Force-Time Curves of Voluntary Muscular Contraction at Varying Tensions

Abstract

A recording spring-loaded hand ergograph with fast moving paper was utilized to obtain a record of the entire hand contraction sequence. The subjects (N=40) were given a series of six contractions, each beginning at a different initial tension: 0, 10, 15, 20, 25, and 30 kilograms. The contractions were separated by one minute and the order was systematically rotated to minimize either learning or fatigue. The development of force was found to progress exponentially according to a three-component mathematical equation. The control group (zero pre-tension) achieved a greater maximal force (F=4.5) than all others, and was the only one with a clear advantage in speed and tension. The rate of change constants were comparable, but the early initial (negative) component disappeared at the 20 kilogram condition and beyond. The factor of rate seemed to be independent of tension level.     

The Effect of Added Weights on Joint Actions in the Vertical Jump

Abstract

Cinematographic records were taken of 17 males during the performance of the vertical jump under four conditions of weighting; namely: no additional weight, and additions of 6, 12, and 18 pounds. Decreases in maximal angular velocity and increases in range of motion and time of the joint actions of the hip, knee, and ankle were noted with increasing amounts of weight. Significant decreases were obtained in the V/t ratio at the hip and knee joints with increasing amounts of weight. If one assumes a constant available force, these adjustments are consistent with an increase in mass (weight) according to the formula F = m V/t.     

The Physique of Women Students at Newcomb College of Tulane University. I. Stature and Weight

Abstract

The physique of women students at Newcomb College of Tulane University. I. Stature and weight. Harley N. Gould, Department of Biology, Newcomb College of Tulane University.

The investigation makes use of twenty years' records of physical measurements taken twice a year on a student population of whom about 80 per cent are from Louisiana. The mean stature of 2991 entering freshmen of the years 1909 to 1928, inclusive, is 63.34 inches and the mean weight of 2993 of them is 116.22 pounds. In the twenty years involved there is no consistent upward or downward trend of freshman height or weight, though the students of the last nine years average slightly taller than those of the first eleven years. Grouped by ages, the entering students fail to show any consistent relation of height or weight with age.

During four college sessions, students increase in height, on the average, three-tenths of an inch, and in weight, nine-tenths of a pound. Height increment is added chiefly in the first two years, and more in winter than in summer. Weight consistently tends to decrease in the winter and increase in the summer throughout the four college years, except for the winter of the freshman year, when the losses and gains nearly balance. Since 1919-20 the seasonal change in weight is much less than in the preceding years. A trend toward slenderness is indicated from 1924 to 1927.     

Relative Endurance of High- and Low-Strength Women

Abstract

The purpose of this study was to analyze the relative endurance ability of women in terms of muscle mass, static muscle strength, and critical occluding tension levels (COTL). Women physical education majors volunteered as subjects for this study (N = 56). The percentages of grip strength used for the relative endurance tests were 30%, 45%, 60%, and 75% with local circulation to the forearm muscles intact and artificially occluded by a pressure cuff. Analysis of the data revealed that there was no significant difference in the endurance times of high- and low-strength women. The relationship between grip strength and relative endurance time for each tension level was insignificant (r = ?.23 to ?.34). These findings were discussed in light of the relatively small differences in muscle mass and similarity in COTL of high- and low-strength women.     

Returning to competition after a serious injury: The role of self-determination

Abstract

We tested hypotheses grounded in self-determination theory regarding athletes' cognitive appraisals and emotional reactions when returning to competition following a serious injury. Professional male athletes (N = 225) competing in the Australian Football League were presented with return-to-competition scenarios that varied with respect to: (1) degree of self-determination and (2) salience of re-injury concern. Significant MANOVA main effects were observed for the degree of self-determination on both primary appraisals and emotional responses as well as for the salience of re-injury concern on emotional response. Follow-up ANOVA polynomial trend analyses provided support for the hypothesized trends for greater self-determination in the return to sport to result in more positive appraisals and affect. Findings support self-determination theory contentions and research indicating the psychological benefits of increased self-determination.     

