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Biomedical subjects

A M Nevill

Publications and source records attributed to A M Nevill.

At least 19 recordsLinked to original sources
PubMed2005

Scaling maximal oxygen uptake to predict cycling time-trial performance in the field: a non-linear approach.

The purpose of the present article is to identify the most appropriate method of scaling VO2max for differences in body mass when assessing the energy cost of time-trial cycling. The data from three time-trial cycling studies were analysed (N = 79) using a proportional power-function ANCOVA model. The maximum oxygen uptake-to-mass ratio found to predict cycling speed was VO2max(m)(-0.32) precisely the same as that derived by Swain for sub-maximal cycling speeds (10, 15 and 20 mph). The analysis was also able to confirm a proportional curvilinear association between cycling speed and energy cost, given by (VO2max(m)(-0.32))0.41. The model predicts, for example, that for a male cyclist (72 kg) to increase his average speed from 30 km h(-1) to 35 km h(-1), he would require an increase in VO2max from 2.36 l min(-1) to 3.44 l min(-1), an increase of 1.08 l min(-1). In contrast, for the cyclist to increase his mean speed from 40 km h(-1) to 45 km h(-1), he would require a greater increase in VO2max from 4.77 l min(-1) to 6.36 l min(-1), i.e. an increase of 1.59 l min(-1). The model is also able to accommodate other determinants of time-trial cycling, e.g. the benefit of cycling with a side wind (5% faster) compared with facing a predominately head/tail wind (P<0.05). Future research could explore whether the same scaling approach could be applied to, for example, alternative measures of recording power output to improve the prediction of time-trial cycling performance.

Adult↗
PubMed2005

Cardiovascular disease risk factors in habitual exercisers, lean sedentary men and abdominally obese sedentary men.

OBJECTIVE: To investigate whether the favourable cardiovascular disease (CVD) risk factor profile of habitual exercisers is attributable to exercise or leanness. DESIGN: Cross-sectional study of 113 nonsmoking men aged 30-45 y. CVD risk factors were compared in exercisers (n=39) and sedentary men (n=74), and in subgroups of lean exercisers (n=37), lean sedentary men (n=46) and obese sedentary men (n=28). Waist girth was used to identify lean (<100 cm) and abdominally obese (> or =100 cm) subgroups. MEASUREMENTS: Blood pressure, physical activity (7-day recall), physical fitness (maximum oxygen consumption) and fasted lipoproteins, apolipoprotein (apo) B, triglycerides, glucose and fibrinogen. RESULTS: Exercisers were fitter and leaner than sedentary men and had a better CVD risk factor profile. Total cholesterol, LDL-cholesterol and apo B concentrations were lower in lean exercisers than in lean sedentary men, suggesting that exercise influences these risk factors. Indeed, time spent in vigorous activity was the only significant predictor of total cholesterol and LDL-cholesterol in multiple linear regression models. Exercise status had little influence on triglycerides and HDL-cholesterol (HDL-C), and unfavourable levels were only evident among obese sedentary men. Waist girth was the sole predictor of triglycerides and HDL-C, explaining 44 and 31% of the variance, respectively. CONCLUSIONS: These findings suggest that the CVD risk factor profile of habitual exercisers is attributable to leanness and exercise. Leanness is associated with favourable levels of HDL-C and triglycerides, while exercise is associated with lower levels of total cholesterol, LDL-cholesterol and apo B.

Adult↗
PubMed2005

Performance characteristics of gas analysis systems: what we know and what we need to know.

