Longitudinal Stability of the Leadership Scale for Sports

This study was designed to examine the role of foot type, height, leg length, and range of motion (ROM) measurements on excursion distances while performing the Star Excursion Balance Test (SEBT), a test of dynamic postural control. Participants (n = 30) performed 3 trials of the SEBT in each of the 8 directions while balancing on the right and left legs. No statistically significant relations were found between foot type or ROM measurements and excursion distances with the SEBT. Significant correlations were revealed between height and excursion distance and leg length and excursion distance with leg length having the stronger correlation. Using raw excursion measures, males were found to have significantly greater excursion distances than females; however, after normalizing excursion distances to leg length, there were no significant differences related to gender. In conclusion, when using the SEBT for experimental or clinical purposes, participants' excursion distances should be normalized to leg length to allow for a more accurate comparison of performance among participants.     

Reliability of a Unilateral Horizontal Leg Power Test to Assess Stretch Load Tolerance

Drop jumping has previously been used to measure fast stretch shorten cycle (SSC) ability and stretch load tolerance. To the knowledge of these authors a test does not exist to achieve this in the horizontal direction. The purpose of this study therefore was to estimate the reliability of a new unilateral horizontal leg power test to assess these qualities. Participants (N = 10) performed three jumps on each leg from distances of 80%, 120%, and 160% of leg length onto a force plate, followed immediately by a jump for maximal distance onto a synthetic track. No significant between- leg differences (p > .05) were found for the dependent variables of ground contact time (GCT), peak propulsive vertical ground reaction force, peak propulsive horizontal ground reaction force, and distances jumped (DJ).Within-trial variability (coefficients of variation) ranged from 3.6% to 10.9%, and test-retest reliability intraclass correlation coefficients from 0.80 to 0.95. GCT and DJ were the variables with highest reliability between trials and days. These two variables should be used to indicate fast SSC (GCT) ability and stretch load tolerance (DJ-GCT) in the horizontal direction. The relationship of these measures to functional performance needs to be established.     

Trial-by-trial analysis or averaging: implications for electromyographic models of rapid limb control

The control of human limb movement has been the focus of research for more than a century. A major issue to emerge from this work is the manner in which the central nervous system regulates electromyographic (EMG) activity to produce movements that differ in distance, velocity, and movement time. However the different methods of analysis often used to analyze EMG data could result in different kinematic-EMG relationships. In this study, participants performed an elbow flexion task to one of five distance goals (between 5 degrees and 50 degrees) using three movement speeds. EMG data from the right elbow flexors were compared using a trial-by-trial analysis and one based on averaged data. Averaging across trials underestimated biceps EMG amplitude at all movement distances and speeds compared to a trial-by-trial analysis. Averaging overestimated EMG burst duration compared to the trial-by-trial analysis. Peak agonist EMG amplitude was positively related to distance and inversely related to movement time. Agonist EMG duration was constant for movement distances less than 30 degrees but increased in the 50 degrees condition. The results support the view that peak EMG amplitude and duration can be controlled independently, but EMG duration changes only for longer distance movements when additional force is required.     

运用仿真计算对跳远踏跳姿势的优化

运用多刚体模型及现代计算机仿真技术,探讨人体在不同姿势下踏板所引起的跳远远度的变化特征,以寻找最佳的起跳着板姿势。结果表明:着板时小腿的姿态角、膝关节角不同组合可以使人体获得相同的远度,故仅凭着板角的大小来衡量着板技术的优劣显然是不合理的;跳远踏跳着板时刻、人体各环节姿态角对跳远距离的影响作用大小并不一致,其重要性排序依次为踏跳腿小腿的姿态角最重要,其次是踏跳腿的膝角,而躯干斜角、大腿夹角及摆动腿的膝角对跳远距离的影响相对较小;运动员在跳远踏跳着板时刻,一定存在一个最佳的踏跳腿膝关节角和小腿与地面的夹角,以这种方式上板,可获得最大的跳远距离。     

Probing the allocation of attention in implicit (motor) learning

We investigated the attention demands associated with implicit and explicit (motor) learning and performance using a probe reaction time paradigm. Two groups of participants learned a golf putting task over eight blocks of 50 trials performed from different distances. One group (errorless learning) began putting from the shortest distance (25 cm) and moved progressively back to the furthest distance (200 cm). A second group (errorful learning) began putting from the furthest distance (200 cm) and moved progressively closer (25 cm). Retention tests were used to assess learning in the two conditions, followed by transfer tests in which participants used either an unusual putter or a very unusual putter. Transfer to the unusual putters had an equivalent effect on the performance of both errorless and errorful learners, but probe reaction times were unaffected in the errorless learners, suggesting that execution of their movements was associated with reduced attention demands. Reducing errors during initial learning trials may encourage an implicit mode of learning and lower the demand for cognitive resources in subsequent performance.     

