596 research outputs found
Can greater muscularity in larger individuals resolve the 3/4 power-law controversy when modelling maximum oxygen uptake?
BACKGROUND: The power function relationship, MR = a.m(b), between metabolic rate (MR) and body mass m has been the source of much controversy amongst biologists for many years. Various studies have reported mass exponents (b) greater than the anticipated 'surface-area' exponent 0.67, often closer to 0.75 originally identified by Kleiber. AIM: The study aimed to provide a biological explanation for these 'inflated' exponents when modelling maximum oxygen uptake (max), based on the observations from this and previous studies that larger individuals develop disproportionately more muscle mass in the arms and legs. RESEARCH DESIGN AND SUBJECTS: A cross-sectional study of 119 professional soccer players from Croatia aged 18-34 was carried out. RESULTS: Here we confirm that the power function relationship between max and body mass of the professional soccer players results in an 'inflated' mass exponent of 0.75 (95% confidence interval from 0.56 to 0.93), but also the larger soccer players have disproportionately greater leg muscle girths. When the analysis was repeated incorporating the calf and thigh muscle girths rather than body mass as predictor variables, the analysis not only explained significantly more of the variance in max, but the sum of the exponents confirmed a surface-area law. CONCLUSIONS: These findings confirm the pitfalls of fitting body-mass power laws and suggest using muscle-girth methodology as a more appropriate way to scale or normalize metabolic variables such as max for individuals of different body sizes
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 upon the objective and subjective workload of referees during Premier 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 %HRmax vs. Football league 81.5 2.2 %HRmax, p < 0.05) and match RPE scores (Premier league 7.8 0.8 vs. Football league 6.9 0.8, p < 0.05) between standards of competition. Referee experience had no effect upon match heart rate and RPE responses to Premier 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 upon 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
Race Analysis and Determination of Stroke Frequency: Stroke Length Combinations during the 50-M Freestyle Event
The aims of this study were to: (1) analyze and compare the stroke
kinematics between junior and senior elite male swimmers in
every section of the race during the 50-m freestyle event, and; (2)
identify stroke frequency (SF)–stroke length (SL) combinations
on swim speed independently for junior and senior swimmers in
each section of the 50-m freestyle event. Eighty-six junior swim-
mers (2019) and 95 seniors (2021) competing in the 50-m long
course meter LEN Championships were analyzed. The t-test in-
dependent samples (p ≤ 0.05) were used to compare juniors and
seniors. The SF and SL combinations on swim speed were ex-
plored using three-way ANOVAs. Senior swimmers were signif-
icantly faster in the 50-m race than juniors (p < 0.001). Speed
presented the largest significant difference (p < 0.001) in section
S0-15 m (start until the 15th meter mark) being seniors fastest.
Both junior and senior swimmers revealed a significant categori-
zation (p < 0.001) by stroke length and stroke frequency in each
race section. It was possible to model several SF–SL combina-
tions for seniors and juniors in each section. The fastest swim
speed in each section, for seniors and juniors independently, was
achieved by a SF–SL combination that may not be the fastest SF
or the longest SL. Coaches and swimmers must be aware that de-
spite the 50-m event being an all-out bout, several SF–SL combi-
nations were observed (independently for juniors and seniors),
and they differ between race sections.This work is supported by national funds (FCT -
Portuguese Foundation for Science and Technology) under the project
UIDB/DTP/04045/2020.info:eu-repo/semantics/publishedVersio
Relaxation mechanism for electron spin in the impurity band of n-doped semiconductors
We propose a mechanism to describe spin relaxation in n-doped III-V
semiconductors close to the Mott metal-insulator transition. Taking into
account the spin-orbit interaction induced spin admixture in the hydrogenic
donor states, we build a tight-binding model for the spin-dependent impurity
band. Since the hopping amplitudes with spin flip are considerably smaller than
the spin conserving counterparts, the resulting spin lifetime is very large. We
estimate the spin lifetime from the diffusive accumulation of spin rotations
associated with the electron hopping. Our result is larger but of the same
order of magnitude than the experimental value. Therefore the proposed
mechanism has to be included when describing spin relaxation in the impurity
band.Comment: 4 page
The effect of host development on the field assessment of disease resistance to Cercospora leaf spots in groundnuts (Arachis hypogaea L.)
