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Players involved in the various football codes compete throughout the calendar year around the world. Therefore, environmental stressors such as temperature and altitude should be considered in preparation for, and during, matches. We aimed to systematically review the observational and quasi-experimental studies that have been specifically designed to quantify the effects of temperature (hot or cold) high altitude on in-match physical performance indicators. A search of electronic databases (Web of Science, Scopus, SPORTDiscus, PubMed/MEDLINE) was conducted, resulting in 19,424 papers being identified as relevant. Following sifting in relation to the eligibility criteria, 12 papers were deemed directly relevant. The reviewed studies scored 6-9 (on a 0-9 scale) for quality assessment using a previously used scale. The major outcome variables relevant to the current review were total distance (m), high speed running (m) and high-speed runs (count) measured during matches. Standardized effect sizes (ES) were heterogeneous across studies for total distance (ES: -0.96 to -0.14) and high-speed running (ES: -0.69 to 0.12) for >1000 m vs sea-level, time spent at the given altitude being a putative factor for this heterogeneity. Heat had mainly detrimental effects on performance, but ES were, again, heterogeneous across studies (ES: -1.25 to 0.26), dependent on temperature. Given the small number of studies that only involved mostly male athletes, and large heterogeneity across studies, more research needs be conducted on physical performance in these environmental conditions, with attention paid to standardizing outcomes and broadening the approaches of studies to guide future decision making in professional sporting environments.

The purpose of this study was to present reference standards for physical performance test outcomes relevant to elite female soccer players. We analysed mixed-longitudinal data (n = 1715 observations) from a sample of 479 elite youth and senior players as part of the English Football Association's national development programme (age range: 12.7 to 36.0 years). Semi-parametric generalized additive models for location, scale and shape (GAMLSS) estimated age-related reference centiles for 5-m sprinting, 30-m sprinting, countermovement jump (CMJ) height, and Yo-Yo Intermittent Recovery Test Level 1 (Yo-Yo IR1) performance. The estimated reference centiles indicated that the median of the distribution of physical performance test scores varied non-linearly with advancing chronological age, improving until around 25 years for each performance variable. These are the first reference ranges for performance test outcomes in elite English female soccer players. These data can assist practitioners when interpreting physical test performance outcomes to track an individual's progress over time and support decision-making regarding player recruitment and development.

Objective: To examine training and match loads undertaken by soccer players competing in the English Premier League.Methods: Using a retrospective design, external (GPS) and internal training loads...

The measurement of relative physiological stress during training is important because this is the stimulus for the long-term adaptive response. Measurements of perceived exertion (RPE) have been reported to correlate with the heart rate during field-based training sessions. Nevertheless, there are few studies on how well RPE tracks with the heart rate over repeated training sessions in elite soccer players. Therefore, we aimed to quantify the within-participant correlations between variability in session-RPE (sRPE) and the heart rate in elite male soccer players, and to determine whether the playing position moderated these correlations. The field-based training of four central defenders, four wide defenders, six central midfielders, two wide midfielders and three attackers from an elite English Premier League squad were monitored over an entire in-season competitive period, giving a total of 1010 individual training sessions for study. Correlations between session-RPE and heart rates were quantified using a within-participant model. The correlation between changes in sRPE and heart rates was r = 0.75 (95% CI: 0.71-0.78). This correlation remained high across the various player positions (wide-defender, r = 0.81; central-defender, r = 0.74; wide midfielder, r = 0.70; central midfielder, r = 0.70; attacker, r = 0.84; P

The possible ways in which a substance or technique can be regarded as “ergogenic” are first listed, and then a systematic account of the evidence that melatonin fulfils the requirements of such roles is undertaken. There is no evidence to indicate that the soporific and hypothermic effects of melatonin cause a decrease in physical performance, though its ability to decrease alertness and cognitive performance has been well established. The hypothermic effects of melatonin might, on the other hand, increase physical performance in two ways. First, they might allow more exercise to be performed before a “critical” temperature that causes the central nervous system to inhibit physical activity is reached. Second, the cutaneous vasodilatation produced by melatonin might promote heat loss during steady-state exercise and so guard against the rise of core temperature. Evidence for either of these roles is currently inadequate and insufficient for a confident judgement to be made. When the role of melatonin in ...

