The biomechanical characteristics of 13 snatch lifts performed by 4 elite athletes were analyzed. Electromyographic data, ground reaction force index (GRFI), knee angular velocities, barbell velocities, and lifting time were obtained 0.2 s before the lift, for the first pulling phase (FP), and for the second pulling phase (SP). The preactivation, normalized electromyographic values correlated negatively with GRFI (p < .01). In the FP and SP, all of the parameters correlated positively with each other except lifting time. GRFI in the FP also correlated positively with GRFI, maximum knee angular velocities, and maximum barbell velocities of the SP (p < .01). In the SP, the ground reaction force reached its maximum first, followed by knee angular velocity and then barbell velocity. Barbell velocity reached its maximum before the knee and the hip joint were fully extended. When the correlation of parameters between the consecutive phases of snatch weight lifting was analyzed, it was demonstrated that the preactivation of trunk and leg muscles is important in the activation of the reflectory system in order to fully utilize the forces for generating lifting speed in the pulling phase.
Yung-Hui Lee, Chin-Yang Huwang and Yang-Hwei Tsuang
Geoffrey Goldspink and Shi Yu Yang
For some time, it has been appreciated that muscle mass is regulated locally as well as systemically. We have cloned the cDNA of two isoforms of IGF-1, which are derived from the IGF-1 gene by alternate splicing. The expression of one of these was only detectable after mechanical stimulation. For this reason, this has been called mechano growth factor (MGF). The MGF is not glycosylated, is smaller, and has a shorter half-life in the unbound state than the systemic liver type IGF-1. As the result of a reading frame shift the MGF peptide also has a different C terminal sequence and thus has different binding protein/receptor affinities. Another splice variant (muscle L.IGF-I) is expressed in muscle during rest but is also upregulated by exercise. The latter is similar to the systemic liver type IGF-1. The evidence suggests that MGF has a high potency for inducing local protein synthesis and preventing apoptosis and therefore has an important role in local tissue repair and remodeling. Our physiological experiments show that stretch and particularly stretch combined with electrical stimulation, rather than stimulation alone are important in inducing MGF expression. The mechanotransduction mechanism is believed to involve the muscle cytoskeleton. During aging, the production of growth hormone and IGF-1 by the liver declines markedly. The discovery of MGF and muscle IGF-1 provides a link between physical activity and gene expression. This underlines the need for the elderly to remain active as the locally produced growth factors supplement the circulating IGF-1 levels.
Jin-Jin Yang and David L. Porretta
Based on Singer’s (1986) method, we investigated the effects of a four-step strategy (ready, look, do, score) on training, maintenance, and generalization of three closed skills (basketball free throw, overhand softball throw, and dart throw) by adolescents (M age = 17.2) with mild mental retardation (MR). A multiple baseline across skills design was used. Performances of 3 males and 3 females across these three skills were examined. Participants averaged a total of 46 sessions for the duration of the study. Results indicated that participants increased performance 18–56% across all three closed skills during the training phase. A total of 4 participants maintained performance on all three skills when reminders were present, and 2 decreased performance when the reminders were removed. All participants exhibited improved performance when a reinforcer was introduced. Moreover, 5 participants were able to generalize the four-step strategy to a different setting.
Donald C. Leigh and Wei-Yang Lu
The dynamical interactions in tennis between ball, strings, and racket, during ball impact and immediately after, are modeled by a system of nonlinear ordinary differential equations that include both damping and elastic properties. During impact, the time history of the deflections, velocities, and forces in all parts of the system were calculated. Some simple experiments were done to determine the elastic and damping properties of the ball and strings, and to verify the theory in the case of a ball rebounding from the strings of a clamped racket head. Among the findings is that there is a trampoline effect even for a clamped racket head. Most interesting is that the rebound velocity of the ball can be increased, the mechanical energy transmitted to the racket can be reduced, and the maximum force transmitted to the holder of the racket can be reduced, all by increasing the damping in the racket.
Senlin Chen, Yang Liu and Jodee Schaben
The purpose of this study was to examine physical activity (PA)/fitness knowledge and its association with PA and sedentary behavior in youth.
Eighth grade students from five schools (N = 660) in a midwestern state completed a PE Metrics written test and the Youth Activity Profile to assess PA/fitness knowledge, PA (at school and after school) and sedentary behavior, respectively.
Participants were clustered into high, medium, and low knowledge groups. Students in the high knowledge group reported higher level of PA after school (p < .05, d = .28) but lower level of sedentary behavior than the low knowledge group (p = .001, d = -.45). The low knowledge group also reported higher PA at school (p < .05, d = .25). PA/Fitness knowledge significantly predicted sedentary behavior, particularly in the low knowledge group (β = -.32, t = -2.46, p < .05, R 2 = .105), after controlling for gender and race/ethnicity.