Higher screen time is associated with overweight,poor dietary habits and physical inactivity in Brazilian adolescents,mainly among girls

Objectives: To analyse the associations between high screen time and overweight, poor dietary habits and physical activity in adolescents according to sex. Methods: The study comprised 515 boys and 716 girls aged 14–17 years from Londrina, Brazil. Nutritional status (normal weight or overweight/obese) was assessed by calculating the body mass index. Eating habits and time spent in physical activity were reported using a questionnaire. The measurement of screen time considered the time spent watching television, using a computer and playing video games during a normal week. Associations between high screen time and dependent variables (nutritional status, eating habits and physical activity levels) were assessed by binary logistic regression, adjusted for sociodemographic and lifestyle variables. Results: Most adolescents (93.8% of boys and 87.2% of girls) spent more than 2 hours per day in screen-time activities. After adjustments, an increasing trend in the prevalence of overweight and physical inactivity with increasing time spent on screen activities was observed for both sexes. Screen times of >4 hours/day compared with <2 hours/day were associated with physical inactivity, low consumption of vegetables and high consumption of sweets only in girls and the consumption of soft drinks in both sexes. Conclusions: The frequency of overweight and physical inactivity increased with increasing screen time in a trending manner and independently of the main confounders. The relationship between high screen time and poor eating habits was particularly relevant for adolescent girls.     

Motivational processes in physical education and objectively measured physical activity among adolescents

PurposeGrounded in self-determination theory (SDT), the present study tested how students’ perceptions of autonomy support from physical education teachers predicts objectively measured moderate-to-vigorous physical activity (MVPA) of adolescents. According to SDT, it was expected that psychological needs and autonomous and controlled forms of motivation would mediate these relationships.MethodsStudents (n = 397) aged from 11 to 15 years in 17 different schools filled in questionnaires regarding SDT variables. In addition, objective MVPA was measured using an accelerometer (ActiGraph GT3X; ActiGraph, Pensacola, FL, USA) for 7 days. Structural equation modelling was used to examine the hypothesized relationships among the study variables.ResultsThe theory-based model showed a good fit with the data: χ² = 642.464, df = 257; comparative fit index = 0.932; non-normed fit index = 0.921; root mean square error of approximation = 0.062; root mean square error of approximation 90% confidence interval: 0.054–0.067. As hypothesized, there was a significant and positive direct relationship between autonomy support and need satisfaction (β = 0.81, p = 0.001). In turn, need satisfaction positively predicted intrinsic motivation (β = 0.86, p = 0.001). Intrinsic motivation was positively related to MVPA (β = 0.29, p = 0.009). A significant indirect effect (β = 0.20, p = 0.004) supported the mediating role of psychological need satisfaction and intrinsic motivation in the relationship between perceived autonomy support and objectively measured MVPA.ConclusionThe findings of the current study support the applicability of the SDT-based model in explaining the antecedents of objectively measured MVPA of adolescents. To enhance adolescents’ daily MVPA, special focus should be put on increasing their intrinsic motivation toward physical education.     

体育教学中防控近视的睫状肌训练频次研究

目的： 分析比较体育教学中低频15次、中频30次,以及高频60次的睫状肌训练对八年级学生视力所产生的不同影响方法： 在体育课中分别对3个实验组进行低频15次、中频30次、高频60次睫状肌训练,测量并分析干预前后实验组与对照组学生的裸眼远视力与动态视力结果： (1)低频15次组学生的裸眼远视力与动态视力无显著性变化;(2)中频30次组学生的动态视力在干预后显著上升,裸眼远视力的提高无显著性差异;(3)高频60次组学生的裸眼远视力与动态视力在干预后均显著上升;(4)对照组学生的裸眼远视力与动态视力呈下降趋势结论： 体育教学中嵌入不同频次的睫状肌训练对八年级学生视力水平的影响不同,其中60次高频训练对裸眼远视力改善效果最佳,30次中频训练对动态视力的改善效果更好,15次低频训练能够基本维持学生裸眼远视力和动态视力的原有水平。在体育教学中进行睫状肌训练能够有效延缓近视的发展速度,促进学生视力水平发展。     

Lifting ‘Round the World': The Goodwill Weightlifting Tours of 1955

Abstract

In the first visit by American athletes to the Soviet Union since World War II, the U.S. weightlifting team included 340-pound Paul Anderson who startled the sports world in June of 1955 by pressing a world record 402 pounds, exceeding that of his Soviet adversary by 77 pounds. The admiration evoked by his colossal size and strength encouraged the State Department to send Anderson and other weightlifters on goodwill tours to counter Soviet expansionism in the Middle East and South Asia. The first tour evoked praise from President Dwight Eisenhower and Vice President Richard Nixon, but the second tour proved disappointing when Anderson was unable to perform as expected and Coach Bob Hoffman made disparaging remarks about local customs, thus inadvertently planting seeds of ill-will. The 1955 weightlifting tours illustrated the likelihood of unanticipated consequences and limitations of using athletics as a Cold War strategy to counter Soviet influence in non-aligned countries. Previous accounts have provided chiefly macroscopic views with only a vague notion of what transpired on the ground during goodwill tours. This study provides a closer view of how they were conducted, examples of interaction between visitors and locals, and their failure to fulfil the strategic aims of the Eisenhower Administration.     

