Accuracy,intra- and inter-unit reliability,and comparison between GPS and UWB-based position-tracking systems used for time–motion analyses in soccer

There is interest in the accuracy and inter-unit reliability of position-tracking systems to monitor players. Research into this technology, although relatively recent, has grown exponentially in the last years, and it is difficult to find professional team sport that does not use Global Positioning System (GPS) technology at least. The aim of this study is to know the accuracy of both GPS-based and Ultra Wide Band (UWB)-based systems on a soccer field and their inter- and intra-unit reliability. A secondary aim is to compare them for practical applications in sport science. Following institutional ethical approval and familiarization, 10 healthy and well-trained former soccer players (20?±?1.6 years, 1.76?±?0.08?cm, and 69.5?±?9.8?kg) performed three course tests: (i) linear course, (ii) circular course, and (iii) a zig–zag course, all using UWB and GPS technologies. The average speed and distance covered were compared with timing gates and the real distance as references. The UWB technology showed better accuracy (bias: 0.57–5.85%), test–retest reliability (%TEM: 1.19), and inter-unit reliability (bias: 0.18) in determining distance covered than the GPS technology (bias: 0.69–6.05%; %TEM: 1.47; bias: 0.25) overall. Also, UWB showed better results (bias: 0.09; ICC: 0.979; bias: 0.01) for mean velocity measurement than GPS (bias: 0.18; ICC: 0.951; bias: 0.03).     

Physical activity and school recess time: differences between the sexes and the relationship between children's playground physical activity and habitual physical activity

The aims of this study were: (1) to observe participation in moderate-to-vigorous physical activity (MVPA) during school recess periods; (2) to determine the relative importance of physical activity during recesses to overall daily physical activity; and (3) to examine differences in physical activity between the sexes during unstructured recess periods. The participants were 22 school children (10 boys, 12 girls) aged 8 - 10 years (mean = 8.9, s = 0.7) in the third and fourth grades. Daily totals for the physical activity variables were calculated by summing the values for each hour of 14 h of physical activity measurements (08:00 to 22:00 h). Recess times (minutes) were as follows: morning 10:30 to 11:00 h and afternoon 15:30 to 16:00 h. We did not differences between boys and girls in daily total accelerometer counts or the overall time spent in MVPA. However, girls were significantly (P < 0.05) more involved (38%) in MVPA during recess time than boys (31%). Participation in MVPA during recess contributes significantly more (P < 0.05) for girls (19%) than boys (15%) to the total amount of physical activity suggested by international health-related physical activity guidelines, while the percentage of time engaged in MVPA during recess time at school accounts for a small amount of the daily MVPA (6% for boys and 8% for girls). The results of this study suggest that school recess time is an important setting to promote MVPA and contributes to daily physical activity in young children, especially in girls.     

Effects of replica running shoes upon external forces and muscle activity during running

Twelve participants ran (9 km · h(-1)) to test two types of running shoes: replica and original shoes. Ground reaction force, plantar pressure and electromyographic activity were recorded. The shoes were tested randomly and on different days. Comparisons between the two experimental conditions were made by analysis of variance (ANOVA) test (P ≤ 0.05). The time to first peak, loading rate of the first peak and impulse of the first 75 ms of stance were significantly different between the shoes (P ≤ 0.05), revealing an increase of impact forces for the replica shoes. The peak plantar pressure values were significantly higher (P ≤ 0.05) when wearing replica shoes. During running, the contact area was significantly smaller (P ≤ 0.05) for the replica shoe. The electromyographic activity of the analysed muscles did not show changes between the two shoes in running. These findings suggest that the use of replica running shoes can increase the external load applied to the human body, but may not change the muscle activity pattern during locomotion. This new mechanical situation may increase the risk of injuries in these movements.     

Interpersonal dynamics and relative positioning to scoring target of performers in 1 vs. 1 sub-phases of team sports

Abstract

In this study, we examined the effects of relative positioning of attacker–defender dyads to the basket on interpersonal coordination tendencies in basketball. To achieve this aim, four right-hand dominant basketball players performed in a 1 vs. 1 sub-phase, at nine different playing locations relative to the basket (from 0° to 180°, in 20° increments). Performers’ movement displacement trajectories were video-recorded and digitized in 162 trials. Results showed that interpersonal coordination tendencies changed according to the scaling of the relative position of performers to the basket.

