Ankle dorsiflexion range of motion is associated with kinematic but not kinetic variables related to bilateral drop-landing performance at various drop heights

Limited evidence is available concerning ankle dorsiflexion range of motion (DF ROM) and its relationship with landing performance from varying drop heights. The aim of this investigation was to determine the relationship between ankle DF ROM and both kinetic and kinematic variables measured during bilateral drop-landings from 50%, 100% and 150% of countermovement jump height. Thirty-nine participants were measured for their ankle DF ROM using the weight-bearing lunge test, after which five bilateral drop-landings were performed from 50%, 100% and 150% of maximal countermovement jump height. Normalized peak vertical ground reaction force (vGRF), time to peak vGRF and loading rate was calculated for analysis, alongside sagittal-plane initial contact angles, peak angles and joint displacement for the hip, knee and ankle. Frontal-plane projection angles were also calculated. Ankle DF ROM was not related to normalized peak vGRF, time to peak vGRF or loading rate (P > 0.05), regardless of the drop height. However, at drop heights of 100% and 150% of countermovement jump height, there were numerous significant (P < 0.05) moderate to large correlations between ankle DF ROM and initial contact angles (r = −0.34 to −0.40) and peak angles (r = −0.42 to −0.52) for the knee and ankle joint. Knee joint displacement (r = 0.39–0.47) and frontal-plane projection angle (r = 0.37–0.40) had a positive relationship with ankle DF ROM, which was consistent across all drop heights. Ankle DF ROM influences coordination strategies that allow for the management of vGRF during bilateral drop-landings, with alterations in alignment for the knee and ankle joints at both initial contact and peak angles.     

Effect of Force Sense to Active Joint Position Sense and Relationships between Active Joint Position Sense,Force Sense,Jumping and Muscle Strength

Abstract

We aimed to investigate the effect of external load on the joint position sense (JPS) accuracy and its relation to the target jump height. The present study also aimed to explore the relationship between force sense (FS) and maximum voluntary isometric contraction (MVIC). Participants’ MVIC levels were determined during the 45-degree knee extension task. Then, participants were asked to execute a knee JPS task with external load (EL-JPS) and with no-load (EL-JPS). To assess jumping accuracy participants were instructed to jump with their 50% of maximum jump height. Results indicated that EL-JPS error values were lower than NL-JPS. EL-JPS was correlated to jumping errors. However, the relationship between NL-JPS and jumping errors was not significant. A significant correlation was found between MVIC and FS errors.     

Reminiscence and strategies of performance in rotary pursuit tracking

The maximum speed at which man detects and corrects errors is analyzed on the pursuit rotor. During the prerest performance, scores of about 220 msec. are found, for both extravertive and introvertive subjects. During the postrest performance a crossover effect appeared: extraverts had scores near 60 msec., while introverts did not surpass 100 msec. The results are discussed in the framework of Eysenck and Frith's (1977) theory of reminiscence.     

Physical fitness of South African primary school children, 6 to 13 years of age: discovery vitality health of the nation study

Basic physical fitness was measured using 8 different measures for 10,295 South African children and youths (5,611 boys, 4,684 girls) ages 6 to 13 years. These measurements included height, weight, Body Mass Index, standing long jump, shuttle run, sit-and-reach, sit-up (EUROFIT testing battery), and cricket ball throw scores. Due to the effects of earlier apartheid laws on separating communities, it was hypothesized that scores for different ethnic groups may differ. Therefore, in addition to the calculation of basic norms and sex differences, ethnic differences were also tested. Height and weight, relative to age, were different between the various ethnic groups (Black, White, and Mixed ancestry) for boys, with Black boys being shorter and lighter than White boys. There were no differences in sit-and-reach flexibility scores between the groups. With the exception of the cricket ball throw for girls, White children had higher scores in most tests. Although not significantly different from the White children, in the majority of cases, the children of mixed ancestral origin had scores that ranged between the other two ethnic groups. These results suggest a need for encouraging fitness in school children, and the reintroduction of formal physical education into the South African school curriculum, especially into schools in which Black children predominate.     