Effects of Weight Reduction on Selected Anthropometric,Physical, and Performance Measures of Wrestlers

Abstract

Eighteen girth, skinfold, cardiovascular, cable tension strength, and response time measurements were obtained in order to assess the effects of weight reduction on a group of college wrestlers. In 10 of the 18 measurements mean differences were found to be significant at the .05 level from the statistical analysis provided by a repeated measures analysis of variance. It was generally concluded that for the ten subjects studied up to 7 percent of body weight may be lost without adversely affecting factors apparently related to wrestling performance —strength, cardiovascular endurance, and response time.     

Comment on Accuracy of References in Research Quarterly for Exercise and Sport (Stull Christina,and Quinn, 1991)

Abstract

An adaptation of the previously developed Exercise and Self-Esteem Model (Sonstroem &; Morgan, 1989) was tested longitudinally with 93 male interscholastic swimmers from nine high schools who were evaluated at pre-, mid-, and postseason. Swimmers completed three self-perception scales that ranged from evaluations of specific swim skills (SKILL) through broader perceived physical competence (PC) to global self-esteem (SE). Performance scores (PERF) were calculated across events by standardizing swim times to a mean of 0 and a standard deviation of 1. Structural modeling analysis across the three time waves indicated an excellent data fit(χ² = 25.46, p > .15). The model was able to explain 84, 83, and 80% of PC, SKILL, and PERF, respectively, at the third testing period. Swim improvement tended to be small (median change = 2.9%). Relationships among variables at each testing period and among the same variables at different testing periods were large and as hypothesized. Several significant relationships occurred between different variables across different testing periods. These were not extinguished when social desirability was added to the model. Social desirability failed to significantly influence subsequent measures of any model variable.     

The dynamic impact characteristics of tennis balls with tennis rackets

Abstract

The dynamic properties of six types of tennis balls were measured using a force platform and high-speed digital video images of ball impacts on rigidly clamped tennis rackets. It was found that the coefficient of restitution reduced with velocity for impacts on a rigid surface or with a rigidly clamped tennis racket. Pressurized balls had the highest coefficient of restitution, which decreased by 20% when punctured. Pressureless balls had a coefficient of restitution approaching that of a punctured ball at high speeds. The dynamic stiffness of the ball or the ball-racket system increased with velocity and pressurized balls had the highest stiffness, which decreased by 35% when punctured. The characteristics of pressureless balls were shown to be similar to those of punctured balls at high velocity and it was found that lowering the string tension produced a smaller range of stiffness or coefficient of restitution. It was hypothesized that players might consider high ball stiffness to imply a high coefficient of restitution. Plots of coefficient of restitution versus stiffness confirmed the relationship and it was found that, generally, pressurized balls had a higher coefficient of restitution and stiffness than pressureless balls. The players might perceive these parameters through a combination of sound, vibration and perception of ball speed off the racket.     

Revisiting the Development of Time Sharing Using a Dual Motor Task Performance

Abstract

The purpose of the study was to investigate the effect of a 2-min. isometric exercise training program on force and fatigue in a skeletal muscle. The subjects (N=60) were divided into two equal groups, control and experimental. The control group was tested twice, once at the beginning of the experiment and again after 20 days. The subjects in the experimental group were tested before embarked on a 20-day period of isometric training. held the tension for 2 min. in the morning and again in the afternoon. Periodic tests were on the 5th, 10th, 15th, and 20th days. Large gains of initial strength were recorded on the 5th day. Isometric training continued beyond five days produced no significant gains in initial strength althoughe was a significant increase in isometric endurance. Isometric exercise continued longer than 15 days resulted in a significant decrease in initial strength and isometric endurance.     

