances in PD have received the attention of medical and research community. Dopamine, the major neurotransmitter implicated in the pathogenesis of PD, plays a pivotal role in the regulation of sleep and circadian homeostasis. Sleep dysfunction affects up to 90% of patients with PD, and may precede the onset of the disease by decades. Sleep dysfunction in PD may be categorized into disturbances of overnight sleep and daytime alertness. Etiology of impaired sleep and alertness in PD is multifactorial. Co-existent primary sleep disorders, medication side effects, overnight re-emergence of motor symptoms, and primary neurodegeneration itself, are main causes of sleep disruption and excessive daytime sleepiness among patients with PD. Increasing body of evidence suggests that the circadian system becomes dysregulated in PD, which may lead to poor sleep and alertness. Treatment options are limited and frequently associated with unwanted side effects. Further studies that will examine pathophysiology of sleep dysfunction in PD, and focus on novel treatment approaches are therefore very much needed. In this article we review the role of dopamine in regulation of sleep and alertness and discuss main sleep and circadian disturbances associated with PD.

The science of fencing: implications for performance and injury prevention

In this review we analyse the data from the literature on fencing with the aim of creating a psychobiological and multi-factorial model of fencing performance. Fencing is an open-skilled combat sport that was admitted to the first modern Olympic Games in Athens (1896). It is mainly practised indoors, with three different weapons: the foil, the sabre and the épée, each contested with different rules. A fencing international tournament may last between 9 and 11 hours. Bouts represent only 18% of total competition time, with an effective fight time of between 17 and 48 minutes. The physical demands of fencing competitions are high, involving the aerobic and anaerobic alactic and lactic metabolisms, and are also affected by age, sex, level of training and technical and tactical models utilized in relation to the adversary. The anthropometrical characteristics of fencers show a typical asymmetry of the limbs as a result of the practice of an asymmetrical sport activity. Fencing produces typical functional asymmetries that emphasize the very high level of specific function, strength and control required in this sport. Moreover, the physical demands of fencing are closely linked to the perceptual and psychological ones, and all are subjected to a continuous succession of changes during the bouts based on the behaviour of the opponent. For this reason it is difficult to identify a significant relationship between any one physiological characteristic and performance, and performance is more likely to be influenced by perceptual and neuro-physiological characteristics. Fencers need to anticipate the opponent and to mask their true intentions with a game of feints and counter-feints, which must be supported by an adequate psycho-physical condition to prevent central and peripheral fatigue. Fencing is not particularly dangerous; however, there is a fine line between a fatal lesion and a simple wound from a broken blade. The suggestions for injury prevention fall into three primary areas: (i) actions that can be taken by participants; (ii) improvements in equipment and facilities; and (iii) administration of fencing competitions. As in every other sport, the prevention of accidents must be accomplished at various levels and above all must involve the institutions that are responsible for safety in sports.

Time-of-day effect on the torque and neuromuscular properties of dominant and non-dominant quadriceps femoris

The study was conducted first, to determine the possibility of a dichotomy between circadian rhythm of maximal torque production of the knee extensors of the dominant and non-dominant legs, and second, to determine whether the possible dichotomy could be linked to a change in the downward drive of the central nervous system and/or to phenomena prevailing at the muscular level. The dominant leg was defined as the one with which subjects spontaneously kick a football. Tests were performed at 06:00, 10:00, 14:00, 18:00, and 22:00 h. To distinguish the neural and muscular mechanisms that influence muscle strength, the electromyographic and mechanical muscle responses associated with electrically evoked and/or voluntary contractions of the human quadriceps and semi-tendinosus muscles for each leg were recorded and compared. The main finding was an absence of interaction between time-of-day and dominance effects on the torque associated with maximal voluntary contraction (MVC) of both quadriceps. A significant time-of-day effect on MVC torque of the knee extensors was observed for the dominant and non-dominant legs when the data were collapsed, with highest values occurring at 18:00 h (p < 0.01). From cosinor analysis, a circadian rhythm was documented (p < 0.001) with the peak (acrophase) estimated at 18:18 +/- 00:12 h and amplitude (one-half the peak-to-trough variation) of 3.3 +/- 1.1%. Independent of the leg tested, peripheral mechanisms demonstrated a significant time-of-day effect (p < 0.05) on the peak-torque of the single and doublet stimulations, with maximal levels attained at 18:00 h. The central activation of the quadriceps muscle of each leg remained unchanged during the day. The present results confirmed previous observations that muscle torque changes in a predictable manner during the 24 h period, and that the changes are linked to modifications prevailing at the muscular, rather than the neural, level. The similar rhythmicity observed in this study between the dominant and non-dominant legs provides evidence that it is not essential to test both legs when simple motor tasks are investigated as a function of the time of day.

Gender differences in the circadian variations in muscle strength assessed with and without superimposed electrical twitches