The Effect of Preliminary Activity on Maximal Motor Performance

Abstract

This study assessed the effect of five selected treatments of preliminary activity on performance in the 60-yard dash, the cricket ball throw for distance, the jump reach, and the bicycle ergometer test of leg speed. The effect of such preliminary activity at different levels of achievement in the same performance tests was also investigated. An experimental sample of 15- to 17-year-old schoolboys (N = 45) underwent a testing program involving four consecutive days, with two sessions daily. On the basis of measures of pretreatment status, the subjects were matched into groups and subsequently exposed to the treatments. The treatments included identical maximal, identical submaximal, general strengthening, general flexibility and control routines. The statistical analysis of the results involved analysis of variance techniques. There was no evidence available indicating either that the treatments had an effect on the chosen motor performances or that there was a difference in this response at certain levels of achievement. As no measures of physiological function were taken, an assessment of the likely reasons for these findings could not be made.     

Conference communications

Abstract

The objective of this study was to provide anthropometric, physiological, and performance characteristics of an elite international handball team. Twenty-one elite handball players were tested and categorized according to their playing positions (goalkeepers, backs, pivots, and wings). Testing consisted of anthropometric and physiological measures of height, body mass, percentage body fat and endurance ([Vdot]O_2max), performance measures of speed (5, 10, and 30 m), strength (bench press and squat), unilateral and bilateral horizontal jumping ability, and a 5-jump horizontal test. Significant differences were found between player positions for some anthropometric characteristics (height and percentage body fat) but not for the physiological or performance characteristics. Strong correlations were noted between single leg horizontal jumping distances with 5-, 10-, and 30-m sprint times (r = 0.51–0.80; P < 0.01). The best predictors of sprint times were single leg horizontal jumping with the dominant leg and the distance measured for the 5-jump test, which when combined accounted for 72% of the common variance associated with sprint ability. In conclusion, performance abilities between positions in elite team-handball players appear to be very similar. Single leg horizontal jumping distance could be a specific standardized test for predicting sprinting ability in elite handball players.     

Systematic reduction of leg muscle activity throughout a standard assessment of running footwear

PurposeThis study aimed to investigate whether there is a systematic change of leg muscle activity, as quantified by surface electromyography (EMG), throughout a standard running footwear assessment protocol at a predetermined running speed.MethodsThirty-one physically active adults (15 females and 16 males) completed 5 testing rounds consisting of overground running trials at a speed of 3.5 m/s. The level of muscle activity from 6 major leg muscles was recorded using surface EMG. The variables assessed were the EMG total intensity as a function of time and the cumulative EMG overall intensity. Systematic effects of the chronological testing round (independent variable) on the normalized EMG overall intensity (dependent variable) were examined using Friedman analysis of variates and post hoc pairwise Wilcoxon signed-rank tests (α = 0.05).ResultsThere was a systematic reduction in overall EMG intensity for all 6 muscles over the time course of the running protocol (p < 0.001) until the fourth testing round when EMG intensities reached a steady state. The one exception was the biceps femoris muscle, which showed a significant reduction of EMG intensity during the stance phase (p < 0.001) but not the swing phase (p = 0.16).ConclusionWhile running at a predetermined speed, the neuromuscular system undergoes an adaptation process characterized by a progressive reduction in the activity level of major leg muscles. This process may represent an optimization strategy of the neuromuscular system towards a more energetically efficient running style. Future running protocols should include a familiarization period of at least 7 min or 600 strides of running at the predetermined speed.     

Stride length: the impact on propulsion and bracing ground reaction force in overhand throwing

Propulsion and bracing ground reaction force (GRF) in overhand throwing are integral in propagating joint reaction kinetics and ball velocity, yet how stride length effects drive (hind) and stride (lead) leg GRF profiles remain unknown. Using a randomised crossover design, 19 pitchers (15 collegiate and 4 high school) were assigned to throw 2 simulated 80-pitch games at ±25% of their desired stride length. An integrated motion capture system with two force plates and radar gun tracked each throw. Vertical and anterior–posterior GRF was normalised then impulse was derived. Paired t-tests identified whether differences between conditions were significant. Late in single leg support, peak propulsion GRF was statistically greater for the drive leg with increased stride. Stride leg peak vertical GRF in braking occurred before acceleration with longer strides, but near ball release with shorter strides. Greater posterior shear GRF involving both legs demonstrated increased braking with longer strides. Conversely, decreased drive leg propulsion reduced both legs’ braking effects with shorter strides. Results suggest an interconnection between normalised stride length and GRF application in propulsion and bracing. This work has shown stride length to be an important kinematic factor affecting the magnitude and timing of external forces acting upon the body.     

