Angular velocity around the longitudinal axis in combination with head movements of springboard divers during twisted somersaults.

The ability of springboard divers to perform and control difficult elements with multiple twisted somersaults before entering the water is of great interest for coaches and researchers. In order to produce twists within somersaults, divers use both 'contact' and 'aerial' techniques. After completing body axes rotations, head movements seem to be important, as they enable visual information in the air. The current study aims at investigating angular velocities around the longitudinal axis in combination with head movements of 13 springboard divers during twisted somersaults. Divers performed forward and backward somersaults with different numbers of half twists. The results revealed maximum longitudinal axis angular velocities between 500°/s and 1300°/s. Moreover, results showed that the use of contact technique was greater in twisted somersaults with backward approaches, and thus higher angular velocities could be achieved. While finishing the twists, head movements in the opposite direction to the longitudinal axis rotation occurred, which allow divers to orient themselves. Twist speeds influenced athletes' head movements to have greater angles and greater rotational velocities. Therefore, it is concluded that fast head movements are necessary in difficult twisted dives to allow orientation in the short phase between finishing the twist and entering the water surface.

Optimization Reduces Knee-Joint Forces During Walking and Squatting: Validating the Inverse Dynamics Approach for Full Body Movements on Instrumented Knee Prostheses.

Because of the redundancy of our motor system, movements can be performed in many ways. While multiple motor control strategies can all lead to the desired behavior, they result in different joint and muscle forces. This creates opportunities to explore this redundancy, for example, for pain avoidance or reducing the risk of further injury. To assess the effect of different motor control optimization strategies, a direct measurement of muscle and joint forces is desirable, but problematic for medical and ethical reasons. Computational modeling might provide a solution by calculating approximations of these forces. In this study, we used a full-body computational musculoskeletal model to (a) predict forces measured in knee prostheses during walking and squatting and (b) study the effect of different motor control strategies (i.e., minimizing joint force vs. muscle activation) on the joint load and prediction error. We found that musculoskeletal models can accurately predict knee joint forces with a root mean squared error of <0.5 body weight (BW) in the superior direction and about 0.1 BW in the medial and anterior directions. Generally, minimization of joint forces produced the best predictions. Furthermore, minimizing muscle activation resulted in maximum knee forces of about 4 BW for walking and 2.5 BW for squatting. Minimizing joint forces resulted in maximum knee forces of 2.25 BW and 2.12 BW, that is, a reduction of 44% and 15%, respectively. Thus, changing the muscular coordination strategy can strongly affect knee joint forces. Patients with a knee prosthesis may adapt their neuromuscular activation to reduce joint forces during locomotion.

Planning Catching Movements: Advantages of Expertise, Visibility and Self-Throwing.

In a ball catching task, the catcher guides their hand to the ball's future trajectory. The hand may start to move even before the exact position is known, and the interceptive movement may be corrected online. Using a recent method for detecting the phases of catching movements we investigate how juggling experience, self-throwing, and delayed visibility of the ball, influence the timing of the hand's trajectory. Specifically, we analyze the time from which the goal position of the movement is known, i.e., the time from which the movement becomes smooth. Seventeen jugglers and twenty controls caught ten balls per each of eight conditions. The results indicate that experts' catching movements acquire the smooth nature of goal-directed movements earlier than novices catching movements do.

Single limb dynamics of jumping turns in dogs.

Maneuverability is of paramount importance for many animals, e.g., in predator-prey interactions. Despite this fact, quadrupedal limb behavior in complicated maneuvers like simultaneous jumping and turning are not well studied. Twenty adult sport Border Collies were recorded while jumping over an obstacle and simultaneously turning. Kinetic and kinematic data were captured in synchrony using eight force plates and sixteen infrared cameras. These dogs were familiar with the task through regular participation in the dog sport agility. The experiments revealed that during landing, higher lateral forces acting in the forelimbs compared to hindlimbs. During landing, the outer limbs produced about twice the inner limbs' force in both vertical and lateral directions, showing their dominant contribution to turning. Advanced dogs showed significantly higher lateral impulse and stronger inner-outer limb asymmetry regarding lateral impulses than beginner dogs, leading to significantly stronger turning for advanced dogs. Somewhat unexpected, skill effects rarely explained global limb dynamics, indicating that landing a turn jump is a constrained motion. Constrained motions leave little space for individual techniques suggesting that the results can be generalized to quadrupedal turn jumps in other animals.

