Weighted vest effects on impact forces and joint work during vertical jump landings in men and women

Weighted vest (WV) use during vertical jump landings (VJL) does not appear to alter peak vertical ground reaction forces (GRF) or peak joint torques. However, WV effects on joint work and sex differences during VJL are not well understood. This study assessed WV effects on vertical GRF and sagittal joint work during VJL in men and women. Twelve men and 12 women performed VJL wearing a WV with zero added mass (unloaded) and with 10% body mass (loaded) while GRF and kinematic data were obtained. Mixed-model analyses of variance (α = 0.05) and effect sizes (ES) were used to assess differences between sexes and/or load conditions. Regardless of sex, greater landing height (p < 0.001; ES = 0.37) and peak vertical GRF (p = 0.001; ES 0.51) occurred when unloaded, while greater landing time (p = 0.001; ES = 0.46) and negative lower extremity work (p < 0.001; ES = 0.41) occurred when loaded through greater negative work about the hip (p = 0.001; ES = 0.27) and ankle (p = 0.020; ES = 0.27). No differences in hip (p = 0.753; ES = 0.03), knee (p = 0.588; ES = 0.07), or ankle (p = 0.580; ES = 0.09) joint displacement were detected between loaded and unloaded conditions. Men exhibited greater landing heights (p < 0.001; ES = 2.49) and greater peak vertical GRF than women (p = 0.007; ES = 1.18), though women exhibited greater negative lower extremity work (p < 0.001; ES = 1.98) than men through greater negative knee (p < 0.001; ES = 1.98) and ankle (p = 0.032; ES = 0.94) work. No sex differences were detected for joint angular displacement about the hip (p = 0.475; ES = 0.30), knee (p = 0.666; ES = 0.18), or ankle (p = 0.084; ES = 0.71). These data revealed a unique load accommodation strategy during VJL with a WV characterized by greater lower extremity joint work performed via increased joint torque despite lesser landing height and peak vertical GRF. Women appear to perform greater lower extremity joint work than men during VJL despite lesser landing height and peak vertical GRF. Current and prospective WV users should be aware of their load accommodation strategy during VJL with an external load. Women may consider developing more refined load accommodation strategies for VJL regardless of whether external loading is applied to avoid performing excessive amounts of lower extremity work.     

An investigation of lower extremity energy dissipation strategies during single-leg and double-leg landing based on sagittal and frontal plane biomechanics

There is limited understanding of the differences in lower extremity energy dissipation strategies between single-leg and double-leg landing maneuvers. This study sought to investigate these differences in sagittal and frontal planes, and explain the differences using kinematics and kinetics. We hypothesized that single-leg and double-leg landing maneuvers involve different lower extremity energy dissipation strategies in both planes. Ten recreational athletes were recruited and instructed to perform double-leg and single-leg landing from 0.60-m height. Force-plates and motion-capture system were used to obtain kinetics and kinematics data respectively. Joint power was taken as product of joint moment and angular velocity. Joint work was computed as integral of joint power over time, whereby negative work represented energy dissipation. In the sagittal plane, the hip and knee showed major contributions to energy dissipation during double-leg landing; the hip and ankle were the dominant energy dissipaters during single-leg landing. In the frontal plane, the hip acted as the key energy dissipater during double-leg landing; the knee contributed the most energy dissipation during single-leg landing. The knee also exhibited greater frontal plane joint ROM, moment and energy dissipation during single-leg landing than double-leg landing. Our findings indicated that different energy dissipation strategies were adopted for double-leg and single-leg landing in sagittal and frontal planes. Considering the prominent frontal plane biomechanics exhibited by the knee during single-leg landing, we expect that this maneuver may have greater likelihood of leading to traumatic knee injuries, particularly non-contact ACL injuries, compared to the double-leg landing maneuver.     

