The influence of circadian rhythm during a sustained submaximal exercise and on recovery process

Repeated Sprint Variations According to Circadian Rhythm at Different Menstrual Cycle Phases

This study assessed the repeated sprint performance in relation to circadian rhythm during different menstrual cycle phases (MCP). Twelve volunteer eumenorrheic women team sport athletes performed 5×6-s cycling sprints in morning (9 am to 10 am) and evening (6 pm to 7 pm) sessions during the mid-follicular (FP, 6th-10th d) and luteal phases (LP, 19th-24th d). Body weight, oral body temperature, resting heart rate and lactate levels together with estradiol, progesterone and cortisol levels were determined before tests. Relative peak and mean power and performance decrements were determined as performance variables and maximum heart rate, lactate and ratings of perceived exertion were determined as physiological variables. Evening body temperatures were significantly higher. Cortisol levels were higher in the morning and in the FP. Resting lactate levels did not vary with MCP or time of day, but a significant MCP x time of day interaction was observed. Body weight showed no change according to time of day and MCP. There was no significant effect of MCP and time of day on performance and physiological variables, in contrast, maximum lactate values were notably higher in the evening. In conclusion, MCP and time of day need not be considered during repeated sprint exercises of eumenorrheic women athletes.

Functional muscle group- and sex-specific parameters for a three-compartment controller muscle fatigue model applied to isometric contractions

The three-compartment controller with enhanced recovery (3CC-r) model of muscle fatigue has previously been validated separately for both sustained (SIC) and intermittent isometric contractions (IIC) using different objective functions, but its performance has not yet been tested against both contraction types simultaneously using a common objective function. Additionally, prior validation has been performed using common parameters at the joint level, whereas applications to many real-world tasks will require the model to be applied to agonistic and synergistic muscle groups. Lastly, parameters for the model have previously been derived for a mixed-sex cohort not considering the differece in fatigabilities between the sexes. In this work we validate the 3CC-r model using a comprehensive isometric contraction database drawn from 172 publications segregated by functional muscle group (FMG) and sex. We find that prediction errors are reduced by 19% on average when segregating the dataset by FMG alone, and by 34% when segregating by both sex and FMG. However, minimum prediction errors are found to be higher when validated against both SIC and IIC data together using torque decline as the outcome variable than when validated sequentially against hypothesized SIC intensity-endurance time curves with endurance time as the outcome variable and against raw IIC data with torque decline as the outcome variable.

Time-of-Day Effects on Anaerobic Power and Concentration of Selected Hormones in Blind Men

Knowledge of the circadian rhythm of the blind person and diurnal changes in anaerobic power and hormones concentration can create the possibility of individualising physical training. The aim of the study was to examine the time-of-day effects on anaerobic performance and the concentration of selected hormones. The measurements were performed at two different times of the day (10:00 a.m., 10:00 p.m.) in blind men at the age of 20–25 years old. The experiment group was chosen by using repeated hormonal tests four times a day so that each selected patient had a sleep/wake cycle even of 24 h. Anaerobic peak power and total work were tested in an anaerobic sprint test, and the concentration of growth hormone, testosterone, cortisol, and melatonin was determined. In blind men, the hormonal response was not driven by the photoperiod as in the control group. In the blind group, at 10:00 p.m., anaerobic peak power and total work results were significantly higher than at 10:00 a.m. and negatively correlated with melatonin levels. No such correlation was found in the control group.

