PubMed Health⌕ Search

Biomedical subjects

A Nevill

Publications and source records attributed to A Nevill.

At least 19 recordsLinked to original sources

The effect of match standard and referee experience on the objective and subjective match workload of English Premier League referees.

The aim of the present study was to examine the effect of match standard and referee experience on the objective and subjective workload of referees during English Premier League and Football League soccer matches. We also examined the relationship between heart rate (HR) and ratings of perceived exertion (RPE) for assessing match intensity in soccer referees. Heart rate responses were recorded using short-range telemetry and RPE scores were collected using a 10-point scale. Analysis revealed a significant relationship between mean match HR and match RPE scores (r=0.485, p<0.05, n=18). There were significant differences in match HR (Premier League 83.6+/-2.6% maximal HR (HRmax) versus Football League 81.5+/-2.2%HRmax, p<0.05) and match RPE scores (Premier League 7.8+/-0.8 versus Football League 6.9+/-0.8, p<0.05) between standards of competition. Referee experience had no effect on match HR and RPE responses to Premier League and Football League matches. The results of the present study demonstrate the validity of using HR and RPE as a measure of global match intensity in soccer referees. Referee experience had no effect on the referees' objective and subjective match workload assessments, whereas match intensity was correlated to competition standard. These findings have implications for fitness preparation and evaluation in soccer referees. When progressing to a higher level of competition, referees should ensure that appropriate levels of fitness are developed in order to enable them to cope with an increase in physical match demands.

Adult↗

Applicability of an allometric power equation to children, adolescents and young adults of extreme body size.

AIM: The aim of this study was to assess the applicability of a regression model for peak power (PP) and total mechanical work (TMW) for healthy children, adolescents and young adults especially in the extreme ranges of stature, mass, and body mass index (BMI). METHODS: A total of 454 children, adolescents and young adults aged 6-20 years volunteered for the study. Subjects, whose stature, mass and BMI were between the 10(th) and the 90(th) centile, were selected to calculate the prediction equation: 267 subjects fulfilled these criteria. Each subject performed two unilateral Wingate tests (ULWAnT), one with each leg. PP (Watts) and TMW (Joules) of the left and right leg were averaged for each individual. Ln(mass), in(stature), age, age(2), gender, and age x gender were used as predictors for in(PP) and ln(TMW). The applicability of the prediction equation was tested on individuals who were less than the 10(th) centile or greater than the 90(th) centile for stature, body mass and BMI. RESULTS: All independent variables were statistically significant (P<0.05) predictors of in(PP), adjusted R(2)=0.93 and all but gender were significant predictors for in(TMW), adjusted R(2)=0.95. However, measured in(PP) and in(TMW) were significantly lower than predicted in(PP) and in(TMW) for subjects >90th centile for stature, body mass, or BMI. CONCLUSIONS: the prediction equations overestimated PP and TMW in children, adolescents and young adults who were heavier than the reference subjects, as indicated by a relatively high body mass or high BMI for age or were taller than the reference subjects. The findings might reflect a deficit in anaerobic capacity in children, adolescents and young adults with relatively large body size for their age.

Adolescent↗

Enhancing specificity in proxy-design for the assessment of bioenergetics.

The purpose of this study was to examine the hypothesis that improved prediction of bioenergetics may be achieved when proxies are designed to simulate closely gold standard laboratory protocols. To accomplish this, a modified 'square' variation (SST) of the classical 20m Multistage Shuttle Run Test (MST) was designed aiming to reduce the stopping, turning and side-stepping manoeuvres. Within two weeks, 50 male volunteers (age 21.5+/-1.6, BMI 24.4+/-2.2) randomly underwent three maximal oxygen uptake (VO2max) assessments using a treadmill test (TT), the SST and MST. To assess SST reproducibility, 10 randomly-selected subjects performed the test twice. Validity results showed that mean predicted VO2max from SST was not significantly different compared to TT VO2max (p>0.05). In contrast, the equivalent value from MST was significantly higher (p<0.001) than TT. Furthermore, TT VO2max correlated with SST and MST at r=0.88 (p<0.001) and r=0.61 (p<0.05), respectively. The '95% limits of agreement' analysis (LIM(AG)) for SST and MST indicated a range of error equal to -0.5+/-5.4 and 8.1+/-8.0 (ml.kg(-1).min(-1)) with a coefficient of variation of +/-6 and +/-8.2%, respectively. Test-retest results for SST revealed no mean difference in VO2max (p>0.05) and a correlation coefficient of r=0.98 (p<0.001), while LIM(AG) demonstrated a range of error equal to -0.2+/-2.6 (ml.kg(-1).min(-1)) with a coefficient of variation of +/-5.6%. It is concluded that, compared to MST, the SST had a higher agreement with TT. The latter may well be explained by the closer simulation in bioenergetics between the two protocols (ie, the continuous nature of SST provides a closer proxy of TT).

