Research in sport and exercise science: the cutting edge.
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Biomechanical Phenomena↗
Biomedical subjects
T Reilly
Publications and source records attributed to T Reilly.
Science and Gaelic football: a review.
This review focuses on Gaelic football and scientific reports of the characteristics of its players and the demands of the game. Anthropometric characteristics vary according to positional role, but top players display high muscularity and good all-round fitness at the peak of the competitive season. Match analysis indicates that exercise intensity is roughly equivalent to that for professional soccer. Average heart rates are approximately 160 beats x min(-1) during competitive matches, and average oxygen consumption is about 72% of maximum. Metabolic fatigue in active muscles is unlikely. Conventional biomechanical and electromyographic techniques are useful in gaining insight into individual games skills. Inadequate attention has been given to injury prevention and to psychological aspects of the game. Although possessing unique characteristics, Gaelic football has many similarities with other football codes, especially Australian Rules football where the ball is played by both hands and feet and where tackling is permitted.
Anthropometry↗
How to show that unicorn milk is a chronobiotic: the regression-to-the-mean statistical artifact.
Few chronobiologists may be aware of the regression-to-the-mean (RTM) statistical artifact, even though it may have far-reaching influences on chronobiological data. With the aid of simulated measurements of the circadian rhythm phase of body temperature and a completely bogus stimulus (unicorn milk), we explain what RTM is and provide examples relevant to chronobiology. We show how RTM may lead to erroneous conclusions regarding individual differences in phase responses to rhythm disturbances and how it may appear as though unicorn milk has phase-shifting effects and can successfully treat some circadian rhythm disorders. Guidelines are provided to ensure RTM effects are minimized in chronobiological investigations.
Biometry↗
Investigation of the effects of the pre-cooling on the physiological responses to soccer-specific intermittent exercise.
Whole-body cooling prior to activity has the potential to reduce thermal strain and fatigue during subsequent endurance exercise. Intermittent activity is associated with greater increases in rectal temperature compared with continuous exercise. Thus, the effect of pre-cooling on thermoregulatory responses was examined during an intermittent test under "normal" environmental conditions. Six male university soccer players [mean (SD) age 27 (2) years; height 1.77 (0.3) m; mass 72.2 (1.5) kg; maximal oxygen consumption 58.9 (3.5) ml x kg(-1) x min(-1)] completed a 90-minute soccer-specific intermittent exercise protocol on a non-motorized treadmill. The run was completed with and without pre-cooling under normal laboratory conditions (20 degrees C) and without pre-cooling in a heated laboratory (26 degrees C). The pre-cooling strategy involved exposure to a cold shower (26 degrees C) for 60 min. The pre-cooling manipulation lowered rectal temperature prior to exercise [-0.6 (0.6) degrees C, range -1.5 degrees C; P < 0.05]. The rectal temperature response to exercise was significantly lower following pre-cooling than in the heated condition [pre-cooled 38.1 (0.6) degrees C, heated 38.6 (0.3) degrees C]. The increase in rectal temperature during the second half of the protocol following pre-cooling was significantly greater than the increase observed under normal or heated conditions (P < 0.05). No significant differences were observed between the three conditions for oxygen consumption, heart rate, minute ventilation, rating of perceived exertion and plasma lactate, glucose or free fatty acid concentrations. Based on the current investigation, it can be concluded that there is no evidence for the beneficial effects of pre-cooling on the physiological responses to soccer-specific intermittent exercise under normal environmental conditions.
Adult↗
Estimates of the daily phase and amplitude of the endogenous component of the circadian rhythm of core temperature in sedentary humans living nychthemerally.
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.
Activities of Daily Living↗
Sport, leisure and ergonomics: the Olympic cycle.
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Awards and Prizes↗
Use of melatonin in recovery from jet-lag following an eastward flight across 10 time-zones.