Field experiments in Nigeria showed that a general score of resistance to C. arachidicola [Mycosphaerella arachidis] and Cercosporidium personatum [M. berkeleyi] did not always relate to the varietal response to disease control and reasons for this were proposed. The prevention of pod production by removal of flowers did not affect pathogen development, but vegetative growth of the treated plants was increased. It was concluded that host and pathogen development could be confounded during the assessment of disease resistance. In future varietal screening trials, the use of single branch comparisons should prevent this confusion.ADDITIONAL ABSTRACT:In a trial at Samaru, Nigeria with 6 groundnut cv. given weekly sprays of Bavistin [carbendazim], av. pod and haulm yields were 2.06 and 6.77 t/ha compared with 1.64 and 4.98 t resp., in unsprayed plots. Fungicide application increased pod yields most (by 0.93 t) in cv. SP 205 and decreased yields by 0.04 t in cv. 59-127. In a 2nd trial, weekly application of Dithane M45 [mancozeb] increased pod and haulm yields of SP 205 but had no effect on those of cv. S38
An Evaluation of Prediction Equations for the 6 Minute Walk Test in Healthy European Adults Aged 50-85 Years
This study compared actual 6 minute walk test (6MWT) performance with predicted 6MWT using previously validated equations and then determined whether allometric modelling offers a sounder alternative to estimating 6MWT in adults aged 50-80 years.We compared actual 6MWT performance against predicted 6MWT in 125 adults aged 50-85 years (62 male, 63 female). In a second sample of 246 adults aged 50-85 years (74 male, 172 female), a new prediction equation for 6MWT performance was developed using allometric modelling. This equation was then cross validated using the same sample that the other prediction equations were compared with.Significant relationships were evident between 6MWT actual and 6MWT predicted using all of the commonly available prediction equations (all P<0.05 or better) with the exception of the Alameri et al prediction equation (P>0.05). A series of paired t-tests indicated significant differences between 6MWT actual and 6MWT predicted for all available prediction equations (all P<0.05 or better) with the exception of the Iwama et al equation (P = .540). The Iwama et al equation also had similar bias (79.8m) and a coefficient of variation of over 15%. Using sample 2, a log-linear model significantly predicted 6MWT from the log of body mass and height and age (P = 0.001, adjusted R2 = .526), predicting 52.6% of the variance in actual 6MWT. When this allometric equation was applied to the original sample, the relationship between 6MWT actual and 6MWT predicted was in excess of values reported for the other previously validated prediction equations (r = .706, P = 0.001). There was a significant difference between actual 6MWT and 6MWT predicted using this new equation (P = 0.001) but the bias, standard deviation of differences and coefficient of variation were all less than for the other equations.Where actual assessment of the 6MWT is not possible, the allometrically derived equation presented in the current study, offers a viable alternative which has been cross validated and has the least SD of differences and smallest coefficient of variation compared to any of the previously validated equations for the 6MWT
Can waist circumference provide a new “third” dimension to BMI when predicting percentage body fat in children? Insights using allometric modelling
Introduction
Body mass index (BMI) is often criticized for not being able to distinguish between lean and fat tissue. Waist circumference (WC), adjusted for stature, is proposed as an alternative weight status index, as it is more sensitive to changes in central adiposity.
Purpose
The purpose of the study is to combine the three dimensions of height, mass, and WC to provide a simple, meaningful, and more accurate index associated with percentage body fat (BF%).
Methods
We employed a four independent sample design. Sample 1 consisted of 551 children (320 boys) (mean ± SD of age = 7.2 ± 2.0 years), recruited from London, UK. Samples 2, 3, and 4 consisted of 5387 children (2649 boys) aged 7 to 17 years recruited from schools in Portugal. Allometric modelling was used to identify the most effective anthropometric index associated with BF%. The data from samples 2, 3, and 4 were used to confirm and cross‐validate the model derived in sample 1.
Results
The allometric models from all four samples identified a positive mass exponent and a negative height exponent that was approximately twice that of the mass exponent and a waist circumference exponent that was approximately half the mass exponent. Consequently, the body shape index most strongly associated with BF% was urn:x-wiley:20476302:media:ijpo12491:ijpo12491-math-0001. The urn:x-wiley:20476302:media:ijpo12491:ijpo12491-math-0002 component of the new index can simply be interpreted as a WC “weighting” of the traditional BMI.
