Comparison of a finite element model of a tennis racket to experimental data   总被引：1，自引：1，他引：0  

Tom Allen  Steve Haake  Simon Goodwill 《Sports Engineering》2009,12(2):87-98

Modern tennis rackets are manufactured from composite materials with high stiffness-to-weight ratios. In this paper, a finite element (FE) model was constructed to simulate an impact of a tennis ball on a freely suspended racket. The FE model was in good agreement with experimental data collected in a laboratory. The model showed racket stiffness to have no influence on the rebound characteristics of the ball, when simulating oblique spinning impacts at the geometric stringbed centre. The rebound velocity and topspin of the ball increased with the resultant impact velocity. It is likely that the maximum speed at which a player can swing a racket will increase as the moment of inertia (swingweight) decreases. Therefore, a player has the capacity to hit the ball faster, and with more topspin, when using a racket with a low swingweight.  相似文献   

Acute effects of walking on inflammatory and cardiovascular risk in sedentary post-menopausal women     

Davis J  Murphy M  Trinick T  Duly E  Nevill A  Davison G 《Journal of sports sciences》2008,26(3):303-309

Biochemical markers of inflammation are emerging as new predictors of risk of cardiovascular disease (CVD) and may alter acutely with exercise. Few studies have been conducted on the effects of walking on these markers or whether different walking intensities elicit varied effects. As there is growing interest in modifiable lifestyle factors such as walking to reduce CVD risk, these inflammatory responses warrant investigation. The aim of this study was to compare the effects of walking at 50% versus 70% of predicted maximal heart rate on C-reactive protein (CRP), plasma fibrinogen, and triglycerides in sedentary post-menopausal women. Twelve post-menopausal women (mean age 58 years, s +/-6; stature 1.62 m, s+/-0.06; body mass 66.8 kg, s +/-6.2) completed two 30-min treadmill walks in a randomized cross-over design. Fasted blood samples were taken (for the determination of plasma fibrinogen, CRP, and lipids) before, immediately after, and 1 and 24 h after exercise. Triglyceride concentrations decreased from pre-exercise to 24 h post exercise at both walking intensities (time x group interaction, P < 0.05). No significant effects were observed for plasma fibrinogen, CRP, total cholesterol, low-density or high-density lipoprotein cholesterol (time x group interaction, P > 0.05). The results of this study suggest that fasting plasma triglycerides are decreased on the morning after 30 min of brisk walking at either 50% or 70% of maximal heart rate (moderate and vigorous intensity).  相似文献   

Short-term optimal load training vs a modified complex training in semi-professional basketball players     

Tomás T. Freitas  Julio Calleja-González  Jorge Carlos-Vivas  Elena Marín-Cascales 《Journal of sports sciences》2019,37(4):434-442

This study investigated the effects on neuromuscular performance of a 6-week Optimal Load Training (OLT) and a novel modified Complex Training (MCT) (complex pairs: the same exercise using a moderate and an OL) in basketball players, in-season. Eighteen male athletes were randomly assigned to one of the protocols. Anthropometric measurements were taken to evaluate body composition. Lower- and upper-body maximum dynamic strength, countermovement jump (CMJ), standing long jump (SLJ), 10-m sprint and change of direction (COD) were also assessed. Moderate-to-large strength gains (presented as percentage change ± 90% confidence limits) were obtained for half-squat (OLT: 10.8 ± 5.3%; MCT: 17.2 ± 11.6%) and hip thrust (OLT: 23.5 ± 17.7%; MCT: 28.2 ± 19.0%). OLT athletes achieved likely small improvements in sprint (1.6 ± 1.6%) and COD (3.0 ± 3.2%). Players in the MCT attained likely moderate improvements in COD (3.0 ± 2.0%) and possibly small in SLJ (2.5 ± 4.6%). No protocol relevantly affected CMJ or body composition. An ANCOVA test revealed unclear between-group differences. In conclusion, both protocols increased basketball players’ strength without the use of heavy loads (> 85% 1RM) and without impairing sprint, CMJ and SLJ performance. These findings suggest that basketball strength and conditioning professionals may use either method to counteract strength losses during the season.  相似文献   

Learning to mentor in sports coaching: a design thinking approach     

Tom Leeder 《Sport, Education and Society》2019,24(2):208-211

Mentoring has been frequently cited as a valuable method of professional development for sports coaches. Nonetheless, there is an absence of scholarly work within the sports coaching field which explores the process of learning to become a coach mentor in detail. ‘Learning to Mentor in Sports Coaching: A Design Thinking Approach’ addresses this very issue with an innovative approach towards mentor training and preparation. The focus of the book is to highlight how design thinking, a systematic method to transform problems into creative solutions, can be adopted to analyse and rewrite mentoring conversations to optimise learning for both mentors and mentees. The central argument of the book maintains that sports coach mentors share similar characteristics and traits to design thinkers in the ways in which they attempt to facilitate and support coach learning and development. This review seeks to examine the focus of the book and consider its contribution to the broader body of literature in this field.  相似文献   

