首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 0 毫秒
1.
    
This study sought to ascertain how multi-dimensional coordination patterns changed with five poling speeds for 12 National Standard cross-country skiers during roller skiing on a treadmill. Self-organizing maps (SOMs), a type of artificial neural network, were used to map the multi-dimensional time series data on to a two-dimensional output grid. The trajectories of the best-matching nodes of the output were then used as a collective variable to train a second SOM to produce attractor diagrams and attractor surfaces to study coordination stability. Although four skiers had uni-modal basins of attraction that evolved gradually with changing speed, the other eight had two or three basins of attraction as poling speed changed. Two skiers showed bi-modal basins of attraction at some speeds, an example of degeneracy. What was most clearly evident was that different skiers showed different coordination dynamics for this skill as poling speed changed: inter-skier variability was the rule rather than an exception. The SOM analysis showed that coordination was much more variable in response to changing speeds compared to outcome variables such as poling frequency and cycle length.  相似文献   

2.
    
The study investigated the effects of arm swing during leg push-off in V2-alternate/G4 skating on neuromuscular activation and force production by the leg muscles. Nine skilled cross-country skiers performed V2-alternate skating without poles at moderate, high, and maximal speeds, both with free (SWING) and restricted arm swing (NOSWING). Maximal speed was 5% greater in SWING (P < 0.01), while neuromuscular activation and produced forces did not differ between techniques. At both moderate and high speed the maximal (2% and 5%, respectively) and average (both 5%) vertical force and associated impulse (10% and 14%) were greater with SWING (all P < 0.05). At high speed range of motion and angular velocity of knee flexion were 24% greater with SWING (both P < 0.05), while average EMG of m. biceps femoris was 31% lower (all P < 0.05) in SWING. In a similar manner, the average EMG of m. vastus medialis and m. biceps femoris were lower (17% and 32%, P < 0.05) during the following knee extension. Thus, swinging the arms while performing V2-alternate can enhance both maximal speed and skiing economy at moderate and, in particularly, high speeds.  相似文献   

3.
    
The purpose of this study was to examine the effect of increasing exercise intensity on the role of joint powers in ergometer double poling (DP), while taking specific dynamic constraints into account. One main question was whether lower-body power contribution increased or decreased with increasing intensity. Nine male Norwegian national-level cross-country skiers performed ergometer DP at low, moderate, high and maximal intensity. Kinematics, and ground (GRF) and poling (Fpoling) reaction forces were recorded and used in link segment modeling to obtain joint and whole-body dynamics. Joint powers were averaged over the cycle, the poling (PP) and recovery (RP) phases. The contribution of these average powers was their ratios to cycle average poling power. At all intensities, the shoulder (in PP) and hip (mostly in RP) generated most power. Averaged over the cycle, lower-body contribution (sum of ankle, knee and hip power) increased from ∼37% at low to ∼54% at maximal intensity (p < .001), originating mostly from increased hip contribution within PP, not RP. The generation of larger Fpoling at higher intensities demanded a reversal of hip and knee moment. This was necessary to appropriately direct the GRF vector as required to balance the moment about center of mass generated by Fpoling (control of angular momentum). This was reflected in that the hip changed from mostly absorbing to generating power in PP at lower and higher intensities, respectively. Our data indicate that power-transfer rather than stretch-shortening mechanisms may occur in/between the shoulder and elbow during PP. For the lower extremities, stretch-shortening mechanisms may occur in hip, knee and trunk extensors, ensuring energy conservation or force potentiation during the countermovement-like transition from body lowering to heightening. In DP locomotion, increasing intensity and power output is achieved by increased lower-body contribution. This is, at least in ergometer DP, partly due to changes in joint dynamics in how to handle dynamic constraints at different intensities.  相似文献   

4.
    
This study analyzed the biomechanical and physiological effects of the arm swing in roller ski skating, and compared leg-skating (i.e. ski skating without poles) using a pronounced arm swing (SWING) with leg-skating using locked arms (LOCKED). Sixteen elite male cross-country skiers performed submaximal stages at 10, 15 and 20 km h−1 on a 2% inclined treadmill in the two techniques. SWING demonstrated higher peak push-off forces and a higher force impulse at all speeds, but a longer cycle length only at the highest speed (all P < .05), indicating a lower force effectiveness with SWING at the two lowest speeds. Additionally, the flexion–extension movement in the lower limbs was more pronounced for SWING. Oxygen uptake was higher for SWING at the two lowest speeds (both P < .05) without any differences in blood lactate. At the highest speed, oxygen uptake did not differ between SWING and LOCKED, but the RER, blood lactate and ventilation were lower with SWING (all P < .05). Taken together, these results demonstrate that utilizing the arm swing in roller ski skating increases the ski forces and aerobic energy cost at low and moderate speeds, whereas the greater forces at high speed lead to a longer cycle length and smaller anaerobic contribution.  相似文献   

5.
    
