A comparison of the mechanical effect of arm swing and countermovement on the lower extremities in vertical jumping

The purposes of this study were to quantify and compare how arm swing and countermovement affect lower extremity torque and work during vertical jumping and to gain insight into the mechanisms that enable the arm swing and countermovement to increase jump height. Five participants maximally performed two types of vertical squat jumps with (SJA) and without (SJ) an arm swing and two types of countermovement vertical jumps with (CJA) and without (CJ) an arm swing. The participants jumped from a force platform and all performances were videotaped with a high-speed video camera (200Hz). Jump heights, joint torques and work were calculated by combining kinematic and kinetic data. It was found that of the four jumping conditions, the participants jumped highest when they used an arm swing with countermovement (i.e., CJA). The increase of the countermovement jump height with an arm swing is the result of the increase of the lower extremity work. In the hip joint, the increase in torque caused by the countermovement predominantly occurred at the beginning of the propulsion phase, while the increase in torque caused by the arm swing occurred in the rest of the propulsion phase. A key finding of our study is that arm swing and countermovement have independent effects on lower extremity work, and their effects are additive in CJA to produce greater jump height.     

Unipodal performance and leg muscle mass in jumping skills among ballet dancers

We examined the vertical jump performance of each leg among 10 right-footed female ballet dancers with 1 yr. of international professional experience (quadrilles: Opera ballerinas). Their mean age was 17.5 yr. (SD=0.3). The maximal height of the unilateral jump was recorded, and muscle mass was evaluated by biphotonic absorptiometry method. Muscle mass and maximal jump height were similar for the two legs. A strong inverse relation was found between the muscle mass of the right leg (67%) and maximal jump height (r=-.81, p<.01) but not for the left leg. These results highlight a functional asymmetry and the effect of motor laterality in dance.     

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.     

An analysis of a discrete complex skill using Bernstein's stages of learning.

The purpose of this study was to provide quantitative data about changes in coordination after practicing a racquetball forehand drive serve. Novice women (N = 10) were videotaped before and after 10 min. of practicing a racquetball forehand drive serve on Day 1, and after 10-min. practice sessions on consecutive Days 2 through 5. The PEAK5 Motion Measurement System was used to evaluate the following dependent variables: (a) range of motion of the wrist, elbow, upper torso, and pelvis from backswing to ball contact: (b) racket head velocity at ball contact; and (c) coordination. Coordination was evaluated based on analysis of the angular velocity graphs of each performance to assess sequencing and timing of the segmental contributions. Shared positive contribution was assessed between adjacent 2-segment combinations: pelvis-torso and elbow-wrist. A repeated-measures analysis of variance indicated racket velocity, pelvic rotation, and upper torso rotation significantly increased over the 5 days of practice. Although participants increased their pelvic and torso ranges of motion and racket velocity, improvement in coordination was not documented.     

Modifications of neuromuscular activity and improvement in performance of a novel motor skill.

The relationship between the modifications in the myoclectrical activity after practice and the performance enhancement was examined regarding a ballistic movement of the elbow. 41 subjects practiced a novel throwing skill, which involved the throw of a ball, performing elbows flexion. Surface electromyograms of four muscles in the elbow region were analyzed, aiming at identifying the changes in the timing and the intensity of muscle activation that may account for improved performance. A repeated-measures analysis of variance identified an improvement in performance scores after practice and a significant decrease in the EMG for the agonists and the primary antagonist. Moreover, a significant increase in the delay of the activity onset in the antagonists was observed after practice. The variations of the EMG for the biceps brachii and the anconeus were significantly elated to improvement in performance. It was concluded that the modifications in the electrical activity of those to muscles were primarily responsible for the physical alterations associated with improved performance.     

Performing the vertical jump: movement adaptations for submaximal jumping

The purpose of this study was to gain insight into the kinematics and kinetics of the vertical jump when jumping for different heights and to investigate movement effectiveness as a criterion for movement control in submaximal jumping. In order to jump high a countermovement is used and large body segments are rotated, both of which consume energy which is not directly used to gain extra jump height. It was hypothesized that the energy used to reach a specified jump height is minimized by limiting the non-effective energy consumed. Standing vertical jumps attempting 100%, 75%, 50%, and 25% of maximal height were performed by a group of 10 subjects. Force and motion data were recorded simultaneously during each performance. We found that jump height increased due to increasing vertical velocity at take off. This was primarily related to an increase in countermovement amplitude. As such, flexion amplitude of the hip joint increased with jump height whereas the ankle and knee joint flexion did not. These findings revealed that for submaximal jumping a consistent strategy was used of maximizing the contribution of distal joints and minimizing the contribution of proximal joints. Taking into account the high inertia of proximal segments, the potential energy deficit due to countermovement prior to joint extension, the advantageous horizontal orientation of the foot segment during stance and the tendon lengths in distal muscles, it was concluded that movement effectiveness is a likely candidate for the driving criterion of this strategy.     