It is important that sources of variation in gas analysis measurements are identified and described in an accurate and informative manner. In this paper, we discussed the potential sources of error, which should be considered in any measurement study on gas analysis systems. We then covered how errors in various terms associated with gas laws propagate to outcome measurements of gas exchange to help quantify the relative importance of sources of error. Finally, we performed a literature survey to explore the statistical methods researchers have employed to arrive at conclusions on the performance characteristics of gas analysis methods. We found examples of excellent practice in the literature, but there were also gaps in the knowledge of error in gas analysis systems. Consequently, we supplied guidelines for future method comparison studies. These guidelines included (i) a sample size of at least 40 participants and the citation of confidence intervals, (ii) a description of the relationships between systematic and random errors and the size of measured value, (iii) the parallel examination of test-retest error within a method comparison study, and (iv) an a priori-made judgement on how much systematic and random error between methods is acceptable for practical applications. We stressed that this judgement should be based on expert-agreed position statements about acceptable error, which unfortunately have yet to be formulated for gas analysis systems.

Breath Tests↗
PubMed2005

Do judges enhance home advantage in European championship boxing?

There have been many examples of contentious points decisions in boxing. Professional boxing is scored subjectively by judges and referees scoring each round of the contest. We assessed whether the probability of a home win (and therefore home advantage) increased when bouts were decided by points decisions rather than knockouts. Overall, we found that bouts ending in points decisions had a significantly higher proportion of home wins than those decided by a knockout, though this effect varied across time, and controlling for relative quality of boxers was only effective when using more recent data. Focusing on these data, again the probability of a home win was higher with a points decision and this effect was consistent as "relative quality" varied. For equally matched boxers ("relative quality" = 0), expected probability of a home win was 0.57 for knockouts, 0.66 for technical knockouts and 0.74 for points decisions. The results of the present study lend general support to the notion that home advantage is more prevalent in sports that involve subjective decision-making. We suggest that interventions should be designed to inform judges to counter home advantage effects.

Boxing↗
PubMed2003

Modeling elite male athletes' peripheral bone mass, assessed using regional dual x-ray absorptiometry.

There is still considerable debate as to whether bone mineral content (BMC) increases in proportion to the projected bone area, A(p), or an estimate of the skeletal bone volume, (A(p))(3/2), being assessed. The results from this study suggest that the bone mass acquisition of elite athletes' arms and legs increases in proportion to the projected bone area, A(p), having simultaneously controlled/removed the effect of the confounding variables of body mass and body fat. Although this supports the use of the traditional bone mineral density ratio (BMD=BMC/A(p)), it also highlights the dangers of overlooking the effect of known confounding variables. Ignoring the effect of such confounding variables, athletic groups whose activities involve upper body strength (rugby, rock climbing, kayaking, weight lifting) had the highest arm BMD, while runners were observed to have the lowest arm BMD (lower than that of the controls). Similarly, leg BMD was highest in rugby players, whose activities included both running and strength training. However, the rugby players were also observed to have the greatest body mass. When the important determinants of body mass, body fat, as well as projected bone area, A(p), were incorporated as covariates into a proportional allometric ANCOVA model for BMC, different conclusions were obtained. The introduction of these covariates had the effect of reducing the sporting differences on adjusted arm BMC, although the "sport" by "side" interaction still identified racket players as the only group with a greater dominant arm BMC (P < 0.05). In contrast, sporting differences in adjusted leg BMC remained highly significant, but with a rearranged hierarchy. The runners replaced the rugby players as having the greatest adjusted leg BMC. The results confirm the benefits of activity on peripheral bone mass as being site-specific but reinforce the dangers of making generalizations about the relative benefits of different exercises ignoring the effects of known confounding variables, such as body size, body composition, and age.

Absorptiometry, Photon↗
PubMed2003

Modelling home advantage in the Summer Olympic Games.

Home advantage in team games is well proven and the influence of the crowd upon officials' decisions has been identified as a plausible cause. The aim of this study was to assess the significance of home advantage for five event groups selected from the Summer Olympic Games between 1896 and 1996, and put home advantage in team games in context with other sports. The five event groups were athletics and weightlifting (predominantly objectively judged), boxing and gymnastics (predominantly subjectively judged) and team games (involving subjective decisions). The proportion of points won was analysed as a binomial response variable using generalized linear interactive modelling. Preliminary exploration of the data highlighted the need to control for the proportion of competitors entered and to split the analysis pre- and post-war. Highly significant home advantage was found in event groups that were either subjectively judged or rely on subjective decisions. In contrast, little or no home advantage (and even away advantage) was observed for the two objectively judged groups. Officiating system was vital to both the existence and extent of home advantage. Our findings suggest that crowd noise has a greater influence upon officials' decisions than players' performances, as events with greater officiating input enjoyed significantly greater home advantage.

