518 research outputs found
Estudo de diversos conceitos de eficiência da locomoção humana no meio aquático
Uma das áreas de interesse na linha fronteira entre a
Biomecânica e a Fisiologia é o estudo da eficiência. Considerase
que a eficiência expressa uma relação objectiva e quantitativa
entre o trabalho mecânico realizado e o gasto energético que
se lhe encontra associado. O estudo da eficiência em actividades
realizadas no meio aquático torna-se ainda mais complexo
devido à dificuldade de quantificar objectivamente as trocas
energéticas entre o nadador e o meio envolvente. No entanto, a
Natação Pura Desportiva é uma das modalidades mais profícuas
no estudo das suas implicações bioenergéticas e das repercussões
em termos de eficiência dos diferentes processos de
locomoção. Assim, foi objectivo do presente trabalho efectuar
uma revisão do actual “estado da arte” sobre o estudo da locomoção
humana n
Economia de nado e tempo limite à velocidade mínima de vo2max: novas descobertas
A economia de nado é uma área de investigação que teve como pioneiros, em Portugal, Vilas-
Boas (1993) e Alves (1995). Passada uma década, novos momentos experimentais foram
realizados e resultados up to date foram obtidos. As mais recentes metodologias foram
empregues e, inclusivamente, uma nova área de treino parece ter emergido - o tempo até à
exaustão à intensidade de nado correspondente à Potencia Aeróbia, isto é, ao consumo
máximo de oxigénio (VO2max)
Determinant kinantropometric factors in swimming
O objetivo deste trabalho é apresentar uma revisão bibliográfica das principais características
cineantropométricas do nadador e a forma como estas influenciam a sua prestação na modalidade. As principais conclusões obtidas foram as seguintes: (i) os nadadores são mais altos e pesados do que a população em
geral; (ii) os nadadores apresentam um elevado índice envergadura/altura, explicitando valores elevados do
diâmetro biacromial e do comprimento dos MS; (iii) verifica-se uma elevada razão entre os diâmetros biacromial
e bicristal, traduzindo um fator decisivo na modalidade: a promoção de um coeficiente de arrasto inferior; (iv)
foram observados elevados valores de comprimento e superfície dos membros dos nadadores (afetando
positivamente a sua capacidade propulsiva); (v) os nadadores de elite apresentam um somatótipo médio
ecto-mesomorfo e as nadadoras são centrais ou mesomorfas equilibradas; (vi) como grupo, os nadadores
apresentam um maior percentual de massa gorda do que outros desportistas, fator este que poderá beneficiários
relativamente à sua flutuabilidade.The aim of this work is to present a bibliographic review, based on the specialized literature, of the kineantropometric characteristics of swimmers and their importance for swimming performance. The main conclusions were: (i) swimmers are taller and heavier than the general population; (ii) swimmers present an high index of arm span/height (explained by a large biacromial diameter and long the upper arm); (iii) high values for the biacromial/bicristal diameter ratio were found, offering a lower drag coefficient; (iv) high length and surface area arm and leg values were observed (which positively influence their propulsion capacity); (v) elite male swimmers presents a ectomorph-endomorph somatotype and elite female swimmers are central or balanced mesomorphs (vi) swimmers exhibit a higher percentage of body mass than other athletes, which may benefit positively their floatation
Factores biomecânicos e bioenergéticos limitativos do rendimento em natação pura desportiva
Um dos objectivos prioritários da Biomecânica
do Desporto é o de, num primeiro momento,
caracterizar um determinado padrão motor e,
num segundo momento, intervir no sentido
de incrementar a efi ciência motora. Esse incremento
da efi ciência do gesto tem como fi nalidade
última permitir que o seu executante aceda
a níveis superiores de rendimento desportivo. Do
exposto, emerge a ideia que a Biofísica encontrase
numa linha fronteira entre a Mecânica Clássica
e a Fisiologia. Neste contexto, a Natação Pura
Desportiva é uma das modalidades mais profícuas
no estudo das implicações bioenergéticas e das
repercussões em termos de efi ciência dos diferentes
modelos de locomoção. Foi objectivo do
presente trabalho efectuar uma revisão do actual
“estado da arte” sobre a relação que se estabelece
entre o rendimento desportivo, as características
bioenergéticas e biomecânicas em Natação Pura
Desportiv
Relationships between some well known indicators of aerobic resistance of swimmers
The concept of the anaerobic threshold (AT) at swimming velocity corresponding to 4 mmol.l-1 blood lactate
concentrations (v4), introduced by Mader et al. (1976) and further developed by following authors, was used
by a large number of scientists and swimming coaches for training and diagnostic purposes. Although it's
considered a good indicator of aerobic capacity of swimmers, some authors disagree of that fixed value,
arguing that the individual AT varies a lot, namely between 2 and 5 mmol.l-1 (Madsen e Lohberg, 1987). The
purpose of this study is to verify the adequacy of the v4 in swimming, comparing it with two other valid
indicators of the AT: critical velocity (cv) and the mean velocity of the 30 min test (vT30).