Diurnal gait fluctuations in single- and dual- task conditions

Gait is one of the most basic movements, and walking activity accomplished in dual task conditions realistically represents daily life mobility. Much is known about diurnal variations of gait components such as muscle power, postural control, and attention. However, paradoxically only little is known about gait itself. The aim of this study was to analyze whether gait parameters show time-of-day fluctuation in simple and dual task conditions. Sixteen young subjects performed sessions at five specific hours (06:00, 10:00, 14:00, 18:00 and 22:00 h), performing a single (walking or counting) and a dual (walking and counting) task. When performing gait in dual task conditions, an additional cognitive task had to be carried out. More precisely, the participants had to count backwards from a two-digit random number by increments of three while walking. Spatio-temporal gait parameters and counting performance data were recorded for analysis. Walking speed significantly decreased, while stride length variability increased when the task condition switched from single to dual. In the single-task condition, diurnal variations were observed in both walking speed and counting speed. Walking speed was higher in the afternoon and in the evening (14:00 and 22:00 h) and lower in the morning (10:00 h). Counting speed was maximum at 10:00 and 14:00 h and minimum at 18:00 h. Nevertheless, no significant diurnal fluctuation was substanytiated in the dual task condition. These results confirm the existing literature about changes in gait between single and dual task conditions. A diurnal pattern of single-task gait could also be highlighted. Moreover, this study suggests that diurnal variations faded in complex dual task gait, when the cognitive load nearly reached its maximum. These findings might be used to reduce the risk for falls, especially of the elderly.

Relationship Between Mobility and Arousal Level After Waking Up

BACKGROUND AND PURPOSE

Falling is an unexpected event for older adults, but few studies have investigated falls related to arousal levels and mobility immediately after waking up in the morning. Therefore, the purpose of this study was to clarify the possible relationship of arousal level and mobility with falls in the early morning hours.

METHODS

We investigated both arousal levels and mobility of 14 community-dwelling older adults after waking up, from 4:00 AM until 2:00 PM. Mobility and arousal levels were evaluated through the following tests: Timed Up and Go, Functional Reach, postural sway, and critical frequency of fusion. Baseline of mobility and arousal levels were measured before sleep and after 5 hours of sleep. Immediately after waking up, each participant's mobility and arousal levels were remeasured and then also remeasured 2 hours later, 6 hours later, and 10 hours later, respectively. Stanford Sleepiness Scale was also chosen to measure the internal state of subjective sleepiness and it was measured 7 times at 2-hour intervals after the participants woke up from sleep.

RESULTS

Significant differences were found between before sleep and after awakening in the score of Timed Up and Go test and Stanford Sleepiness Scale. The speed of Timed Up and Go test after awaking was slower than that before sleep. The Stanford Sleepiness Scale showed high states of sleepiness.

CONCLUSION

We found that the decrease in arousal level in the early morning may affect mobility. The awareness of the degree of arousal levels may increase fall prevention in older adults in the early morning hours.

Sleep, circadian rhythms, and athletic performance

Sleep deprivation and time of day are both known to influence performance. A growing body of research has focused on how sleep and circadian rhythms impact athletic performance. This review provides a systematic overview of this research. We searched three different databases for articles on these issues and inspected relevant reference lists. In all, 113 articles met our inclusion criteria. The most robust result is that athletic performance seems to be best in the evening around the time when the core body temperature typically is at its peak. Sleep deprivation was negatively associated with performance whereas sleep extension seems to improve performance. The effects of desynchronization of circadian rhythms depend on the local time at which performance occurs. The review includes a discussion of differences regarding types of skills involved as well as methodological issues.

Circadian disruption and remedial interventions: effects and interventions for jet lag for athletic peak performance