Starting from the observation that many open issues in linguistics hinge on problems of semantics, we discuss three core semantic notions: categories, agency, and qualification or semiosis. We argue that the origin of these coincide with the emergence of self-regulatory systems, systems that control their own persistence as localizable dynamical systems. When such systems interact a metasystem transition can occur in which the regulatory capacity per system is increased through the mechanisms of extension and specialization. Newly arising mutual dependencies force the formerly independent systems to coordinate their behaviour which leads them to effectively become a single system – a novel agency at a higher level of organization – thus qualifying the emergence of a novel language or code. We go on to argue that natural languages are instances of such naturally occurring conventionalization processes, corroborating the view that language should primarily be characterized as coordination.  相似文献   

6.
In these notes we review emergent phenomena in complex systems, emphasizing ways to identify potential underlying universal mechanisms that generate complexity. The discussion focuses on the emergence of collective behavior in dynamical systems when they are poised near a critical point of a phase transition, either by tuning or by self-organization. We then present the rationale for our proposal that the brain is naturally poised near criticality and review recent results as well as the implications of this view of the functioning brain.  相似文献   

7.
    
Visual information plays an adaptive role in the relation between bimanual force coupling and error corrective processes of isometric force control. In the present study, the evolving distribution of the relative phase properties of bimanual isometric force coupling was examined by scaling within a trial the temporal feedback rate of visual intermittency (short to long presentation intervals and vice versa). The force error (RMSE) was reduced, and time-dependent irregularity (SampEn) of the force output was increased with greater amounts of visual information (shorter intermittency). Multi-stable coordination patterns of bimanual isometric force control were differentially shifted toward and away from the intrinsic dynamics by the changing the intermittency of visual information. The distribution of Hilbert transformed relative phase values showed progressively a predominantly anti-phase mode under less intermittent visual information to predominantly an in-phase mode with limited (almost no) visual information. Correlation between the hands showed a continuous reduction, rather than abrupt “transition,” with increase in visual information, although no mean negative correlation was realized, despite the tendency towards an anti-phase distribution. Lastly, changes in both the performance outcome and bimanual isometric force coordination occurred at visual feedback rates faster than the minimal visual processing times established from single limb movement and isometric force protocols.  相似文献   

8.
    
The main aim of the present study was to examine differences in behavioral problems in toddlers born very preterm in Brazil and Italy. The sample comprised 154 toddlers (18–24 months of age) born very preterm, including 76 toddlers from Brazil and 78 toddlers from Italy. The Child Behavior Checklist was used to assess behavioral problems. Specific sociodemographic factors (i.e., maternal age at childbirth and maternal education) and neonatal factors (i.e., gestational age, sex, and length of hospitalization) were tested as potential mediators of country-related differences in behavioral problems. Brazilian toddlers presented more internalizing, externalizing, and total behavioral problems compared with their Italian counterparts. The effect of country on the toddlers’ internalizing and total behavioral problems was mediated by maternal age at childbirth and education. Independent effects of country, maternal age at childbirth, and maternal education emerged for externalizing behavioral problems. No significant effect emerged for neonatal variables. These findings suggest that sociodemographic factors, in addition to country-related differences, should be considered when assessing the risk of behavioral problems in preterm toddlers.  相似文献   

9.
10.
    