Boxing↗
PubMed2003

Physiological factors associated with low bone mineral density in female endurance runners.

OBJECTIVE: To explore potential factors that could be associated with low bone mineral density (BMD) in female endurance runners. METHODS: Fifty two female endurance runners (1,500 m to marathon), aged 18-44 years, took part. Body fat percentage, lumbar spine BMD, and femoral neck BMD were measured using the Hologic QDR 4,500w bone densitometer. Data on training, menstrual cycle status, osteoporosis, and health related factors were obtained by questionnaire. Dietary variables were assessed from a prospective seven day dietary record of macronutrients and micronutrients. RESULTS: The mean (SD) lumbar spine and femoral neck BMD were 1.11 (0.11) and 0.89 (0.12) g/cm(2) respectively. A backward elimination regression analysis showed that age, body mass, body fat, distance run, magnesium, and zinc intake were the variables significantly associated with BMD. Lumbar spine BMD (g/cm(2)) = -1.90 + (0.0486 x age (years)) + (0.342 x log mass (kg)) - (0.000861 x age(2) (years)) - (0.00128 x distance (km/week)), with an R(2) = 30.1% (SEE = 0.089 (95% confidence interval (CI) 0.05 to 0.23); p<0.001). Femoral neck BMD (g/cm(2)) = -2.51 - (0.00989 x age (years)) + (0.720 x log mass (kg)) + (0.000951 x magnesium (mg/day)) -(0.0289 x zinc (mg/day)) - (0.00821 x body fat (%)) - (0.00226 x distance (km/week)), with an R(2) = 50.2% (SEE = 0.100 (95% CI 0.06 to 0.22); p<0.001). The negative association between skeletal BMD and distance run suggested that participants who ran longer distances had a lower BMD of the lumbar spine and femoral neck. Further, the results indicated a positive association between body mass and BMD, and a negative association between body fat and BMD. CONCLUSIONS: The results suggest a negative association between endurance running distance and lumbar spine and femoral neck BMD, with a positive association between body mass and femoral neck and lumbar spine BMD. However, longitudinal studies are required to assess directly the effect of endurance running and body mass on BMD, and to see if the addition of alternative exercise that would increase lean body mass would have a positive effect on BMD and therefore help to prevent osteoporosis.

Adipose Tissue↗
PubMed2002

Determinants of 2,000 m rowing ergometer performance in elite rowers.

This study examined the physiological determinants of performance during rowing over 2,000 m on an ergometer in finalists from World Championship rowing or sculling competitions from all categories of competion rowing (19 male and 13 female heavyweight, 4 male and 5 female lightweight). Discontinuous incremental rowing to exhaustion established the blood lactate threshold, maximum oxygen consumption (VO(2max)) and power at VO(2max); five maximal strokes assessed maximal force, maximal power and stroke length. These results were compared to maximal speed during a 2,000 m ergometer time trial. The strongest correlations were for power at VO(2max), maximal power and maximal force (r=0.95; P<0.001). Correlations were also observed for VO(2max) (r=0.88, P<0.001) and oxygen consumption (VO(2)) at the blood lactate threshold (r=0.87, P=0.001). The physiological variables were included in a stepwise regression analysis to predict performance speed (metres per second). The resultant model included power at VO(2max), VO(2) at the blood lactate threshold, power at the 4 mmol x l(-1) concentration of blood lactate and maximal power which together explained 98% of the variance in the rowing performance over 2,000 m on an ergometer. The model was validated in 18 elite rowers, producing limits of agreement from -0.006 to 0.098 m x s(-1) for speed of rowing over 2,000 m on the ergometer, equivalent to times of -1.5 to 6.9 s (-0.41% to 1.85%). Together, power at VO(2max), VO(2) at the blood lactate threshold, power at 4 mmol x l(-1) blood lactate concentration and maximal power could be used to predict rowing performance.