Subjective, physiological and physical performance variables are affected following travel across multiple time-zones (jet-lag). The objective of the study was to examine the effects of oral melatonin in alleviating jet-lag by investigating its effects on subjects who had flown from London to Eastern Australia, 10 time-zones to the east. Melatonin (5 mg day(-1)) or placebo capsules were administered to 14 experimental (13 males and 1 female) and 17 control subjects (15 males and 2 females), respectively, in a double-blind study; the time of administration was in accord with the current consensus for maximizing its hypnotic effect. Grip strength and intra-aural temperature were measured on alternate days after arrival at the destination, at four different times of day (between the times 07:00 - 08:00 h, 12:00 - 13:00 h, 16:00 - 17:00 h and 19:00 - 20:00 h local time). In addition, for the first 6 - 7 days after arrival in Australia, subjective ratings of jet-lag on a 0 - 10 visual analogue scale and responses to a Jet-lag Questionnaire (incorporating items for tiredness. sleep, meal satisfaction and ability to concentrate) were recorded at the above times and also on retiring (at about midnight). Subjects continued normally with their work schedules between the data collection times. Subjects with complete data (13 melatonin and 13 placebo subjects), in comparison with published data, showed partial adjustment of the diurnal rhythm in intra-aural temperature after 6 days. A time-of-day effect was evident in both right and left grip strength during adjustment to Australian time; there was no difference between the group taking melatonin and that using the placebo. Right and left grip strength profiles on day 6 were adjusted either by advancing or delaying the profiles, independent of whether subjects were taking melatonin or placebo tablets. Subjects reported disturbances with most measures in the Jet-lag Questionnaire but, whereas poorer concentration and some negative effects upon sleep had disappeared after 3 - 5 days, ratings of jet-lag and tiredness had not returned to 'zero' (or normal values), respectively, by the sixth day of the study. Subjects taking melatonin showed no significant differences from the placebo group in perceived irritability, concentration, meal satisfaction, ease in getting to sleep and staying asleep, frequency of bowel motion and consistency of the faeces. These results suggest that, in subjects who, after arrival, followed a busy schedule which resulted in frequent and erratic exposure to daylight, melatonin had no benefit in alleviating jet-lag or the components of jet-lag, and it did not influence the process of phase adjustment.
Adult↗
Do subjective symptoms predict our perception of jet-lag?
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 (p < 0.05) 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.
Adult↗
Talent identification and development in soccer.
In this review, we attempt to integrate the main research findings concerned with talent identification and development in soccer. Research approaches in anthropometry, physiology, psychology and sociology are considered and, where possible, integrated. Although some progress has been made in identifying correlates of playing success, it appears that no unique characteristics can be isolated with confidence. Both biological and behavioural scientists have indicated a strong genetic component in performance of sports such as soccer; nevertheless, the influence of systematic training and development programmes should not be underestimated. We conclude that the sport and exercise sciences have an important support role in the processes of identifying, monitoring and nurturing talented soccer players towards realizing their potential.
Anthropometry↗
Anthropometric and physiological predispositions for elite soccer.
This review is focused on anthropometric and physiological characteristics of soccer players with a view to establishing their roles within talent detection, identification and development programmes. Top-class soccer players have to adapt to the physical demands of the game, which are multifactorial. Players may not need to have an extraordinary capacity within any of the areas of physical performance but must possess a reasonably high level within all areas. This explains why there are marked individual differences in anthropometric and physiological characteristics among top players. Various measurements have been used to evaluate specific aspects of the physical performance of both youth and adult soccer players. The positional role of a player is related to his or her physiological capacity. Thus, midfield players and full-backs have the highest maximal oxygen intakes ( > 60 ml x kg(-1) x min(-1)) and perform best in intermittent exercise tests. On the other hand, midfield players tend to have the lowest muscle strength. Although these distinctions are evident in adult and elite youth players, their existence must be interpreted circumspectly in talent identification and development programmes. A range of relevant anthropometric and physiological factors can be considered which are subject to strong genetic influences (e.g. stature and maximal oxygen intake) or are largely environmentally determined and susceptible to training effects. Consequently, fitness profiling can generate a useful database against which talented groups may be compared. No single method allows for a representative assessment of a player's physical capabilities for soccer. We conclude that anthropometric and physiological criteria do have a role as part of a holistic monitoring of talented young players.