The circadian rhythm in muscle strength was analysed in 12 males (28 +/- 4 years, 79.6 +/- 12.3 kg, 1.80 +/- 0.05 m) and eight females (28 +/- 4 years, 60.3 +/- 5.5 kg, 1.61 +/- 0.08 m). After two familiarization sessions, participants were tested at six different times of the day (02:00, 06:00, 10:00, 14:00, 18:00 and 22:00 hours), the order of which was randomly assigned over 3-4 days. Rectal temperature (T(rec)) was measured over 30 min before each test. Peak isokinetic torques (PT) of knee extensors and flexors were then measured at 1.05 rad s(-1) and 3.14 rad s(-1) through a 90 degrees range of motion. Maximal isometric voluntary contraction (MVC) of knee extensors and flexors was measured at 60 degrees of knee flexion and the MVC of knee extensors was also assessed with superimposed electrical twitches (50 Hz, 250 V, 200 mus pulse width) in order to control for motivational effects. Three trials were performed in each condition, separated by 3 min recovery, and the highest values were retained for subsequent analyses. A significant circadian rhythm was observed for T(rec) in both males and females (acrophase, Phi, 17:29 and 16:40 hours; mesor, Me, 37.0 and 36.8 degrees C; amplitude, A, 0.28 and 0.33 degrees C for males and females, respectively). The mesor of T(rec) was higher in males than in females (p < 0.05). Significant circadian rhythms were observed for knee extensor PT at 3.14 rad s(-1) in males (Phi, 17:06 hours; Me, 178.2 N m; A, 4.7 N m) and for knee extensor PT at 1.05 rad s(-1) in females (Phi, 15:35 hours; Me, 128.7 N m; A, 3.7 N m). In males, the MVC of knee extensors demonstrated a significant circadian rhythm, but only when electrical twitches were superimposed (Phi, 16:17 h; Me, 302.1 N m; A, 13.6 N m). Acrophases of all indices of muscle strength were not statistically different between the two groups and were located in the afternoon (12:47 < Phi < 17:16 hours). The amplitude (percentage of mesor) of extensors MVC (electrically stimulated) was higher in males (6.4%) than in females (4.2%; p < 0.05). Significant circadian rhythms were not consistently observed for all indices of muscle strength whatever the gender. Our group of female subjects tended to show lower circadian amplitudes than the males. In males, maximal voluntary contraction of electrically stimulated muscles followed a circadian curve, which was not significant without the superimposed twitches. These results suggest that motivation could have a masking effect on the circadian rhythm in muscle performance and strengthen the view that peripheral factors are implicated in this rhythm.

Right- and left-brain hemisphere. Rhythm in reaction time to light signals is task-load-dependent: age, gender, and handgrip strength rhythm comparisons

In healthy mature subjects simple reaction time (SRT) to a single light signal (an easy task) is associated with a prominent rhythm with tau = 24 h of dominant (DH) as well as nondominant (NDH) hand performance, while three-choice reaction time (CRT), a complex task, is associated with tau = 24 h of the DH but tau < 24 h of the NDH. The aims of the study were to assess the influence of age and gender on the difference in tau of the NDH and DH, as it relates to the corresponding cortical hemisphere of the brain, in comparison to the rhythm in handgrip strength. Healthy subjects, 9 (5 M and 4 F) adolescents 10-16 yr of age and 15 (8 M and 7 F) adults 18-67 yr of age, active between 08:00 +/- 1 h and 23:00 +/- 1:30 h and free of alcohol, tobacco, and drug consumption volunteered. Data were gathered longitudinally at home and work 4-7 times daily for 11-20 d. At each test time the following variables were assessed: grip strength of both hands (Dynamometer: Colin-Gentile, Paris, France); single reaction time to a yellow signal (SRT); and CRT to randomized yellow, red, or green signal series with varying instruction from test to test (Psycholog-24: Biophyderm, France). Rhythms in the performance in SRT, CRT, and handgrip strength of both DH and NDH were explored. The sleep-wake rhythm was assessed by sleep-logs, and in a subset of 14 subjects it was also assessed by wrist actigraphy (Mini-Motionlogger: AMI, Ardsley NY). Exploration of the prominent period tau of time series was achieved by a special power spectra analysis for unequally spaced data. Cosinor analysis was used to quantify the rhythm amplitude A and rhythm-adjusted mean M of the power spectral analysis determined trial tau. A 24h sleep-wake rhythm was detected in almost all cases. In adults, a prominent tau of 24 h characterized the performance of the easy task by both the DH and NDH. In adults a prominent tau of 24 h was also detected in the complex CRT task performed by the DH, but for the NDH the tau was < 24 h. This phenomenon was not gender-related but was age-related since it was seldom observed in adolescent subjects. Hand-side differences in the grip strength rhythms in the same individuals were detected, the tau being ultradian rather than circadian in adolescent subjects while in mature subjects the tau frequently differed from that of the rhythm in CRT. These findings further support the hypothesis that functional biological clocks exist in both the left and right hemispheres of the human cortex.

Interindividual differences in the flexibility of human temporal organization: pertinence to jet lag and shiftwork

Interindividual variability in the human temporal structure is seldom taken into account, especially in studies devoted to the effects of shiftwork and jet lag. The understated postulate is that humans can be treated as a pure strain species. This paper reviews some facts and concepts with special reference to interindividual changes in the rhythm period tau and the resulting dyschronism. The following points are addressed. (1) Subjects and methods (importance of longitudinal field studies on shift workers). (2) Criteria for tolerance to shiftwork and jet lag. (3) Interindividual differences and shiftwork problems (subject type; the association between good shiftwork tolerance and stable temporal structure; dychronism with tau s differing from 24h and from variable to variable. (4) The genetic background of circadian dyschronism. The Dian-circadian genetic model of biological rhythms. It allows understanding of one's susceptibility to dyschronism, which was actually observed in approximately equal to 30% of subjects studied longitudinally. (5) Practical implications of interindividual differences (dissociate problems of passengers after a transmeridian flight-who have to adjust their temporal structure to local time-from problems of shiftworkers-who need to prevent alteration of their temporal structure; the advantage for the latter of participating in a rapid rotation system rather than a weekly rotation; emphasis that the suitability of a given subject for a given shiftworking condition is likely to be estimated only after a trial span of time including longitudinal study of a set of rhythms.