Multimodal Sensorimotor Integration of Visual and Kinaesthetic Afferents Modulates Motor Circuits in Humans.

Optimal motor control requires the effective integration of multi-modal information. Visual information of movement performed by others even enhances potentials in the upper motor neurons through the mirror-neuron system. On the other hand, it is known that motor control is intimately associated with afferent proprioceptive information. Kinaesthetic information is also generated by passive, external-driven movements. In the context of sensory integration, it is an important question how such passive kinaesthetic information and visually perceived movements are integrated. We studied the effects of visual and kinaesthetic information in combination, as well as isolated, on sensorimotor integration, compared to a control condition. For this, we measured the change in the excitability of the motor cortex (M1) using low-intensity Transcranial magnetic stimulation (TMS). We hypothesised that both visual motoneurons and kinaesthetic motoneurons enhance the excitability of motor responses. We found that passive wrist movements increase the motor excitability, suggesting that kinaesthetic motoneurons do exist. The kinaesthetic influence on the motor threshold was even stronger than the visual information. Moreover, the simultaneous visual and passive kinaesthetic information increased the cortical excitability more than each of them independently. Thus, for the first time, we found evidence for the integration of passive kinaesthetic- and visual-sensory stimuli.

Gaze, head and eye movements during somersaults with full twists.

Somersaults with or without twists are the most important elements in sports such as gymnastics or trampolining. Moreover, to perform elements with the highest possible difficulty gymnasts should show good form and execution during the flight phase. In order to ensure perfect body control and a safe landing, gaze behavior has been proven to be crucial for athletes to orientate in the air. As eye movement and head movement are closely coordinated, both must be examined while investigating gaze behavior. The aim of the current study is to analyze athletes' head motion and gaze behavior during somersaults with full twists. 15 skilled trampoline gymnasts performed back straight somersaults with a full twist (back full) on the trampoline. Eye movement and head movement were recorded using a portable eye-tracking device and a motion capture suit. The results indicate that gymnasts use the trampoline bed as a fixation point for orientation and control the back full, whereas the fixation onsets for athletes of a better performance class occur significantly later. A strong coordination between gymnasts' eye movement and head movement could be determined: stabilizing the gaze during the fixation period, the eyes move in combination with the head against the twisted somersault direction to counteract the whole body rotation. Although no significant differences could be found between the performance classes with regard to the maximum axial head rotations and maximum head extensions, there seems to be a trend that less skilled gymnasts need orientation as early as possible resulting in greater head rotation angles but a poorer execution.

Gaze behavior of trampoline gymnasts during a back tuck somersault.

In trampolining, gymnasts perform a variety of rotational jumping elements and have to demonstrate perfect control of the body during the flying phase. The performance of a somersault should include an opening phase, i.e. the legs are fully extended pointing vertically at 180° called "kick-out". As previous studies have shown, gaze behavior is essential for the controlling during the flight phase and to prepare for a perfect landing. Gymnasts supposedly use the trampoline bed as orientation and differences in gaze behavior can be expected, depending on how a somersault is performed. The present study investigates the gaze behavior of gymnasts during a back tuck somersault on the trampoline. Eleven experienced trampoline gymnasts performed back tuck somersaults with and without a kick-out while wearing a light weight portable eye-tracking device. All subjects fixated their gaze on a specific point at the trampoline bed and thus used visual information to prepare for landing. During the period of fixation, gymnasts' eyes moved continuously downwards to counteract the backwards head movement. The point of fixation differed between each somersault. Apparently, the fixation position depended on the gymnast's landing position in the bed. Performing a somersault with a kick-out allows gymnasts to orient themselves earlier and thus prepare sooner for landing. Unexpectedly, gymnasts of a higher performance class fixated the bed later compared to less experienced athletes. Supposedly, gymnasts of a better class can allow themselves to fixate later in order to optimize the form and execution of a somersault.