Physical education focused on conveying PA/fitness knowledge is warranted to educate youth to move more and sit less.
Jong Hyun Yang and Young Suk Lee
The purpose of this study was to find the defensive stance and calculate an optimal defense position for goalkeepers while blocking forward jump shots made from a distance of 9 m. Nine men’s handball matches were recorded and 78 video clips were selected for analysis. These are the top class goalkeepers, which included players from the national team and reserve team of Korea. The goalkeeper’s actual defensive position was significantly different from instructional suggestions; the width of both feet of the goalkeeper was approximately 2.5 times the width of the shoulders, and the hands were at waist height. The goalkeeper’s actual defense position was about 1.10 (± 0.3) m from the goal line and also significantly different than instructional material (0.75 m). The optimal defense position, which was calculated from the goalkeeper’s actual movement, was 1.44 m from the goal line, because the ratio of goalkeeper’s defensive area in relation to the total area to be defended is highest at this point. In summary, we recommended that handball goalkeepers move forward, about a half step (0.34 m), when defending a forward jump shot made from 9 m, and instructional material should be modified according to the findings from this study.
Sijie Tan, Chunhua Yang and Jianxiong Wang
The purpose of this study was to apply the lactate threshold concept to develop a more evidence-informed exercise program for obese children. 60 obese children (26 girls and 34 boys, age: 9–10 years, BMI: 25.4 ± 2.2kg/m2) were recruited and half of them were randomly selected to be trained for eight weeks with a controlled exercise intensity at lactate threshold. The trained children achieved significant improvements on their body composition and functional capacity compared with the control group. The findings suggested that the training program with intensity at lactate threshold is effective and safe for 9–10 year old children with obesity.
Chih-Hsiang Yang and David E. Conroy
Mindful walking has emerged as a potential intervention strategy to improve mental health and promote well-being in adult and clinical populations. This strategy has not been implemented specifically with older adults to date. This study evaluated the feasibility, acceptability, sustainability, and preliminary efficacy of a mindful walking program for reducing negative affect in older adults. Community-dwelling older adults (n = 29) completed a 1-month, outdoor mindful walking program distributed across eight 30-min sessions. Responses from postprogram and follow-up questionnaires revealed that mindful walking was well-accepted, highly valued, and maintained after the program ended. Analysis from the pre- and postwalk surveys also suggested the preliminary efficacy of a mindful walking program for reducing negative affect. Positive results identified in the current feasibility study indicate readiness for randomized controlled trials to further examine the efficacy and effectiveness of a mindful walking intervention for promoting health and well-being in older populations.
Yang Liu, Yan Tang, Zhen-Bo Cao, Pei-Jie Chen, Jia-Lin Zhang, Zheng Zhu, Jie Zhuang, Yang Yang and Yue-Ying Hu
Internationally comparable evidence is important to advocate for young people’s physical activity. The aim of this article is to present the inaugural Shanghai (China) Report Card on Physical Activity for Children and Youth.
Since no national data are available, the working group developed the survey questionnaire and carried out the school surveys for students (n = 71,404), parents (n = 70,346), and school administrators and teachers (n = 1398). The grades of 9 report card indicators were assigned in accordance with the survey results against a defined benchmark: A is 81% to 100%; B is 61% to 80%; C is 41% to 60%, D is 21% to 40%; F is 0% to 20%.
The 9 indicators were graded as follows: Overall Physical Activity Levels (F), Organized Sport Participation (F), Active Play (D-), Active Transportation (C-), Sedentary Behavior (F), Family and Peers (B), School (B+), Community and the Built Environment (D+), and Government (D).
Levels of physical activity and sedentary behavior were low and below the respective recommended guidelines. Interventions and policies at the community level should be encouraged to promote physical activity and reduce sedentary behavior. Future national surveys should be encouraged to strengthen Shanghai’s Report Card on Physical Activity for Children and Youth.
Risto Telama, Xiaolin Yang, Mirja Hirvensalo and Olli Raitakari
The aim of this study was to investigate how participation in organized competitive youth sport predicts adult physical activity. A random sample of 2,309 boys and girls ages 9–18 years participated in the Cardiovascular Risk in Young Finns Study in 1980, and 1,606 (70%) of them again in 2001. Physical activity was measured using a short, validated questionnaire. The results showed that participation in youth sport, and persistent participation in particular, significantly predicted adult physical activity. Participation in sport competitions increased the probability of high activity in adulthood more among males than females.