The effects of enhanced abdominal activation on quadriceps muscle activity levels during selected unilateral lower extremity exercises

The purpose of this study was to investigate the effect of Abdominal Enhancement (AE) on the muscle activation of vastus medialis obliquus (VMO), vastus lateralis (VL) and rectus femoris (RF) muscle activation levels during eccentric, isometric and concentric phases of single leg raise (SLR), single leg wall squat (SLWS) and forward lunge (FL) exercises. Sixteen healthy individuals (Age: 24.6 ± 1.7 years) were included in the study. Internal Obliques/Transversus Abdominis (IO/TA), VMO, RF and VL muscle activation levels were measured by surface EMG during the exercises in two conditions: with and without AE. The abdominal drawing-in technique was used for AE. Repeated-measures analysis of variance was performed for statistical analysis. With AE, the average of IO/TA muscle activation level was 28.9%. VMO and VL muscle activation levels were significantly greater with AE during SLR (p = .02), SLWS (p < .001) and FL (VMO, p = .008, VL, p = .04) exercises. The effect of AE on VMO muscle activation level ranged from 2.5% to 5% (Effect size range: 0.54 to 0.91) and VL muscle activation level ranged from 2.1% to 5.5% (Effect size range: 0.35–1.24). RF muscle activation level did not change with AE (p > .05). The results of this study showed that AE increased VMO and VL muscle activities during SLR, SLWS and FL exercises but the corresponding changes were small. Even if this is not enough for muscle strengthening, exercises with AE may be used to enhance knee joint stability while controlling lumbopelvic stability.     

Effect of stimulant medication on lower extremity response time of boys with attention deficit hyperactivity disorder

Children with attention deficit hyperactivity disorder (ADHD) have been labeled as "inefficient movers"; however, little research has examined the effect of stimulant medication on lower extremity movements. 16 boys, 11 to 13 years old, with ADHD performed a lower-limb choice-response time task, both on and off medication. When nonmedicated, children had significantly slower reaction times to all three targets and significantly slower movement times for the contralateral and midline movements. For both conditions, children had significantly faster movement time when using the right leg than the left leg. These findings suggest that movement characteristics of children with ADHD are different under medicated and nonmedicated situations.     

Age and gender moderate the effects of localized muscle fatigue on lower extremity joint torques used during quiet stance

This study examined the effects of localized muscle fatigue, age, and gender on lower extremity joint torques used during quiet stance. Thirty-two participants performed exercises designed to fatigue the ankle plantarflexors, knee extensors, torso extensors, or shoulder flexors. Body kinematics and ground reaction forces were obtained both before and after the exercises, and joint torques were derived via inverse dynamics. Single joint fatigue affected torque variability at all lower extremity joints, with similar changes for both age groups. Males and females exhibited increased ankle torque variability after different tasks, with males showing more variability after ankle fatigue and females after shoulder and lumbar fatigue. Correlations between peak torques and torque variability differed between males and females and between age groups in certain cases. The results of this study suggested that both age and gender moderate the effects of fatigue on postural control and should be considered when developing strategies to prevent occupational falls.     

Focus on the positive: Anxiety modulates the effects of emotional stimuli on hemispheric attention

People with high levels of trait anxiety are said to orient attention selectively to threatening stimuli ( and ), but this effect is sometimes difficult to replicate. We suggest a reason for this difficulty is that typical tests of the spatial attention bias in anxiety failed to consider together: (1) the differential effects of positive and threatening stimuli on attention in anxiety, (2) the separate contributions of each hemisphere to the attention bias, and (3) whether the attention bias in anxiety is restricted to orienting or can be observed more strongly in the conflict or alerting networks of attention. We compared the effects of schematic angry, happy, and neutral face cues using a lateralized version of Posner’s Attention Network Task (Lateralized Attention Network Test) which distinguishes spatial Orienting Cost (due to an invalid cue; disengagement) from spatial Orienting Benefit (due to a valid cue; hypervigilance), and which considers executive Conflict resolution and Alerting in addition to spatial Orienting in each hemisphere separately. We tested participants with high and low trait anxiety measured by the STAI-TA (Spielberger, Gorsuch, & Lushene, 1983). Surprisingly, happy face cues rather than angry face cues interacted with target visual field and participant level of anxiety. Happy face cues presented to participants with low anxiety elicited maximal Orienting Benefit and minimal Orienting Cost for targets presented to the left visual field. Anxious individuals failed to benefit from happy cues in the left visual field. We suggest that lateralized positive cues can provide a more sensitive index of attention changes in anxiety than is provided by centrally-presented threatening cues.     

