Programming Time as a Function of Movement Constraint

Abstract

Although the benefits of exercise are well documented, an international problem of physical inactivity exists. More research, especially theory based, has been recommended. One promising approach for studying exercise behavior is that proposed in the Transtheoretical Model (TTM) of behavior change. This model, however, has received minimal cross-cultural attention and, relative to the current study, measurement instruments have only recently been translated into the Finnish language. The purpose of this study was to assess American and Finnish college students' exercise behaviors on the basis of TTM. Participants were American (n = 169) and Finnish (n = 168) college students who completed language-specific measures of exercise behavior, stage of change, processes of change, decisional balance, self-efficacy, and temptation. The only cultural difference observed was that the American participants rated themselves higher on barrier self-efficacy relative to the Finnish participants. Regardless of nationality or gender, participants classified by their stage of change differed on all the core constructs assessed. These results generally support the utility of TTM for understanding American and Finnish college students' exercise behavior.     

足球运动与运动视觉功能

阐述了足球运动对视觉功能的要求,且对视觉的需求都是综合性的.优秀运动员必须具备良好的视觉功能,而相关的视觉功能训练可望提高运动成绩.     

Proximity-to-goal as a constraint on patterns of behaviour in attacker-defender dyads in team games

The aim of this study was to determine whether spatiotemporal interactions between footballers and the ball in 1 vs. 1 sub-phases are influenced by their proximity to the goal area. Twelve participants (age 15.3 ± 0.5 years) performed as attackers and defenders in 1 vs. 1 dyads across three field positions: (a) attacking the goal, (b) in midfield, and (c) advancing away from the goal area. In each position, the dribbler was required to move beyond an immediate defender with the ball towards the opposition goal. Interactions of attacker-defender dyads were filmed with player and ball displacement trajectories digitized using manual tracking software. One-way repeated measures analysis of variance was used to examine differences in mean defender-to-ball distance after this value had stabilized. Maximum attacker-to-ball distance was also compared as a function of proximity-to-goal. Significant differences were observed for defender-to-ball distance between locations (a) and (c) at the moment when the defender-to-ball distance had stabilized (a: 1.69 ± 0.64 m; c: 1.15 ± 0.59 m; P < 0.05). Findings indicate that proximity-to-goal influenced the performance of players, particularly when attacking or advancing away from goal areas, providing implications for training design in football. In this study, the task constraints of football revealed subtly different player interactions than observed in previous studies of dyadic systems in basketball and rugby union.     

运动视觉功能训练在竞技体育中的应用

分析运动视觉的构成、作用及训练学基础,认为运动视觉功能训练的方法手段富有创造性,经过系统测试找出运动员视觉能力的不足,根据专项需要对运动员视觉系统加压,有效提高运动员的运动视觉能力和对视觉信息的处理及反应能力,进而提高运动员的运动表现.     

Level of gymnastic skill as an intrinsic constraint on postural coordination.

In this study, we considered the interacting effects of expertise in gymnastics, the type of support surface and the required frequency of head movement on the emergence of postural modes of coordination. A group of elite female gymnasts and a control group of non-gymnasts were asked to track the fore-aft motion of a target with their heads. Two support surface conditions (a balance beam vs the floor) were crossed with four frequencies of target motion. The relative phase between the angular motion of the ankles and hips was analysed. Two stable patterns emerged: an in-phase mode and an anti-phase mode, with the hip-ankle relative phase close to 0 degrees and 180 degrees, respectively. Increasing target frequency produced a change from in-phase to anti-phase coordination, in conditions where no instructions were given to the participants (Experiment 1) as well as in those where participants were instructed to maintain an in-phase mode for as long as possible (Experiment 2). This change, however, occurred earlier for the non-gymnasts than for the gymnasts. We conclude that 0 degrees and 180 degrees are two stable postural coordination modes, that expertise in gymnastics leads to a functional modification of existing patterns of coordination, and that expertise in general can be considered an intrinsic constraint on coordination.     

The time course of muscle-tendon properties and function responses of a five-minute static stretching exercise

Abstract

The purpose of this study was to investigate the time course of the changes of muscle-tendon mechanical properties and the function responses of the plantar flexor muscles following 5?×?60?s of static stretching.

Fourteen healthy volunteers were tested on four separate days in a random order with three different rest times (0, 5, 10?min) after 5?×?60?s of stretching or following a control period without stretching. During each test, the dorsiflexion range of motion (RoM), passive resistive torque (PRT), and maximum voluntary contraction (MVC) were measured with a dynamometer. Ultrasonography of the gastrocnemius medialis (GM) muscle-tendon junction displacement and motion capture allowed us to determine the length changes in the tendon and muscle, respectively, and hence to calculate their stiffness.