The exercise-related response of the rate-pressure-product (RPP) is a prognostic marker of autonomic imbalance, cardiovascular mortality, and silent myocardial ischemia in hypertension. In view of the well-known 24 h variation in out-of-hospital sudden cardiac events, our aim was to investigate whether the reactivity of RPP to everyday physical activities varies over the 24 h. Ambulatory measurements of systolic blood pressure (BP) and heart rate were recorded every 20 min for 24 h in 440 diurnally active patients attending a hypertension clinic. Wrist activity counts were summed over the 15 min that preceded a BP measurement. An RPP reactivity index was derived for each of twelve 2 h data bins by regressing the change in RPP against the change in logged activity counts. The RPP showed 24 h variation (p0.0005), with a peak of 11,004 (95% CI = 10,757 to 11,250) beat . min(-1) . mmHg occurring at 10:00 h (2 h after mean wake-time). The overall 24 h mean of RPP reactivity was 477 beat . min(-1) . mmHg . logged activity counts(-1) (95% CI = 426 to 529). The largest increase in RPP reactivity occurred within the first 2 h after waking (p0.0005). There were no subsequent significant differences in RPP reactivity up to 14 h after waking. The lowest RPP reactivity was found 18-20 h after waking, with a peak-to-trough variation of 593 beat . min(-1) . mmHg . logged activity counts(-1) (95% CI = 394 to 791, p0.0005). Although this variation was not moderated by BP status, age, or sex, less variability in RPP reactivity was found for the medicated individuals during the waking hours. These data suggest that under conditions of normal living, the reactivity of RPP to a given change in physical activity increases markedly during the first 2 h after waking from nocturnal sleep, the time when out-of-hospital sudden cardiac events are also most common. Therefore, these data add weight to the notion that reactivity of RPP to physical activity could be a prognostic marker of autonomic imbalance and cardiovascular mortality, although more research is needed to assess the specific prognostic value of 24 h ambulatory measurements of RPP and physical activity.

In this historical review covering the past 25 years, we reflect on the content of manuscripts relevant to the Sport Performance section of the Journal of Sports Sciences. Due to the wide diversity of sport performance research, the remit of the Sport Performance section has been broad and includes mathematical and statistical evaluation of competitive sports performances, match- and notation-analysis, talent identification, training and selection or team organization. In addition, due to the academic interests of its section editors, they adopted a quality-assurance role for the Sport Performance section, invariably communicated through key editorials that subsequently shaped the editorial policy of the Journal. Key high-impact manuscripts are discussed, providing readers with some insight into what might lead an article to become a citation "classic". Finally, landmark articles in the areas of "science and football" and "notation analysis" are highlighted, providing further insight into how such articles have contributed to the development of sport performance research in general and the Journal of Sports Sciences in particular.

The aim of this study was to determine the effects of a post-lunch nap on subjective alertness and performance following partial sleep loss. Ten healthy males (mean age 23.3 years, s = 3.4) either napped or sat quietly from 13:00 to 13:30 h after a night of shortened sleep (sleep 23:00-03:00 h only). Thirty minutes after the afternoon nap or control (no-nap) condition, alertness, short-term memory, intra-aural temperature, heart rate, choice reaction time, grip strength, and times for 2-m and 20-m sprints were recorded. The afternoon nap lowered heart rate and intra-aural temperature. Alertness, sleepiness, short-term memory, and accuracy at the 8-choice reaction time test were improved by napping (P0.05), but mean reaction times and grip strength were not affected (P0.05). Sprint times were improved. Mean time for the 2-m sprints fell from 1.060 s (s(x) = 0.018) to 1.019 s (s(x) = 0.019) (P = 0.031 paired t-test); mean time for the 20-m sprints fell from 3.971 s (s(x) = 0.054) to 3.878 s (s(x) = 0.047) (P = 0.013). These results indicate that a post-lunch nap improves alertness and aspects of mental and physical performance following partial sleep loss, and have implications for athletes with restricted sleep during training or before competition.

Swain (1997) employed the mathematical model of Di Prampero et al. (1979) to predict that, for cycling time-trials, the optimal pacing strategy is to vary power in parallel with the changes experienced in gradient and wind speed. We used a more up-to-date mathematical model with validated coefficients (Martin et al., 1998) to quantify the time savings that would result from such optimization of pacing strategy. A hypothetical cyclist (mass = 70 kg) and bicycle (mass = 10 kg) were studied under varying hypothetical wind velocities (-10 to 10 m x s(-1)), gradients (-10 to 10%), and pacing strategies. Mean rider power outputs of 164, 289, and 394 W were chosen to mirror baseline performances studied previously. The three race scenarios were: (i) a 10-km time-trial with alternating 1-km sections of 10% and -10% gradient; (ii) a 40-km time-trial with alternating 5-km sections of 4.4 and -4.4 m x s(-1) wind (Swain, 1997); and (iii) the 40-km time-trial delimited by Jeukendrup and Martin (2001). Varying a mean power of 289 W by +/- 10% during Swain's (1997) hilly and windy courses resulted in time savings of 126 and 51 s, respectively. Time savings for most race scenarios were greater than those suggested by Swain (1997). For a mean power of 289 W over the "standard" 40-km time-trial, a time saving of 26 s was observed with a power variability of 10%. The largest time savings were found for the hypothetical riders with the lowest mean power output who could vary power to the greatest extent. Our findings confirm that time savings are possible in cycling time-trials if the rider varies power in parallel with hill gradient and wind direction. With a more recent mathematical model, we found slightly greater time savings than those reported by Swain (1997). These time savings compared favourably with the predicted benefits of interventions such as altitude training or ingestion of carbohydrate-electrolyte drinks. Nevertheless, the extent to which such power output variations can be tolerated by a cyclist during a time-trial is still unclear.

