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81.
Maximal-intensity isometric and dynamic exercise performance after eccentric muscle actions 总被引:3,自引:2,他引:1
A well-documented observation after eccentric exercise is a reduction in maximal voluntary force. However, little is known about the ability to maintain maximal isometric force or generate and maintain dynamic peak power. These aspects of muscle function were studied in seven participants (5 males, 2 females). Knee extensor isometric strength and rate of fatigue were assessed by a sustained 60 s maximal voluntary contraction at 80 degrees and 40 degrees knee flexion, corresponding to an optimal and a shortened muscle length, respectively. Dynamic peak power and rate of fatigue were assessed during a 30 s Wingate cycle test. Plasma creatine kinase was measured from a fingertip blood sample. These variables were measured before, 1 h after and 1, 2, 3 and 7 days after 100 repetitions of the eccentric phase of the barbell squat exercise (10 sets x 10 reps at 80% concentric one-repetition maximum). Eccentric exercise resulted in elevations in creatine kinase activity above baseline (274+/-109 U x l(-1); mean +/- s(x)) after 1 h (506+/-116 U x l(-1), P < 0.05) and 1 day (808+/-117 U x l(-1), P < 0.05). Isometric strength was reduced (P < 0.05) for 7 days (35% at 1 h, 5% at day 7) and the rate of fatigue was lower (P < 0.05) for 3 days at 80 degrees and for 1 day at 40 degrees. Wingate peak power was reduced to a lesser extent (P < 0.05) than isometric strength at 1 h (13%) and, although the time course of recovery was equal, the two variables differed in their pattern of recovery. Eccentrically exercised muscle was characterized by an inability to generate high force and power, but an improved ability to maintain force and power. Such functional outcomes are consistent with the proposition that type II fibres are selectively recruited or damaged during eccentric exercise. 相似文献
82.
Williams AM Weigelt C Harris M Scott MA 《Research quarterly for exercise and sport》2002,73(4):386-395
This study examined age-related differences in the role of visual proprioception during a lower limb interceptive action and how this varies as a function of skill and practice. In Experiment 1, skilled and less-skilled 8-, 10-, and 12-year-old boys controlled a soccer ball using their preferred foot under full vision and when sight of the effector was occluded. With the exception of the high-skilled 12-year-olds and low-skilled 8-year-olds, participants showed a decrement in peformance when denied access to visual proprioception. In Experiment 2, the effect of practicing under different informational constraints was examined for 12 year-old boys. Children performed varying amounts of practice under full vision, or in a condition where sight of the foot was occluded, before being transferred to the alternative viewing condition. Participants who practiced under occluded viewing conditions showed greater relative improvement in performance over practice and transfer sessions compared with a full vision control group. Some support is provided for the manipulation of visual informational constraints as an effective pedagogical approach to motor learning. 相似文献
83.
Simulated tennis matchplay in a controlled environment 总被引:2,自引:2,他引:0
The aim of this study was to develop an exercise protocol to simulate tennis matchplay on a 'category 2' surface. Match analyses were used to form the basis for the design of the protocol. The protocol involved playing against a tennis ball serving machine. Part A of the protocol comprised 92 min 46 s of simulated tennis matchplay; Part B consisted of continuous hitting to the point of 'volitional fatigue' or when the required hitting frequency for two consecutive ball feeds could no longer be maintained. Ten elite tennis players (5 males, 5 females) volunteered to participate in the study, which was performed on an indoor tennis court (Matchplay, En-Tout-Cas). Their age, body mass and estimated maximal oxygen uptake were as follows: males, 21.7 +/- 1.0 years, 73.6 +/- 2.6 kg and 58.0 +/- 1.7 ml x kg(-1) x min(-1), respectively; females, 21.9 +/- 1.3 years, 62.3 +/- 2.0 kg and 42.2 +/- 0.7 ml x kg x min(-1), respectively (mean +/- sx). Heart rate, change in body mass and time to volitional fatigue were monitored. The heart rate responses of the participants to the simulated matchplay (range: 140-157 beats x min(-1), 73-81% peak heart rate) were consistent with the results of previous studies, for 'actual' matchplay. This protocol was successful in simulating similar physiological responses in Part A to 'actual' matchplay on a 'category 2' surface, in a controlled environment; it was also a sensitive evaluation tool of skilled performance in Part B. The current protocol may be used as a baseline protocol for studying the influence of, for example, training and dietary intervention on performance. 相似文献
84.
85.
This study examined the motivational profiles of elite youth athletes to determine whether individual differences in goal orientation corresponded with differential levels of imagery use. Two hundred ninety male (n = 88) and female (n = 202) young athletes (M = 16.6 years, SD = 1.48) completed the Perceptions of Success Questionnaire (POSQ, Roberts, Treasure, & Balague, 1998) to assess dispositional goal orientations and the Sport Imagery Questionnaire (Hall, Mack, Paivio, & Hausenblas, 1998) to assess frequency and function of imagery use. A two-stage cluster analysis on the POSQ scores revealed a three-cluster solution with a multivariate analysis of variance indicating significant differences among cluster groups in imagery use. Athletes in Cluster 3 (higher task/higher ego) used significantly more imagery, regardless of the function than athletes in Cluster 1 (lower task/moderate ego) or Cluster 2 (moderate task/lower ego). These findings are discussed with reference to the role of achievement motivation in influencing young athletes' behavioral investments in mental strategies. 相似文献
86.
Stone ME Foxman C Sostack M Francar L Hall P Markwell LG 《Medical reference services quarterly》2003,22(2):93-105
The librarians at four hospital libraries describe the electronic reference service, "Ask A Librarian," offered at their institutions. The hospitals are vastly different in size and in number of library staff, and offer the "Ask A Librarian" service to different clientele. The article illustrates that both large hospitals with a large library staff and small hospitals with a solo librarian and some volunteers can offer this type of service. 相似文献
87.
88.
In this longitudinal study, we assessed the frequency of birth dates for boys selected for the Football Association National School. Birthdays were divided into three periods of the year: January to April, May to August and September to December. We compared data over a 5 year period and concluded that there is indeed a bias towards selecting older children. Furthermore, analysis of separate data revealed a shift of bias when comparing two different start dates, namely September and January. Our findings show that the youngest children from the January start date (born September to December) are selected significantly more often than the youngest children from the September start date (born May to August). Interestingly, even when the influence of body mass was reduced, the selection bias towards the older players remained. 相似文献
89.
Information--movement coupling is a fundamental concept, integral to theorizing on the coordination of goal-directed activity in ecological psychology. In this paper, we examine the implications of this concept for the design of experimental research and the organization of practice during the acquisition of movement coordination in sport tasks. The task vehicle for our analysis is interceptive actions, in particular self-paced extrinsic timing tasks exemplified by serving in sports such as volleyball. Recent research highlighting the relevance of information--movement coupling for the process of practice in sport is discussed. We conclude that information--movement coupling represents an important principle for the structural organization of research and practice in self-paced extrinsic timing tasks and that further work is required to verify its significance across a range of sport movements. 相似文献
90.
We present a developmentally grounded perspective on the study of social life in cultures that examines the sources of the coexistence of sociability and opposition, harmony and conflict, acceptance and critique. The coexistence of these elements, it is proposed, is systematically connected both to the development of distinct domains of thought and to the dynamics of participation in more and less hierarchical social relationships in society. 相似文献