Optimal jumping strategies from compliant surfaces: a simple model of springboard standing jumps

A simple model of standing dives is used to investigate optimal jumping strategies from compliant surfaces and applied to springboard diving. The human model consists of a massless leg actuated by knee torque, and a lumped torso mass centered above the leg. The springboard is modeled as a mass-spring system. Maximum jump height for a male and a female is calculated by controlling knee-torque activation level as a function of time. The optimization includes constraints on minimum and maximum knee angle, rate of change of normalized activation level, and contact duration. Simulation results for maximal springboard depression and diver takeoff velocity agree reasonably with experimental data, even though larger board tip velocities are necessarily predicted earlier during the contact period. Qualitatively similar multiple pulse knee-torque activation patterns are found over various conditions and are different from those in rigid-surface jumping. The model is less able to predict accurately jump height at high fulcrum number since jumpers may have difficulty behaving optimally at non-preferred fulcrum settings. If strength is proportional to the product of mass and leg length, increasing leg length is more effective in increasing jump height than is increasing mass.     

Differential effects of differing intensities of acute exercise on speed and accuracy of cognition: A meta-analytical investigation

The primary purpose of this study was to examine, using meta-analytical techniques, the differential effects of differing intensities of acute exercise on speed and accuracy of cognition. Overall, exercise demonstrated a small, significant mean effect size (g = 0.14, p < 0.01) on cognition. Examination of the comparison between speed and accuracy dependent variables showed that speed accounted for most of the effect. For speed, moderate intensity exercise demonstrated a significantly larger mean effect size than those for low and high intensities. For speed of processing during moderate intensity exercise, central executive tasks showed a larger effect size than recall and alertness/attention tasks; and mean effect size for counterbalanced or randomized studies was significantly greater than for studies in which a pre-exercise followed by during or post-exercise protocol was used. There was no significant difference between mean effect sizes when testing took place post-exercise compared to during exercise for speed but accuracy studies demonstrated a significantly larger mean effect size post-exercise. It was concluded that increased arousal during moderate intensity exercise resulted in faster speed of processing. The very limited effect on accuracy may be due to the failure to choose tests which are complex enough to measure exercise-induced changes in accuracy of performance.     

Differential effects of differing intensities of acute exercise on speed and accuracy of cognition: A meta-analytical investigation

The primary purpose of this study was to examine, using meta-analytical techniques, the differential effects of differing intensities of acute exercise on speed and accuracy of cognition. Overall, exercise demonstrated a small, significant mean effect size (g = 0.14, p < 0.01) on cognition. Examination of the comparison between speed and accuracy dependent variables showed that speed accounted for most of the effect. For speed, moderate intensity exercise demonstrated a significantly larger mean effect size than those for low and high intensities. For speed of processing during moderate intensity exercise, central executive tasks showed a larger effect size than recall and alertness/attention tasks; and mean effect size for counterbalanced or randomized studies was significantly greater than for studies in which a pre-exercise followed by during or post-exercise protocol was used. There was no significant difference between mean effect sizes when testing took place post-exercise compared to during exercise for speed but accuracy studies demonstrated a significantly larger mean effect size post-exercise. It was concluded that increased arousal during moderate intensity exercise resulted in faster speed of processing. The very limited effect on accuracy may be due to the failure to choose tests which are complex enough to measure exercise-induced changes in accuracy of performance.     

Role of arms in somersaulting from compliant surfaces: a simulation study of springboard standing dives

The role of arms in compliant-surface jumping for maximizing backward somersault rotations is studied using multi-segment models and is applied to springboard diving. The surface (springboard) is modeled by a rigid bar with a rotational spring with a hinged end and point mass at the tip. Planar four- and five-segment human models are used (with the fifth segment representing the arms) and are driven by torque actuators at the ankle, knee, hip, and shoulder. Each joint torque is the product of maximum isometric torque and three variable functions depending on instantaneous joint angle, angular velocity, and activation level, respectively. Movement simulation starts from a balanced initial posture and ends at jump takeoff. The objective is to find joint torque activation patterns during board contact so that the number of backward rotations in flight is maximized. Kinematic differences in jumps with and without arms are mainly in smaller takeoff vertical velocity and more flexed knee and hip in the former. In both jumps, joint torque/activations are similar in their minor flexion-full extension patterns. Maximum hip torque is larger with arms but maximum knee torque is larger without arms. Except at the knee, more joint work can be done with arm swing. Total angular momentum is increased considerably by arm motion because of its remote contribution. Consequently segment remote contributions to total angular momentum are much larger in jumping with arms. Shoulder strength helps generate angular momentum only to a certain limit. If more work is used to generate horizontal velocity away from the board, the amount of total angular momentum is reduced.     

Top executive pay and firm performance

A study examining longitudinal data obtained from theDisclosure database for 390 large American firms yielded complex and unclear patterns of correlations between firm performance and executive pay. An examination of the data indicates that the relationship between firm performance and executive compensation may be nonlinear. Among performance measures, total assets was found to have the strongest association with executive pay. It was concluded that the scale of discretionary resources available to the firm better predicts executive pay than profitability or efficiency ratios.     