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.     

Response amendment in fencing: differences between elite and novice subjects

Reaction time (RT), movement time (MT), total response time (RMT), and accuracy of 3 elite and 3 novice fencers were studied under a dual response paradigm requiring a full lunge. Electromyographic activity (EMG) from selected arm and leg muscles was used to compare response profiles of the two groups. Although the elite subjects had slower MTs, their faster RTs resulted in significantly shorter total response times. The EMG analysis showed that in comparison to the novice subjects, onset of muscle activity was significantly faster for the elite group in five of the six muscles studied. In addition, the elite subjects showed more coherent muscle synergies and more consistent patterns of muscle coordination. Although the requirement to change targets (signalled by the arrival of a second stimulus) led to slightly more target misses for the elite group, the overall frequency was low, which indicates that it did not pose difficulty for either group. The present findings show that measures of response timing and neuromuscular coordination differentiate skill level in the fencing lunge and draw attention to practical implications for skill assessment and training.     

Optimum take-off angle in the standing long jump

The aim of this study was to identify and explain the optimum projection angle that maximises the distance achieved in a standing long jump. Five physically active males performed maximum-effort jumps over a wide range of take-off angles, and the jumps were recorded and analysed using a 2-D video analysis procedure. The total jump distance achieved was considered as the sum of three component distances (take-off, flight, and landing), and the dependence of each component distance on the take-off angle was systematically investigated. The flight distance was strongly affected by a decrease in the jumper's take-off speed with increasing take-off angle, and the take-off distance and landing distance steadily decreased with increasing take-off angle due to changes in the jumper's body configuration. The optimum take-off angle for the jumper was the angle at which the three component distances combined to produce the greatest jump distance. Although the calculated optimum take-off angles (19-27 degrees) were lower than the jumpers' preferred take-off angles (31-39 degrees), the loss in jump distance through using a sub-optimum take-off angle was relatively small.     

Tuning in to another person's action capabilities: perceiving maximal jumping-reach height from walking kinematics

Three experiments investigated the ability to perceive the maximum height to which another actor could jump to reach an object. Experiment 1 determined the accuracy of estimates for another actor's maximal reach-with-jump height and compared these estimates to estimates of the actor's standing maximal reaching height and to estimates of the perceiver's own maximal reaching and reach-with-jump height. Perception of another actor's maximum reach-with-jump height was less accurate than the other estimates, but still accurate to within 8% error. The actor's reach-with-jump height was modified in Experiment 2 by attaching weights around the actor's ankles. Perceivers, who were explicitly aware of the manipulation, adjusted their maximum reach-with-jump estimates for the actor accordingly. In Experiment 3, perceivers were not explicitly aware of the weight manipulation, but provided significantly lower maximum reach-with-jump estimates after watching the actor walk while wearing the weights compared to estimates obtained after watching the actor walk while not wearing the weights. The results suggest that the actor's walking pattern was informative about the actor's capacity to produce a different action, jumping to reach an object.     

Effect of localized muscle fatigue on vertical ground reaction forces and ankle joint motion during running

The purpose of this study was to examine the changes in the vertical ground reaction force (VGRF) and ankle joint motion during the first 50% of the stance phase of running following fatiguing exercise of either the dorsiflexors or the invertors of the foot. VGRFs, sagittal and rearfoot kinematic data were collected from 11 female recreational runners running at 2.9 m/second on a treadmill prior to and following localized muscle fatigue of either the invertors or dorsiflexors of the right foot. Loading rate of the impact peak force significantly increased following fatiguing exercise of the dorsiflexors, while the peak magnitudes of the impact and push-off forces remained unchanged. There were significant decreases in dorsiflexion at heel contact, but no significant difference in any rearfoot motion parameters tested following dorsiflexor fatigue. Following fatiguing exercise of the invertors, impact peak magnitude, push-off peak magnitude and the rate of decline of the impact peak force significantly decreased; there was no change in the loading rate of the impact peak force. Invertor fatigue also resulted in a less inverted foot position at heel contact, but there were no significant differences in any other kinematic parameters tested. The results demonstrate that localized muscle fatigue of either the invertors or dorsiflexors can have a significant effect on the loading rates, peak magnitudes and ankle joint motion seen during running. These changes, due to localized muscle fatigue, may play a role in many common lower extremity running injuries.     