Jet lag has potentially serious deleterious effects on performance in athletes following transmeridian travel, where time zones are crossed eastwards or westwards; as such, travel causes specific effects related to desynchronization of the athlete's internal body clock or circadian clock. Athletes are particularly sensitive to the effects of jet lag, as many intrinsic aspects of sporting performance show a circadian rhythm, and optimum competitive results require all aspects of the athlete's mind and body to be working in tandem at their peak efficiency. International competition often requires transmeridian travel, and competition timings cannot be adjusted to suit individual athletes. It is therefore in the interest of the individual athlete and team to understand the effects of jet lag and the potential adaptation strategies that can be adopted. In this review, we describe the underlying genetic and physiological mechanisms controlling the circadian clock and its inherent ability to adapt to external conditions on a daily basis. We then examine the fundamentals of the various adaptation stimuli, such as light, chronobiotics (e.g. melatonin), exercise, and diet and meal timing, with particular emphasis on their suitability as strategies for competing athletes on the international circuit. These stimuli can be artificially manipulated to produce phase shifts in the circadian rhythm to promote adaptation in the optimum direction, but care must be taken to apply them at the correct time and dose, as the effects produced on the circadian rhythm follow a phase-response curve, with pronounced shifts in direction at different times. Light is the strongest realigning stimulus and careful timing of light exposure and avoidance can promote adjustment. Chronobiotics such as melatonin can also be used to realign the circadian clock but, as well as timing and dosage issues, there are also concerns as to its legal status in different countries and with the World Anti-Doping Agency. Experimental data concerning the effects of food intake and exercise timing on jet lag is limited to date in humans, and more research is required before firm guidelines can be stated. All these stimuli can also be used in pre-flight adaptation strategies to promote adjustment in the required direction, and implementation of these is described. In addition, the effects of individual variability at the behavioural and genetic levels are also discussed, along with the current limitations in assessment of these factors, and we then put forward three case studies, as examples of practical applications of these strategies, focusing on adaptations to travel involving competition in the Rugby Sevens World Cup and the 2016 Summer Olympics in Rio de Janeiro, Brazil. Finally, we provide a list of practice points for optimal adaptation of athletes to jet lag.

Endurance time is joint-specific: a modelling and meta-analysis investigation

Static task intensity-endurance time (ET) relationships (e.g. Rohmert's curve) were first reported decades ago. However, a comprehensive meta-analysis to compare experimentally-observed ETs across bodily regions has not been reported. We performed a systematic literature review of ETs for static contractions, developed joint-specific power and exponential models of the intensity-ET relationships, and compared these models between each joint (ankle, trunk, hand/grip, elbow, knee, and shoulder) and the pooled data (generalised curve). 194 publications were found, representing a total of 369 data points. The power model provided the best fit to the experimental data. Significant intensity-dependent ET differences were predicted between each pair of joints. Overall, the ankle was most fatigue-resistant, followed by the trunk, hand/grip, elbow, knee and finally the shoulder was most fatigable. We conclude ET varies systematically between joints, in some cases with large effect sizes. Thus, a single generalised ET model does not adequately represent fatigue across joints. STATEMENT OF RELEVANCE: Rohmert curves have been used in ergonomic analyses of fatigue, as there are limited tools available to accurately predict force decrements. This study provides updated endurance time-intensity curves using a large meta-analysis of fatigue data. Specific models derived for five distinct joint regions should further increase prediction accuracy.

Working around the clock: circadian rhythms and skeletal muscle

The study of the circadian molecular clock in skeletal muscle is in the very early stages. Initial research has demonstrated the presence of the molecular clock in skeletal muscle and that skeletal muscle of a clock-compromised mouse, Clock mutant, exhibits significant disruption in normal expression of many genes required for adult muscle structure and metabolism. In light of the growing association between the molecular clock, metabolism, and metabolic disease, it will also be important to understand the contribution of circadian factors to normal metabolism, metabolic responses to muscle training, and contribution of the molecular clock in muscle-to-muscle disease (e.g., insulin resistance). Consistent with the potential for the skeletal muscle molecular clock modulating skeletal muscle physiology, there are findings in the literature that there is significant time-of-day effects for strength and metabolism. Additionally, there is some recent evidence that temporal specificity is important for optimizing training for muscular performance. While these studies do not prove that the molecular clock in skeletal muscle is important, they are suggestive of a circadian contribution to skeletal muscle function. The application of well-established models of skeletal muscle research in function and metabolism with available genetic models of molecular clock disruption will allow for more mechanistic understanding of potential relationships.

Sports performance: is there evidence that the body clock plays a role?