We observed an increase in RoM and decrease in MVC at 0, 5, and 10?min post-stretching. This could be attributed to an increase in muscle elongation which lasted at least 10?min. A decrease in muscle-tendon stiffness was observed immediately, but not 5 or 10?min after the stretching. A decrease in PRT and muscle stiffness was observed up to 5?min after the stretching. No changes were detected in tendon stiffness or in any variable in the control group.

The effects of a 5?×?60?s static stretching exercise changes the muscle-tendon functions (RoM, MVC), which are related to mechanical changes of the muscle but not the tendon structure, respectively. Although the functional changes last for at least 10?min, changes in muscle stiffness were only observed up to 5?min after the stretching exercise.     

Human kinematics and event control: on-line movement registration as a means for experimental manipulation

In human movement and sports science, manipulations of perception and action are common and often comprise the control of events, such as opening or closing liquid crystal goggles. Most of these events are externally controlled, independent of the actions of the participants. Less common, although sometimes desirable, are event manipulations that are dependent on the unconstrained movements of participants. As an example, we describe a method we used previously to manipulate vision of basketball jump shooters on the basis of on-line registration of their own movements. The shooters wore liquid crystal goggles that opened or shut as a function of specific kinematic features of these movements. The novel aspect of this method is that the criteria for detecting movement patterns and performing the appropriate manipulations are adjustable to the specific sport context and the complexity and variations of the unconstrained movements. The method was implemented as a finite state machine: a computer system that can be used for pattern recognition. We discuss this method, how it works and the potential it has for studying perceptual-motor skills in sport. Furthermore, the results of the basketball experiment are briefly summarized and complemented with new analyses.     

Human kinematics and event control: on-line movement registration as a means for experimental manipulation

In human movement and sports science, manipulations of perception and action are common and often comprise the control of events, such as opening or closing liquid crystal goggles. Most of these events are externally controlled, independent of the actions of the participants. Less common, although sometimes desirable, are event manipulations that are dependent on the unconstrained movements of participants. As an example, we describe a method we used previously to manipulate vision of basketball jump shooters on the basis of on-line registration of their own movements. The shooters wore liquid crystal goggles that opened or shut as a function of specific kinematic features of these movements. The novel aspect of this method is that the criteria for detecting movement patterns and performing the appropriate manipulations are adjustable to the specific sport context and the complexity and variations of the unconstrained movements. The method was implemented as a finite state machine: a computer system that can be used for pattern recognition. We discuss this method, how it works and the potential it has for studying perceptual-motor skills in sport. Furthermore, the results of the basketball experiment are briefly summarized and complemented with new analyses.     

Perceptual judgments for stair climbing as a function of pitch angle

Two experiments explored perception and action for stair climbing, with manipulations to the stair dimensions. In Experiment 1, a custom-built apparatus manipulated the stair dimensions, while three groups of participants made perceptual judgments of climbability. The groups differed significantly for absolute leg length (p < .0001), but there was no significant difference between the groups when stair dimensions were calculated relative to leg length. The selected tread depths and riser heights reflected constant proportions of participants' leg length. Using the pitch angles formed as a composite metric, the results revealed that all groups selected 60 degrees as the limit for climbability. Experiment 2 scaled pitch angle systematically from 20 degrees to 80 degrees, and participants judged 65 degrees and beyond to be unclimbable. These results provided evidence that pitch angle might be used in perceptual judgments for stair climbability.     

Optimal pacing in road cycling using a nonlinear power constraint

In the individual road cycling discipline known as a time-trial, variable power pacing under variable grade conditions leads to improved performance. However, it is unclear whether these power variations result in an optimal finishing time. Typical pacing strategies use an average power constraint, which requires maintaining a constant speed regardless of grade fluctuations; however, this is physiologically infeasible for cyclists. We used an exponentially weighted average (EWA) power constraint in which a nonlinear relationship between the power output and physiological cost was assumed. We defined the optimal pacing (OP) strategy by minimizing the total cycling time subject to the EWA power constraint, and set the EWA of the power output of both the OP and constant power (CP) strategies to the same baseline value. The model showed that the OP strategy outperformed the CP strategy in terms of minimizing the finishing time under variable grade conditions, the power distribution of the OP strategy was identical to that of the CP strategy under constant grade conditions, and the average power output of the OP strategy was always lower than that of the CP strategy under variable grade conditions. Numerical simulations were performed on two hypothetical 40-km courses using both the CP and OP strategies. We found that under variable grade conditions, the time-saving rates of the OP strategy relative to the CP strategy were 2.7 and 2.8% for the two simulated courses.     

