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1.
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2.
The present study explored the method of testing muscle mechanical properties through the linear force–velocity (F–V) relationships obtained from loaded vertical jumps. Specifically, we hypothesised that the F–V relationship parameters depicting the force, power, and velocity of the tested muscles will differ among individuals of different physical fitness. Strength trained, physically active, and sedentary male participants (N = 10 + 10 + 10; age 20–29 years) were tested on maximum countermovement and squat jumps where manipulation of external loads provided a range of F and V data. The observed F–V relationships of the tested leg muscles were approximately linear and mainly strong (median correlation coefficients ranged from 0.77 to 0.92; all p < 0.05), independently of either the tested group or the jump type. The maximum power revealed higher values in the strength trained than in the physically active and sedentary participants. This difference originated from the differences in F-intercepts, rather than from the V-intercepts. We conclude that the observed parameters could be sensitive enough to detect the differences among both the individuals of different physical fitness and various jump types. The present findings support using loaded vertical jumps and, possibly, other maximum performance multi-joint movements for the assessment of mechanical properties of active muscles.  相似文献   

3.
This article introduces a new theory, the Affective–Reflective Theory (ART) of physical inactivity and exercise. ART aims to explain and predict behavior in situations in which people either remain in a state of physical inactivity or initiate action (exercise). It is a dual-process model and assumes that exercise-related stimuli trigger automatic associations and a resulting automatic affective valuation of exercise (type-1 process). The automatic affective valuation forms the basis for the reflective evaluation (type-2 process), which can follow if self-control resources are available. The automatic affective valuation is connected with an action impulse, whereas the reflective evaluation can result in action plans. The two processes, in constant interaction, direct the individual towards or away from changing behavior. The ART of physical inactivity and exercise predicts that, when there is an affective–reflective discrepancy and self-control resources are low, behavior is more likely to be governed by the affective type-1 process. This introductory article explains the underlying concepts and main theoretical roots from which the ART of physical inactivity and exercise was developed (field theory, affective responses to exercise, automatic evaluation, evaluation-behavior link, dual-process theorizing). We also summarize the empirical tests that have been conducted to refine the theory in its present form.  相似文献   

4.
The similarities between the way performance knowledge is transmitted for martial and theatrical artists have been examined by Phillip Zarrilli. Zarrilli argues that strips of codified behaviour present artists with restricted fields of choice, a precise vocabulary of techniques and strictly prescribed parameters within which to operate. We extend this argument to include combat athletes, particularly boxers, proposing a closer examination of choice, agency and creative freedom within the boxer–trainer and actor–director relationship. Drawing upon autoethnographic data, and participant interviews, we explore how trainers, boxers, directors and actors talk about creative freedom as it relates to their relationships. This co-authored article uses two discrete voices to explore this creative freedom: P. Solomon Lennox writes from a boxer’s perspective and George Rodosthenous from a director’s point of view.  相似文献   

5.
The purpose of this study was to quantify the inter-session reliability of force–velocity–power profiling and estimated maximal strength in youth. Thirty-six males (11–15 years old) performed a ballistic supine leg press test at five randomized loads (80%, 100%, 120%, 140%, and 160% body mass) on three separate occasions. Peak and mean force, power, velocity, and peak displacement were collected with a linear position transducer attached to the weight stack. Mean values at each load were used to calculate different regression lines and estimate maximal strength, force, velocity, and power. All variables were found reliable (change in the mean [CIM] = ? 1 to 14%; coefficient of variation [CV] = 3–18%; intraclass correlation coefficient [ICC] = 0.74–0.99), but were likely to benefit from a familiarization, apart from the unreliable maximal force/velocity ratio (CIM = 0–3%; CV = 23–25%; ICC = 0.35–0.54) and load at maximal power (CIM = ? 1 to 2%; CV = 10–13%; ICC = 0.26–0.61). Isoinertial force–velocity–power profiling and maximal strength in youth can be assessed after a familiarization session. Such profiling may provide valuable insight into neuromuscular capabilities during growth and maturation and may be used to monitor specific training adaptations.  相似文献   