Effect of Short-Term Training on Reaching Behavior in Infants: A Randomized Controlled Clinical Trial

The purpose of this study was to test the effect of short-term training on reaching behavior in infants at the onset of reaching. The study was a single-blind, parallel group design, randomized controlled clinical trial. Thirty healthy infants were randomly assigned to a social control group (n = 15) or a reaching training group (n = 15). Infants began the study up to 3 days after the onset of reaching and were assessed three times across 2 days: pretraining (before training), posttraining 1 (after 1 session of training), and posttraining 2 (after 3 sessions of training). The reaching training group received 3 sessions of training by a physical therapist while the control group received a similar amount of time sitting in the therapist's lap. The data were analyzed using repeated-measures analyses of variance, and independent-samples tests with Bonferroni adjustments. Short-term training resulted in increased frequency of object contacts, shorter and smoother reaches, and improved hand positioning. The few short training sessions likely provided opportunities for infants to explore and learn to select movements from their existing movement repertoire. These results demonstrate that adaptive changes in infants' novel behaviors can emerge rapidly, and highlight the need for increased understanding of how to most effectively time early interventions.     

Cognitive constraint on the ‘automatic pilot’ for the hand: Movement intention influences the hand’s susceptibility to involuntary online corrections

Research suggests that the reaching hand automatically deviates toward a target that changes location (jumps) during the reach. In the current study, we investigated whether movement intention can influence the target jump’s impact on the hand. We compared the degree of trajectory deviation to a jumped target under three instruction conditions: (1) GO, in which participants were told to go to the target if it jumped, (2) STOP, in which participants were told to immediately stop their movement if the target jumped, and (3) IGNORE, in which participants were told to ignore the target if it jumped and to continue to its initial location. We observed a reduced response to the jump in the IGNORE condition relative to the other conditions, suggesting that the response to the jump is contingent on the jump being a task-relevant event.     

Evaluating movement performance: What you see isn’t necessarily what you get

With the goal of reducing injury and enhancing performance, movement screening tools score an individual’s movements against a standard and because it is a predictor of injury symmetry is often included in the score. Movement quality screening tools only consider kinematic asymmetry, which may underestimate the degree of asymmetry present during movement. Consider joint forces: if these forces are atypical, additional stress is created and control is reduced, which can lead to injury if the asymmetry is not addressed. The purpose of this study is to investigate movement symmetry in the kinematic, kinetic and muscle activity components of movement during a parallel squat.Thirty-four healthy individuals completed five body-weight, parallel squats. A motion capture system, two portable force plates, and electromyography (EMG) sensors recorded the squat motion, ground reaction forces and muscle activity. The variables of interest were the joint angles, joint moments, and EMG waveforms. Cross-correlations and normalized root-mean-square values were calculated for the left and right ankles, knees, and hips for each variable. A repeated-measures analysis of variance (ANOVA) tested for differences in symmetry (cross-correlation and nRMS) between the kinematic, kinetic, and muscle activity components at the ankle, knee, and hip during the squat.At all joints the kinematic component had the highest degree of symmetry, and the kinetic and muscle activity components showed poorer symmetry, with the muscle activity component being the least symmetric. The differences in symmetry between movement components suggests that movement performance evaluations should not rely exclusively on kinematics and observation to identify potential movement faults.     

Benefits of Blocked Over Serial Feedback on Complex Motor Skill Learning

The effects of blocked versus serial feedback (FB) on the learning of a complex motor skill-the production of slalom-type movements on a ski-simulator-were examined. FB was given about force onset, which is considered to be a measure of movement efficiency; relatively late force onsets characterize expert performance. One group of participants (blocked FB; n = 10) received FB about 1 foot per day; for example, for the right foot on Days 1 and 3 and for the left foot on Days 2 and 4. For another group (serial FB; n = 10), the foot about which FB was received was switched on consecutive trials on each of 4 days of practice. Learning was assessed on no-FB trials at the beginning of Days 2, 3, and 4, and on Day 5. Even though there were no differences between groups in force onset, the blocked FB group produced significantly larger movement amplitudes and higher movement frequencies than the serial FB group on the retention test on Day 5. Thus, contrary to the learning of more simple skills (e.g., T. D. Lee & H. Carnahan, 1990), constantly changing the movement component that FB is provided about did not seem to be beneficial for the learning of more complex skills. The findings add to the increasing evidence showing that practice variables that have been shown to enhance the learning of simple skills can actually be detrimental to the learning of complex skills.     