Correlations between Success in Student Teaching and Success on the Job

Purpose: This exploratory study examined the notion of Seefeldt's (1980) hypothesized motor skill “proficiency barrier” related to composite levels of health-related physical fitness (HRF) in young adults. Method: A motor skill competence (MSC) index composed of maximum throwing and kicking speed and jumping distance in 187 young adults aged 18 to 25 years old was evaluated against a composite index of 5 health-related fitness (HRF) test scores. MSC (high, moderate, and low) and HRF indexes (good, fair, and poor) were categorized according to normative fitness percentile ranges. 2 separate 3-way chi-square analyses were conducted to determine the probabilities of skill predicting fitness and fitness predicting skill. Results: Most correlations among HRF and MSC variables by gender demonstrated low-to-moderate positive correlations in both men (12/15; r = .23–.58) and women (14/15; r = .21–.53). Chi-square analyses for the total sample, using composite indexes, demonstrated statistically significant predictive models, χ ² (1, N = 187) = 66.99, p < .001, Cramer's V = .42. Only 3.1% of low-skilled (2 of 65) individuals were classified as having a “good” HRF. Only 1 participant (out of 65) who demonstrated high MSC was classified as having “poor” HRF (1.5%). Conclusion: Although individual correlations among individual MSC and HRF measures were low to moderate, these data provide indirect evidence for the possibility of a motor skill “proficiency barrier” as indicated by low composite HRF levels. This study may generate future research to address the proficiency barrier hypothesis in youth as well as adults.     

Perceiving the affordance of string tension for power strokes in badminton: Expertise allows effective use of all string tensions

Abstract

Affordances mean opportunities for action. These affordances are important for sports performance and relevant to the abilities developed by skilled athletes. In racquet sports such as badminton, different players prefer widely different string tension because it is believed to provide opportunities for effective strokes. The current study examined whether badminton players can perceive the affordance of string tension for power strokes and whether the perception of affordance itself changed as a function of skill level. The results showed that string tension constrained the striking performance of both novice and recreational players, but not of expert players. When perceptual capability was assessed, perceptual mode did not affect perception of the optimal string tension. Skilled players successfully perceived the affordance of string tension, but only experts were concerned about saving energy. Our findings demonstrated that perception of the affordance of string tension in badminton was determined by action abilities. Furthermore, experts could adjust the action to maintain a superior level of performance based on the perception of affordance.     

Factors Related to Rural Young Adolescents' Participation in Outdoor,Noncompetitive Physical Activity

Purpose: Young adolescents who have little interest in participating in competitive team sports are at an increased risk for physical inactivity. Noncompetitive outdoor physical activity can provide young adolescents with increased opportunities to participate in physical activities that appeal to them and have positive health effects. The purpose of this study was to examine factors related to rural young adolescents' participation in noncompetitive outdoor physical activity to inform intervention design. Method: Young adolescents aged 10 to 14 years old (N = 1,032) from 1 rural county completed a self-administered questionnaire assessing constructs from self-determination theory (SDT) and the theory of planned behavior (TPB) related to noncompetitive outdoor physical activity. Structural equation modeling was used to examine an integrated conceptual model of hypothesized relationships among constructs. Results: The hypothesized conceptual model provided a good fit to the data with greater perceptions of autonomy support and self-determined motivation having statistically significant positive indirect effects on participation in noncompetitive outdoor physical activity mediated by the constructs of the TPB. All direct paths in the model were statistically significant; however, the direct effect of attitudes on intention was weak (.08) and self-determined motivation had no indirect effect on intention through attitudes (.03). Conclusions: Constructs of SDT and TPB should be accounted for by interventions targeting noncompetitive outdoor physical activity among young adolescents. More research is needed to determine young adolescents' preferences for noncompetitive and competitive physical activity and the potential influence that noncompetitive outdoor physical activity may have on total daily physical activity.     

The effects of imagery training on fast isometric knee extensor torque development

Abstract

We hypothesized that imagery training would improve the fast onset of neuromuscular activation and thereby fast knee extensor isometric torque development. Forty young healthy participants, not involved in strength training, were assigned to one of four groups: physical training, imagery training, placebo training or control. The three training groups had three 15 min sessions per week for 4 weeks, with a 90° knee angle but were tested also at 120°. At 90° knee angle, maximal torque increased (～8%) similarly in all three training groups. The torque–time integral (contractile impulse) over the first 40 ms after torque onset (TTI40) increased (P < 0.05) after physical training (by ～100%), but only at 90°. This increase was significantly different from the delta values (change pre to post) in the control and placebo groups, whereas delta values in the imagery group were similar to those in the placebo group. The increases in TTI40 following physical training were related (r ² = 0.81, P < 0.05) to significant increases of knee extensor rectified surface EMG at torque onset (EMG40). In conclusion, only physical training led to a knee angle specific increase of contractile impulse that was significantly different from placebo and controls and that was related to improved onset of neuromuscular activation.     