Focus of attention and placebo utility

The effects of focus of attention and expected drug effects on reactions to a placebo were examined in two experiments. In the first experiment self-aware and non-self-aware subjects were given a placebo that was said to be either performance-facilitating or inhibiting and then they worked on a set of arithmetic problems. It was expected that the non-self-aware subjects, but not the self-aware subjects, would display a self-serving bias in their attributions regarding the effects of the placebo. Specifically, it was predicted that non-self-aware subjects would attribute more arousal to the performance-inhibiting drug than the performance-facilitating drug since such attributions would be more psychologically beneficial or “useful” in the sense that they would make actual performance on the task look more impressive. Consistent with these predictions, there was evidence of a self-serving bias in drug reactions only among the non-self-focused subjects. Those who were made self-aware did not respond differentially to the two types of drug information. Instead, they appeared to respond in line with their actual (aroused) internal states by attributing some arousal to both drugs. In the second experiment arousal was reduced by eliminating the task, and this time self-focused subjects again appeared to be more aware of their actual internal states, as they reported less reaction to the placebo, regardless of the effects ascribed to it. Two conclusions are drawn from these results: (a) perceived drug utility does effect placebo responsiveness, and (b) self-focused attention increases awareness of internal states, but not necessarily the causes of those states.     

Evidence of proactive forefoot control during landings on inclined surfaces

The notion of proactive control of landings is generally accepted, and some underlying mechanisms have already been described. Only little is known on adjustments at the foot level, however. The authors therefore investigated the foot and ankle behavior of 24 participants as they landed on differently inclined surfaces. A 4-segment model of the foot and ankle provided 3-dimensional kinematics. They also analyzed activation patterns from several muscles and the ground reaction force. Participants anticipated the different surfaces, as shown by the forefoot kinematics and the activation patterns before touch down. Anticipation of the surface inclination led to adjustments in forefoot orientation and probably also in joint stiffness. The authors suggest that those adjustments tend to enhance the self-stabilizing potential of the mechanical system. The enhancement of that potential would ease the subsequent stabilization, reducing the demands on the neural system.     

Gender differences in the variability of lower extremity kinematics during treadmill locomotion

The authors examined whether there were gender differences in the variability of basic gait parameters (stride length, stride time) and 3-dimensional (3D) rotations of the hip, knee, and ankle joints during treadmill locomotion of 18 men and 15 women at 4 different gait speeds (walking at 5 km/hr, running at 8, 10, and 12 km/hr). The authors used 2-way analyses of variance to assess the data. No gender differences in the mean values or variability of basic gait parameters were detected. However, the women exhibited lower variability than did the men for 6 individual joint rotations: (a) transverse plane rotations of the ankle joint at 8, 10, and 12 km/hr, (b) transverse plane rotations of the hip and knee joints at 12 km/hr, and (c) sagittal plane rotations of the ankle joint at 12 km/hr. When collapsed across all 3D lower extremity rotations, the data showed that the women had lower variability than did the men at 12 km/hr. Reduced variability may result in more localized mechanical stress on anatomical structures and could therefore be a risk factor for injury in women at high gait speeds. The results also suggested that gender differences in variability may not be consistent across different levels of the motor system.     

Focus of attention and automaticity in handwriting

This study investigated the nature of automaticity in everyday tasks by testing handwriting performance under single and dual-task conditions. Item familiarity and hand dominance were also manipulated to understand both cognitive and motor components of the task. In line with previous literature, performance was superior in an extraneous focus of attention condition compared to two different skill focus conditions. This effect was found only when writing with the dominant hand. In addition, performance was superior for high familiarity compared to low familiarity items. These findings indicate that motor and cognitive familiarity are related to the degree of automaticity of motor skills and can be manipulated to produce different performance outcomes. The findings also imply that the progression of skill acquisition from novel to novice to expert levels can be traced using different dual-task conditions. The separation of motor and cognitive familiarity is a new approach in the handwriting domain, and provides insight into the nature of attentional demands during performance.     

The vertical nature of dominance-submission: Individual differences in vertical attention

Dominance-submission has been linked to verticality in studies of metaphor, judgment, and online processing. In all cases, dominance has been associated with higher locations in vertical space, whereas submission has been associated with lower locations in vertical space. The present studies sought to extend this class of vertical metaphors to individual differences in spatial attention. Two studies were conducted. In both, dominance-submission was assessed as an individual difference variable and covert spatial attention tasks were used to assess biases in vertical selective attention. As predicted, dominant individuals were faster to respond to higher spatial probes, whereas submissive individuals were faster to respond to lower spatial probes. These results reinforce a vertical theory of dominance-submission, importantly extending it to individual differences and basic processes of selective attention. Findings are discussed in relation to theories of embodiment, metaphor, personality, and attention.     