Adult↗

Left ventricular morphology and function in female athletes: a meta-analysis.

The purpose of the present study was to examine the impact of physical training upon cardiac structure and function, and identify physiologic upper limits in female athletes. Meta-analytical techniques were applied to 13 published echocardiographic studies examining cardiac structure and function in female athletes. The study group included 890 athletes and 333 controls. For comparison of sporting discipline, studies were partitioned into 3 categories (endurance, strength/sprint, team). Significant (p < 0.05) effect sizes were observed for all structural measures between athletes and controls. Significant effect size differences existed between sporting groups for LVIDd and LVM only, with endurance and team game athletes demonstrating the largest effect sizes compared to strength trained athletes. No significant effect of training was observed for left ventricular diastolic or systolic function, with the exception of stroke volume where a significant effect size difference was observed between athletes and controls with no observed difference between sporting groups. Maximum reported upper limits for LV wall thickness and LVIDd in female athletes were 12 mm and 66 mm respectively. Chronic exercise training results in cardiac enlargement in female athletes. The nature of physiologic adaptation is similar to that observed in male athletes. LV wall thickness values greater than 12 mm in female athletes should be viewed with caution and indicate a more comprehensive evaluation to establish a physiological or pathological basis for the observed left ventricular enlargement.

Adaptation, Physiological↗

The validity of capillary blood sampling in the determination of human growth hormone concentration during exercise in men.

BACKGROUND: Studies measuring human growth hormone (hGH) in blood during exercise have mainly used venous sampling. The invasive nature of this procedure makes evaluation of hGH impossible in various exercise environments. OBJECTIVE: To determine whether capillary sampling could offer an alternative sampling method. METHODS: Capillary and venous blood samples were collected for determination of hGH at the end of each exercise stage during an incremental exercise test in 16 male club level competitive cyclists (mean (SD) age 30.8 (8.0) years, body mass 72.2 (7.1) kg, body fat 12.9 (3.5)%, peak oxygen consumption 4.18 (0.46) l x min(-1)). Linear regression, from a plot of venous v capillary blood hGH concentration, showed a correlation coefficient of r = 0.986 (p<0.001). When geometric means and log transformations were used, a coefficient of variation of 14.2% was demonstrated between venous and capillary flow for hGH concentration. The mean ratio limits of agreement were 0.62 (1.72)-that is, 95% of the ratios were contained between 0.36 and 1.07, with a mean of 0.62. CONCLUSIONS: Capillary blood sampling is an acceptable alternative to venous sampling for determining hGH concentration during rest and exercise. Sample sites should not be used interchangeably: one site should be chosen and its use standardised.

Adult↗

Greek adolescents, fitness, fatness, fat intake, activity, and coronary heart disease risk.

BACKGROUND: A dramatic increase in adult mortality rates from coronary heart disease (CHD) in Greece, accompanied by increased prevalence of CHD risk factors in children, has been documented. However, there is controversy about the independent effects of certain lifestyle parameters on primary CHD risk factors. AIMS AND METHODS: To examine the association between CHD risk factors (HDL-C, LDL-C, HDL-C/TC, triglycerides, systolic and diastolic blood pressure) and lifestyle parameters (fitness, fatness, fat intake, and physical activity) in 210 12-year old Greek pupils. RESULTS: Correcting for the fixed factors of gender and maturation, analyses of covariance (ANCOVA) with backward elimination of the lifestyle covariates revealed significant associations between three CHD risk factors (HDL-C, HDL-C/TC, systolic blood pressure) and physical activity levels. In contrast, the covariates aerobic fitness, fatness and fat intake failed to reach significance with any of the CHD risk factors. CONCLUSIONS: In Greek schoolchildren, primary CHD risk factors are mainly associated with physical activity levels, independently of fitness, fatness, and/or fat intake. Prevention strategies should concentrate on enhancing physical activity early in life, if the increased prevalence of Greek adult CHD mortality is to be diminished.

Adolescent↗

The development of new purification methods to assess the circadian rhythm of body temperature in Mongolian gerbils.