Subjects were 30 juvenile swimmers of the Porto regional swimming team (with ages between 12 and 15
years). V4 was determined according to the 2 x 400m protocol, being the first repetition performed at 85% of
the personal best and the second one at maximum speed (a rest period higher than 30 min was respected
between repetitions). Samples of 25 μl of capillary blood were collected at 3, 5 and 7 min of recovery and
analysed for blood lactate concentration with an Accusport analyser (Boheringer Manheim). CV was assessed
based in the results of maximal tests of 100 e 400m and was considered as the slope of the regression line
calculated between the test distances and the respective times. The ratio between the distance achieved and
the duration of the test, i.e., 30 min of continuous swimming assessed the vT30.
The mean values of the different variables are presented in Table 1. These results showed that the mean values
of v3, v4 and v5, cv and vT30 are very similar; only v8 is statistically different of some other parameters (v3,
v4, cv and vT30). We can also see strong positive correlation (r³0.91) between all the parameters (with exception
of v8) regardless the stronger values between V5 and the other two tests.info:eu-repo/semantics/publishedVersio
Predicting the intra-cyclic variation of the velocity of the centre of mass from segmental velocities in butterfly stroke: a pilot study
The purpose of this study was to analyze the relationship between the
intra-cycle variation of the horizontal velocity of displacement of the
center of mass (dV), the hand’s and feet’s velocity, as well as, to identify
the variables that most predict the dV’s, in butterfly stroke. The study
was divided in two parts. The aim of Part I was to investigate the behavior
of variables in study at slow swimming velocities and the purpose of
Part II was the same but at high swimming velocities. 3 male Portuguese
swimmers and 1 female swimmer, of international level were studied in
Part I. The swimmers were submitted to an incremental set of 200 m
butterfly swims. In the Part II, 7 Portuguese male swimmers of national
and international level were studied. Each swimmer performed two
maximal 25 m butterfly swims. Both protocols were recorded from four
different plans, allowing a 3D analysis. It was calculated the dV, the 3D
components (Vx, Vy, Vz) of the hand’s velocity and the 2D components
(Vx, Vy) of the feet’s velocity. Several variables presented significant
correlation coefficients with dV at all selected velocities (high velocity
ranged from r = 0.58 for Vx-out to r = 0.82 for Vy-1dwn; slow velocity
ranged from r = -0.45 for Vx-1dwn to r=0.73 for Vx-ups; overall velocity
ranged from r= 0.34 for Vz-ent to r = 0.82 for Vx-ins). It was also
computed a regression model to predict dV. For high velocity (up to
1.75 ± 0.09 m.s-1), the variables that best predict dV were Vy during the
first downbeat, Vx and Vy during the arm’s insweep (r2 = 0.93). At slow
velocity (up to 1.48 m.s-1), the variables included in the forward step-bystep
regression model were Vx during upsweep, Vy and Vx during
insweep (r2 = 0.69). For overall velocity, the variables that most fit the
regression model were Vx during upsweep, Vy during second downbeat
and Vz during entry (r2= 0.94). In order to reduce dV, butterfliers should
increase hand’s velocity in all orthogonal components at the end of the
underwater path, should increase the vertical velocity durin
Influence of the chemical composition on the machinability of brasses
Although brasses are essentially copper and zinc alloys, they also contain other alloying elements such as lead, silicon, aluminium, iron,
tin, manganese, nickel or arsenic whose presence and content are responsible for the wide variety of properties inherent to these materials.
In this article, the effect of the chemical composition of brasses, considering each alloying element and the effective copper content, upon
the machinability has been investigated.
For that purpose, machinability tests have been carried out on a CNC lathe under lubricated conditions. The study includes both commercial
alloys and samples prepared in laboratory. The experimental procedure consists on turning operations, during which cutting forces and surface
roughness obtained in brass workpieces are measured. The chip class is accordingly evaluated.