Validity and reliability of visual ratings of the vertical jump

The validity and reliability of visual estimates of the kinematics of the vertical jump as would be common in qualitative analysis of human movement was studied. Sagittal plane videotapes of 12 females performing vertical jumps were rated on two occasions by three samples of subjects: 6 basketball coaches, 10 kinesiology students, and 5 kinesiology professors. Visual ratings were compared to values quantified by biomechanical analysis using the Peak Performance Technologies system. Assistant collegiate basketball coaches were unable to rate discrete body angles in the vertical jump accurately or consistently. Six of 10 college student raters could accurately and consistently rate over-all range of motion. Since only one of the kinesiology professors could accurately and consistently rate range of motion compared to the majority of the students, professional experience did not affect the ability to rate range of motion in the vertical jump in these subjects.     

Variations on the vertical jump: individual adaptations to changing task demands

Here we explored the coordination of joint behaviors exhibited during the vertical jump and variations of that jump. By manipulating the take-off angle, we required an adjustment to changing task demands. It was hypothesized that kinematic features of the jump would change but that spatiotemporal relationships essential to propulsion would remain invariant across all conditions. To test this hypothesis, six adult male subjects performed jumps at six different take-off angles. An analysis of cinematographic data revealed that individual subjects changed the sequence and timing of lower-extremity joint reversals. In contrast, the covariation of joint behaviors during the propulsive phase and the timing of maximum intersegmental extension velocities were extremely stable within each individual across changes in task. We argue that the flexibility to alter sequence and timing is part of a strategy that permits adaptation to the context and facilitates a continued coordination among variables associated with propulsion.     

Focus of attention in groups: a self-attention perspective

In three studies, we examined the hypothesis, derived from self-attention theory, that the focus of attention of individuals in groups varies as a function of group composition. In naturally occurring, nonlaboratory settings, Studies 1 and 2 demonstrated a decrease in first-person singular pronoun usage as the proportionate number of discussants in a group increased. In a laboratory setting, Study 3 demonstrated an increase in self-reported self-focus as the number of subjects decreased relative to the number of experimenters. These results support the conceptualization of self-focused attention as a mediator of group composition effects.     

冥想对注意能力的影响

所有冥想方法都要对注意进行管理, 注意是冥想的核心机制。近期研究发现, 冥想显著提高了持续性注意、执行注意和选择性注意分配等多种注意能力。认知神经科学研究发现, 冥想使注意资源分配更有效; 长期冥想者表现出更高的失匹配负波波幅和更低的β波幅; 冥想增强了中央执行网络有关脑区的功能联结, 提高了突出网络有关脑区的活动; 注意聚焦冥想降低了默认网络有关脑区的活动。另外, 作为一种提高注意能力的方法, 冥想不仅适用于注意缺陷多动障碍患者和已康复的抑郁症患者等有注意相关障碍的临床群体, 也适用于儿童和老年人等多种年龄阶段的健康群体。未来应通过追踪研究探讨冥想的长期效果; 探索冥想中注意与情绪的交互作用; 根据群体特征设计出更有针对性的冥想。     

Effect of attention control on sustained attention during induced anxiety

Anxiety has wide-reaching and complex effects on cognitive performance. Although it can intrude on cognition and interfere with performance, it can also facilitate information processing and behavioural responses. In a previous study, we showed that anxiety induced by threat of shock facilitates performance on the Sustained Attention to Response Task, a vigilance test, which probes response inhibition to infrequent nogo stimuli. The present study sought to identify factors that may have contributed to such improved performance, including on- and off-task thinking (assessed with thought probes) and individual differences in attention control, as measured with the Attention Control Scale. Replicating our prior finding, we showed that shock threat significantly reduced errors of commission on the nogo trials. However, we extended this finding in demonstrating that this effect was driven by subjects with low attention control. We therefore confirm that anxiety increases inhibitory control of prepotent responses—a mechanism which is adaptive under threat—and show that this effect is greater in those who rely more upon such prepotent responding, i.e., those with low attentional control.     