Limb dynamics in agility jumps of beginner and advanced dogs.

A considerable body of work has examined the dynamics of different dog gaits, but there are no studies that have focused on limb dynamics in jumping. Jumping is an essential part of dog agility, a dog sport in which handlers direct their dogs through an obstacle course in a limited time. We hypothesized that limb parameters like limb length and stiffness indicate the skill level of dogs. We analyzed global limb parameters in jumping for 10 advanced and 10 beginner dogs. In experiments, we collected 3D kinematics and ground reaction forces during dog jumping at high forward speeds. Our results revealed general strategies of limb control in jumping and highlighted differences between advanced and beginner dogs. In take-off, the spatially leading forelimb was 75% (P<0.001) stiffer than the trailing forelimb. In landing, the trailing forelimb was 14% stiffer (P<0.001) than the leading forelimb. This indicates a strut-like action of the forelimbs to achieve jumping height in take-off and to transfer vertical velocity into horizontal velocity in landing (with switching roles of the forelimbs). During landing, the more (24%) compliant forelimbs of beginner dogs (P=0.005) resulted in 17% (P=0.017) higher limb compression during the stance phase. This was associated with a larger amount of eccentric muscle contraction, which might in turn explain the soft tissue injuries that frequently occur in the shoulder region of beginner dogs. For all limbs, limb length at toe-off was greater for advanced dogs. Hence, limb length and stiffness might be used as objective measures of skill.

Opposite asymmetries of face and trunk and of kissing and hugging, as predicted by the axial twist hypothesis.

The contralateral organization of the forebrain and the crossing of the optic nerves in the optic chiasm represent a long-standing conundrum. According to the Axial Twist Hypothesis (ATH) the rostral head and the rest of the body are twisted with respect to each other to form a left-handed half turn. This twist is the result, mainly, of asymmetric, twisted growth in the early embryo. Evolutionary selection tends to restore bilateral symmetry. Since selective pressure will decrease as the organism approaches symmetry, we expected a small control error in the form of a small, residual right-handed twist. We found that the mouth-eyes-nose (rostral head) region shows a left-offset with respect to the ears (posterior head) by up to 0.8° (P < 0.01, Bonferroni-corrected). Moreover, this systematic aurofacial asymmetry was larger in young children (on average up to 3°) and reduced with age. Finally, we predicted and found a right-sided bias for hugging (78%) and a left-sided bias for kissing (69%). Thus, all predictions were confirmed by the data. These results are all in support of the ATH, whereas the pattern of results is not (or only partly) explained by existing alternative theories. As of the present results, the ATH is the first theory for the contralateral forebrain and the optic chiasm whose predictions have been tested empirically. We conclude that humans (and all other vertebrates) are fundamentally asymmetric, both in their anatomy and their behavior. This supports the thesis that the approximate bilateral symmetry of vertebrates is a secondary feature, despite their being bilaterians.

Neck muscle responses of driver and front seat passenger during frontal-oblique collisions.