The Role of the Components of Knowledge of Results Information in Error Correction

Abstract

The purpose of this study was to determine the usefulness of the components of a knowledge of results (KR) statement for organizing response correction. Forty-eight subjects learned to move a handle to a criterion location on a linear positioning apparatus. Error direction and distance components of the KR statement were manipulated across four independent groups. Two 4 × 15 Analyses of Variances were calculated on absolute error (AE) and constant error (CE) scores. The groups main effect, trials main effect, and the interaction groups × trials effect were significant for both analyses. Groups receiving directional information were more accurate in error correction than was the distance only group. Manipulation of distance information also influenced error correction on the initial trials. The results were interpreted as an indication that the learner's initial error corrections are based on directional information and that the distance of the error information which initially lacks meaning interferes with initial response accuracy.     

Dissociation between running economy and running performance in elite Kenyan distance runners

The purpose of this study was to investigate the relationship between running economy (RE) and performance in a homogenous group of competitive Kenyan distance runners. Maximal aerobic capacity (VO_2max) (68.8 ± 3.8 ml?kg^?1?min^?1) was determined on a motorised treadmill in 32 Kenyan (25.3 ± 5.0 years; IAAF performance score: 993 ± 77 p) distance runners. Leg anthropometry was assessed and moment arm of the Achilles tendon determined. While Achilles moment arm was associated with better RE (r² = 0.30, P = 0.003) and upper leg length, total leg length and total leg length to body height ratio were correlated with running performance (r = 0.42, P = 0.025; r = 0.40, P = 0.030 and r = 0.38, P = 0.043, respectively), RE and maximal time on treadmill (t_max) were not associated with running performance (r = ?0.01, P = 0.965; r = 0.27; P = 0.189, respectively) in competitive Kenyan distance runners. The dissociation between RE and running performance in this homogenous group of runners would suggest that RE can be compensated by other factors to maintain high performance levels and is in line with the idea that RE is only one of many factors explaining elite running performance.     

Summary knowledge of results

Summary knowledge of results (KR) involves delaying the presentation of KR until a predetermined number of trials has been completed. Schmidt, Young, Swinnen, and Shapiro (1989) found an optimal summary length of 15 trials (compared to 1, 5, and 10) and Schmidt, Lange, and Young (1990) found an optimum length of 5 trials (compared to 1, 10, and 15) for 1 and 2 kinematic degree of freedom timing tasks, respectively. Experiment 1 was designed to determine the optimal summary length for learning a simple isometric force production task. The results indicated better retention for the 16-trial summary than for 8- or 1-trial summaries. Experiment 2 was an initial attempt to determine the locus of the 16-trial summary effect. Specifically, Experiment 2 focused on the role played by both the information provided in the summary presentations and the practice per se of the first 14 trials in the 16-trial block. The results suggest KR is important to ensure response stability. However, it also appears important to restrict the subject's immediate utilization of KR. This latter requirement may potentially aid the parameterization process, resulting in a reduction in response bias.     

Variance and Invariance in Expert and Novice Triple Junipers

Abstract

The purpose of this study was to examine relative timing, relative distance, and effector independence characteristics of the triple jump. We videotaped expert and novice triple jumpers using standing and running starts. On some trials, the triple jumpers were required to take off from their nondominant leg. Gentner's (1987) interaction test was used to assess the proportional duration model in describing the timing of the component submovements. For both experts and novices, the proportional durations varied with the type of start. For experts, the relative timing of the jump components was independent of the take-off leg. The findings were mixed for the novices. Similar results were obtained when relative distance was examined. These results are discussed with respect to constructs related to variability in skilled performance.     

Probing the allocation of attention in implicit (motor) learning

Abstract

We investigated the attention demands associated with implicit and explicit (motor) learning and performance using a probe reaction time paradigm. Two groups of participants learned a golf putting task over eight blocks of 50 trials performed from different distances. One group (errorless learning) began putting from the shortest distance (25 cm) and moved progressively back to the furthest distance (200 cm). A second group (errorful learning) began putting from the furthest distance (200 cm) and moved progressively closer (25 cm). Retention tests were used to assess learning in the two conditions, followed by transfer tests in which participants used either an unusual putter or a very unusual putter. Transfer to the unusual putters had an equivalent effect on the performance of both errorless and errorful learners, but probe reaction times were unaffected in the errorless learners, suggesting that execution of their movements was associated with reduced attention demands. Reducing errors during initial learning trials may encourage an implicit mode of learning and lower the demand for cognitive resources in subsequent performance.     