Jump performance and augmented feedback: Immediate benefits and long-term training effects

Drop jumps and their adaptations to training have been extensively investigated. However, the influence of augmented feedback (aF) on stretch-shortening cycle (SSC) was not scrutinized so far despite the well-known positive effects of aF on motor performance and motor learning. The aim of the present study was therefore to investigate the effects of aF by evaluating immediate within-session effects and long-term adaptations. 34 participants were assigned to three groups that trained drop jumps with different relative frequencies of aF about their jump height: 100%, 50%, or 0%. A significant within-session effect of aF on jump height was observed before and also after the training period (pre: +4.6%; post: +2.6%). In the long-term (comparing pre- to post-measurement), the 100% group showed the greatest increase in jump height (+14%), followed by the 50% (+10%) and the 0% group (+6%). The importance of aF on drop jumps is therefore twofold: (i) to immediately increase jump performance and (ii) to improve long-term training efficacy. In contrast to the proposition of the guidance hypothesis, high frequency of aF seems to be beneficial when maximizing SSC-performance. As jump height cannot be quantified without objective technical measures it is recommended to include them into daily training.     

Interval endurance capacity of talented youth soccer players

The purpose of this study, in which 113 talented youth soccer players (M = 16.0 yr., SD = 1.5), selected by their age and level of performance participated, was to investigate interval endurance capacity needed to play at the highest level of competition in the age-category 12 through 18. Multivariate analyses of covariance with factors of level of performance and age category showed that players ages 16 through 18 years outscored the players ages 12 through 15 years on the interval endurance capacity (p < .05). In both age categories, elite players outscored less skilled players (p < .05). In the age category 12-15 years, the elite players participated more in soccer training than less skilled players (p < .05), whereas less skilled players participated more in additional training than the elite players (p < .05). No differences were found for total training (p > .05). In conclusion, development of the interval endurance capacity seems crucial for a talented youth soccer player to be successful.     

The stability of precision grip force in older adults

The exceedingly large grip forces that many older adults employ when lifting objects with a precision pinch grip (Cole, 1991) may compensate for a reduced capability to produce a stable isometric force. That is, their grip force may fluctuate enough from moment to moment to yield grip forces that approach the force at which the object would slip from grasp. We examined the within-trial variability of isometric force in old (68-85 years, n = 13) and young (n = 11) human subjects (a) when they were asked to produce a constant pinch force at three target levels (0.49, 2.25, and 10.5 N) with external support of the arm, hand, and force transducer and (b) when they were asked to grasp, lift, and hold a small test object with a precision grip. Pinch force produced in the first task was equally stable across the two subject groups during analysis intervals that lasted 4 s. The elderly subjects produced grip forces when lifting objects that averaged twice as much as those produced by the young subjects. The force variability during the static (hold) phase of the lift for the old subjects was comparable with that used by the young subjects, after adjusting for the difference in grip force. The failure to observe less stable grip force in older adults contradicts a similar recent study. Differences in task (isometric grip force versus isometric abduction torque of a single digit) may account for this conflict, however. Thumb and finger forces for grip are produced through coactivation of many muscles and thus promote smooth force output through temporal summation of twitches. We conclude that peripheral reorganization of muscle in older adults does not yield increased instability of precision grip force and therefore does not contribute directly to increased grip forces in this population. However, force instability may affect other grip configurations (e.g., lateral pinch) or manipulation involving digit abduction or adduction forces.     

Force-displacement differences in the lower extremities of young healthy adults between drop jumps and drop landings

We measured ground reaction force and lower extremity shortening in ten healthy, young adults in order to compare five trials of drop jumps to drop landings. Our dependent variable was the percentage of displacement (shortening) between the markers on the ASIS and second metatarsal heads on each LE, relative to the maximum shortening (100% displacement) for that trial at the point of greatest ground reaction force. We defined this as “percent displacement at maximum force” (%d_Fmax). The sample mean %d_Fmax was 0.73% ± 0.14% for the drop jumps, and 0.47% ± 0.09% for the drop landings. The mean within-subject difference score was 0.26% ± 0.20%. Two-tailed paired t test comparing %d_Fmax between the drop jump and drop landing yielded P = 0.002. For all participants in this study, the %d_Fmax was greater in drop jumps than in drop landings. This indicates that in drop jumps, the point of maximum force and of maximum shortening was nearly simultaneous, compared to drop landings, where the point of maximum shortening followed that of maximum force by a greater proportion. This difference in force to displacement behavior is explained by linear spring behavior in drop jumps, and linear damping behavior in drop landings.     