BACKGROUND: Low-velocity motor vehicle crashes often lead to severe and chronic neck disorders also referred to as whiplash-associated disorders (WAD). The etiology of WAD is still not fully understood. Many studies using a real or simulated collision scenario have focused on rear-end collisions, whereas the kinematics and muscular responses during frontal-oblique collisions have hardly been investigated. In particular for rear-end collisions, drivers were shown to have a higher WAD risk than front seat passengers. Yet, independently from the impact direction, neither the muscular nor the kinematic responses of drivers and front seat passengers have been compared to date, although some findings indicate that the neck muscles have the potential to alter the head and neck kinematics, and that the level of neck muscle activity during impact may be relevant for the emergence of WAD. OBJECTIVE: In this study, we quantitatively examined the subjects' neck muscle activity during low-velocity left-frontal-oblique impacts to gain further insights into the neuromuscular mechanism underlying whiplash-like perturbations that may lead to WAD. METHODS: In a within-subject study design, we varied several impact parameters to investigate their effect on neck muscle response amplitude and delay. Fifty-two subjects experienced at least ten collisions while controlling for the following parameters: change in velocity Δv (3 / 6 km/h), seating position (driver / front seat passenger), and deliberate pre-tension of the musculature (tense / relaxed) to account for a potential difference between an expected and an unexpected crash. Ten of the 52 subjects additionally ran the same experimental conditions as above, but without wearing a safety belt. FINDINGS: There were significant main effects of Δv and muscle pre-tension on the reflex amplitude but not of seating position. As for the reflex delay, there was a significant main effect of muscle pre-tension, but neither of Δv nor of seating position. Moreover, neither the safety belt nor its asymmetrical orientation had an influence on the reflexive responses of the occupants. CONCLUSION: In summary, we did not find any significant differences in the reflex amplitude and delay of the neck musculature between drivers and front seat passengers. We therefore concluded that an increased risk of the driver sustaining WAD in frontal-oblique collisions, if it exists, cannot be due to differences in the reflexive responses.

Analyzing the kinematics of hand movements in catching tasks-An online correction analysis of movement toward the target's trajectory.

Free, 3-D interceptive movements are difficult to visualize and quantify. For ball catching, the endpoint of a movement can be anywhere along the target's trajectory. Furthermore, the hand may already have begun to move before the subject has estimated the target's trajectory, and the subject may alter the targeted position during the initial part of the movement. We introduce a method to deal with these difficulties and to quantify three movement phases involved in catching: the initial, non-goal-directed phase; the goal-directed phase, which is smoothly directed toward the target's trajectory; and the final, interception phase. Therefore, the 3-D movement of the hand was decomposed into a component toward the target's trajectory (the minimal distance of the hand to the target's parabolic [MDHP] trajectory) and a component along this trajectory. To identify the goal-directed phase of the MDHP trajectory, we employed the empirical finding that goal-directed trajectories are minimally jerky. The second component, along the target's trajectory, was used to analyze the interaction of the hand with the ball. The method was applied to two conditions of a ball-catching task. In the manipulated condition, the initial part of the ball's flight was occluded, so the visibility of the ball was postponed. As expected, the onset of the smooth part of the movement shifted to a later time. This method can be used to quantify anticipatory behavior in interceptive tasks, allowing researchers to gain new insights into movement planning toward the target's trajectory.

Vision adds to haptics when dyads perform a whole-body joint balance task.

When two or more people aim to produce joint action outcomes they need to coordinate their individual actions in space and time. Successful joint action performance has been reported to depend, among others, on visual and somatosensory information provided to the joint actors. This study investigated whether and how the systematic manipulation of visual information modulates real-time joint action when dyads performed a whole-body joint balance task. To this end, we introduced the Joint Action Board (JAB) where partners guided a ball through a maze towards a virtual hole by jointly shifting their weight on the board under three visual conditions: (1) the Follower had neither visual access to the Leader nor to the maze; (2) the Follower had no visual access to the maze but to the Leader; (3) the Follower had full visual access to both the Leader and to the maze. Joint action performance was measured as completion time of the maze task; interpersonal coordination was examined by means of kinematic analyses of both partners' motor behaviour. We predicted that systematically adding visual to the available haptic information would result in a significant increase in joint performance and that Leaders would change their coordination behavior depending on these conditions. Results showed that adding visual information to haptics led to an increase in joint action performance in a Leader-Follower relationship in a joint balance task. In addition, interpersonal coordination behavior (i.e. sway range of motion, time-lag between partner's bodies etc.) changed dependent on the provided visual information between partners in the jointly executed task.