Time course of changes in novice jumpers' countermovement vertical jump performance

Time course of changes in jump height was examined to assess whether it was related to changes in the underlying mechanics or muscle activity. In Phase I, 11 novice female students performed 10 maximal jumps for eight consecutive days from two force plates. Jump height, impulse duration (t(IMP)), and mean vertical ground reaction force (VGRF) were compared using repeated-measures analysis of variance. Jump height was significantly higher (7.7%) on Days 3-8 when compared to Days 1 and 2; t(IMP) and VGRF were unchanged across days. In a followup study (Phase II), 14 novice female students performed 10 maximal jumps for five consecutive days. Electromyographic activity of five leg muscles was recorded to identify the relative onset of each muscle's activity. Using repeated-measures analysis of variance, jump height was significantly higher (4.2%) on Days 2 to 5 compared to Day 1; however, no significant changes were found across Days, for t(IMP), VGRF, or the onset of muscle activity. The findings indicate that jump performance can improve rapidly in novice jumpers but the underlying muscle activation remained unchanged.     

Nonlinear approach to study the acute effects of static and dynamic stretching on local dynamic stability in lower extremity joint kinematics and muscular activity during pedalling

Researchers have reported contradictory results on the effect of static and dynamic stretching on subsequent performance. Due to the importance of performance through static and dynamic stretching, the aim of this study is to investigate the acute effects of static and dynamic stretching protocols on local dynamic stability in lower extremity joint kinematics and muscular activities during pedalling using a nonlinear dynamics approach. Using a randomised crossover trial design, fifteen active males participated voluntarily in this research (mass: 69.02 ± 10.52 kg, height: 174.00 ± 6.74 cm, and age: 21.20 ± 1.47 years) and completed a pedalling trial in situations of without stretching (WS), after static (SS), and dynamic stretching (DS) of lower extremity. The lower extremity joint angles in the sagittal plane and the electrical activity of soleus, gastrocnemius medialis, tibialis anterior, vastus medialis, biceps femoris, and rectus femoris muscles were collected during 30 pedalling cycles at 70 rates per minute. The results of the repeated measure ANOVA indicated that the knee and ankle angle largest LyE was significantly lower in DS compared to WS and SS. The largest LyE in muscle activity is also significantly lower for all the muscles after DS compared to WS and SS (P ≤ 0.05). Regarding the positive effects of DS on the joints and the muscle activity local dynamic stability, it is suggested to use DS than SS in the warm-up program before repetitive activities like pedalling.     

Effect of movement speed on lower and upper body biomechanics during sit-to-stand-to-sit transfers: Self-selected speed vs. fast imposed speed

Preferred and fast speed sit-to-stand and stand-to-sit (STS) tests are prevalent in literature, but biomechanical changes between the different speeds of STS have never been studied. Understanding differences between these STS techniques will better inform experimental design for research assessing functional ability in clinical populations. The purpose of this study was to investigate the effect of different speeds of STS transfers on lower body and trunk kinematics and kinetics in healthy adults. Nineteen healthy middle-aged and older adults participated in this study. Two different speeds of STS were tested: self-selected speed and fast speed (as quickly as possible). Ten Vicon cameras and two AMTI force platforms were used to collect three-dimensional kinematic and kinetic data. During sit-to-stand transfer, peak knee extension velocity and knee extension moment were significantly increased for the fast speed STS as compared to the preferred speed STS. During stand-to-sit transfer, peak knee extension moment and lower back moment were significantly increased while STS time was decreased for the fast speed STS as compared to the preferred speed STS. Our results indicate that the fast speed STS could be more challenging for participants compared to the preferred speed STS evidenced by greater knee and lower back joint movements. Therefore, fast STS tests should be reconsidered when testing middle-aged and older adults with chronic low back pain and knee joint problems.     

Focus of attention and causal attributions of actors and observers

An experiment was conducted to test the hypothesis that actors' and observers' causal attributions are a function of their focus of attention. In the presence of observer-subjects, actor-subjects made a choice among several art works in a supposed decision-making study. The experiment was a 2 × 2 × 2 factorial design with the factors (1) source of attribution (actors, observers); (2) camera (actor videotaped, actor not videotaped); and (3) situational stability (stable, dynamic environment). As predicted by the focus of attention-causal attribution notion, it was found that actors attributed more causality to the situation than observers under normal circumstances, when the camera was not operative, but that videotaping the actor reversed the usual actor-observer pattern such that actors attributed less causality to the situation than did observers. Further, when the environment was stable, actors attributed more causality to the situation in the no camera condition than in the camera condition, while observers attributed less to the situation in the no camera conditions than in the camera conditions. Additionally, both actors and observers attributed more causality to the situation when the environment was dynamic than when the environment was stable.