Measures of dynamic stability: Detecting differences between walking overground and on a compliant surface

Numerous measures of dynamic stability have been proposed to gauge fall risk in the elderly, including stride interval variability and variability of the center of mass. However, these measures have been deemed inadequate because they do not take into account temporal information. Therefore, research on the measurement of dynamic stability has turned to other analysis methods such as stride interval dynamics and the maximum Lyapunov exponent. Stride interval dynamics reflect the statistical persistence of an individual’s stride interval time series and the Lyapunov exponent quantifies local dynamic stability – the sensitivity of the system to infinitesimal perturbations. In this study, we compare the ability of these measurement tools to detect changes between overground and compliant-surface walking, a condition known to affect stability, to determine their aptness as measures of dynamic stability. Fourteen able-bodied participants completed three 15 min walks, two overground and one on a compliant surface. Our results show that the Lyapunov exponent may be more sensitive to gait changes than stride interval dynamics and gait variability measures.     

Escape behavior under different fixed ratios and shock intensities

The effects of ratio length and shock intensity on bar pressing were examined in three rats in two escape-from-shock experiments. In Experiment I, shock intensity was held constant while the schedule was varied from FR 1 to FR 20. The latency of the first escape response increased with FR length while the escape rate, computed as over-all rate in shock minus latency of the first response, decreased at FR 20. In Experiment II, the schedule was held constant at FR 5 while shock intensity was manipulated. Latency decreased as intensity increased, while escape rate increased with intensity, passing through a maximum for two subjects. Responses occurring during the last 100 sec of the 2-min escape period decreased as the FR increased for all subjects, and decreased as shock intensity increased for two subjects.     

The effects of leadership style and exercise program choreography on enjoyment and intentions to exercise

ObjectiveThe purpose of the study was to examine the independent (main) and interactive effects of leadership style and exercise program choreography on the enjoyment and future exercise intentions of novice female exercisers.DesignA randomized 2 (leadership style)×2 (exercise choreography) factorial in which a manipulation of leadership style (instructionally and motivationally enriched vs. bland) was crossed with a manipulation of exercise choreography style consisting of either a restricted or a varied set of exercises.MethodsNovice female exercisers (N=75) completed measures of exercise enjoyment and intentions to engage in future step aerobics classes following a 40-minute introductory session of step aerobics.ResultsSignificant (p<0.05) main effects were detected for leadership style and exercise choreography on enjoyment. Socially enriched leadership and varied choreography were associated with greater enjoyment. There were no main or interaction effects for exercise intention.ConclusionsResults show that social and structural factors impact on positive psychological outcomes in a structured exercise setting. Practitioners are encouraged to use these and previous findings to plan introductory exercise sessions. Future research should look at the impact of leadership style, choreography, and class group dynamics on behavioral manifestations such as adherence.     

Antecedent exercise and its effects on self-stimulation

The purpose of this study was to evaluate the effects of physical exercise on the self-stimulatory and on-task behaviors of an 8-year-old with developmental disabilities. For 10 min prior to a structured play session, the subject engaged in roller skating. This antecedent activity resulted in a decrease in the subject's self-stimulatory behavior and a corresponding increase in his on-task performance. Applications to educational programs and suggestions for future research are discussed.     

呼吸训练对心血管反应性及指温影响的研究

Delmonte(1985)的研究发现,静默可以使被试的心率、血压水平、皮肤电阻水平显著下降。Hans Zeier(1984)的研究也得到了类似的结果。Kistler(1998)等人认为指尖温度是自主神经系统活动反应的指标。Gwent,Pearson等人(1991)在进行心率研究时发现。内倾者比外倾者表现出较大的反应。我们在行为治疗中发现。腹式呼吸可以使被试手指温度持续上升。升高的时间和保持长度优于自生训练,皮肤温度升高与心血管反应性有关,为探讨腹式呼吸对心血管反应性的影响而提出本课题。     

Using implicit attitudes of exercise importance to predict explicit exercise dependence symptoms and exercise behaviors

Objectives“Fast” (i.e., implicit) processing is relatively automatic; “slow” (i.e., explicit) processing is relatively controlled and can override automatic processing. These different processing types often produce different responses that uniquely predict behaviors. In the present study, we tested if explicit, self-reported symptoms of exercise dependence and an implicit association of exercise as important predicted exercise behaviors and change in problematic exercise attitudes.DesignWe assessed implicit attitudes of exercise importance and self-reported symptoms of exercise dependence at Time 1. Participants reported daily exercise behaviors for approximately one month, and then completed a Time 2 assessment of self-reported exercise dependence symptoms.MethodUndergraduate males and females (Time 1, N = 93; Time 2, N = 74) tracked daily exercise behaviors for one month and completed an Implicit Association Test assessing implicit exercise importance and subscales of the Exercise Dependence Questionnaire (EDQ) assessing exercise dependence symptoms.ResultsImplicit attitudes of exercise importance and Time 1 EDQ scores predicted Time 2 EDQ scores. Further, implicit exercise importance and Time 1 EDQ scores predicted daily exercise intensity while Time 1 EDQ scores predicted the amount of days exercised.ConclusionImplicit and explicit processing appear to uniquely predict exercise behaviors and attitudes. Given that different implicit and explicit processes may drive certain exercise factors (e.g., intensity and frequency, respectively), these behaviors may contribute to different aspects of exercise dependence.     