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7.
Abstract

The main aim of this study was to determine the test–retest reliability of existing tests of health-related fitness. Participants (mean age 14.8 years, s = 0.4) were 42 boys and 26 girls who completed the study assessments on two occasions separated by one week. The following tests were conducted: bioelectrical impedance analysis (BIA) to calculate percent body fat, leg dynamometer, 90° push-up, 7-stage sit-up, and wall squat tests. Intra-class correlation (ICC), paired samples t-tests, and typical error expressed as a coefficient of variation were calculated. The mean percent body fat intra-class correlation coefficient was similar for boys (ICC = 0.95) and girls (ICC = 0.93), but the mean coefficient of variation was considerably higher for boys than girls (22.2% vs. 12.2%). The boys' coefficients of variation for the tests of muscular fitness ranged from 9.0% for the leg dynamometer test to 26.5% for the timed wall squat test. The girls' coefficients of variation ranged from 17.1% for the sit-up test to 21.4% for the push-up test. Although the BIA machine produced reliable estimates of percent body fat, the tests of muscular fitness resulted in high systematic error, suggesting that these measures may require an extensive familiarization phase before the results can be considered reliable.  相似文献   

8.
Abstract

In this study, we used recently developed technology to determine the force–time profile of elite swimmers, which enabled coaches to make informed decisions on technique modifications. Eight elite male swimmers with a FINA (Federation Internationale de Natation) rank of 900+ completed five passive (streamline tow) and five net force (arms and leg swimming) trials. Three 50-Hz cameras were used to video each trial and were synchronized to the kinetic data output from a force-platform, upon which a motorized towing device was mounted. Passive and net force trials were completed at the participant's maximal front crawl swimming velocity. For the constant tow velocity, the net force profile was presented as a force–time graph, and the limitation of a constant velocity assumption was acknowledged. This allowed minimum and maximum net forces and arm symmetry to be identified. At a mean velocity of 1.92 ± 0.06 m · s?1, the mean passive drag for the swimmers was 80.3 ± 4.0 N, and the mean net force was 262.4 ± 33.4 N. The mean location in the stroke cycle for minimum and maximum net force production was at 45% (insweep phase) and 75% (upsweep phase) of the stroke, respectively. This force–time profile also identified any stroke asymmetry.  相似文献   

9.
Paul Rouse 《国际体育史杂志》2013,30(11-12):1521-1522
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10.
Three physical activity questionnaires were validated against heart rate (HR) monitoring and motion accelerometer data. All three methods were carried out simultaneously on 62 children ages 4–8 years on 4 consecutive days. The questionnaires were filled in by the children's parents and teachers. The reported time of physical activity with moderate to vigorous intensity, expected to increase HR above 140 beats per minute (bpm), correlated with the time of HR ≥ 140 bpm and ≥ 150 bpm (r = .40, p < .01) and with the accelerometer score (r = .53, p < .0001). Correlation between the HR ≥ 140 bpm and accelerometer score was r = .45, p < .001, and between the HR ≥ 150 bpm and accelerometer score, it was r = .41, p < .01  相似文献   

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12.
ABSTRACT

The aim of this study was to examine the challenges of being either a parent–coach or a child–athlete of a coach within the context of Swedish youth sport. Conceptually, this paper draws on educational and sociological theories regarding changing perspectives in child-rearing. The results are based on data gathered from interviews with parent–coaches and child–athletes (age 13–15) of coaches involved in team sports. The results indicate that a range of meanings emerged through these unique sets of interactions, resulting in both positive and negative experiences for both children and their parents. To manage the perceived challenges, four behavioural strategies were used including fairness, distancing, defence and quitting. Overall, this study provides a deeper understanding of the challenges of these unique dual roles in relation to contemporary child-rearing perspectives.  相似文献   