The development of ambulatory blood pressure monitoring devices and the beat-by-beat measurement of heart rate have enabled it to be established that there are circadian rhythms in heart rate and blood pressure in subjects living normally. Investigations of these variables have led to quantification of their fall at night, and rapid rise on awakening and becoming active in the morning. These changes are of particular interest insofar as abnormalities in them are associated with cardiovascular problems and morbidity in patients and also act as risk factors in otherwise healthy individuals. It has also been shown that there are many other variables of the cardiovascular system. The causes of the circadian rhythms in heart rate and blood pressure are outlined, with particular stress upon the role of the autonomic nervous system, as assessed from low- and high-frequency components of the variation in heart rate measured beat-by-beat. Activity increases blood pressure, but there is evidence that this ...

Elite athletes and their coaches are accustomed to international travel for purposes of training or sports competition. Recreational participants are similarly, if less frequently, exposed to travel stress. Transient negative effects that constitute travel fatigue are quickly overcome, whereas longer-lasting difficulties are associated with crossing multiple time-zones. Jet-lag is linked with desynchronization of circadian rhythms, and its impact depends on the duration and direction of flight, flight schedule, and individual differences. Athletes’ performances are likely to be affected for some days until the body clock is readjusted in harmony with local time. Knowledge of the physiological characteristics of the body clock can be used to develop behavioural strategies that accelerate readjustment, in particular the timing of outdoor or bright light exposure, perhaps melatonin ingestion, meals, and exercise. Attempts to promote sleep by use of drugs that adjust the body clock, induce sleepiness or promote wakefulness are relevant but discouraged in travelling athletes. Support staff should develop appropriate education programmes for their athletes who can then make informed choices about their behaviour and minimize the transient effects of jet-lag on their well-being and performance.

Changes in rectal temperature during mild exercise in the middle of the rising (11:00 h) and falling (23:00 h) phases of the circadian rhythm of resting core temperature have been compared. Seven healthy males were studied at rest, while exercising on a cycle ergometer (60 min at 80 W), and during the first 30 min of recovery. Rectal temperature, forearm blood flow, and forearm sweat rate were measured at 1 min intervals throughout. During exercise, there were significant time-of-day differences in the profiles of all three variables, and in the thresholds for increases in forearm blood flow and sweating. Forearm blood flow and sweat rate were recruited more rapidly and to a greater extent with evening exercise, and rectal temperature rose less. Analysis of covariance, with rectal temperature as the covariate, indicated the associations between it and forearm blood flow or sweating were significantly different (p0.05) between the two times of day. There were also significant (p0.05) time-of-day effects for forearm blood flow and sweating that were independent of rectal temperature. During recovery, rectal temperature fell more quickly in the late evening than late morning. Forearm blood flow and sweating also showed time-of-day differences, but these did not co-vary with rectal temperature. Control of rectal temperature during exercise and recovery appears to be more effective in the late evening than late morning, and differences in forearm blood flow and sweating, as well as factors independent of these two variables, contribute to this difference. The results support our "heat-gain/heat-loss modes" hypothesis.

Football (soccer) training and matches are scheduled at different times throughout the day. Association football involves a variety of fitness components as well as psychomotor and game-related cognitive skills. The purpose of the present research, consisting of two separate studies, was to determine whether game-related skills varied with time of day in phase with global markers of both performance and the body clock. In the first study, eight diurnally active male association football players (19.1+/-1.9 yrs of age; mean+/-SD) with 10.8+/-2.1 yrs playing experience participated. Measurements were made on different days at 08:00, 12:00, 16:00, and 20:00 h in a counterbalanced manner. Time-of-day changes in intra-aural temperature (used as a marker of the body clock), grip strength, reaction times, flexibility (markers of aspects of performance), juggling and dribbling tasks, and wall-volley test (football-specific skills) were compared. Significant (repeated measures analysis of variance, ANOVA) diurnal variations were found for body temperature (p0.0005), choice reaction time (p0.05), self-rated alertness (p0.0005), fatigue (p0.05), forward (sit-and-reach) flexibility (p0.02), and right-hand grip strength (p0.02), but not left-hand grip strength (p=0.40) nor whole-body (stand-and-reach) flexibility (p=0.07). Alertness was highest and fatigue lowest at 20:00 h. Football-specific skills of juggling performance showed significant diurnal variation (p0.05, peak at 16:00 h), whereas performance on the wall-volley test tended to peak at 20:00 h and dribbling showed no time-of-day effect (p=0.55). In a second study, eight diurnally active subjects (23.0+/-0.7 yrs of age) completed five test sessions, at the same times as in the first study but with a second session at 08:00 h. Test-re-test comparisons at 08:00 h for all components indicated good reliability. Intra-aural temperature showed a significant time-of-day effect (p0.001) with mean temperature at 16:00 h (36.4 degrees C) higher than at 08:00 h (35.4 degrees C). There was no significant effect of chronotype on the temperature acrophase (peak time) (p0.05). Diurnal variation was found for performance tests, including sit-and-reach flexibility (p0.01) and spinal hyper-extension (p0.05). Peaks occurred between 16:00 and 20:00 h and the daytime changes paralleled the temperature rhythm. Diurnal variation was also found for football-specific tests, including dribbling time (p0.001, peak at 20:00 h) and chip test performance (p0.01), being more accurate at 16:00 h (mean error=0.75 m) than at 08:00 h (mean error=1.01 m). Results indicate football players perform at an optimum between 16:00 and 20:00 h when not only football-specific skills but also measures of physical performance are at their peak. Body temperature peaked at a similar time, but positive mood states seemed to peak slightly earlier. While causal links cannot be established in these experiments, the results indicate that the diurnal variation of some aspects of football performance is affected by factor(s) other than body temperature alone.