Increased Throwing Accuracy Improves Children's Catching Performance in a Ball-Catching Task from the Movement Assessment Battery (MABC-2).

The Movement Assessment Battery for Children (MABC-2) is a functional test for identifying deficits in the motor performance of children. The test contains a ball-catching task that requires the children to catch a self-thrown ball with one hand. As the task can be executed with a variety of different catching strategies, it is assumed that the task success can also vary considerably. Even though it is not clear, whether the performance merely depends on the catching skills or also to some extent on the throwing skills, the MABC-2 takes into account only the movement outcome. Therefore, the purpose of the current study was to examine (1) to what extent the throwing accuracy has an effect on the children's catching performance and (2) to what extent the throwing accuracy influences their choice of catching strategy. In line with the test manual, the children's catching performance was quantified on basis of the number of correctly caught balls. The throwing accuracy and the catching strategy were quantified by applying a kinematic analysis on the ball's trajectory and the hand movements. Based on linear regression analyses, we then investigated the relation between throwing accuracy, catching performance and catching strategy. The results show that an increased throwing accuracy is significantly correlated with an increased catching performance. Moreover, a higher throwing accuracy is significantly correlated with a longer duration of the hand on the ball's parabola, which indicates that throwing the ball more accurately could enable the children to effectively reduce the requirements on temporal precision. As the children's catching performance and their choice of catching strategy in the ball-catching task of the MABC-2 are substantially determined by their throwing accuracy, the test evaluation should not be based on the movement outcome alone, but should also take into account the children's throwing performance. Our findings could be of particular value for the development of simple but informative catching assessments, and may provide additional insights into the causes of performance deficits in ball catching.

Motor-Evoked Potentials in the Lower Back Are Modulated by Visual Perception of Lifted Weight.

Facilitation of the primary motor cortex (M1) during the mere observation of an action is highly congruent with the observed action itself. This congruency comprises several features of the executed action such as somatotopy and temporal coding. Studies using reach-grasp-lift paradigms showed that the muscle-specific facilitation of the observer's motor system reflects the degree of grip force exerted in an observed hand action. The weight judgment of a lifted object during action observation is an easy task which is the case for hand actions as well as for lifting boxes from the ground. Here we investigated whether the cortical representation in M1 for lumbar back muscles is modulated due to the observation of a whole-body lifting movement as it was shown for hand action. We used transcranial magnetic stimulation (TMS) to measure the corticospinal excitability of the m. erector spinae (ES) while subjects visually observed the recorded sequences of a person lifting boxes of different weights from the floor. Consistent with the results regarding hand action the present study reveals a differential modulation of corticospinal excitability despite the relatively small M1 representation of the back also for lifting actions that mainly involve the lower back musculature.

An Internal Focus Leads to Longer Quiet Eye Durations in Novice Dart Players.

While the benefits of both an external focus of attention (FOA) and of a longer quiet eye (QE) duration have been well researched in a wide range of sporting activities, little is known about the interaction of these two phenomena and how a potential interaction might influence performance. It was this study's aim to investigate the interaction and potential effect on performance by using typical FOA instructions in a dart throwing task and examining both the QE and performance outcome. The results replicate neither the benefit of an external FOA nor the benefit of a longer QE duration. However, an interaction was observed, as QE was prolonged by an earlier onset and later offset in the internal focus condition only. As the typical effect of a performance benefit due to an external focus could not be replicated, the interaction must be interpreted with caution. The results are discussed and interpreted in light of the inhibition hypothesis and possible avenues for future research are suggested.

Comment on "Cortical folding scales universally with surface area and thickness, not number of neurons".