Irony in The Twilight Zone: How the Series Critiqued Postwar American Culture David Melbye. Rowman & Littlefield, 2016.          下载免费PDF全文

Tom Pace 《Journal of American culture (Malden, Mass. : 2003)》2017,40(2):191-191

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Antioxidant-rich beetroot juice does not adversely affect acute neuromuscular adaptation following eccentric exercise     

Tom Clifford  Oliver Bell  Daniel J. West  Glyn Howatson  Emma J. Stevenson 《Journal of sports sciences》2017,35(8):812-819

This study examined the effects of beetroot juice on the repeated bout effect (RBE) to eccentric exercise. Twenty-nine recreationally active males performed two bouts of 100-drop jumps, separated by 14–21 days. Using a double-blind, independent groups design, participants consumed either a higher dose beetroot juice (H-BT; 250 ml, n = 10), a lower dose beetroot juice (L-BT; 125 ml, n = 9) or an isocaloric placebo (PLA; 250 ml, n = 10) for 3 days after bout 1; no drinks were consumed after bout 2. Maximal isometric voluntary contraction (MIVC), countermovement jump (CMJ), pressure-pain threshold (PPT) and creatine kinase (CK) were measured pre, post, 24, 48 and 72 h following both bouts. In bout 2, CMJ and MIVC recovered quicker and CK activity was attenuated (versus bout 1) (P < 0.05) in all groups, demonstrating an RBE. At 24 h post bout 1, MIVC was 84.1 ± 16.1, 83.6 ± 11.6, 79.7 ± 15.1% relative to baseline values in the H-BT, L-BT and PLA groups, respectively; at 24 h post bout 2, MIVC recovered to 90.7 ± 13.7, 92.9 ± 6.9, 87.8 ± 6.9, in the H-BT, L-BT and PLA groups, respectively. These findings suggest that supplementation with antioxidant-rich beetroot juice does not adversely affect acute adaptations to a bout of eccentric exercise.  相似文献   

Strangers Drowning: Grappling with Impossible Idealism,Drastic Choices,and the Overpowering Urge to Help Larissa MacFarquhar. New York: Penguin Press, 2015.          下载免费PDF全文

Tom Cooper 《Journal of American culture (Malden, Mass. : 2003)》2016,39(4):474-475

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Decision boundaries and receiver operating characteristic curves: new methods for determining accelerometer cutpoints   总被引：2，自引：1，他引：1  

Jago R  Zakeri I  Baranowski T  Watson K 《Journal of sports sciences》2007,25(8):937-944

We propose and evaluate the utility of an alternative method (decision boundaries) for establishing physical activity intensity-related accelerometer cutpoints. Accelerometer data collected from seventy-six 11- to 14-year-old boys during controlled bouts of moderate- and vigorous-intensity field physical activities were assessed. Mean values and standard deviations for moderate- and vigorous-intensity activities were obtained and normal equivalents generated. The decision boundary (the point of intersection of overlapping distributions) was used to create a lower-bound vigorous-intensity cutpoint. Receiver operating characteristic (ROC) curves compared the sensitivity and specificity of the new cutpoint and mean values with the actual activity. There was a 96.5% probability that participants performing vigorous-intensity physical activity were accurately classified when using the decision boundary of 6700 counts per minute, in contrast to the 50% accurately classified when the mean value was used. Inspection of the empirical ROC curve indicated that the decision boundary provided the optimal threshold to distinguish between moderate and vigorous physical activity for this dataset. In conclusion, decision boundaries reduced the error associated with determining accelerometer threshold values. Applying these methods to accelerometer data collected in specific populations will improve the precision with which accelerometer thresholds can be identified.  相似文献   

The clien-consultant handbook. Edited by C.R. Bell and L. Nadler. Gulf Publishing Company. Houston,Texas. 1979. 290 pages. Hardbound. $18.95     

Tom Schwen  Mary Pat Lynch 《Performance Improvement》1982,21(4):43-43

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Introduction to Word Processing by Hal Glatzer,Sybex, Inc., Berkeley,CA, 1981, 164 pp. plus appendixes, $12.95 (paper), ISBN 0-89588–076–8     

Tom Schwen  Mary Pat Lynch 《Performance Improvement》1982,21(10):18-18

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