Identification with sport teams as a function of the search for certainty

Based on ideas from subjective uncertainty reduction theory, we examined the extent to which individuals hold similar sport team preferences to their family and friends. We also assessed the extent to which perceived sport importance and personal need for structure are influential in the development of team identification. Australian high school students aged 15.5+/-1.0 years (mean+/-s) completed questionnaires containing the Personal Need for Structure Scale, the Relational-Interdependent Self-Construal scale, a Team Identification Scale, and items assessing perceptions of sport importance and team preferences. As expected, correlations indicated that preferences for sport teams were significantly related to the preferences of family and friends. Separate analyses of variance confirmed the remaining hypotheses. More specifically, individuals who perceived that sport was important identified with the team more than individuals who perceived sport to be less important. Also, individuals high in personal need for structure scored higher in cognitive/affective team identification than those low in this need. Individuals with differing needs for structure did not differ in their scores on other dimensions of team identification. The results support the notion that cognitive/emotional attachments to sport teams are influenced by perceptions of the importance of sport and by needs for subjective structure. It is possible that other psychological motives, such as the desire for self-esteem, facilitate the development of evaluative dimensions of team identification.     

Strategic decisions of ice hockey coaches as a function of game location.

Two studies were performed to determine the influence of game location on the strategic decisions of ice hockey coaches. In study 1, coaches from the National (n = 23) and Ontario Hockey Leagues (n = 17) indicated the degree to which they had their teams forecheck assertively at home versus away. In study 2, video analysis of 62 National Hockey League games was used to verify the extent to which teams in this league use an assertive forechecking strategy at home versus away. In study 1, coaches reported that they implemented a more assertive forechecking style at home versus away (P < 0.001). The results of the video analysis in study 2 were consistent with the coaches' reports: teams used a more assertive forechecking style at home versus away (P < 0.03). The results are discussed in terms of their implications for the home advantage in the National Hockey League.     

Acquisition of a complex basketball-dribbling task in school children as a function of bilateral practice order

The purpose of this study was to investigate order-of-practice effects for the acquisition of a complex basketball skill in a bilateral transfer paradigm. The task required participants to dribble as fast as possible in slalom-like movements across six javelins and return to the initial position. Fifty-two right-handed school children (M age = 11.7years) practiced this skill in eight sessions over 4 weeks under one of two training schedules: (a) with the dominant hand, before changing to their nondominant hand (D-ND group), or (b) with the nondominant hand, before changing to the dominant hand (ND-D group). All tests were conducted with the right hand or the left hand only, and a transfer test was given with both hands alternating. The results of a retention test yielded significantly larger learning gains for the ND-D group as compared to the D-ND group. It is interesting that this performance advantage was independent of the respective hand tested. The same pattern of result was found in the transfer test, with significantly shorter movement times for the ND-D group with both hands alternating. Such order-of-practice effects for the acquisition of complex skills can be explained with hemispheric brain asymmetries for the processing of specific task requirements.     

Muscular strength and endurance as a function of age and activity level.

Muscular strength, endurance, and rate of fatigue were studied in populations of various ages actively engaged in strength and endurance training, as compared with those not engaged in such activities. The strength and fatigability of the elbow flexor muscles were studied for 62 subjects at the ages of 20 (n = 11 active, 10 inactive), 35 (n = 11 active, 10 inactive), and 50 (n = 10 active, 10 inactive) years, tested within 2 years of the appropriate age. They performed a 6-min bout of maximal rhythmic contractions of the dominant arm at a rate of 30 contractions per min. Force applied to the transducer was converted into electrical activity and transmitted to a recorder, where differences in mean values for initial strength, final strength, absolute endurance, and relative endurance were examined for significance. Rates of fatigue and the fatigue curves were also obtained for each group. Results revealed significantly less muscular strength, absolute endurance, and relative endurance as the age of the subjects increased, but no significant difference for age was found in final strength at the conclusion of the exercise bout. Significant differences were found between active and inactive subjects in initial strength, final strength, and absolute endurance in favor of the active subjects. No significant interaction between activity level and age was found for any of the dependent variables. The rates of fatigue were similar for all ages except for the inactive 20-year-old subjects, whose rate of fatigue was markedly slower than that found for all other groups of subjects.(ABSTRACT TRUNCATED AT 250 WORDS)