Six Mongolian gerbils were studied for 8-10d while housed in separate cages in a 12:12h light-dark (L-D) cycle (lights on at 07:00h). Recordings of body temperature, heart rate, and spontaneous activity were made throughout. The temperature and heart rate rhythms were "purified" to take into account the effects of activity, and then the rhythm of temperature was further purified to take into account other masking influences ("non-activity masking effects" or NAME,). The methods employed in the purification processes involved linear regression analysis or analysis of covariance, the latter using functions of activity and NAME as covariates. From these methods, it was possible to obtain not only an estimate of the endogenous component of the temperature rhythm but also a measure of circadian changes in the sensitivity of temperature to masking effects. Even though all purification methods removed many of the effects of spontaneous activity from the temperature record, there remained temperature fluctuations at the L-D and D-L transitions that appeared to be independent of activity. The NAME was of only very marginal value in the purification process. Comparison of the purification methods indicated that the linear methods were inferior (both from a biological viewpoint and when the results were compared mathematically) to those that allowed the rate of rise of temperature due to increasing amounts of activity to become progressively less. The sensitivity of temperature and heart rate to the masking effects of activity showed a circadian rhythm, with sensitivities in the resting phase being greater than those in the active phase. These findings are compatible with the view that thermoregulatory reflexes are induced by spontaneous activity of sufficient amount, and that there is a circadian rhythm in the body temperature at which these reflexes are initiated and in their effectiveness.

Analysis of Variance↗

Identifying some determinants of "jet lag" and its symptoms: a study of athletes and other travellers.

BACKGROUND: Travelling across multiple time zones disrupts normal circadian rhythms and induces "jet lag". Possible effects of this on training and performance in athletes were concerns before the Sydney Olympic Games. OBJECTIVE: To identify some determinants of jet lag and its symptoms. METHODS: A mixture of athletes, their coaches, and academics attending a conference (n = 85) was studied during their flights from the United Kingdom to Australia (two flights with a one hour stopover in Singapore), and for the first six days in Australia. Subjects differed in age, sex, chronotype, flexibility of sleeping habits, feelings of languor, fitness, time of arrival in Australia, and whether or not they had previous experience of travel to Australia. These variables and whether the body clock adjusted to new local time by phase advance or delay were tested as predictors for jet lag and some of its symptoms by stepwise multiple regression analyses. RESULTS: The amount of sleep in the first flight was significantly greater in those who had left the United Kingdom in the evening than the morning (medians of 5.5 hours and 1.5 hours respectively; p = 0.0002, Mann-Whitney), whereas there was no significant difference on the second flight (2.5 hours v 2.8 hours; p = 0.72). Only the severity of jet lag and assessments of sleep and fatigue were commonly predicted significantly (p<0.05) by regression analysis, and then by only some of the variables. Thus increasing age and a later time of arrival in Australia were associated with less jet lag and fatigue, and previous experience of travel to Australia was associated with an earlier time of getting to sleep. Subjects who had adjusted by phase advance suffered worse jet lag during the 5th and 6th days in Australia. CONCLUSIONS: These results indicate the importance of an appropriate choice of itinerary and lifestyle for reducing the negative effects of jet lag in athletes and others who wish to perform optimally in the new time zone.

Adult↗

Temperature profiles, and the effect of sleep on them, in relation to morningness-eveningness in healthy female subjects.

There were 15 healthy female subjects, differing in their position on the "morningness-eveningness" scale, studied for 7 consecutive days, first while living a sedentary lifestyle and sleeping between midnight and 08:00 and then while undergoing a "constant routine." Rectal temperature was measured at regular intervals throughout this time, and the results were subjected to cosinor analysis both before and after "purification" for the effects of physical activity. Results showed that there was a phase difference in the circadian rhythm of core temperature that was associated with the morningness score, with calculations that "morning types" would be phased earlier than "evening types" by up to about 3 h. This difference in phase (which was also statistically significant when the group was divided by a median split into a "morning group" and an "evening group") could not be attributed to effects of waking activity and existed in spite of the subjects keeping the same sleep-wake schedule. Moreover, it persisted when the subjects' data had been purified and when the data were obtained from the constant routine. That is, there was an endogenous component to this difference in phase of the core temperature. The morning group also showed a greater fall of core temperature during sleep; this was assessed in two ways, the main one being a comparison of constant routine and nychthemeral data sets after correction for any effects of activity. Even though the morning group was sleeping at a later phase of their circadian temperature rhythm than was the evening group, neither group showed a fall of temperature due to sleep that varied with time elapsed since the temperature acrophase. It is concluded that another factor that differs between morning and evening types is responsible for this difference.

Behavior↗

Effect of oral glucose on leucine turnover in human subjects at rest and during exercise at two levels of dietary protein.