The Estimation of [Vdot]O2max from Maximal and Sub-Maximal Measurements in Males,Age 10–39

Abstract

The purpose of this study was to assess the relationship between physiological and anthropometrical variables and 15-km time trial (TT) cycling performance time. Twenty-two competitive cyclists averaged 59.7 ml · kg^–1 · min^–1 for maximal oxygen consumption ([Vdot]O_2max), 42.8 ml · kg^–1 · min^–1 for anaerobic threshold (AT), and 23.5 min for the 15 km TT race. The relationship between [Vdot]O_2max and cycling performance time was r = – 0.68, (p < .01) while the correlation between AT and performance time was r = – 0.93, (p <.01). Applying stepwise multiple regression analysis, the two-variable model of the AT and the body circumference ratio, thigh+calf:arm+chest, was found to correlate highly with cycling performance time (r =0.966). It was concluded that the successful cyclists are characterized by the ability to consume large amounts of oxygen prior to ventilatory changes associated with the anaerobic threshold as well as a larger lower to upper body circumference ratio which may favorably decrease wind resistance while cycling.     

Physical Education Students’ Ownership,Empowerment, and Satisfaction With PE and Physical Activity

Individuals experiencing a highly caring, task-involving, and low ego-involving exercise climate have reported greater ownership in exercise class and empowerment to exercise in general. Purpose: This study examined the relationship between ownership and empowerment in exercise, with 2 context-specific outcomes, satisfaction with physical education (PE) and physical activity, respectively. Given the mission of PE to foster individuals’ lifelong physical activity habit, the perceptions of high school students were collected for this study. Ownership in exercise was hypothesized to be significantly, positively correlated with students reporting satisfaction in PE more than their satisfaction in physical activity, whereas empowerment in exercise was hypothesized to be more strongly, positively correlated with students’ physical activity satisfaction. A second purpose of this study was to test the measurement quality of the updated Empowerment in Exercise Scale (EES; now 13 items). Method: High school students (N = 502, 43% female) in a Midwestern U.S. school district completed a survey. Results: Confirmatory factor analysis supported the internal measurement structure of the EES (λ = .62–.91; McDonald’s omega = .89) across student gender (strong invariance). Additionally, the structural equation modeling analysis revealed only 1 parameter moderated by the students’ gender (latent mean of ownership). The hypotheses were supported, such that ownership in exercise was more strongly correlated with PE satisfaction (r = .87) and empowerment in exercise had a stronger correlation with physical activity satisfaction (r = .92). Conclusion: These results support the beneficial effect a satisfying experience in PE can have on students’ satisfaction with physical activity outside of school.     

Psychological effects of rapid weight loss and attitudes towards eating among professional jockeys

Abstract

We examined the psychological effects of rapid weight loss among a sample of 41 professional jockeys (mean age 30.9 years, s = 7.0). Participants completed the Brunel Mood Scale (BRUMS) and the Eating Attitudes Test-26 (EAT-26) to establish the relationships between rapid weight loss, mood, and attitudes towards eating. These instruments were administered on three occasions: at the jockeys' minimal weight (achieved through rapid weight loss), their optimal riding weight (when they were not excessively restricting their weight and felt healthy), and their relaxed weight (when there were no forthcoming light rides or no rides at all). It was hypothesized that when riding at minimal weight, jockeys would record a more negative mood profile compared with scores recorded at optimal or relaxed weights. The same trend was expected for eating attitudes. These hypotheses were supported as jockeys reported significantly more negative mood profiles and eating attitudes at minimal weight. The EAT-26 scores indicated the presence of disordered attitudes towards eating at this weight. These results suggest that jockeys' endeavours to reach the minimum weight limit stipulated by governing bodies are likely to jeopardize their psychological well-being. Dialogue surrounding the appropriateness of current weight regulations is therefore encouraged.