PERFORMANCE DETERMINING FACTORS IN ELITE SPRINTERS DURING SPRINT START AND TWO FOLLOWING SUCCESSIVE SUPPORTS

Sprint start out of the blocks and successive acceleration are technically challenging as the athlete goes from a bended to a forward leaning position. Therefore, the body center of mass (COM) has to be accelerated forward and upwards. Optimal sprinting performance relies on attaining maximal forward acceleration. However, adequate vertical acceleration must be generated to reach sufficient height to prepare for the following step (Weyand, 2000). Horizontal acceleration is mainly determined by the horizontal ground reaction force that will affect sprint velocity and therefore final sprint performance (Mero, 1988). Kinematics and kinetics of the start action and maximal sprinting were intensively studied; however little is known on the transition from the set position to the running position during the first two strides. This study aims to identify the factors in the start action as well as in the first and second contact after block clearance that determine sprinting performance in terms of speed and acceleration

Sprint start kinetics of amputee and non-amputee sprinters

The purpose of this study was to explore the relationship between the forces applied to the starting blocks and the start performances (SPs) of amputee sprinters (ASs) and non-amputee sprinters (NASs). SPs of 154 male and female NASs (100-m personal records [PRs], 9.58–14.00 s) and 7 male ASs (3 unilateral above knee, 3 unilateral below knee, 1 bilateral below knee; 100 m PRs, 11.70–12.70 s) with running specific prostheses (RSPs) were analysed during full-effort sprint starts using instrumented starting blocks that measured the applied forces in 3D. Using the NAS dataset and a combination of factor analysis and multiple regression techniques, we explored the relationship between force characteristics and SP (quantified by normalized average horizontal block power). Start kinetics were subsequently compared between ASs and NASs who were matched based on their absolute 100 m PR and their 100 m PR relative to the world record in their starting class. In NASs, 86% of the variance in SP was shared with five latent factors on which measured parameters related to force application to the rear and front blocks and the respective push-off directions in the sagittal plane of motion were loaded. Mediolateral force application had little influence on SP. The SP of ASs was significantly reduced compared to that of NASs matched on the basis of relative 100-m PR (−33.8%; d = 2.11, p < 0.001), while a non-significant performance reduction was observed when absolute 100-m PRs were used (−17.7%; d = 0.79, p = 0.09). These results are at least partially explained by the fact that force application to the rear block was clearly impaired in the affected legs of ASs

Testing Multiple Coordination Constraints with a Novel Bimanual Visuomotor Task

The acquisition of a new bimanual skill depends on several motor coordination constraints. To date, coordination constraints have often been tested relatively independently of one another, particularly with respect to isofrequency and multifrequency rhythms. Here, we used a new paradigm to test the interaction of multiple coordination constraints. Coordination constraints that were tested included temporal complexity, directionality, muscle grouping, and hand dominance. Twenty-two healthy young adults performed a bimanual dial rotation task that required left and right hand coordination to track a moving target on a computer monitor. Two groups were compared, either with or without four days of practice with augmented visual feedback. Four directional patterns were tested such that both hands moved either rightward (clockwise), leftward (counterclockwise), inward or outward relative to each other. Seven frequency ratios (3∶1, 2∶1, 3∶2, 1∶1, 2∶3. 1∶2, 1∶3) between the left and right hand were introduced. As expected, isofrequency patterns (1∶1) were performed more successfully than multifrequency patterns (non 1∶1). In addition, performance was more accurate when participants were required to move faster with the dominant right hand (1∶3, 1∶2 and 2∶3) than with the non-dominant left hand (3∶1, 2∶1, 3∶2). Interestingly, performance deteriorated as the relative angular velocity between the two hands increased, regardless of whether the required frequency ratio was an integer or non-integer. This contrasted with previous finger tapping research where the integer ratios generally led to less error than the non-integer ratios. We suggest that this is due to the different movement topologies that are required of each paradigm. Overall, we found that this visuomotor task was useful for testing the interaction of multiple coordination constraints as well as the release from these constraints with practice in the presence of augmented visual feedback

Excitability of the Motor Cortex Ipsilateral to the Moving Body Side Depends on Spatio-Temporal Task Complexity and Hemispheric Specialization

