Reliability and validity of field-based measures of leg stiffness and reactive strength index in youths

Abstract

The aim of the study was to assess the reliability of a mobile contact mat in measuring a range of stretch–shortening cycle parameters in young adolescents. Additionally, vertical leg stiffness using contact mat data was validated against a criterion method using force–time data. The reliability study involved 18 youths completing a habituation and three separate test sessions, while 20 youths completed a single test session for the validity study. Participants completed three trials of a squat jump, countermovement jump, and maximal hopping test and a single trial of repeated sub-maximal hopping at 2.0 Hz and 2.5 Hz. All tests were performed on the contact mat. Reliability statistics included repeated-measures analysis of variance, intraclass correlation coefficient, and coefficient of variation (CV), while the correlation coefficient (r) and typical error of estimate (TEE) were reported for the validity study. Squat jump height was the most reliable measure (CV = 8.64%), while leg stiffness during sub-maximal hopping, and reactive strength index produced moderate reliability (CV = 10.17–13.93% and 13.98% respectively). Measures of leg stiffness obtained from contact mat data during sub-maximal hopping were in agreement with the criterion measure (r = 0.92–0.95; TEE = 6.5–7.5%), but not during maximal hopping (r = 0.59; TEE = 41.9%). The contact mat was deemed a valid tool for measuring stretch–shortening cycle ability in sub-maximal but not maximal hopping. Although reliability of performance was generally moderate, the tests offer a replicable assessment method for use with paediatric populations.     

Effects of playing surface on physiological responses and performance variables in a controlled football simulation

Abstract

In spite of the increased acceptance of artificial turf in football, few studies have investigated if matches are altered by the type of surface used and no research has compared physiological responses to football activity on artificial and natural surfaces. In the present study, participants performed a football match simulation on high-quality artificial and natural surfaces. Neither mean heart rate (171 ± 9 beats · min^?1 vs. 171 ± 9 beats · min^?1; P > 0.05) nor blood lactate (4.8 ± 1.6 mM vs. 5.3 ± 1.8 mM; P > 0.05) differed between the artificial and natural surface, respectively. Measures of sprint, jumping and agility performance declined through the match simulation but surface type did not affect the decrease in performance. For example, the fatigue index of repeated sprints did not differ (P > 0.05) between the artificial, (6.9 ± 2.1%) and natural surface (7.4 ± 2.4%). The ability to turn after sprinting was affected by surface type but this difference was dependent on the type of turn. Although there were small differences in the ability to perform certain movements between artificial and natural surfaces, the results suggest that fatigue and physiological responses to football activity do not differ markedly between surface-type using the high-quality pitches of the present study.     

Influence of regression model and initial intensity of an incremental test on the relationship between the lactate threshold estimated by the maximal-deviation method and running performance

Abstract

This study investigated the influence of the regression model and initial intensity during an incremental test on the relationship between the lactate threshold estimated by the maximal-deviation method and performance in elite-standard runners. Twenty-three well-trained runners completed a discontinuous incremental running test on a treadmill. Speed started at 9 km · h^?1 and increased by 1.5 km · h^?1 every 4 min until exhaustion, with a minute of recovery for blood collection. Lactate–speed data were fitted by exponential and polynomial models. The lactate threshold was determined for both models, using all the co-ordinates, excluding the first and excluding the first and second points. The exponential lactate threshold was greater than the polynomial equivalent in any co-ordinate condition (P < 0.001). For both models, the lactate threshold was lower when all co-ordinates were used than when the first and the first and second points were excluded (P < 0.001). 10-km race pace was correlated with both the exponential and polynomial lactate thresholds for all the co-ordinate conditions (r ≥ 0.75, P < 0.001 and r ≥ 0.56, P < 0.05, respectively). The results suggest that the exponential lactate threshold should be used instead of the polynomial equivalent since it is more strongly associated with performance and is independent of the initial intensity of the test.     