The statistic treatment of the results enables the establishment of correlations between the studied machinability parameters and the chemical
composition of different kinds of brasses
Swimming bioenergetics: integrating biomechanical and physiological data into a coherent biophysical model for performance and training
The purpose of the present paper is to synthesise a number of scientific contributions of our research group, into a coherent corpus of knowledge related to swimming biophysics, specially centred on the availability and use of energy in swimming. After an introductory part that intends to underline the relevance of this approach base on the conceptualization of the swimmer, and swimming action itself, as a thermodynamic system and its mechanical output, we will survey a number of studies and respective contributions for a more advanced understanding of swimming performance, that can be transferred into training and enhancement of swimmers’ working capacity.
Most of the studies referred were conducted over samples of swimmers of both genders and of different types, from university/participative swimmers to Portuguese elite swimmers, crossing the large population of trained national level swimmers. Those swimmers were studied in the four different competitive swimming strokes, accomplishing progressive protocols based over distances of 200 m. Physiologic parameters like VO2 (and associated ventilatory and respiratory parameters), post exercise capillary blood [La-] peaks, and heart rate, were directly measured. Kinematical parameters were also measured in the different studies, ranging from simple semi-quantitative parameters, like stroke length (SL), and stroke frequency (SF), to more elaborated biomechanical data, like intracyclic speed fluctuations and propulsive segments kinematics.
The focus of interest ranged from swimming economy of different strokes and genders (and of different technical alternatives of the same stroke), to the effects over energy cost of intracyclic speed fluctuations. Energetic input determinant factors, like swimming VO2 kinetics, including VO2 slow component, and VO2 time limit, and its determinants, will also be analysed
The influence of stroke mechanics into energy cost of elite swimmers
The purpose of this study was to analyze the
relationships between energy cost (C), swimming velocity
(v), stroke frequency (SF) and stroke length (SL) in toplevel
swimmers. Eighteen elite swimmers (four freestylers,
five backstrokers, five breaststrokers and four butterflyers)
performed an intermittent set of n 9 200 m swims (n B 8)
with increasing velocity. The oxygen consumption was
measured breath-by-breath by a portable metabolic cart
(K4 b2, Cosmed, Rome, Italy). A respiratory snorkel and
valve system with low hydrodynamic resistance was used
to measure pulmonary ventilation and collect expiratory
gases. Blood samples were taken from the ear lobe before
and after each swim to analyze the blood lactate concentration
(YSI 1500L, Yellow Springs, OH, USA). At
Backstroke, Breaststroke and Butterfly strokes, increases of
SF were associated to increases of C, even when controlling
the v. The increases in SL only promoted significant
decreases in the C in Breaststroke. There was a significant
and polynomial relationship between v and SF for all
competitive swimming techniques. The polynomial relationship
between v and SL was significant only in Freestyle
and Butterfly stroke. Partial correlations between v and SF
controlling the effect of SL and between v and SL controlling
the effect of SF, were positive and significant for
all techniques. It is concluded that manipulation of stroke
mechanics variables (SF and SL) may be one of the factors
through which C in competitive swimming can be altered
for a given v
Comparative Study of the Response of Kinematical Variables from the Hip and the Center of Mass in Butterfliers
The aim of this study was to compare the intracyclic variation of kinematical variables from the
hip and the center of mass (CM) with the purpose to assess if the analysis of kinematical
variables of the hip might replace the study of the kinematical variables of the CM. Seven
Portuguese male swimmers of national and intemational levei were studied. Each swimmer
performed 3 sets of3x25 meters, at a constant velocity and as close as possible to the maximum,
using exclusively frontal inspiration cycles, lateral inspiration cycles and non-inspiratory cycles
in each set. Two pairs of cameras were used to create "dual media" images. Another cam era was
set behind an underwater window in the endwall. One last camera was placed above the water
surface. The study comprised the analysis of complete stroke cycles in buttert1y using the "Ariel
Performance Analysis System" from Ariel Dynamics Inc. Some of the correlations between the
maximal vertical amplitude of displacement of the hip and the CM didn't present significant
values. AlI the correlations between the horizontal velocity and horizontal acceleration of the
hip and the CM were significant in all breathing models. However, only one swimmer presented
in both cases r>=O.95. So, apparently, the hip does not represent properly the intracyclic
variations ofthe kinematical variables ofthe CM.info:eu-repo/semantics/publishedVersio
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