Laboratory strength measures of talented and less talented Greek children ages 9 to 10 years

The purpose was twofold: (1) to assess whether laboratory tests can distinguish talented groups and less talented groups of children identified by their total scores in a battery of field tests and (2) to evaluate whether scores in field and laboratory tests are correlated. 36 children (ages 9 to 10 years) were divided into groups of higher and lower total scores on standing long jump, medicine ball throw, and sprint. Both groups were tested for maximum isometric force, force produced at the initial 100 msec., reactive force index, drop jump height, squat jump height, and maximum pedaling rate. Analysis showed the talented group had significantly (p < or = .05) higher scores on maximum isometric force, force produced in the initial 100 msec., and drop jump height than less talented children. Moderate to high correlations were found among scores for field performance tests with maximum pedaling rate. In conclusion, the laboratory tests distinguished the talented and less talented children in maximal isometric force, the force produced at the initial 100 msec., the reactive force index, and the drop jump height.     

Simple rotary motion is integrated across fixations

Participants were shown a line rotating at a constant angular velocity and were asked to judge whether motion was continuous or whether the line jumped (i.e., moved either forward or backward in the rotary cycle). In two experiments, the participants were significantly better than chance in detecting these jumps in simple rotary motion even when the jumps occurred during a saccade. Moreover, in Experiment 2, when the jump occurred during a saccade followed by a masking flash, perception of the jump was at least as good as when it occurred during a fixation followed by a masking flash. These results complement and extend the findings of Verfaillie and co-workers, who found that perceptions of some changes in biological motion were as good across fixations as when they occurred during a fixation. These findings are in contrast to the common finding, in the reading literature, that people are consciously "blind" to many changes in the text and to those, in the scene perception literature, in which detection of static changes across fixations is above chance but plausibly well below the level that would be expected if the change occurred during a fixation.     

Mechanical output about the ankle in countermovement jumps and jumps with extended knee

In this study the mechanical output (e.g., force, contraction velocity, instantaneous power) about the ankle was measured during a jump with and without occurrence of transportation of power and pre-stretch potentiation. To examine this, a model of the m. triceps surae was used. Eleven subjects performed a maximal one-legged countermovement jump (CMJ) and a maximal one-legged jump with extended knee (EKJ). Ground reaction forces, cinematographic data and electromyograms of m. triceps surae were recorded. The power output, defined as the product of moment and angular velocity, and work done about the ankle were higher during CMJ (1404 W, 130 J) than during EKJ (852 W, 76 J). The peak moments were the same during both jumps. The model of the m. triceps surae showed that the power delivered by m. triceps surae was higher during CMJ than during EKJ, as a result of catapult-action of m. gastrocnemius tendon. The difference in work done is explained, in addition to transportation of energy, by a greater contraction range of m. soleus during CMJ. There is no reason to assume that pre-stretch potentiation plays a role in the difference in mechanical output. The results show that the mechanical output of muscles in complex movements is strongly dependent on the dynamics of the movement, and not only on its contractile capacity.     

Incremental exercise, plasma concentrations of catecholamines, reaction time, and motor time during performance of a noncompatible choice response time task

The primary purpose was to examine the effect of incremental exercise on a noncompatible response time task. Participants (N=9) undertook a 4-choice noncompatible response time task under 3 conditions, following rest and during exercise at 70% and 100% of their maximum power output. Reaction and movement times were the dependent variables. Maximum power output had been previously established on an incremental test to exhaustion. A repeated-measures multivariate analysis of variance yielded a significant effect of exercise intensity on the task, observation of the separate univariate repeated-measures analyses of variance showed that only movement time was significantly affected. Post hoc Tukey tests indicated movement time during maximal intensity exercise was significantly faster than in the other two conditions. The secondary purpose of the study was to assess whether increases in plasma concentrations of adrenaline and nor-adrenaline during exercise and power output would act as predictor variables of reaction and movement times during exercise. Catecholamine concentrations were based on venous blood samples taken during the maximum power output test. None of the variables were significant predictors of reaction time. Only power output was a significant predictor of movement time (R2 = .24). There was little support for the notion that peripheral concentrations of catecholamines directly induce a central nervous system response.     

Spiroergometric studies in diseases of the muscles

37 patients with muscle disease (23 myopathies and 14 neurogenic muscle diseases) were studied by spiroergometric investigations. The multivariate analysis of variance (MA-NOVA) and linear discriminant analyses indicated the diagnostic effectiveness of the maximal work capacity/maximal cardiac frequency ratio. The sensitivity was found to be 0.81 and the specificity was found to be 0.43.