Adolescent↗
A multidisciplinary approach to talent identification in soccer.
The requirements for soccer play are multifactorial and distinguishing characteristics of elite players can be investigated using multivariate analysis. The aim of the present study was to apply a comprehensive test battery to young players with a view to distinguishing between elite and sub-elite groups on the basis of performance on test items. Thirty-one (16 elite, 15 sub-elite) young players matched for chronological age (15-16 years) and body size were studied. Test items included anthropometric (n = 15), physiological (n = 8), psychological (n = 3) and soccer-specific skills (n = 2) tests. Variables were split into separate groups according to somatotype, body composition, body size, speed, endurance, performance measures, technical skill, anticipation, anxiety and task and ego orientation for purposes of univariate and multivariate analysis of variance and stepwise discriminant function analysis. The most discriminating of the measures were agility, sprint time, ego orientation and anticipation skill. The elite players were also significantly leaner, possessed more aerobic power (9.0 +/- 1.7 vs 55.5 +/- 3.8 ml x kg(-1) x min(-1)) and were more tolerant of fatigue (P < 0.05). They were also better at dribbling the ball, but not shooting. We conclude that the test battery used may be useful in establishing baseline reference data for young players being selected onto specialized development programmes.
Adolescent↗
Physiological responses to laboratory-based soccer-specific intermittent and continuous exercise.
The aim of this study was to devise a laboratory-based protocol for a motorized treadmill that was representative of work rates observed during soccer match-play. Selected physiological responses to this soccer-specific intermittent exercise protocol were then compared with steady-rate exercise performed at the same average speed. Seven male university soccer players (mean +/- s: age 24 +/- 2 years, height 1.78 +/- 0.1 m, mass 72.2 +/- 5.0 kg, VO2max 57.8 +/- 4 ml x kg(-1) x min(-1)) completed a 45-min soccer-specific intermittent exercise protocol on a motorized treadmill. They also completed a continuous steady-rate exercise session for an identical period at the same average speed. The physiological responses to the laboratory-based soccer-specific protocol were similar to values previously observed for soccer match-play (oxygen consumption approximately 68% of maximum, heart rate 168 +/- 10 beats x min(-1)). No significant differences were observed in oxygen consumption, heart rate, rectal temperature or sweat production rate between the two conditions. Average minute ventilation was greater (P < 0.05) in intermittent exercise (81.3 +/- 0.2 l x min(-1)) than steady-rate exercise (72.4 +/- 11.4 l x min(-1)). The rating of perceived exertion for the session as a whole was 15 +/- 2 during soccer-specific intermittent exercise and 12 +/- 1 for continuous exercise (P < 0.05). The physiological strain associated with the laboratory-based soccer-specific intermittent protocol was similar to that associated with 45 min of soccer match-play, based on the variables measured, indicating the relevance of the simulation as a model of match-play work rates. Soccer-specific intermittent exercise did not increase the demands placed on the aerobic energy systems compared to continuous exercise performed at the same average speed, although the results indicate that anaerobic energy provision is more important during intermittent than during continuous exercise at the same average speed.
Adult↗
A comparison of the immediate effects of moderate exercise in the late morning and late afternoon on core temperature and cutaneous thermoregulatory mechanisms.
Twelve healthy male subjects each undertook two bouts of moderate exercise (70% VO2max for 30 minutes) in the morning (08:00) and late afternoon (18:00) at least 4 days apart. Measurements were made of heart rate, core (rectal) temperature, sternum skin temperature, and forearm skin blood flow during baseline conditions, during the bout of exercise, and throughout a 30-minute recovery period. Comparisons were made of the changes of heart rate, temperature, and skin blood flow produced by the exercise at the two times of day. Student t tests indicated that baseline values for core temperature (37.15 degrees C +/- 0.06 degrees C vs. 36.77 degrees C +/- 0.06 degrees C) and sternum temperature (33.60 degrees C +/- 0.29 degrees C vs. 32.70 degrees C + 0.38 degrees C) were significantly (p < .05) higher in the late afternoon than the early morning. Two-way analysis of variance (ANOVA) indicated that the increases in core and sternum temperatures during exercise were significantly less (p = .0039 and .0421, respectively) during the afternoon bout of exercise compared with the morning, even though the work loads, as determined by changes in heart rate, were not significantly different (p = .798) at the two times of testing. There were also tendencies for resting forearm skin blood flow to be higher in the afternoon than in the morning and for exercise to produce a more rapid rise in this variable in the afternoon. The possible mechanisms producing these responses to exercise are discussed in terms of those that are responsible for the normal circadian rhythm of core temperature. It is concluded that the body's ability to remove a heat load is less in the early morning, when the circadian system is in a "heat gain" mode, than in the late afternoon, when heat gain and "heat loss" modes are balanced more evenly.