Unilateral movements are mainly controlled by the contralateral hemisphere, even though the primary motor cortex ipsilateral (M1ipsi) to the moving body side can undergo task-related changes of activity as well. Here we used transcranial magnetic stimulation (TMS) to investigate whether representations of the wrist flexor (FCR) and extensor (ECR) in M1ipsi would be modulated when unilateral rhythmical wrist movements were executed in isolation or in the context of a simple or difficult hand-foot coordination pattern, and whether this modulation would differ for the left versus right hemisphere. We found that M1ipsi facilitation of the resting ECR and FCR mirrored the activation of the moving wrist such that facilitation was higher when the homologous muscle was activated during the cyclical movement. We showed that this ipsilateral facilitation increased significantly when the wrist movements were performed in the context of demanding hand-foot coordination tasks whereas foot movements alone influenced the hand representation of M1ipsi only slightly. Our data revealed a clear hemispheric asymmetry such that MEP responses were significantly larger when elicited in the left M1ipsi than in the right. In experiment 2, we tested whether the modulations of M1ipsi facilitation, caused by performing different coordination tasks with the left versus right body sides, could be explained by changes in short intracortical inhibition (SICI). We found that SICI was increasingly reduced for a complex coordination pattern as compared to rest, but only in the right M1ipsi. We argue that our results might reflect the stronger involvement of the left versus right hemisphere in performing demanding motor tasks

Association of Southeast Asian Nations, People's Republic of China, and India Growth and the Rest of the World: The Role of Trade

This paper explores the impact of past and future growth in the Association of Southeast Asian Nations (ASEAN)1 Since the mid-1990s, ACI growth has improved the non-oil terms of trade of the developed countries. There have also been strong complementarities between ACI suppliers of intermediate inputs and PRC exports. More developed Asian countries have benefited from PRC capital goods demand. ACI growth has, however, put competitive pressures on other less-developed manufacturing exporters, worsening their terms of trade and constraining their pricing ability. ACI growth has been especially beneficial for oil and minerals commodity producers. On the other hand, net food importers and oil importing countries have been adversely affected by high import costs. , the People's Republic of China (PRC), and India - here referred to as the ACI countries - on aggregate welfare, relative wages, and global emissions in the rest of the world. It outlines several analytical frameworks, considers effects over the past decade and, based on consensus forecasts, the implications of that growth for the rest of the world in the decades to come. Future ACI growth provides opportunities and challenges for the rest of the world. For developed countries the opportunities are for selling high-end services and capital and consumer goods in the ACI markets and enjoying the benefits from intra-industry trade; the challenges will come from increased head-to-head competition in manufactured goods and services that should become more intense in future decades. For medium-income producers currently at between 30% and 60% of US levels, there will be a tougher tradeoff between more intensive competition with the PRC and serving the growing middle classes in ACI countries. For poorer countries, there will greater opportunities for becoming part of global supply chains in manufactured exports. Standard frameworks that assume internal factor mobility suggest continuing pressures for wage inequality in developed countries. But these hinge on the assumption that the ACI and developed countries will continue to produce similar products and that the ACI will specialize in unskilled labor-intensive products. In fact, as their exports become more technology - intensive and developed countries more specialized these pressures could be alleviated. On the one hand, as the "flying geese" process continues, exports from countries with lower incomes than the PRC are likely to displace PRC labor-intensive exports rather than domestic production in developed countries. On the other hand, while it may cause job loss and erode the returns to specific factors, PRC export growth is less likely to be a source of wage inequality in advanced economies

Taking two to tango:fMRI analysis of improvised joint action with physical contact

<div><p>Many forms of joint action involve physical coupling between the participants, such as when moving a sofa together or dancing a tango. We report the results of a novel two-person functional MRI study in which trained couple dancers engaged in bimanual contact with an experimenter standing next to the bore of the magnet, and in which the two alternated between being the leader and the follower of joint improvised movements. Leading showed a general pattern of self-orientation, being associated with brain areas involved in motor planning, navigation, sequencing, action monitoring, and error correction. In contrast, following showed a far more sensory, externally-oriented pattern, revealing areas involved in somatosensation, proprioception, motion tracking, social cognition, and outcome monitoring. We also had participants perform a “mutual” condition in which the movement patterns were pre-learned and the roles were symmetric, thereby minimizing any tendency toward either leading or following. The mutual condition showed greater activity in brain areas involved in mentalizing and social reward than did leading or following. Finally, the analysis of improvisation revealed the dual importance of motor-planning and working-memory areas. We discuss these results in terms of theories of both joint action and improvisation.</p></div

Trading Efficiency of Fund Families: Impact on Fund Performance and Investment Behavior

Mutual funds are part of larger organizations, which make decisions with consequences for all their member funds. This study examines how the efficiency of trading desks operated by fund families affects the performance and trading of affiliated funds. We introduce a novel approach to measure the efficiency of trading desks, which allows for comparisons across families with different investable universes. By operating efficient trading desks, which reduce trading costs, fund families improve the performance of their funds significantly. Furthermore, the lower trading costs resulting from more efficient trading desks enable mutual funds to trade more and hold less liquid portfolios