The perception of length on curved and flat surfaces

In three experiments, observers judged the apparent extents of spatial intervals along the surface of a curved cylinder or a flat plane that was binocularly viewed in a natural, indoor environment. The observers' judgments of surface lengths were precise and reliable but were also inaccurate and subject to relatively large constant errors. These distortions differed among the observers, but they tended to perceive lengths oriented along the curved dimension of the cylinder as being longer than physically equivalent lengths in the noncurved dimension. This phenomenon did not occur when the observers judged curved and noncurved paths on the flat surface. In addition, some observers' judgments of length were affected by changes in the distance to the cylinder, whereas others were affected by the cylinder's orientation in space. These results demonstrate that the perception of length on surfaces is highly dependent on the particular context in which the length occurs.     

The influence of self-reported exercise addiction on acute emotional and physiological responses to brief exercise deprivation

Objectives: To examine the association between self-reported exercise addiction among competitive runners and their emotional and physiological response to a one-day deprivation from scheduled training.Design: A controlled experiment was utilised with random selection to exercise-deprived and control groups to examine the causal link between acute exercise deprivation and the presence and magnitude of withdrawal symptoms.Method: Club-level runners (n=60) who had been training at least five times weekly towards a major regional competition (30 women and 30 men, average age: 24.2 years) volunteered to abstain from a one-day training fixture with less than 24-hours’ notice. All subjects completed the Profile of Mood States (POMS), Running Addiction Scale (RAS) and resting heart rate (RHR) measurements. From this group, 15 men and 15 women were randomly selected to miss the next scheduled training (exercise-deprived group), while the remaining 30 runners continued their training uninterrupted (controls). Both groups repeated POMS and RHR measures within 24 hours after the experiment.Results: The exercise-deprived group reported significant withdrawal-like symptoms of depressed mood, reduced vigour and increased tension, anger, fatigue and confusion (measured by POMS), as well as significantly elevated RHR, within 24 hours after the missed training session. The control group showed no changes in mood or RHR. More importantly, the observed negative mood changes and RHR response in the exercise-deprived group were moderated by self-reported exercise addiction. The sub-median RAS scorers experienced significantly less mood change and RHR shifts than the higher scoring half of the sample. Further, correlations between RAS scores and the magnitude of increases in tension, anger, confusion, depression and RHR ranged from 0.46 to 0.58.Conclusions: Self-reported exercise addiction in habitual exercisers moderates their emotional and physiological responses to a short-term controlled exercise deprivation, indicating that the magnitude of these responses may, in turn, serve as early markers of exercise dependence.     

The effect of life events and exercise program format on the adoption and maintenance of exercise behavior.

This study prospectively investigated the effects of major life events on subsequent exercise adherence rates of individuals (N = 173) participating in a 2-year, randomized, controlled clinical trial of 3 different exercise conditions (higher-intensity home-based; lower-intensity home-based; and higher-intensity class-based). For 3 of 4 6-month exercise-adherence periods, an analysis of variance indicated a significant main effect (p < .05) for major life events. Compared with participants reporting 0 or 1 major life event, exercise adherence in the maintenance phase was significantly lower for those reporting 3 or 4 major life events regardless of the exercise condition. No significant life-event-exercise-adherence relationship was found in the adoption phase of exercise participation (i.e., Months 1 to 6). The deleterious effect of life events emphasizes the importance of instruction regarding how to prepare for high-risk situations that can lead to missed exercise sessions or to program attrition.     

薪酬水平和薪酬差距对企业运营结果影响的元分析

以国内外113篇企业薪酬水平和薪酬差距领域的实证研究(254个效应值, 438880家企业)为样本, 采用基于结构方程模型的元分析方法检验了企业平均薪酬水平、垂直薪酬差距和水平薪酬差距对企业创新、绩效和离职等运营结果的影响。元分析结果显示, 平均薪酬水平不仅能够显著提升企业的创新和绩效水平, 也会抑制企业内部的离职水平; 垂直和水平薪酬差距对企业绩效的主效应并不显著, 但其对企业创新具有显著的抑制作用, 并能够显著提升企业的离职水平。进一步的调节效应检验表明, 国家地域因素调节了薪酬水平与企业绩效之间的关系, 即中国企业的平均薪酬水平对企业绩效的促进作用显著高于美国企业。研究结果对于企业的薪酬管理具有一定的借鉴意义。     

Extraversion and exercise addiction

Extraversion has been suggested as a factor associated with addiction. This claim was tested in relation to exercise addiction. Twelve exercise addicts were compared with 12 nonaddicted individuals who were committed to regular exercise and with 12 nonexercising individuals drawn from the same student population. Addicted exercisers did not differ from nonaddicted exercisers in extraversion, although exercisers as a group were more extraverted than nonexercisers. The results are interpreted as evidence against the claim that extraversion is a component of the addictive personality profile.