Adult↗
A comparison of some different methods for purifying core temperature data from humans.
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.
Body Temperature↗
Some factors influencing the sensitivity of body temperature to activity in neonates.
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.
Adult↗
Anemia, iron and pregnancy outcome.
When maternal anemia is diagnosed before midpregnancy, it has been associated with an increased risk of preterm delivery. Maternal anemia detected during the later stages of pregnancy, especially the third trimester, often reflects the expected (and necessary) expansion of maternal plasma volume. Third-trimester anemia usually is not associated with increased risk of preterm delivery. High hemoglobin concentration, elevated hematocrit and increased levels of serum ferritin late in pregnancy, however, all have been associated with increased preterm delivery. This increased risk may reflect in part the failure to expand maternal plasma volume adequately, thus diminishing appropriate placental perfusion. Although controlled trials of iron supplementation during pregnancy have consistently demonstrated positive effects on maternal iron status at delivery, they have not demonstrated reductions in factors that are associated with maternal anemia, i.e., increased risk of preterm delivery and infant low birth weight. One reason for discordant findings may be the exclusion of many gravidas with iron deficiency from these trials or the data concerning gravidas with pregnancy outcomes such as preterm delivery from the analysis. Finally, recent concerns have been voiced about harmful effects of iron supplementation during pregnancy. No adverse effects of iron supplementation on pregnancy outcome have been demonstrated to date. Questions about the efficacy of iron supplementation during pregnancy for reducing adverse outcomes such as preterm delivery and side effects from iron supplementation, including the potential for oxidation of lipids and DNA, require further research in iron-deficient women.
Anemia, Iron-Deficiency↗
Investigation of anthropometric and work-rate profiles of elite South American international soccer players.
BACKGROUND: The aim of the current investigation was to determine the movement profiles of elite South American soccer players during international competition and examine the relationship between anthropometric profile and work-rate variables. METHODS: Seventeen full-time professional soccer players were filmed while competing for their countries. Anthropometric profiles were obtained for eleven of these players. Six full-time professional players from the English Premier League were also filmed for comparative purposes. RESULTS: The South American international players covered significantly less (p<0.05) total distance during match-play than English Premier League players (International, 8638+/-1158 m; English Premier League, 10104+/-703 m). The total distance covered during the second half of the game was significantly reduced (p<0.05) compared to the first half distance for both groups of players (mean+/-SD first half 4605+/-625 m; mean+/-SD second half 4415+/-634 m). The data for both groups of players were combined to evaluate positional differences in the workrate profile. Midfield players covered a significantly greater (p<0.05) distance than forward players (midfield, 9826+/-1031 m; forwards, 7736+/-929 m) and defenders covered a greater (p<0.05) distance jogging backwards than forward players (defenders, 276+/-155 m; forwards, 68+/-25 m). Forwards sprinted a greater distance (p<0.05) than defensive players (defenders, 231+/-142 m; forwards, 557+/-142 m). Mean somatotype was a balanced mesomorph (2-5 1/2-2). Body mass and muscle mass was related to the total distance covered (r=0.43, r=0.53, p<0.05). CONCLUSIONS: Based on these data, it seems that an individual's work-rate profile is dependent upon the type of competition and the playing position. Relationships between anthropometric profile and work-rate are complex due to the interaction between the variables that determine work-rate.
Adult↗