Trait self-control has in several studies been found negatively linked to stress. These studies have, however, mostly relied on student and/or one-country samples. Study 1 investigated the generalizability of the relationship between trait self-control and stress through a four-country survey (N = 4097). The results showed consistently strong and negative relationships between trait self-control and stress across the four countries. Study 2 investigated the relationship between trait self-control and daily stress through a two-week diary study (N = 594; nobs = 7880), showing that trait self-control was negatively related to daily stress and stress variability. Together, the two studies show that trait self-control’s negative link to stress generalizes beyond students and the United States.  相似文献   

11.
Parenting skills, such as Autonomy Support (AS), have been proposed as a potential mechanism explaining the intergenerational contiguity of Executive Function (EF). However, few studies have focused on mothers and fathers among non-Western families. The current study investigated the role of maternal and paternal AS in the relation between parental EF and infant EF at 14 months of age among 123 Dutch and 63 Chinese first-time mothers and fathers and their infants. Multiple-group structural equation models were built for mothers and fathers separately with country as a grouping variable. Results showed that parental AS did not mediate the relation between parent EF and infant EF at 14 months. Mean-level differences were found in parental AS, maternal EF, and infant inhibition across countries, while no country differences were found in the relation between parent EF, AS and infant EF. Our findings suggested that individual differences in early EF may not be stable enough to be reliably predicted from parental factors across the Netherlands and China.  相似文献   

12.
The philosophical argument between Jean-Paul Sartre and Albert Camus can be summarised in their conflicting accounts of skiing and swimming. For Sartre skiing exemplifies the struggle of existence and the angst of the alienated ego. For Camus, swimming represents some glimmering of collective harmony, the possibility of transcendence. Sartre's thinking is inflected by quantum theory and the ‘steady state’, whereas Camus is more of a wave theorist, with a lingering nostalgia for the ‘primeval atom’ and a fondness for peak experiences. Put together their separate ways of analysing consciousness suggest a two-phase account of cognition.  相似文献   

13.
Using a nationwide sample of 2656 eighteen- to twenty-nine-year-olds, the first part of the present study addressed the question of how non-traditional as compared to traditional living arrangements related to young people’s self-perception of being either adolescent or adult. Being in a romantic relationship increased the likelihood of feeling adult. Modern adult living arrangements (living alone in a single household or sharing an apartment with peers) increased the likelihood of feeling adolescent. Employing a longitudinal sample of 461 twenty- to twenty-seven-year-olds, changes in job status and sources of income were studied with regard to their connections to the emergence of subjective adulthood or the regression to subjective adolescence, respectively. No association between adult or adolescent self-perception and issues of work and material autonomy was found, but the emergence of subjective adulthood was related to romantic relationships and parenthood. Findings are discussed with reference to young people’s volatile living conditions and transient commitments implied by social change.  相似文献   

14.
Most models of response time (RT) in elementary cognitive tasks implicitly assume that the speed-accuracy trade-off is continuous: When payoffs or instructions gradually increase the level of speed stress, people are assumed to gradually sacrifice response accuracy in exchange for gradual increases in response speed. This trade-off presumably operates over the entire range from accurate but slow responding to fast but chance-level responding (i.e., guessing). In this article, we challenge the assumption of continuity and propose a phase transition model for RTs and accuracy. Analogous to the fast guess model (Ollman, 1966), our model postulates two modes of processing: a guess mode and a stimulus-controlled mode. From catastrophe theory, we derive two important predictions that allow us to test our model against the fast guess model and against the popular class of sequential sampling models. The first prediction--hysteresis in the transitions between guessing and stimulus-controlled behavior--was confirmed in an experiment that gradually changed the reward for speed versus accuracy. The second prediction--bimodal RT distributions--was confirmed in an experiment that required participants to respond in a way that is intermediate between guessing and accurate responding.  相似文献   

15.
    
This study examined coordination of the spine and pelvis during lateral bending of the trunk in older adults. Thirty-four healthy subjects (17 young and 17 older adults) demonstrated lateral bending at a controlled speed while holding a bar at approximately 180 degrees of shoulder flexion. Kinematic data collection was completed on the thoracic spine, lumbar spine, and pelvis. The coupling angle was calculated to examine the thorax–lumbar, lumbar–pelvis, and thorax–pelvis coordination patterns. The older adults demonstrated a reduced range of motion (ROM) of the lumbar spine, while both groups revealed similar ROM in the thorax and in the pelvis. The coupling angle between the straightening and bending phases was different only for the older adults in the thorax–lumbar (23.4 ± 8.0 vs. −1.6 ± 4.4, p = 0.004) and the lumbar–pelvis (65.4 ± 7.2 vs. 86.1 ± 7.8, p = 0.001) coordination. However, there was no group difference in the thorax–pelvis coordination. These findings indicate that age-related changes in the lumbar region affect coordination patterns only during the bending phase. The older adults preserved a similar pattern of movement to the young adults during the straightening phase, but the coordination variability of the coupling angles was greater for the older adults than for the young adults. This movement pattern suggests that the older adults lacked consistent trunk control in an attempt to optimize lateral bending coordination.  相似文献   

16.
基于多重任务的心理信息加工原理,提出一种可以更好地利用分离的双重任务操作绩效测量和计算操作者手脚协调能力的方法,并提出手-脚协调估计值K的计算方法。经手脚协调任务实验验证,手-脚协调估计值K可以较好地用于测量操作者的手脚协调能力。  相似文献   

17.
    