The cerebrum of large mammals is convoluted, whereas that of small mammals is smooth. Mota and Herculano-Houzel (Reports, 3 July 2015, p. 74) inspired a model on an old theory that proposed a fractal geometry. I show that their model reduces to the product of gray-matter proportion times the folding index. This proportional relation describes the available data even better than the fractal model.

Perception of biological motion from size-invariant body representations.

The visual recognition of action is one of the socially most important and computationally demanding capacities of the human visual system. It combines visual shape recognition with complex non-rigid motion perception. Action presented as a point-light animation is a striking visual experience for anyone who sees it for the first time. Information about the shape and posture of the human body is sparse in point-light animations, but it is essential for action recognition. In the posturo-temporal filter model of biological motion perception posture information is picked up by visual neurons tuned to the form of the human body before body motion is calculated. We tested whether point-light stimuli are processed through posture recognition of the human body form by using a typical feature of form recognition, namely size invariance. We constructed a point-light stimulus that can only be perceived through a size-invariant mechanism. This stimulus changes rapidly in size from one image to the next. It thus disrupts continuity of early visuo-spatial properties but maintains continuity of the body posture representation. Despite this massive manipulation at the visuo-spatial level, size-changing point-light figures are spontaneously recognized by naive observers, and support discrimination of human body motion.

Decussation as an axial twist: A comment on Kinsbourne (2013).

One of the great mysteries of the brain, which has puzzled all-time students of brain form and function, is the contralateral organization of the forebrain and the crossings of its major afferent and efferent connections. As a novel explanation, two recent studies have proposed that the rostral part of the head, including the forebrain, is rotated by 180° with respect to the rest of the body (de Lussanet and Osse, 2012; Kinsbourne, 2013). Kinsbourne proposes one 180° turn while we consider the 180° being the result of two 90° turns in opposite directions. We discuss the similarities and differences between the two hypotheses.

Observing a movement correction during walking affects evoked responses but not unperturbed walking.

Seeing an action activates neurons in the premotor, motor, and somatosensory cortex. Since a significant fraction of these pyramidal neurons project to the spinal motor circuits, a central question is why we do not automatically perform the actions that we see. Indeed, seeing an action increases both cortical and spinal excitability of consistent motor patterns that correspond to the observed ones. Thus, it is believed that such imitative motor patterns are either suppressed or remain at a sub-threshold level. This would predict, however, that seeing someone make a corrective movement while one is actively involved in the same action should either suppress evoked responses or suppress or modulate the action itself. Here we tested this prediction, and found that seeing someone occasionally stepping over an obstacle while walking on a treadmill did not affect the normal walking pattern at all. However, cutaneously evoked reflexes in the anterior tibial and soleus muscles were modulated as if the subject was stepping over an obstacle. This result thus indicates that spinal activation was not suppressed and was neither at sub-threshold motor resonance. Rather, the spinal modulation from observed stepping reflects an adaptive mechanism for regulating predictive control mechanisms. We conclude that spinal excitability during action observation is not an adverse side-effect of action understanding but reflects adaptive and predictive motor control.

A computational model unifies apparently contradictory findings concerning phantom pain.

Amputation often leads to painful phantom sensations, whose pathogenesis is still unclear. Supported by experimental findings, an explanatory model has been proposed that identifies maladaptive reorganization of the primary somatosensory cortex (S1) as a cause of phantom pain. However, it was recently found that BOLD activity during voluntary movements of the phantom positively correlates with phantom pain rating, giving rise to a model of persistent representation. In the present study, we develop a physiologically realistic, computational model to resolve the conflicting findings. Simulations yielded that both the amount of reorganization and the level of cortical activity during phantom movements were enhanced in a scenario with strong phantom pain as compared to a scenario with weak phantom pain. These results suggest that phantom pain, maladaptive reorganization, and persistent representation may all be caused by the same underlying mechanism, which is driven by an abnormally enhanced spontaneous activity of deafferented nociceptive channels.