13.
The aim of the present study was to examine the effects of viscoelastic properties of human tendon structures during stretch?–?shortening cycle exercise. The elongation of tendon and aponeurosis of the medial gastrocnemius muscle of 26 participants was measured by ultrasonography while they performed ramp isometric plantar flexion up to the voluntary maximum, followed by a ramp relaxation. The relationship between estimated muscle force and tendon elongation during the ascending phase was fitted to a linear regression, the slope of which was defined as stiffness. The percentage of the area within the muscle force?–?tendon elongation loop relative to the area beneath the curve during the ascending phase was defined as hysteresis. In addition, maximal voluntary concentric contractions at 2.09 and 3.14 rad?·?s?1 with and without prior eccentric contractions were performed. The difference in the concentric torque at equivalent joint angles with and without prior eccentric contractions (i.e. pre-stretch augmentation) was negatively correlated with stiffness (P <?0.05) and hysteresis (P <?0.05). Furthermore, there was a higher correlation between the pre-stretch augmentation and the viscoelastic properties index – that is, the sum of normalized score values of stiffness and hysteresis (P <?0.01) – than with either stiffness or hysteresis alone. The results of this study suggest that performance during stretch?–?shortening cycle exercise is significantly affected by the viscoelastic properties of the tendon structures.  相似文献   

14.
Abstract

An investigation was undertaken to determine possible age and race difference between Black and Caucasian girls ages 6, 7, and 8 years. Ninety female subjects were administered 28 test items measuring speed, muscular power, agility, flexibility, balance, muscular endurance, and cardiorespiratory endurance. Few significant differences were observed between adjacent ages but 8-year-old females were significantly superior to the 6-year-old subjects on most motor performance variables utilized. For race comparisons, no significant differences were noted for measures of flexibility, muscular endurance, cardiorespiratory endurance, speed, balance, or muscular power. The Black subjects were significantly superior on two measures of agility while the Caucasian subjects performed significantly better on the time-limit shuttle run and grip strength.  相似文献   

15.
Abstract

The aim of the study was to verify differences between age groups of female judo matches in time-motion and technical–tactical analysis. The sample was composed of pre-cadet (13–14 years, n = 148), cadet (15–16 years, n = 228), junior (17–19 years, n = 104) and senior (>20 years, n = 237) groups. The time-motion indicators consisted of total combat time, standing combat time, displacement without contact, gripping time, total time of techniques, groundwork combat time and pause time, per match and by each combat/pause cycle. Technical and tactical variables were also collected. The one-way analysis of variance and a post hoc test were conducted, P ≤ 0.05. Cadets, with a median of 7 (2, 12), had a number of combat/pause cycles different from junior, with 3 (1, 8.5). Regarding time-motion per match and per cycle, senior had longer total combat time, standing combat time and gripping time than other groups. Senior presented lower frequency of leg techniques than pre-cadet, cadet and junior. Time-motion and technical–tactical variables effects in female judo athletes emphasise the difference between seniors and other groups.  相似文献   

16.
Abstract

By analyzing China’s approaches to elite cycling, this paper seeks to answer the question why the bicycle kingdom failed to produce any Olympic cycling champions. Many factors could explain China’s lack of medal success on the international stage, ranging from the limited degree of organizational specialization, problems regarding the quantity and quality of domestic coaches, to the lack of influence in the international governing body and more importantly the tension between the national team and provincial teams. However, there have been a series of developments contributing to China’s notable progress in cycling in the 2000s in general and in the London Olympiad in particular, the most important of which were the recruitment of world-leading coaches and the organization of overseas training. All these culprits and positive developments are discussed, not only to explain China’s overall poor medal performance in cycling at the Olympic Games yet with some gradual progress in recent years, but also to provide a representative through which China’s approaches to many non-traditional and less-successful sports can be understood. Four semi-structured interviews were conducted, accompanied by comprehensive document analysis derived from official documents and website information of associated sports governing bodies and influential media in China.  相似文献   