Adult↗
PubMed2001

Home advantage in the Winter Olympics (1908-1998).

We obtained indices of home advantage, based on the medals won by competing nations, for each event held at the Winter Olympics from 1908 to 1998. These indices were designed to assess home advantage while controlling for nation strength, changes in the number of medals on offer and the performance of 'non-hosting' nations. Some evidence of home advantage was found in figure skating, freestyle skiing, ski jumping, alpine skiing and short track speed skating. In contrast, little or no home advantage was observed in ice hockey, Nordic combined, Nordic skiing, bobsled, luge, biathlon or speed skating. When all events were combined, a significant home advantage was observed (P = 0.029), although no significant differences in the extent of home advantage were found between events (P > 0.05). When events were grouped according to whether they were subjectively assessed by judges, significantly greater home advantage was observed in the subjectively assessed events (P = 0.037). This was a reflection of better home performances, suggesting that judges were scoring home competitors disproportionately higher than away competitors. Familiarity with local conditions was shown to have some effect, particularly in alpine skiing, although the bobsled and luge showed little or no advantage over other events. Regression analysis showed that the number of time zones and direction of travel produced no discernible trends or differences in performance.

Female↗
PubMed2001

Selected issues in the design and analysis of sport performance research.

The aim of this review is to discuss some issues in the design and statistical analysis of sport performance research, rather than to supply an authoritative 'cookbook' of methods. In general, we try to communicate some possible solutions to the conundrum of how to maintain both internal and external validity, as well as optimize statistical power, in applied sport performance research. We start by arguing that some sport performance research has been overly concerned with physiological predictors of performance, at the expense of not providing a valid and reliable description of the exact nature of the task in question. We show how the influence of certain factors on competitive performances can be described using linear or logistic regression. We discuss the choice of analysis for factorial repeated-measures designs, which is complicated by the assumption of 'sphericity' in a univariate general linear model, and the relatively low statistical power of the multivariate approach when used with small samples. We consider a little-used and simpler technique known as 'analysis of summary statistics'. In multi-group pre- and post-test designs, a useful technique can be to pair-match individuals on their performance scores in a counterbalanced fashion before the intervention or control has been introduced. Finally, we outline how confidence intervals can help in making statements about the probability of the population difference in performance exceeding the value designated as being worthwhile or not.

Humans↗
PubMed2001

Stability of psychometric questionnaires.

In 1999, Wilson and Batterham proposed a new approach to assessing the test-retest stability of psychometric questionnaires. They recommended assessing the proportion of agreement - that is, the proportion of participants that record the same response to an item - using a test-retest design. They went on to use a bootstrapping technique to estimate the uncertainty of the proportion of agreement. The aims of this short communication are (1) to demonstrate that the sampling distribution of the proportion of agreement is well known (the binomial distribution), making the technique of 'bootstrapping' redundant, and (2) to suggest a much simpler, more sensitive method of assessing the stability of a psychometric questionnaire, based on the test-retest differences (within-individuals) for each item. Adopting methods similar to Wilson and Batterham, 97 sport students completed the Social Physique Anxiety Scale on two occasions. Test-retest differences were calculated for each item. Our results show that the proportion of agreement ignores the nature of disagreement. Items 4 and 11 showed similar agreement (44.3% and 43.3% respectively), but 89 of the participants (91.8%) differed by just +/-1 point when responding to item 4, indicating a relatively stable item. In contrast, only 78 of the participants (80.4%) recorded a difference within +/- 1 point when responding to item 11, suggesting quite contrasting stability for the two items. We recommend that, when assessing the stability of self-report questionnaires using a 5-point scale, most participants (90%) should record test-retest differences within a reference value of +/- 1.