Does a concurrent cognitive task affect the dynamics of bimanual rhythmic coordination? In‐phase coordination was performed under manipulations of phase detuning and movement frequency and either singly or in combination with an arithmetic task. Predicted direction‐specific shifts in stable relative phase from 0° due to detuning and movement frequency were amplified by the cognitive task. Nonlinear cross‐recurrence analysis suggested that this cognitive influence on the locations of the stable points or attractors of coordination entailed a magnification of attractor noise without a reduction in attractor strength. An approximation to these findings was achieved through parameter changes in a motion equation in relative phase. Results are discussed in terms of dual‐task performance as limited resources, dynamics rather than chronometrics, and reparameterization rather than degradation.  相似文献   

18.
    
In the absence of pre‐established communicative conventions, people create novel communication systems to successfully coordinate their actions toward a joint goal. In this study, we address two types of such novel communication systems: sensorimotor communication, where the kinematics of instrumental actions are systematically modulated, versus symbolic communication. We ask which of the two systems co‐actors preferentially create when aiming to communicate about hidden object properties such as weight. The results of three experiments consistently show that actors who knew the weight of an object transmitted this weight information to their uninformed co‐actors by systematically modulating their instrumental actions, grasping objects of particular weights at particular heights. This preference for sensorimotor communication was reduced in a fourth experiment where co‐actors could communicate with weight‐related symbols. Our findings demonstrate that the use of sensorimotor communication extends beyond the communication of spatial locations to non‐spatial, hidden object properties.  相似文献   

19.
    
Multiple instruments have been developed and used to measure quantitative job insecurity (i.e., insecurity to lose the job as such), often without systematic evaluation of their psychometric characteristics across countries and language barriers. This may hamper consistent and reliable cross-study and cross-country comparisons. This study's aim was to introduce and validate the four-item Job Insecurity Scale (JIS) developed by De Witte across five European countries (i.e., Belgium, The Netherlands, Spain, Sweden, and the UK). Overall, the results demonstrated the construct validity (i.e., configural invariance and invariance of the measurement model parameters), the reliability (internal consistency of the items), and the criterion validity (with respect to affective organizational commitment, perceived general health, and self-reported performance) of the JIS. The different translations of the JIS can thus be considered as valid and reliable instruments to measure job insecurity and can be used to make meaningful comparisons across countries. Furthermore, the JIS translations may be utilized to assess how job insecurity is related to outcomes.  相似文献   

20.
This study explores the adjustment process of five Western ex-Buddhist monks to life after the monastery, using an in depth case study approach and thematic analysis. Participants discussed their initial experience of leaving, the process of creating a new life and their relationship with the past. The findings indicated that while each case was unique, significant common themes emerged as features of the adjustment process. The adjustment had been multi-dimensional, challenging, difficult, confusing, complex and profound for the participants. They had to contend with issues of grief, delayed development, missing out on life experiences, difficulties with intimacy, money, identity, depression, anxiety and confusion. This was combined with the hope and promise of many newly found freedoms involved in establishing a new life and identity. Parallels are drawn to the experience of Catholic priests and nuns who have departed their Orders, Vietnam veterans, ex-cult members and individuals who have left total institutions where their identity and daily lives were highly prescribed. The adjustment experience of ex-Buddhist monks extends the literature on Buddhist monks and provides an example of a life transition of interest to the helping professions because of its potential relevance to a range of major transitions for which clients may seek assistance. Tim Mapel is a lecturer in the Bachelor of Applied Social Sciences degree at the Eastern Institute of Technology in New Zealand. He has a Master’s degree in counseling and works with individuals, couples and groups. He has a passion for the practice of mindfulness and for facilitating a sense of aliveness in people’s lives. He is an advanced Psychodrama trainee and spent 12 years living as an ordained Buddhist monk. Originally from Boston, USA he has lived in the UK, Switzerland, and now considers New Zealand home.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号