In this study we investigated the patterns of play resulting in goals scored in International field hockey. In total 70 women’s international field hockey matches were observed. Only goals scored f...

To understand better how disruption to daily routines and circadian factors affect food intake, some aspects of 361 passengers' eating habits during long-haul flights across eight time zones were investigated. Two meals were provided during each flight. Passengers stated whether or not they had eaten part or all of each meal and the reasons for this decision. They were also asked to give their responses to it (appetite beforehand, enjoyment during the meal, and satiety afterwards), and the type of meal they would prefer to have eaten, given an unrestricted choice. There were few occasions (

The immediate effects of ingesting melatonin in the daytime include decreased alertness and body temperature. To date, no researcher has examined whether daytime ingestion of melatonin leads to impairments in variables relevant to short-term (10 min) athletic performance. Twelve physically active participants (mean +/- s age = 25.2 +/- 5.0 years, body mass = 81.4 +/- 12.1 kg and chronotype = 33.8 +/- 6.3 units) ingested 5 mg of melatonin or placebo at 11:45 hours in a double-blind experiment. At 13:00 and 17:00 hours, subjective alertness was measured, together with intra-aural temperature, reaction time (two-, four- and eight-choice), short-term memory recall and grip strength. Performance, ratings of perceived exertion (RPE) and heart rate were also recorded during a 4-km cycling time trial. At 13:00 hours, the mean +/- s intra-aural temperature was 0.49 +/- 0.79 degrees C lower after ingestion of melatonin than after placebo (p = 0.015), but this difference was not apparent at 17:00 hours. At both 13:00 and 17:00 hours, melatonin reduced (p0.05) alertness, short-term memory and exercise heart rate by 1.5 +/- 1.8 units, 1 +/- 1 digits and 6 +/- 9 beats.min(-1), respectively (mean +/- s). Eight-choice reaction time was also slower at both times of day after ingesting melatonin. Melatonin did not influence time trial performance or RPE (p0.05). The effects of 5 mg of melatonin seem more pronounced for mental rather than physical components of short-term athletic performance, although the cardiovascular responses to exercise are affected. Some effects of melatonin were apparent 5 h after ingestion when the hypothermic effects of melatonin had dissipated.

Twelve healthy adults were studied, singly or in groups of up to four, in an Isolation Unit before (control days) and for 3 days after a simulated time-zone transition to the east across 8 time zones (the clock being changed from 15:00 to 23:00h). Subjects were free to choose how to pass their waking hours (though naps were forbidden), and to eat what and when they wanted. A wide selection of food was provided, though the subjects had to prepare it. Subjects completed food intake questionnaire on waking and at 3h intervals during the waking day. This questionnaire assessed the reasons for choosing not to eat a meal or, if a meal was eaten, the reasons for doing so, the type of meal chosen and the reasons for this choice, and subjective responses to the meal (hunger before, enjoyment during, and satiety afterwards). Subjects also recorded the incidence and degree of indigestion and jet lag at 3 h intervals after the time-zone transition. Following the time-zone transition, the subjects experienced significant amounts of jet lag and recorded a significant increase in the incidence of indigestion. They also showed significant changes in their pattern of food intake, but, whereas the patterns of food intake were no longer significantly different from control days by the third post-shift day, the symptoms of jet lag and indigestion were still present then. The distribution of daytime meals was significantly affected on the first post-shift day, with a redistribution of the times that the main, hot meals were eaten; these times indicated some influence of an unadjusted body clock. On this day also, the reasons for determining food intake continued to be dominated by hunger and appetite (hunger even increasing in the frequency with which it was cited), and the reason for not eating a meal, by a lack of hunger. On both control and post-shift days, there was a marked effect of meal type upon the responses to food intake, with cold food being rated least and large hot meals most when appetite before the meal, enjoyment during it, and satiety afterward were considered. However, evidence suggested that the degree to which larger hot meals were preferred to cold meals was significantly less marked after the time-zone transition. On control days, sleep was unbroken; whereas, after the time-zone transition, all subjects woke on at least one of the 3 nights studied. During the first post-shift night, about half of the subjects ate a meal, the reason given being that they were "hungry." On those occasions when subjects woke but did not eat a meal, the reason cited was because they "could not be bothered" as frequently as because they were "not hungry.". A simulated time-zone transition is associated with significant changes to the incidence of indigestion, pattern of food intake, and subjective responses to food. However, these changes are generally transient and are only weakly linked to the sensation of jet lag.