The aim of this study was to determine the effect of glucose supplementation on leucine turnover during and after exercise and whether variation in the previous dietary protein content modulated this effect. Postabsorptive subjects received a primed constant [1-13C, 15N]leucine infusion for 6 h, after previous consumption of a high (1.8 g kg-1 day-1, HP, n = 16) or low (0.7 g kg-1 day-1, LP, n = 16) protein diet for 7 days. The subjects were studied at rest; during 2 h of exercise, during which half of the subjects from each dietary protocol received 0.75 g kg-1 h-1 glucose (HP + G, LP + G) and the other half received water (HP + W, LP + W); then again for 2 h of rest. Glucose supplementation suppressed leucine oxidation (P < 0.01) by 20% in subjects consuming the high protein diet (58.2 +/- 2.8 micromol kg-1 h-1, HP + G; 72.4 +/- 3.9 micromol kg-1 h-1, HP + W) but not the low protein diet (51.1 +/- 5.9 micromol kg-1 h-1, LP + G; 51.7 +/- 5.5 micromol kg-1 h-1, LP + W), with no difference in skeletal muscle branched-chain 2-oxo acid dehydrogenase (BCOADH) activity between groups. Glucose supplementation did not alter the rate of whole-body protein synthesis or breakdown. The sparing effect of glucose on leucine oxidation appears only to occur if previous protein intake was high. It was not mediated by a suppression of BCOADH fractional activity but may be due to reduced substrate availability.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗

Training effects of accumulated daily stair-climbing exercise in previously sedentary young women.

BACKGROUND: The health and fitness benefits associated with short, intermittent bouts of exercise accumulated throughout the day have been seldom investigated. Stair climbing provides an ideal model for this purpose. METHODS: Twenty-two healthy female volunteers (18-22 years) were randomly assigned to control (N = 10) or stair-climbing (N = 12) groups. Stair climbers then underwent a 7-week stair-climbing program, progressing from one ascent per day in week 1 to six ascents per day in weeks 6 and 7, using a public access staircase (199 steps). Controls were instructed to maintain their normal lifestyle. Standardized stair-climbing tests were administered to both groups immediately before and after the program. Each paced ascent lasted 135 s, during which oxygen uptake (VO(2)) and heart rate (HR) were monitored continuously. Blood lactate concentration was also measured immediately following each test ascent. Fasting blood samples from before and after the program were analyzed for serum lipids. Data were analyzed using a two-way ANOVA with repeated measures. RESULTS: Relative to the insignificant changes in the control group, the stair-climbing group displayed a rise in HDL cholesterol concentration (P<0.05) and a reduced total:HDL ratio (P<0.01) over the course of the program. VO(2) and HR during the stair-climbing test were also reduced, as was blood lactate (all P<0.01). CONCLUSION: A short-term stair-climbing program can confer considerable cardiovascular health benefits on previously sedentary young women, lending credence to the potential public health benefits of this form of exercise.

Adolescent↗

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↗

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↗

Effects of activity-rest schedules on physiological strain and spinal load in hospital-based porters.

Workers in physically demanding occupations require rest breaks to recover from physiological stress and biomechanical loading. Physiological stress can increase the risk of developing musculoskeletal disorders and repeated loading of the spine may increase the potential for incurring back pain. The aim of the study was to assess the impact of an altered activity-rest schedule on physiological and spinal loading in hospital-based porters. An existing 4-h activity-rest schedule was obtained from observations on eight male porters. This schedule formed the normal trial, which included two 5- and one 15-min breaks. An alternative 4-h schedule was proposed (experimental condition) that had two breaks each of 12.5 min. It was hypothesized that the experimental trial is more effective in promoting recovery from physiological strain and spinal shrinkage than the normal trial, due to the 5-min breaks being insufficient to allow physiological variables to return to resting levels or the intervertebral discs to reabsorb fluid. Ten males performed both test conditions and oxygen uptake VO2, heart rate, minute ventilation VE, perceived exertion and spinal shrinkage were recorded. There were no significant differences in any of the measured variables between the two trials (p > 0.05). Median heart rates were 78 (range 71-93) and 82 (71-90) beats.min(-1) for the normal trial and the experimental trial respectively, indicating that the activity was of low intensity. The light intensity was corroborated by the oxygen uptakes (0.75, range 0.65-0.94 1.min(-1)). Spinal shrinkage occurred to the same extent in the two trials (2.12 +/- 3.16 mm and 2.88 +/- 2.92 mm in the normal trial and the experimental trial respectively). Varying the length and positioning of the rest breaks did not significantly affect the physiological responses or magnitude of spinal shrinkage between the two trials. More physically demanding work than the porters' schedule should induce greater physiological fatigue and spinal shrinkage. The ratio between activity and rest breaks would then become more important.

Adult↗

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↗

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↗