Age-related changes in multi-finger interactions in adults during maximum voluntary finger force production tasks

This study aimed to continue our characterization of finger strength and multi-finger interactions across the lifespan to include those in their 60s and older. Building on our previous study of children, we examined young and elderly adults during isometric finger flexion and extension tasks. Sixteen young and 16 elderly, gender-matched participants produced maximum force using either a single finger or all four fingers in flexion and extension. The maximum voluntary finger force (MVF), the percentage contributions of individual finger forces to the sum of individual finger forces during four-finger MVF task (force sharing), and the non-task finger forces during a task finger MVF task (force enslaving), were computed as dependent variables. Force enslaving during finger extension was greater than during flexion in both young and elderly groups. The flexion-extension difference was greater in the elderly than the young adult group. The greater independency in flexion may result from more frequent use of finger flexion in everyday manipulation tasks. The non-task fingers closer to a task finger produced greater enslaving force than non-task fingers farther from the task finger. The force sharing pattern was not different between age groups. Our findings suggest that finger strength decreases over the aging process, finger independency for flexion increases throughout development, and force sharing pattern remains constant across the lifespan.     

A validation of the five-factor model of personality in academically talented youth across observers and instruments

Four instruments—the NEO-Five-Factor Inventory (NEO-FFI), the Adjective Check List (ACL), the Myers–Briggs Type Indicator (MBTI) and the California Child Q-Set (CCQ)—and two data sources—self reports and parental ratings—were used to assess personality dimensions according to the five-factor model of personality in 870 academically talented youth (mean age = 13.77) from the U.S.A. Data from the parents of 565 of these children were also analysed. The factor structure of the self and parent reports, the convergence between the two sources of reports and the correlations of the adjectives in the ACL with the scores on the NEO-FFI were all consistent with previous results obtained from adults. The findings largely support the notion that the five-factor model as derived from data from adults is applicable to academically talented youth.     

Children with developmental coordination disorder are equally able to generate force but show more variability than typically developing children

Several studies have suggested that children with developmental coordination disorder (DCD) have difficulties in the fine-tuning of manual force. However, parameterization of the generated force per se is hard to test under normal circumstances as movement planning and execution are also involved. In the present study, an isometric force production task was used to test the hypothesis that children with DCD have a decreased ability to scale force to a required force level and to maintain steady low to submaximal forces. We also tested if the developmental trends were different between the children with DCD and typically developing (TD) children. Twenty-four children with DCD and 24 matched TD children, divided over three age groups (7-9-11 years) participated in this study. Analysis of the data showed that DCD and TD children are equally able to adapt their generated force to the required levels, however DCD children produced a less steady force, even more variable than in the youngest TD children. These results suggest that problems in force control in children with DCD are caused by a higher level of inherent noise of the output system. Since younger DCD children are much more affected than older ones it is suggested that these children are able to learn a strategy to cope with their increased stochastic variability, especially at higher force levels.     

Thinking about muscles: the neuromuscular effects of attentional focus on accuracy and fatigue

Although the effects of attention on movement execution are well documented behaviorally, much less research has been done on the neurophysiological changes that underlie attentional focus effects. This study presents two experiments exploring effects of attention during an isometric plantar-flexion task using surface electromyography (sEMG). Participants' attention was directed either externally (towards the force plate they were pushing against) or internally (towards their own leg, specifically the agonist muscle). Experiment 1 tested the effects of attention on accuracy and efficiency of force produced at three target forces (30, 60, and 100% of the maximum voluntary contraction; MVC). An internal focus of attention reduced the accuracy of force being produced and increased cocontraction of the antagonist muscle. Error on a given trial was positively correlated with the magnitude of cocontraction on that trial. Experiment 2 tested the effects of attention on muscular fatigue at 30, 60 and 100%MVC. An internal focus of attention led to less efficient intermuscular coordination, especially early in the contraction. These results suggest that an internal focus of attention disrupts efficient motor control in force production resulting in increased cocontraction, which potentially explains other neuromechanical findings (e.g. reduced functional variability with an internal focus).     