We discuss current knowledge on the description, impact, and underlying causes of circadian rhythmicity in sports performance. We argue that there is a wealth of information from both applied and experimental work, which, when considered together, suggests that sports performance is affected by time of day in normal entrained conditions and that the variation has at least some input from endogenous mechanisms. Nevertheless, precise information on the relative importance of endogenous and exogenous factors is lacking. No single study can answer both the applied and basic research questions that are relevant to this topic, but an appropriate mixture of real-world research on rhythm disturbances and tightly controlled experiments involving forced desynchronization protocols is needed. Important issues, which should be considered by any chronobiologist interested in sports and exercise, include how representative the study sample and the selected performance tests are, test-retest reliability, as well as overall design of the experiment.

This review first examines reliable and convenient ways of measuring core temperature for studying the circadian rhythm, concluding that measurements of rectal and gut temperature fulfil these requirements, but that insulated axilla temperature does not. The origin of the circadian rhythm of core temperature is mainly due to circadian changes in the rate of loss of heat through the extremities, mediated by vasodilatation of the cutaneous vasculature. Difficulties arise when the rhythm of core temperature is used as a marker of the body clock, since it is also affected by the sleep-wake cycle. This masking effect can be overcome directly by constant routines and indirectly by "purification" methods, several of which are described. Evidence supports the value of purification methods to act as a substitute when constant routines cannot be performed. Since many of the mechanisms that rise to the circadian rhythm of core temperature are the same as those that occur during thermoregulation in exercise, there is an interaction between the two. This interaction is manifest in the initial response to spontaneous activity and to mild exercise, body temperature rising more quickly and thermoregulatory reflexes being recruited less quickly around the trough and rising phase of the resting temperature rhythm, in comparison with the peak and falling phase. There are also implications for athletes, who need to exercise maximally and with minimal risk of muscle injury or heat exhaustion in a variety of ambient temperatures and at different times of the day. Understanding the circadian rhythm of core temperature may reduce potential hazards due to the time of day when exercise is performed.

In this paper, we identify appropriate statistical methods for analysing categorical differences in discrete variables or 'performance indicators' resulting from performance analysis. The random mechanisms associated with discrete events do not follow a normal distribution; that is, the normal distribution is a continuous not a discrete probability distribution. We propose appropriate statistical methods based on two key discrete probability distributions, the Poisson and binomial distributions. Two approaches are proposed and compared using examples from notational analysis. The first approach is based on the classic chi-square test of significance (both the goodness-of-fit test and the test of independence). The second approach adopts a more contemporary method based on log-linear and logit models fitted using the statistical software GLIM. Provided relatively simple one-way and two-way comparisons in categorical data are required, both of these approaches result in very similar conclusions. However, as soon as more complex models or higher-order comparisons are required, the approach based on log-linear and logit models is shown to be more effective. Indeed, when investigating those factors and categorical differences associated with binomial or binary response variables, such as the proportion of winners when attempting decisive shots in squash or the proportion of goals scored from all shots in association football, logit models become the only realistic method available. By applying log-linear and logit models to discrete events resulting from notational analysis, greater insight into the underlying mechanisms associated with sport performance can be achieved.