The Dynamics of Leisure Motivation: The Effects of Outcome on Leisure Needs

Abstract

Predicated upon the premise that leisure needs are socially determined and therefore dynamic qualities of leisure motivation, this field study investigated the effects of outcome (winning, losing, no outcome) of leisure participation on male and female subjects' leisure needs. Subjects were 438 players of 60 teams in the intramural basketball program comprised of competitive and recreational leagues. Factor analysis produced seven need factors, of which three dealt with interpersonal relationships, two with competence and two with escape or diversion. ANOVAs performed on the resultant factor scores showed that successful and unsuccessful leisure experiences strongly shaped subjects' needs for leisure participation, but these effects were often mediated by the sex of subjects and the competitive levels of leagues in which they played. Generally, winning and losing had just the opposite effects on males' and females' needs; winning increased females' and decreased males' needs. The effects of competitiveness of league types suggested that competitive and recreational leagues serve different psychological functions for males and females because the two leagues are expected to fulfill different leisure needs.     

Is movement variability important for sports biomechanists?

This paper overviews the importance for sports biomechanics of movement variability, which has been studied for some time by cognitive and ecological motor skills specialists but, until quite recently, had somewhat been overlooked by sports biomechanists. The paper considers biomechanics research reporting inter- and intra-individual movement variability in javelin and discus throwing, basketball shooting, and locomotion. The overview does not claim to be comprehensive and we exclude such issues as the theoretical background to movement and coordination variability and their measurement. We overview evidence, both theoretical and empirical, of inter-individual movement variability in seeking to achieve the same task goal, in contrast to the concept of “optimal” movement patterns. Furthermore, even elite athletes cannot reproduce identical movement patterns after many years of training, contradicting the ideas of motor invariance and “representative” trials. We contend that movement variability, far from being solely due to neuromuscular system or measurement “noise” – as sports biomechanists may have previously supposed – is, or could be, functional. Such functionality could allow environmental adaptations, reduce injury risk, and facilitate changes in coordination patterns. We conclude by recommending that sports biomechanists should focus more of their research on movement variability and on important related topics, such as control and coordination of movement, and implications for practice and skill learning.     

Major League Baseball and the Dominican Republic: What is in the best interest of the players?

This case is about Major League Baseball and the Dominican Republic. We explore how Major League Baseball has used this Caribbean island as an inexpensive labor market and the social problems of the situation. Specifically, we examine Corporate Social Responsibility, the leadership of Sandy Alderson, ethics and the various stakeholders involved. We also look into possible reform alternatives while addressing the central question: What is in the best interest of the players?     

Towards a Collaborative Approach to Teacher Empowerment

This paper outlines a project based on an approach to teacher empowerment through collaborative action research. Using accounts from teachers involved in the project, the conditions necessary for the development of collegiality on in-service courses are explored. The nature and significance of agenda setting and ways of introducing tools for empowerment are described. The use of collaborative autobiography (CA), interpersonal process recall (1PR) and a general supervisory framework (GSF) are analysed in detail. The paper concludes with comment on the extent to which teachers are empowered by these tools to reconstruct the complex relationships between power, knowledge, ideology and schooling which dominate much of their working lives.     

‘Good books’: is there a future for academic writing within the educational publishing industry?

This paper draws on questionnaire responses received (via e‐mail) during the period 2002–2003 from senior commissioning editors located within seven of the major UK publishing outlets. Drawing on the analytical framework of an earlier study by Nixon (1999 Nixon, J. (1999). Teachers, writers, professionals. Is there anybody out there. British Journal of Sociology of Education, 20(2): 207–221. [Taylor & Francis Online], [Web of Science ®] [Google Scholar]), it focuses on the mediation of educational studies by market forces operating within and upon the educational publishing industry. More specifically it explores issues relating to the construction of readership, authorship and editorship within that force field of market pressures. Central to the argument is the claim that, in its increasing exposure to market forces, the public space afforded by educational publishing is now highly restrictive. The paper concludes with a call for a sustained debate on the future of academic publishing in general, and educational publishing in particular.