The effects of instructional cues on performance and mechanics during a gross motor movement

Externally focused instructions specific to performance have shown to improve body mechanics (Gokeler et al., 2015; Welling, Benjaminse, Gokeler, & Otten, 2016). However, the effect of using an external focus instruction may have been more profound if the content of the instruction had been relevant to mechanics. Therefore, the present study examined the effects of externally focused instructions specific to performance and externally focused instructions specific to body mechanics on mechanics and performance. Twenty-four adults (n = 12 males; n = 12 females) performed a series of drop jumps following external focus cues that were specific to performance and landing mechanics. Participants completed a drop jump followed by a maximal effort vertical jump. The initial contact, maximal angle, and range of motion at the knee in the sagittal and frontal plane motion were measured for mechanics and the height of the second vertical jump was measured for performance. The results suggest external focus instructions specific to performance are beneficial for performance, but not for improving landing mechanics. This suggests that external focus instructions must be specific to the contents of the instruction.     

Practice effects on decreasing and increasing force-control during periodic isometric movements of the index finger

The present study examined whether improvement in control while decreasing force to achieve a lower force target would be facilitated by comparison of performance while increasing force to achieve a higher force target. Participants practiced control of isometric force and timing during a unimanual force production task cycling between 5 and 10% of maximum voluntary contraction with a target interval of 500 msec. Although errors and variability of both peak and valley forces and interval decreased during early practice, the valley force was still more inaccurate and variable than the peak force in the final practice. Variabilities of both forces did not decrease when the valley force was synchronized with an audible metronome pulse but did decrease when the peak force was synchronized with it.     

Spatial-frequency-dependent visible persistence and specific reading disability

Visible persistence duration for sine-wave gratings was measured in 9-year-old normal and specific-reading-disabled children. Experiment 1 investigated the influence of stimulus duration on visible persistence. The results demonstrated a Reading Group X Spatial Frequency interaction with disabled readers showing a smaller increase in persistence duration with increasing spatial frequency than controls. This interaction was greatest with stimulus durations longer than 80 msec. In Experiments 2a and 2b persistence was measured across a range of contrasts from .1 to .5. The stimulus durations employed were 100 msec in Experiment 2a and 300 msec in Experiment 2b. In both experiments, increasing contrast decreased persistence duration at 2 and 12 cycles per degree (c/deg) for the control group. In the specific-reading-disabled group, however, contrast had little effect on the persistence of 2-c/deg gratings in either experiment. In Experiment 2a the persistence of the 12-c/deg grating decreased with increasing contrast for both groups. In Experiment 2b contrast had significantly less effect on persistence duration in the specific-reading-disabled group, however, contrast had little effect on the persistence of 2-c/deg ratings in either experiment. In Experiment 2b contrast had significantly less effect on persistence duration in the specific-reading-disabled group than in the control group at 12 c/deg. Consequently, contrast had less effect on persistence in specific-reading-disabled children than in normal readers, especially at durations longer than the "critical duration" for each spatial frequency. Experiment 3 extended this finding to gratings with spatial frequencies of 4 and 8 c/deg. These results indicate a difference between normal and specific-reading-disabled children in cortical visible persistence. Two scores of visual processing were derived from the above experiments. On these scores the reading-disabled children were divided into Visual Disabled Readers (approximately 70%--eight subjects) and Nonvisual Disabled Readers (approximately 30%--four subjects). The percentages of disabled readers in each category remained constant when the sample size was increased to 61 normal and disabled readers.     