Adult↗
PubMed2001

Resting metabolic rate in obese and nonobese Chinese Singaporean boys aged 13-15 y.

BACKGROUND: Previous studies investigating the hypothesis that a low resting metabolic rate (RMR) is a cause of obesity yielded discrepant findings. Two explanations for these findings are the use of imprecise methods to determine obesity and a failure to control for differences in fat mass (FM) and fat-free mass (FFM) when comparing RMR values. OBJECTIVE: This study tested the hypothesis that RMR is lower in obese than in nonobese boys (with the use of precise methods to quantify body fatness and with adjustment for differences in both FM and FFM). DESIGN: Forty Chinese Singaporean boys aged 12.8-15.1 y were recruited. Boys were classified as obese (n = 20) or nonobese (n = 20) on the basis of their adiposity index (ratio of FM to FFM: >0.60 = obese, <0.40 = nonobese) determined by dual-energy X-ray absorptiometry. RMR was determined by using indirect calorimetry. RMR values were compared by using both linear (analysis of covariance) and log-linear (analysis of covariance with log-transformed data) regression to control for differences in FM and FFM. RESULTS: Age, height, and FFM did not differ significantly between groups. Body mass was 13 kg greater and FM was 16 kg greater in the obese boys than in the nonobese boys (P < 0.001). After control for FFM and FM, RMR did not differ significantly between the groups. CONCLUSION: When body composition is appropriately controlled for, RMR does not differ significantly between obese and nonobese boys.

Absorptiometry, Photon↗
PubMed2001

Effect of training on accumulated oxygen deficit and shuttle run performance.

BACKGROUND: The purpose of the present study was to investigate changes in physiological, metabolic and performance parameters resulting from an intense 6 week training programme. METHODS: Sixteen volunteers were divided into a control (CN; 4 men and 2 women) and training group (TR; 6 men and 4 women). Laboratory measures included maximal aerobic power (VO2max), submaximal oxygen uptake (10.5 percent or 6 degrees treadmill inclination) and accumulated oxygen deficit (AOD). Performance was assessed during 20 metre shuttle run tests (PST, progressive shuttle run test; HIST, high intensity shuttle run test). RESULTS: TR improved their HIST performance (m) significantly compared with CN, identified by a significant "group-by-training" interaction (p<0.01). Similarly, AOD values improved more in TR compared with CN (p<0.01). There was a trend for TR to further reduce blood pH values after training compared with CN, although this decrease (approximately 0.05 units) did not attain statistical significance. The change in AOD was strongly correlated with the change in run time to exhaustion (r=0.76, p<0.01) and the change in estimated total work output (r=0.69, p<0.01) during 10.5 percent gradient running and modestly correlated with the change in HIST performance (r=0.49, p<0.05, assuming a directional test). CONCLUSIONS: The results of the present study suggest changes in the anaerobic capacity, determined as AOD, due to training may be reflected in corresponding changes in laboratory and field performance.

Adult↗
PubMed2000

Different patterns of brisk walking are equally effective in decreasing postprandial lipaemia.