Nine healthy females were studied about the time of the spring equinox, while living in student accommodation and aware of the passage of solar time. After 7 control days, during which a conventional lifestyle was lived, subjects underwent a 24-h 'constant routine', followed by 17 days' on a 27-h 'day' (9h sleep and 18h wake). Throughout the experiment, regular recordings of (non-dominant) wrist activity (every 30 s) and rectal temperature (every 6min) were made. Only the control and 27-h (experimental) 'days' have been analysed in the present report. From each subject, 24-h profiles of raw temperature (consisting of 240 points) were obtained: one (control days), by averaging the control days; the other (experimental days), by conflating 16 consecutive 27-h 'days'. Activity data were first collected into 240 points by summing them over 6-min intervals; they were then converted into three data sets (each of 240 points) for control and, separately, for experimental days. These data sets were summed activities in the previous 18 min (A18), summed activity over the previous 18-30min (A30), and summed activity over the previous 30-42 min (A42). The raw temperature data sets for control and experimental days were separately analysed by ANCOVA using two time-of-day factors: 'hours' (24 levels) and 'six-minute-intervals' (10 levels). The covariate was the three activity data sets; in order to make the analysis more versatile, a cubic polynomial model was used, with a linear, quadratic and cubic term for each of these activity data sets. Moreover, the effects of activity upon core temperature were separately assessed for four 6-h sections of the 24-h profile, centred on its low, rising, high and falling phases. The main results were as follows: 1. All three activity data sets made significant contributions to the model, but that by the A30 data set was the most powerful of the three. This supports the use of activity files covering the previous 30min in other 'purification' methods. 2. Although the linear term was the one that was significant most frequently, quadratic and (negative) cubic terms were also present on several occasions. This result indicates that the effect of activity upon core temperature can be approximated by a linear function (as has been done in other 'purification' models), but that, with wider ranges of activity, a sigmoid curve would be more accurate, indicative of the process of thermoregulation. 3. During the experimental days, the effect of activity upon temperature was greater in the rising than the falling temperature phase, and greater in the low than in the high phase. These results are predicted from current understanding of the circadian rhythm of thermoregulation. 4. During control days, the effects of activity were more complex, probably due to the factors that were present at some, but not all, phases - factors such as sleep, meals, changes in posture, lighting, and so on. 5. The ANCOVA also enabled the temperature profiles, corrected for the effects of activity (and, therefore, to be considered as 'purified'), to be displayed. We conclude that the use of ANCOVA to tackle the problem of purifying' raw temperature data is a promising one. So far, it has produced results that accord with those from other purification' methods and with predictions based on our current understanding of the circadian rhythm of thermoregulation.

Seventeen healthy adults exercised for 30 min (70% VO2max), at different times of the day and night throughout a 24 h period. The effect on the phase of core temperature rhythm was assessed by comparing the rhythms on the day immediately before and immediately after the day of exercise with the participants living normally on these 2 days. Assessments were made upon data that had been corrected for the thermogenic effects of sleep and activity. When exercise was performed in the period between 4 h before and 1 h after the temperature minimum, there was a phase delay of 1.03 +/- 0.78 h (mean +/- s; n = 6); when performed between 3 and 8 h after the temperature minimum, there was a phase advance of 1.07 +/- 1.23 h (n = 9). Both means were significantly different from zero (Student's one-sample t-tests: P0.05). Performed at other times, exercise had no significant effect on the phase of the temperature rhythm. The phase changes were not significantly different from those previously observed by us in sedentary individuals exposed to domestic lighting. We conclude that the amount of physical activity has very little effect on the body clock.

A total of 39 subjects were studied after a flight from the UK to either Sydney or Brisbane (10 time-zones to the east). Subjects varied widely in their age, their athletic ability, whether or not they were taking melatonin, and in their objectives when in Australia. For the first 6 days after arrival, subjects scored their jet-lag five times per day and other subjective variables up to five times per day, using visual analogue scales. For jet-lag, the scale was labelled 0 = no jet-lag to 10 = very bad jet-lag; the extremes of the other scales were labelled - 5 and + 5, indicating marked changes compared with normal, and the centrepoint was labelled 0 indicating 'normal'. Mean daily values for jet-lag and fatigue were initially high (+ 3.65 +/- 0.35 and + 1.55 +/- 0.22 on day 1, respectively) and fell progressively on subsequent days, but were still raised significantly (p0.05) on day 5 (fatigue) or day 6 (jet-lag). In addition, times of waking were earlier on all days. By contrast, falls in concentration and motivation, and rises in irritability and nocturnal wakings, had recovered by day 4 or earlier, and bowel activity was less frequent, with harder stools, on days 1 and 2 only. Also, on day 1, there was a decrease in the ease of getting to sleep (- 1.33 +/- 0.55), but this changed to an increase from day 2 onwards (for example, + 0.75 +/- 0.25 on day 6). Stepwise regression analysis was used to investigate predictors of jet-lag. The severity of jet-lag at all the times that were measured was strongly predicted by fatigue ratings made at the same time. Its severity at 08:00 h was predicted by an earlier time of waking, by feeling less alert 30 min after waking and, marginally, by the number of waking episodes. Jet-lag at 12:00 and 16:00 h was strongly predicted by a fall of concentration at these times; jet-lag at mealtimes (12:00, 16:00 and 20:00 h) was predicted by the amount of feeling bloated. Such results complicate an exact interpretation that can be placed on an assessment of a global term such as jet-lag, particularly if the assessment is made only once per day.

