Mathematical modelling as a tool to assessment of loads in volleyball player’s shoulder joint during spike

This article deals with kinematic and kinetic conditions in volleyball attack and identifies loads in the shoulder joint. Joint angles and velocities of individual segments of upper limb were measured with the use of the motion capture system XSENS. Muscle forces and loads in skeletal system were calculated by means of mathematical model elaborated in AnyBody system. Spikes performed by players in the best and worst way were compared with each other. The relationships were found between reactions in shoulder joint and flexion/extension, abduction/adduction and rotation angles in the same joint and flexion/extension in the elbow joint. Reactions in shoulder joint varied from 591 N to 2001 N (in relation to body weight [BW] 83–328%).

The analysis proved that hand velocity at the moment of the ball hit (which varied between 6.8 and 13.3 m s^–1) influences on the value of reaction in joints, but positions of individual segments relative to each other are also crucial. It was also proved in objective way, that position of the upper limb during spike can be more or less harmful assuming that bigger reaction increases possibility of injury, what can be an indication for trainers and physiotherapists how to improve injury prevention.     

Computerized Agility Training Improves Change-of-Direction and Balance Performance Independently of Footwear in Young Adults

Understanding the effects of training in different footwear on sporting performance would be useful to coaches and athletes. Purpose: This study compared the effects of computerized agility training using 3 types of footwear on change-of-direction and balance performance in young adults. Method: Thirty recreationally active young adults (M_age = 22.8 ± 3.1 years; M_height = 1.71 ± 0.7 m; M_bodymass = 73.4 ± 10.3 kg) were randomly assigned to a 6-week computerized agility training intervention in 1 of 3 footwear groups (n = 10/group): barefoot, minimal footwear, or traditional shoes. Participants had no previous barefoot or minimal-footwear training experience. Dependent variables included change-of-direction test time to completion, Star Excursion Balance Test, and single-leg stability evaluation. Testing was performed at the start of the training program, after 2 weeks, after 4 weeks, and at the end of the training program. Results: No group or time interactions were found for any of the dependent variables. Time main effects were observed for the performance measures of change of direction, Star Excursion, and single-leg-with-eyes-open stability evaluation. Participants improved in all 3 tests as early as 2 weeks into the intervention, with improvements continuing through the entire 6-week intervention. Conclusions: The lack of interaction and footwear effects suggests that agility and balance improvements during foot agility training are independent of footwear in a recreationally active young-adult population. Computerized agility training improves change-of-direction and balance performance within 2 weeks of training implementation. Future studies should consider footwear training effects in different populations, including frail older adults and athletes.     

Self-concept and self-esteem reexamined

Three “self” constructs are differentiated: the “self,” that is, the “real” self; the “self-concept,” which is the information or cognitions an individual has about his “self;” and “self-esteem,” which is the judgment and feelings about the “self.” An individual's self-concept can be characterized by its realism or unrealism, its completeness or incompleteness, or by the complexity of the concepts used to describe the self. Self-esteem, but not self-concept, can be described as being positive or negative. Developmental considerations and implications are discussed.     

Pygmalion in the classroom

In 1965 the authors conducted an experiment in a public elementary school, telling teachers that certain children could be expected to be “growth spurters,” based on the students' results on the Harvard Test of Inflected Acquisition. In point of fact, the test was nonexistent and those children designated as “spurters” were chosen at random. What Rosenthal and Jacobson hoped to determine by this experiment was the degree (if any) to which changes in teacher expectation produce changes in student achievement. Robert Rosenthal is professor of social psychology at Harvard University. Lenore Jacobson is an elementary school principal in the South San Francisco Unified School District.