Athletic performance shows a time-of-day effect, possible causes for which are environmental factors (which can be removed in laboratory studies), the sleep-wake cycle and the internal "body clock". The evidence currently available does not enable the roles of these last two factors to be separated. Even so, results indicate that the body clock probably does play some role in generating rhythms in sports performance, and that to deny this is unduly critical. Protocols to assess the separate roles of the body clock and time awake are then outlined. A serious impediment to experimental work is muscle fatigue, when maximal or sustained muscle exertion is required. Dealing with this problem can involve unacceptably prolonged protocols but alternatives which stress dexterity and eye-hand co-ordination exist, and these are directly relevant to many sports (shooting, for example). The review concludes with suggestions regarding the future value to sports physiology of chronobiological studies.

Interpretation of EMG integral or RMS and estimates of "neuromuscular efficiency" can be misleading in fatiguing contraction

In occupational and sports physiology, reduction of neuromuscular efficiency (NME) and elevation of amplitude characteristics, such as root mean square (RMS) or integral of surface electromyographic (EMG) signals detected during fatiguing submaximal contraction are often related to changes in neural drive. However, there is data showing changes in the EMG integral (I(EMG)) and RMS due to peripheral factors. Causes for these changes are not fully understood. On the basis of computer simulation, we demonstrate that lengthening of intracellular action potential (IAP) profile typical for fatiguing contraction could affect EMG amplitude characteristics stronger than alteration in neural drive (central factors) defined by number of active motor units (MUs) and their firing rates. Thus, relation of these EMG amplitude characteristics only to central mechanisms can be misleading. It was also found that to discriminate between changes in RMS or I(EMG) due to alterations in neural drive from changes due to alterations in peripheral factors it is better to normalize RMS of EMG signals to the RMS of M-wave. In massive muscles, such normalization is more appropriate than normalization to either peak-to-peak amplitude or area of M-wave proposed in literature.

Análise da fadiga muscular localizada em atletas e sedentários através de parâmetros de freqüência do sinal eletromiográfico

Embora a análise no domínio da freqüência do sinal eletromiográfico (EMG) seja empregada na caracterização do processo de fadiga muscular localizada, sua aplicação, especificamente a da freqüência mediana (Fmed), é pouco explorada no âmbito esportivo. O objetivo do presente estudo foi verificar a viabilidade da aplicação do sinal EMG, através de sua análise no domínio da freqüência, como parâmetro para determinação e diferenciação no comportamento da fadiga muscular localizada. Dois grupos de sujeitos, um caracterizado como atletas (n =12) e outro como sedentários (n =12), foram submetidos a análises baseadas em procedimentos executados em três diferentes situações experimentais, todos envolvendo a modalidade de exercício isométrico: i) teste máximo para determinação da contração isométrica voluntária máxima (CIVM); ii) teste de fadiga, sustentado por 35 seg. a 80% da CIVM; iii) teste de recuperação, sustentado por 10 seg. a 80% da CIVM; neste ultimo foi monitorado o comportamento da Fmed nos três primeiros (Fmedi) e três últimos segundos (Fmedf) do sinal EMG no músculo tibial anterior durante o teste de fadiga. Durante os 10 segundos do teste de recuperação foi calculada a Fmed referente a todo o período (Fmedr). parâmetro utilizado no cálculo do índice de recuperação muscular (IRM). Os resultados apontam que a Fmedf apresentou valor menor em relação à Fmedi em ambos os grupos (p < 0,05). Quando comparado com o grupo de sedentários, o grupo de atletas apresentou valores maiores de Fmedi e Fmedf (p < 0,05). O valor médio e desvio-padrão do IRM para o grupo de atletas foram de 62,1% ± 28,7 e, para o grupo de sedentários, de 55,2% ± 27,8 (p > 0,05). Dessa forma, os resultados apresentados neste estudo permitem inferir a viabilidade na aplicação de parâmetros no domínio da freqüência do sinal EMG para a determinação e diferenciação do comportamento da fadiga muscular localizada.