Fifteen healthy female subjects were studied for eight days while living conventionally. Subjects were free to choose the ways they spent their time within a framework of regular times of retiring and rising; in practice, much of the waking time was spent in sedentary activities. Nine of the subjects were aware of the natural light-dark cycle, this approximating to a 12:12 L:D schedule at the time of year when the study took place. Before the study, subjects were assessed for their degree of "morningness" by questionnaire; throughout the study, they wore a rectal probe, and an activity meter on their non-dominant wrist. The timing (phase) and amplitude of the circadian rectal temperature rhythm were assessed on each day by cosinor analysis as well as by a method based on visual inspection of the data. These two parameters were also assessed after the temperature data for each day had been "purified" by a number of methods. From these results it was possible to investigate the effect of purification upon the amplitude of the circadian rhythm of temperature. Also, the day-by-day variability of phase, and the relationship between morningness and phase, were compared using these methods of phase estimation, and using cross-correlation between data sets from adjacent days; in all cases, raw and purified temperature data were used. There was a significantly greater amount of daily variation in phase using purified rather than raw data sets, and this difference was present with all methods of purification as well as with all methods for estimating phase. Purification decreased the amplitude of the circadian temperature rhythm by about 30%. Finally, there was a significant correlation between the morningness score of the subjects and the phase of the circadian temperature rhythm, the phase becoming earlier with increasing morningness; when this relationship was re-examined using purified data, it became more marked. These results reflect the masking effects exerted upon raw temperature data by lifestyle. The extent to which the purification methods enable the endogenous component of a circadian rhythm - and, by implication, the output of the endogenous circadian oscillator - to be estimated in subjects living normally is addressed.

In adult humans, core temperature is influenced by activity; the sensitivity of core temperature to such effects shows a phase dependence and is also influenced by the environment and whether the individual is asleep or awake. We have investigated if similar effects are evident in neonates, in whom thermoregulation and the circadian rhythm of core temperature are not fully developed. Eleven full-term, healthy babies were studied singly (light 07:00-19:00) at 2 days of age and again 4 weeks after birth; between these times, they were tended routinely on a communal ward. On study days, 10-minute recordings were made of rectal and skin (abdominal) temperature, heart rate (HR), and behavioral state. Sensitivities of the temperatures to activity ("arousal") were assessed throughout the 24h by measuring the gradient of (temperature/HR). Sensitivities measured at 01:00, 05:00, 09:00, 13:00, 17:00, and 21:00 were used as dependent variables in stepwise regression and linear regression analyses, with "subjects," "light versus dark," "behavioral state," and "difference between time of measurement and the acrophase of the endogenous component of the temperature rhythm" (ignoring sign) as possible predictors. (Acrophases of the temperature rhythms had been estimated from 24h data purified using the behavioral state record.) Light versus dark acted as a significant predictor of the sensitivity of rectal temperature to arousal on day 2 and week 4, the sensitivity increasing in the light, and there was limited evidence for behavioral state acting as a predictor on day 2. Neither factor was a significant predictor when the sensitivity of the babies' skin temperatures to arousal was investigated. There was also some evidence that the difference between the time of measurement and the temperature acrophase acted as a predictor of sensitivity to arousal in both rectal (day 2) and skin (week 4) temperature, with larger differences decreasing the sensitivity. These results indicate that there are masking effects on body temperature due to arousal in neonates, the size of which depends on both internal and external factors. However, this sensitivity of temperature to arousal shows differences from the sensitivity of temperature to physical activity in both adult humans and adult mice. One possible explanation of this result is that temperature regulation and the circadian system are not fully developed in humans at this age.

Nine healthy females were studied about the time of the spring equinox while living in student accommodations and aware of the passage of solar time. After 7 control days, during which a conventional lifestyle was lived under a 24h "constant routine," the subjects lived 17 x 27h "days" (9h sleep in the dark and 18h wake using domestic lighting, if required). Throughout the experiment, recordings of wrist activity and rectal (core) temperature were taken. The raw temperature data were assessed for phase and amplitude by cosinor analysis and another method, "crossover times," which does not assume that the data set is sinusoidal. Two different purification methods were used in attempts to remove the masking effects of sleep and activity from the core temperature record and so to measure more closely the endogenous component of this rhythm; these two methods were "purification by categories" and "purification by intercepts." The former method assumes that the endogenous component is a sinusoid, and that the masking effects can be estimated by putting activity into a number of bands or categories. The latter method assumes that a temperature that would correspond to complete inactivity can be estimated from measured temperatures by linear regression of these on activity and extrapolation to a temperature at zero activity. Three indices were calculated to assess the extent to which exogenous effects had been removed from the temperature data by these purification methods. These indices were the daily variation of phase about its median value; the ratio of this variation to the daily deviation of phase about midactivity; and the relationship between amplitude and the square of the deviation of phase from midactivity. In all cases, the index would decrease in size as the contribution of the exogenous component to a data set fell. The purification by categories approach was successful in proportion to the number of activity categories that was used, and as few as four categories produced a data set with significantly less masking than raw data. The method purification by intercepts was less successful unless the raw data had been "corrected" to reflect the direct effects of sleep that were independent of activity (a method to achieve this being produced). Use of this purification method with the corrected data then gave results that showed least exogenous influences. Both this method and the purification by categories method with 16 categories of activity gave evidence that the exogenous component no longer made a significant contribution to the purified data set. The results were not significantly influenced by assessing amplitude and phase of the circadian rhythm from crossover times rather than cosinor analysis. The relative merits of the different methods, as well as of other published methods, are compared briefly; it is concluded that several purification methods, of differing degrees of sophistication and ease of application to raw data, are of value in field studies and other circumstances in which constant routines are not possible or are ethically undesirable. It is also concluded that such methods are often somewhat limited insofar as they are based on pragmatic or biological, rather than mathematical, considerations, and so it is desirable to attempt to develop models based equally on mathematics and biology.