Conclusions
Compared with using BMI and WC in isolation, urn:x-wiley:20476302:media:ijpo12491:ijpo12491-math-0003could provide a more effective and equally noninvasive proxy for BF% in children that can be used in public and community health settings
Bone mineral density in vocational and professional ballet dancers
Summary: According to existing literature, bone health in ballet dancers is controversial. We have verified that, compared to controls, young female and male vocational ballet dancers have lower bone mineral density (BMD) at both impact and non-impact sites, whereas female professional ballet dancers have lower BMD only at non-impact sites.
Introduction: The aims of this study were to (a) assess bone mineral density (BMD) in vocational (VBD) and professional (PBD) ballet dancers and (b) investigate its association with body mass (BM), fat mass (FM), lean mass (LM), maturation and menarche.
Methods: The total of 152 VBD (13 ± 2.3 years; 112 girls, 40 boys) and 96 controls (14 ± 2.1 years; 56 girls, 40 boys) and 184 PBD (28 ± 8.5 years; 129 females, 55 males) and 160 controls (27 ± 9.5 years; 110 female, 50 males) were assessed at the lumbar spine (LS), femoral neck (FN), forearm and total body by dual-energy X-ray absorptiometry. Maturation and menarche were assessed via questionnaires.
Results: VBD revealed lower unadjusted BMD at all anatomical sites compared to controls (p < 0.001); following adjustments for Tanner stage and gynaecological age, female VBD showed similar BMD values at impact sites. However, no factors were found to explain the lower adjusted BMD values in VBD (female and male) at the forearm (non-impact site), nor for the lower adjusted BMD values in male VBD at the FN. Compared to controls, female PBD showed higher unadjusted and adjusted BMD for potential associated factors at the FN (impact site) (p < 0.001) and lower adjusted at the forearm (p < 0.001). Male PBD did not reveal lower BMD than controls at any site.
Conclusions: both females and males VBD have lower BMD at impact and non-impact sites compared to control, whereas this is only the case at non-impact site in female PBD. Maturation seems to explain the lower BMD at impact sites in female VBD
Improving reference equations for cardiorespiratory fitness using multiplicative allometric rather than additive linear models: Data from the Fitness Registry and the Importance of Exercise National Database Registry
New improved reference equations for cardiorespiratory fitness have recently been published, using Data from the Fitness Registry and the Importance of Exercise National Database (FRIEND Registry). The new linear equation for VO2max (ml.kg−1.min−1) was additive, derived using multiple-linear regression. An alternative multiplicative allometric model has also been published recently, thought to improve further the quality of fit. The purpose of the current study was to compare the accuracy and quality/goodness-of-fit of the linear, additive model with the multiplicative allometric model using the FRIEND database. The results identified that the allometric model out performs the linear model based on all model-comparison criteria. The allometric model demonstrates; 1) greater explained variance (R2 = 0.645; R = 0.803) vs. (R2 = 0.62; R = 0.79), 2) residuals that were more normally distributed, 3) residuals that yielded less evidence of curvature, 4) superior goodness-of-fit statistics i.e., greater maximum log-likelihood (MLL) and smaller Akaike Information Criterion (AIC) statistics, 5) less systematic bias together with smaller unexplained standard error of estimates. The Bland and Altman plots also confirmed little or no evidence of curvature with the allometric model, but systematic curvature (lack-of-fit) in the linear model. The multiplicative allometric model to predict VO2max was; VO2max (ml.kg−1.min−1) = M-0.854 · H1.44 · exp. (0.424–0.346 · (sex) -0.011.age), where M = body mass and H = height (R2 = 0.645; R = 0.803) and sex is entered as a [0,1] indicator variable (male = 0 and female = 1). Another new insight obtained from the allometric model (providing construct validity) is that the height-to-body-mass ratio is similar to inverse body mass index or the lean body mass index, both associated with leanness when predicting VO2max. In conclusion adopting allometric models will provide more accurate predictions of VO2max (ml.kg−1.min−1) using more plausible, biologically sound and interpretable models.Published versio
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