The purpose of this study was to identify the mechanical characteristics of the hands-between-the-feet grab starting technique which contribute to a faster start. Twenty-four high school swimmers performed four trials of a grab start followed by a glide to a distance of 9 m. The results suggested that to obtain a faster start, swimmers should (a) move the center of mass fast in the forward direction while the feet are in contact with the starting block, (b) maximize the force exerted through the feet in the backward direction, and (c) maximize the force exerted through the hands against the starting block in the forward and upward direction.
Antonio C.S. Guimaraes and James G. Hay
Manuel Hulliger, Scott J. Day, Antonio Guimaraes, Walter Herzog and Yuan-Ting Zhang
The experimental simulation method was based upon the separate activation of up to 10 small groups of motor units (MU) in an acute nerve-muscle preparation. The investigator was able to precisely control and systematically alter the features of MU pool activation strategies. No implicit assumptions were made regarding MU properties. The purpose of this study was to evaluate the validity of this method. Three criteria were formulated and found to be satisfied: First, in the time domain, visual and audio displays of simulated EMG were indistinguishable from physiological EMG. Secondly, in the frequency domain, power spectra of simulated EMG revealed the typical features of EMG recorded during voluntary activation in the cat. Thirdly, the well-known mono-tonic relationship between EMG magnitude and force was readily reproduced, alüiough strictly linear relations were not found. In addition. the relationship between the pool's ensemble activation rate and EMG magnitude showed distinct gain compression, mostly attributable to signal cancellation.
Tathyane Krahenbuhl, Ezequiel Moreira Gonçalves, Roseane de Fatima Guimarães, Gil Guerra-Júnior and Antonio de Azevedo Barros-Filho
To examine the influence of participation in competitive sports on bone parameters, as assessed by quantitative ultrasound (QUS) of the phalanges in female adolescents.
Female adolescents (n = 329, 13.0–16.7 years old) were classified into handball (n = 55), swimming (n = 49) and control (n = 225) groups. QUS was used to evaluate the amplitude-dependent speed of sound (AD-SoS) and bone transmission time (BTT), and their z-scores (zAD-SoS and zBTT) were calculated. Anthropometric measurements and Tanner’s stages were also obtained.
Swimmers had higher AD-SoS (2089 ± 43.8 m/s) and zAD-SoS (0.47 ± 0.8) than controls (2060 ± 54.0 m/s; 0.09 ± 1.0; both p ≤ .05) and both groups of athletes had higher BTT (handball: 1.44 ± 0.2 μs; swimming: 1.45 ± 0.2) and zBTT (handball: 0.71 ± 0.8; swimming: 0.72 ± 1.1) than the control group (1.37 ± 0.2 μs; 0.32 ± 0.9; all p ≤ .05). Swimmers had a higher total training time (TTT: 52.5 ± 27.6 months) and frequency of training per week (FT: 5.38 ± 0.1) compared with the handball group (35.9 ± 18.1; 3.32 ±0.8; p ≤ .05). zAD-SoS, BTT and zBTT were positively correlated with FT, while BTT and zBTT showed a positive correlation with TTT.
Sports practice influences bone parameters and higher bone parameter values are related to the amount of time and frequency of weekly training. The differences in phalangeal QUS parameters are independent of the impact of weight-bearing exercise.
Alex Antonio Florindo, Vanessa Valente Guimarães, Chester Luiz Galvão Cesar, Marilisa Berti de Azevedo Barros, Maria Cecília Goi Porto Alves and Moisés Goldbaum
To estimate the prevalence of and identify factors associated with physical activity in leisure, transportation, occupational, and household settings.
This was a cross-sectional study aimed at investigating living and health conditions among the population of São Paulo, Brazil. Data on 1318 adults aged 18 to 65 years were used. To assess physical activity, the long version of the International Physical Activity Questionnaire was applied. Multivariate analysis was conducted using a hierarchical model.
The greatest prevalence of insufficient activity related to transportation (91.7%), followed by leisure (77.5%), occupational (68.9%), and household settings (56.7%). The variables associated with insufficient levels of physical activity in leisure were female sex, older age, low education level, nonwhite skin color, smoking, and self-reported poor health; in occupational settings were female sex, white skin color, high education level, self-reported poor health, nonsmoking, and obesity; in transportation settings were female sex; and in household settings, with male sex, separated, or widowed status and high education level.
Physical activity in transportation and leisure settings should be encouraged. This study will serve as a reference point in monitoring different types of physical activities and implementing public physical activity policies in developing countries.