Fourteen ambulatory subjects, varying in their amount of habitual physical activity, were studied for 24 h during a total of 25 "typical" days. Rectal temperature was recorded every 6 minutes, an activity diary was filled in every half hour, and wrist activity and heart rate were monitored every minute. Actimetry and heart rate data generally showed close parallelism with each other and with the masking effects on body temperature. Psychological stressors such as public speaking produced a greater effect on heart rate and body temperature than on wrist movement, while typing produced high values for wrist movement, but affected heart rate and temperature much less. When data for the circadian rhythm of body temperature were purified, the diary, actimetry, and measurement of heart rate were all useful in reducing masking effects, but the present evidence indicates that heart rate can be more successful than actimetry--as judged by the closeness of the purified data to a sinusoid. This superiority of heart rate monitoring over wrist activity as a method of purification might be because core temperature can be increased by stressor-induced thermogenesis, as well as by physical activity, and because wrist movement can, with some activities, give an inaccurate estimate of the factors that contribute to whole-body thermogenesis.

Systolic (SBP) and diastolic blood pressure (DBP), heart rate (HR) and locomotor activity have been measured at 1-min intervals for 24 h in Sprague-Dawley (N = 5) and for 2x24 h in transgenic hypertensive (N = 4) rats. The animals were freely mobile and entrained to a 12:12 LD cycle (lights on at 0700). The endogenous circadian component of the cardiovascular variables was removed from the raw data, and then correlations between activity and the residual component (raw data minus the endogenous component) of SBP, DBP and HR were calculated. This calculation was performed twice, in the mid-light and mid-dark phases. We have investigated if the mean size of the correlation coefficients depended on cardiovascular variable (SBP, DBP or HR), phase (D or L) or strain (Sprague-Dawley, SPD, or Transgenic, TG, rats). Nearly all correlations were positive and ANOVA's showed a significant effect of cardiovascular variable for both strains, with correlations for HR being significantly higher than those for SBP and DB...

The activity records of five groups of healthy or ill subjects have been measured for 4-26 days by an accelerometer placed on the nondominant wrist. These data, together with a record of times retiring to/rising from bed, have been used to produce a series of dichotomy indices for comparing the amounts of activity when in bed and out of bed. Reliable differences between individuals were found, with healthy subjects showing a greater degree of dichotomy than one subject with delayed sleep phase syndrome or three subjects with colorectal cancer. The method is convenient for extended data collection and offers the possibility of describing an individual's activity profile in a variety of circumstances.

Three investigations were carried out to examine the concurrent validity and the reliability of a portable dynamometer (Takei Kiki Kogyo) for the measurement of back and leg strength. First, leg extension strength of 19 subjects was measured using the Takei dynamometer and compared to the isometric knee extension strength of the dominant (right) leg measured using a computer-controlled dynamometer (Lido Active, Davis, CA). The back extension strength of 18 subjects was also compared between the two dynamometers. Second, back and leg strengths of 36 subjects, aged 19-30 years, were measured twice using the Takei dynamometer. Six days separated the test and retest. Third, back and leg strengths of four subjects, aged 21-30 years, were measured at six different times of the solar day. Significant relations (p0.001) were obtained between the Takei and Lido dynamometers for leg strength (r = 0.90) and back strength (r = 0.79). Significant test-retest correlations (p0.001) were found for leg strength (r = 0.80) and back strength (r = 0.91). Group mean (+/- SD) leg strength values of test (1450.4 +/- 428.6 N) and retest (1432.8 +/- 449.1 N) did not differ ((p0.05). A small (4.5%) but significant difference was found between the test (1057.2 +/- 309.9 N) and retest (1106.2 +/- 334.4 N) mean values for back strength (p0.05). A time of day effect was evident for back and leg strength (p0.05); on average the peak times occurred at 16:53 h and 18:20 h, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Part One: Ergonomics and disabled athletes. Part Two: Environmental factors, ergonomic aids and exercise performance. Part Three: Equipment design and technique analysis. Part Four: Training and fitness assessment. Part Five: Methodology and measurment techniques. Part Six: Health benefits of exercise and workplace-based programmes. Author Index. Subject Index.

In many sports, performance has increased as the result of technological progress. Some developments, such as the fastskin suit in swimming, have had a direct impact on performance (Chatard & Wilso...

(2002). Sport performance: variable or construct? Journal of Sports Sciences: Vol. 20, No. 4, pp. 291-292.