17.
The Coach–Athlete Relationship Questionnaire was developed to effectively measure affective, cognitive, and behavioral aspects, represented by the interpersonal constructs of closeness, commitment, and complementarity, of the quality of the relationship within the context of sport coaching. The current study sought to determine the internal reliability and factorial validity of the long (the 29-item Long Version Coach–Athlete Relationship Questionnaire) and short (11-item Coach–Athlete Relationship Questionnaire and 13-item Greek Coach–Athlete Relationship Questionnaire) versions of the Coach–Athlete Relationship Questionnaire with a sample of 800 Chinese coaches and athletes. Results supported the internal reliability across all Coach–Athlete Relationship Questionnaire versions examined, while confirmatory factor analyses (CFA) only supported the factorial validity of the three-factor first-order model of the 11-item Coach–Athlete Relationship Questionnaire. The results are discussed in terms of their implications for theory, research, and practice.  相似文献   

18.
The game of hurling is ranked as one of the fastest and most skilful field games in the world. It is played by a stick, hurley, made of ash wood and a ball, sliotar, made of a cork core or similar viscoelastic materials. Better standardisation of the game equipment requires analysing impacts to quantify precisely the effect of variations in equipment design on the resultant impact force at low and high striking speeds. Therefore, the purpose of the present study was to use a high-speed camera to (1) characterise the impact dynamics in term of impact force magnitude and duration, and (2) investigate whether a relationship exists between the game equipment and the magnitude of the impact force. An air cannon unit (ACU) test rig was set up to cause the sliotar to strike the hurley at predetermined speeds. A high-speed camera operating at 12,500 frames per second (fps) was used to capture 32 experimental impacts covering a range of sliotar and hurley brands, impact locations and impact speeds. The factor ??sliotar brand?? was identified as the most significant factor for the impact force among other main factors and two-factor interactions at a constant speed and it had a significant effect with up to 27?% difference between sliotar brands. It was demonstrated that, at higher impact speeds, the force?Cdeformation curves of the sliotar brands varied significantly, even though similar force?Cdeformation curves have been reported at quasi-static compression and similar COR values at low impact speeds using the standard free-drop test. This is the first known study to characterise the unique, highly non-linear and anisotropic sliotar?Churley impact using high-speed camera technology. It highlights the need for a tighter standard for sliotar materials and manufacturing to increase uniformity between different brands and strongly suggests that the standard free-drop test is not sufficient to characterise and compare game equipment.  相似文献   

19.
Abstract

Previous work on dynamics of interpersonal interactions in 1 vs. 1 sub-phases of basketball has identified changes in interpersonal distance between an attacker and defender as a potential control parameter for influencing organizational states of attacker–defender dyads. Other studies have reported the constraining effect of relative velocity between an attacker and defender in 1 vs. 1 dyads. To evaluate the relationship between these candidate control parameters, we compared the impact of both interpersonal distance and relative velocity on the pattern-forming dynamics of attacker–defender dyads in the sport of rugby union. Results revealed that when interpersonal distance achieved a critical value of less than 4 m, and relative velocity values increased or were maintained above 1 m · s?1, a successful outcome (i.e. clean attempt) for an attacker was predicted. Alternatively, when values of relative velocity suddenly decreased below this threshold, at the same critical value of interpersonal distance, a successful outcome for the defender was predicted. Data demonstrated how the coupling of these two potential, nested control parameters moved the dyadic system to phase transitions, characterized as a try or a tackle. Observations suggested that relative velocity increased its influence on the organization of attacker–defender dyads in rugby union over time as spatial proximity to the try line increased.  相似文献   

20.
Abstract

The aims of this study were to examine training characteristics, body composition, muscular strength, and endurance in sport climbers, and to demonstrate the relationship among these components by means of structural equation modelling. Altogether, 205 sport climbers (136 males, 69 females), with a performance RP (red point) of grade 4 to 11 on the Union Internationale des Association d'Alpinisme (UIAA) scale, took part in the study. The proposed structural model, with latent variable hand–arm strength and endurance (developed from reference values for simple tests), indicated by three manifest variables (grip strength, bent-arm hang, and finger hang) and three exogenous variables (body fat, volume of climbing, and climbing experience), explained 97% of the variance in climbing performance. The relationship between body fat and climbing experience/volume with climbing performance was not direct, but was better explained using the mediator hand–arm strength and endurance. We conclude that these simple tests, together with percent body fat, volume of climbing, and climbing experience, can satisfactorily predict climbing performance.  相似文献   

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