An Analysis of World Weightlifting Records

Abstract

Summary knowledge of results (KR) involves delaying the presentation of KR until a predetermined number of trials has been completed. Schmidt, Young, Swinnen, and Shapiro (1989) found an optimal summary length of 15 trials (compared to 1, 5, and 10) and Schmidt, Lange, and Young (1990) found an optimum length of 5 trials (compared to 1, 10, and 15) for 1 and 2 kinematic degree of freedom timing tasks, respectively. Experiment 1 was designed to determine the optimal summary length for learning a simple isometric force production task. The results indicated better retention for the 16-trial summary than for 8- or 1-trial summaries. Experiment 2 was an initial attempt to determine the locus of the 16-trial summary effect. Specifically, Experiment 2 focused on the role played by both the information provided in the summary presentations and the practice per se of the first 14 trials in the 16-trial block. The results suggest KR is important to ensure response stability. However, it also appears important to restrict the subject's immediate utilization of KR. This latter requirement may potentially aid the parameterization process, resulting in a reduction in response bias.     

Acquisition of Elementary Swimming Skills by Negro and White College Women

Abstract

This study was undertaken to compare Negro and white college women in beginning swimming on performance, motor ability, buoyancy, and body measurements. Thirteen Negro and 44 white nonswimmers were assigned to one of four classes for eight weeks of instruction. The criterion of a nonswimmer was the inability to propel the body 15 feet in a prone position with the face immersed. Preliminary tests included the Scott Motor Ability Test and measurements of height, weight, sitting height, leg length, shoulder width, hip width, and breathing capacity. Buoyancy was assessed by hydrostatic weighing. Learning rate was recorded as the number of trials required to execute successfully 15 progressive swimming skills. The Fox Power Test was administered as a measure of terminal achievement. Evidence indicated that the Negro group was significantly superior in motor ability, while the white group was significantly superior in swimming performance and was more buoyant. Because of the difficulty experienced by the Negro group with skills demanding buoyancy, swimming progressions for nonbuoyant college women should not utilize horizontal flotation as an integral component.     

Short- and long-term reliability of leg extensor power measurement in middle-aged and older adults

Muscular power is important for maintaining physical functioning with aging. Proper quantification of the reliability of muscular power tests is crucial to inform monitoring of individuals and sample size planning for interventional studies. This study evaluated short- and long-term reliability of leg extensor power measurement in 72 adults (age 62.7 ± 8.6 years). Participants completed four repeat trials on the Nottingham leg extensor power rig, with a further trial twelve weeks later. Mean change, typical error, and intraclass correlation coefficients (ICC) were calculated. For short-term reliability, mean change in power output was trivial after two trials (1.2–4.8%). Typical errors were small following four trials in the dominant leg of males (10.9–5.8%), three in the non-dominant leg of males (9.9–6.2%) and the dominant leg of females (10.0–9.6%) and two in the non-dominant leg in females (8.3%). Intraclass correlation coefficients (ICCs) were very high (0.88–0.96). For long-term reliability, mean change remained trivial (1.0–2.5%), typical errors remained small (5.8–8.6%), and ICCs very high (0.94–0.96). The leg extensor power rig is a reliable method for assessing lower body muscular power, both short- and long-term, with only minimal habituation effects.     

Assessment of the power performance of racing cyclists

A 30-s 'all-out' power protocol was studied in four groups of racing cyclists including internationals (n = 8), Category 1 (n = 10), Category 2 (n = 15) and Category 3 (n = 11). Following warm-up each subject completed five trials interspersed by 3 min of low intensity exercise on an ergowheel racing cycle ergometry system at a power output of 15 W kg-1 body weight, generated at 130 rev min-1. Temporal indices of performance included delay time (DT) to achieve the power criterion, total time (TT) of the maintenance of the power criterion and the ratio of TT/DT. 'Explosive' leg strength was assessed from a vertical jump. The results indicated that international and Category 1 cyclists had lower DT (2.2 +/- 0.1 s and 2.1 +/- 0.0 s, respectively; P less than 0.05), higher TT (28.1 +/- 0.7 s and 27.0 +/- 0.7 s, respectively; P less than 0.05) and elevated TT/DT (12.8 and 12.9, respectively; P less than 0.01). 'Explosive' leg strength was also higher (P less than 0.05) in the internationals than in the other groups of cyclists. The protocol provides a sport-related method for the assessment of short term endurance performance ability in racing cyclists which may be of value in identifying the anaerobic capability of individual cyclists.