Self-perception and the career aspirations of mathematically talented female adolescents

The role of self-perceptions of career-relevant abilities in understanding the career aspirations of mathematically talented adolescent females is studied. Female high school sophomores rated themselves on the 12 self-estimates of ability in Holland's Self-Directed Search. Based on her ideal career aspiration, each student was assigned to one of six career-aspiration groups. The results of the multiple discriminant function analysis indicated that nontraditional math career aspirants could be discriminated from the remaining five career-aspiration groups on the basis of seven self-estimates of ability. Further discriminations were less distinct although classification accuracy for all six career groups surpassed that expected by chance alone.     

A Common Force-Sharing Pattern in Joint Action That Consists of Four People

The authors examined the force-sharing patterns in a joint action performed by a group of two, three, or four people compared with a solo action. In the joint actions, 28 participants produced periodic isometric forces such that the sum of forces they produced cycled between 5% and 10% maximum voluntary contraction with the right hand at 1 Hz. In both the three- and four-person tasks, the correlation between forces produced by two of the three or four participants was negative, and the remaining one or two participants produced intermediate forces. The errors of force and interval and force variabilities were smaller in four- and three-people groups than individuals. Four- and three-people groups thus performed better than individuals.     

Different gripping intervals in reproducibility of force-decreasing curve and muscle oxygenation kinetics during sustained maximal gripping

The purpose was to examine the properties and reproducibility of the force-decreasing curve and muscle-oxygenation kinetics measured by near infrared spectroscopy in sustained isometric grip and rhythmic repeated grip measurements using various contraction intervals (2 to 5 sec.). 10 healthy young adults performed both grip tests for 6 min., during which muscle-oxygenation kinetics were measured. The intraclass correlation coefficients of the time to reach the minimum value for oxygenated hemoglobin and myoglobin tended to become lower with longer relaxation time, especially over a 3-sec. interval. Although blood-flow obstruction closely influences the initial decreasing grip force during both grip tests with a 2-sec. interval, the decreasing grip force during rhythmic repeated gripping with over a 3-sec. interval is low. Hence, the physiological mechanism related to rhythmic repeated grip with over a 3-sec. interval may differ from that related to sustained isometric grip and rhythmic repeated grip with a 2-sec. interval.     

Reaction times and electromechanical delay in reactions of increasing and decreasing force

The purpose of this study was to compare reaction times and electromechanical delay between reactions to increase force from rest and reactions to decrease force from an active state in the quadriceps femoris of healthy young adults. Force, position, and electromyographic data were recorded from 35 subjects reacting to a forced knee-flexion perturbation. Electromechanical delay was assessed through cross-correlation of the filtered EMG and force data. Reaction time to increase force (M= 159.9 msec., 95% CI= 149.9-169.9 msec.) was significantly longer than RT to decrease force (M= 124.4 msec., 95% CI= 118.7-130.1 msec.). This difference was partially caused by a difference in electromechanical delay (RT to increase force electromechanical delay was 63 msec., 95% CI=60-67 msec., greater than the RT to decrease force electromechanical delay of 49 msec., 95% CI=46-52 msec.). This difference in reaction time could be important in identifying and interpreting physiologically meaningful changes in muscle force and in intermuscular coordination during movement.     

Grip Control in Children before,during, and after Impulsive Loading

The manipulation of small objects requires continuous contributions from both predictive and reactive mechanisms. The authors aimed to study the development of predictive and reactive mechanisms used by children from 6 to 14 years of age to manage impulsive loading. The load of a handheld object was increased rapidly by the drop of a weight hung on the object. The drop was triggered either by the child (predictive condition) or by the examiner (reactive condition). Regardless of the condition, the control strategy was refined with age. Younger children were unable to adapt their grip force (GF) to the friction of their fingers, whereas the older children provided GF that was well adapted to their variable coefficient of friction, thereby producing a secure grip. This reflected either an inadequate amount of force or an inability to integrate cutaneous information from the fingers in younger children. Additionally, a modulation with age for both predictive and reactive mechanisms was observed. All together, the better predictive abilities and the more secure grip exhibited by older children allow decreased slipping and improved performance in an impulsive loading task.