Stable in-phase modes of coordination were observed between performers’ longitudinal and lateral displacements (50.47% and 43.02%) on the left side of the court. On the right side of the court, a shift in the dominant mode of coordination was observed to a defender lead-lag of ?30°, both for longitudinal and lateral displacements (30.51% and 32.65%). These results suggest how information about dribbler hand dominance and relative position to the basket may have constrained attacker–defender coordination tendencies in 1 vs. 1 sub-phases of basketball.     

Aerobic exercise did not have compensatory effects on physical activity levels in type 2 diabetes patients

Although exercise promotes beneficial effects in diabetic patients, some studies have questioned the degree of their importance in terms of the increase in total energy expenditure. In these studies, the decrease of physical activity levels (PAL) was referred as “compensatory effect of exercise”. However, our aim was to investigate whether aerobic exercise has compensatory effects on PAL in type 2 diabetes patients. Eight volunteers (51.1 ± 8.2 years) were enrolled in a supervised exercise programme for 8 weeks (3 d · wk^?1, 50–60% of VO₂ peak for 30–60 min). PAL was measured using tri-axial accelerometers in the 1st, 8th and 12th weeks. Biochemical tests, cardiorespiratory fitness, anthropometric assessment and body composition were measured in the 2nd and 11th weeks. Statistical analysis was performed using non-parametric tests (Friedman and Wilcoxon, P < 0.05). We found no significant differences in PAL between intervention periods, and participants spent the majority of their awake time in sedentary activities. However, the exercise programme generated a significant 14.8% increase in VO₂ peak and a 15% reduction in fructosamine. The exercise programme had no compensatory effects on PAL in type 2 diabetes patients, but improved their cardiorespiratory fitness and glycaemic control.     

Learning-by-Consuming and the Dynamics of the Demand and Prices of Cultural Goods

The major distinctive feature of cultural goods is that consumers must learn how to consume them, implying that preferences should be modelled as intertemporally dependent. The canonical model in the literature uses a habit formation analogy. In this paper, we discuss in detail, though in the simplest setup, a consistent preference structure for that model. Then, we derive the implications for the dynamics of two aggregate equilibrium models, a fixed price model and a flexible price model. The learning-by-consuming behaviour is characterised by a preference structure displaying bounded adjacent complementarity in the demand for the cultural good. This implies that there will be short run complementarity between the stocks of culture and financial wealth and that the adjustment of the demand for cultural goods, or of their relative price, will have some inertia. In the exogenous price model, we find that increases in income will raise the long run demand for cultural goods while increases in the relative price will decrease it. In the endogenous price model, an increase in the supply of cultural goods will imply an initial undershooting of the price of cultural goods followed by an upward transition process. Our results seem to be consistent with the empirical results on the demand for cultural goods and seem to offer an explanation for the Baumol and Bowen paradox.JEL Classification: Z1, E21Earlier versions of this paper have been presented at the 1st Conference of the Sociedade Portuguesa de Investigação em Economia (SPiE, 1997) and at the Xth Conference of the Association for Cultural Economics International, 1998, Barcelona.     

Bayesian Learning from Arts Goods? – A Comment

This comment considers the applicability of the Cyert and DeGroot model of adaptive utility in modeling consumer choice behavior with respect to arts goods. An illustration of the consumer’s choice behavior on expenditure shares is simulated as a simple Markov chain. This is followed by a discussion of policy implications regarding the pricing and subsidization of arts goods.     

Preferences need no inferences, once again: germinal elements in the public perceptions of genetically modified foods in Colombia

This paper explores the public perceptions of genetically modified foods in Colombia in a phase considered germinal: the topic was too novel at the time of research. The analysis covers media, informal conversations, and the word associations made by a sample of residents in the city of Bogotá. The results show that the public capability of associating with the topic, even intuitively, is due to the availability of culture themes, the primary categories that help conceptual elaborations, and the construction of common-sense theories. Three themes are proposed: natural/artificial, tradition/change, and health/disease. It is argued that cultural themes are not only cognitive, but also affectively laden entities, which explains the evaluative force expressed by social beliefs. Acknowledging the relevance of the non-attitude thesis, the author suggests that people associate novel objects with latent cultural meanings, explaining why words, images, and metaphors are readily available in elaborating social knowledge.