OBJECTIVE: To compare the effects of different patterns of brisk walking on day-long plasma triacylglycerol concentrations in sedentary adults. DESIGN: A three-trial, repeated measures design in which subjects were studied in the fasted state and throughout a day during which they consumed three standardized, mixed meals. On different occasions, subjects undertook no exercise (control), walked briskly for 10 min before each meal (short walks) or walked briskly for 30min before breakfast (long walk). SUBJECTS: Seven postmenopausal sedentary women and three sedentary men aged between 34 and 66y, with body mass index between 24 and 35 kg/m2. MEASUREMENTS: Plasma concentrations of triacylglycerol, non-esterified fatty acids, glucose and insulin, metabolic rate and whole-body substrate oxidation in the fasted state and at hourly intervals for 3 h after each meal. RESULTS: Postprandial plasma triacylglycerol concentrations were lower (P= 0.009) during the walking trials than during the control trial (average values: control 2.08 +/- 0.28 mmol/l; short walks 1.83 +/- 0.22mmol/l; long walk 1.84 +/- 0.22mmol/l (mean+/-s.e.) but did not differ between the two patterns of walking. The difference between control and walking trials increased as successive meals were consumed (interaction of trial x meal P= 0.03). Plasma triacylglycerol concentration increased during the 3 h after breakfast, changed little after lunch and decreased after the evening meal (interaction of meal x time P=0.001). When both walking trials were treated as one condition, walking increased postprandial fat oxidation (average values: control, 0.066 +/- 0.009 g/min;walking 0.074 +/- 0.008 g/min; P < 0.01). CONCLUSIONS: Thirty minutes of brisk walking, undertaken in one session or accumulated throughout a day, reduces postprandial plasma triacylglycerol concentrations and increases fat oxidation.

Adult↗
PubMed2000

Modelling handgrip strength in the presence of confounding variables: results from the Allied Dunbar National Fitness Survey.

Differences in handgrip strength, caused by risk factors such as physical inactivity, will be influenced by 'confounding' variables, e.g. age, body size. The aims of the study were to identify the confounding variables associated with handgrip strength and to assess the benefit that physical activity plays in maintaining grip strength within a population, having adjusted for differences in these confounding variables. The most appropriate linear body size dimension associated with grip strength was height rather than demispan. Non-linear associations with age and body mass were also identified. Handgrip strength peaked in the age group 25 - 34 years for male subjects and in the age group 35 - 44 years for female subjects. Similarly, handgrip strength increased with body mass until it peaked at a body mass of approximately 100 kg for male and 90 kg for female subjects; thereafter a rapid decline in grip strength was observed. Differences in handgrip strength were found to be significantly associated with levels of physical activity even having controlled for differences in age and body size (height, mass and percentage body fat), but the observed association was not linear. The level of physical activity necessary to maintain an optimal level of handgrip strength was found to be a balance of moderate or vigorous occasions of physical activity.

Adult↗
PubMed2000

Human erythrocyte and plasma amino acid concentrations during exercise.

PURPOSE: This investigation examined the effects of exercise and maltodextrin (Md) or placebo (Pl) ingestion on plasma and erythrocyte concentrations of amino acids. METHODS: The erythrocyte and plasma concentrations of 17 amino acids, as well as plasma glucose and insulin, were analyzed in eight healthy trained male subjects before, during, and 25 min after 90-min cycle ergometer exercise at 65% peak oxygen uptake. The two treatments involved ingestion of orange-flavored water (Pl) or orange-flavored 10% maltodextrin solution (Md). RESULTS: Two-way ANOVA revealed 1) that plasma concentrations of alanine and tyrosine changed significantly during the treatments, 2) that the plasma concentrations were significantly different between treatments for glycine and threonine, 3) that all erythrocyte concentrations increased significantly throughout the treatments except for arginine and tyrosine, and 4) that there were no significant differences in erythrocyte concentrations between the treatments. Three-way ANOVA highlighted the significant differences in the time responses between plasma and erythrocyte concentrations; the changes in erythrocyte levels from rest being significantly different from plasma for all amino acids except aspartic acid, glycine, and ornithine. Plasma glucose concentrations became elevated and remained above rest values in Md but fell below rest values in Pl: the differences in concentration between treatments were significant. Correspondingly, plasma insulin was significantly higher in Md during exercise. CONCLUSION: These results highlight that far from being slow in the uptake of amino acids, the erythrocyte in fact sequesters amino acids at an appreciable rate during exercise without a corresponding elevation in the plasma amino acids. For a greater understanding of amino acid changes during exercise, the analysis of both plasma and erythrocytes is recommended.

Administration, Oral↗