A Kinetic Analysis of the Ground Leg During Sprint Running     

Ralph Mann  Paul Sprague 《Research quarterly for exercise and sport》2013,84(2):334-348

Abstract

Fifteen highly skilled sprinters were filmed while running at maximum velocity. The results were digitized and computer processed with interest focused on the muscle moments generated about the hip, knee, and ankle of the ground leg. Muscle activity about the hip consisted of extensor (concentric) dominance from foot descent, through foot strike, and into mid-support. Muscle dominance shifted to the hip flexors (eccentric) during mid-support and continued through takeoff. Muscle dominance at the knee demonstrated a pattern of flexor (eccentric, then concentric) dominance from foot descent through foot strike and into mid-support. Knee extensors (eccentric, then concentric) then achieved dominance through takeoff. During the later stages of takeoff, the dominance decreased or reversed briefly to flexor (eccentric) activity prior to a period of minimal activity following the toe-off position. From a period of minimal activity prior and subsequent to ground contact, the plantar flexors (eccentric, then concentric) of the foot were dominant throughout the ground phase. Qualitatively, the unexpected knee flexor dominance during foot strike was generated to limit the braking action created during this portion of ground contact. The unanticipated hip flexor dominance during takeoff served to rotate the upper body forward and into the approaching air phase. In addition, both of these actions allowed efficient use of the two-joint muscles of the leg during the critical phases of ground contact. Finally, the minimizing or reversing of the knee extensor dominance during the later stages of takeoff served to protect the joint from injury. Quantitatively, the magnitude of hip extensor/knee flexor activity during foot strike was significantly related (r = .70, p = .01) to the prior occurrences of related leg injury in the subjects.  相似文献   

Estimating Energy Expenditure With the RT3 Triaxial Accelerometer     

Ralph Maddison  Yannan Jiang  Stephen Vander Hoorn  Cliona Ni Mhurchu  Carlene M.M. Lawes  Anthony Rodgers 《Research quarterly for exercise and sport》2013,84(2):249-256

The RT3 is a relatively new triaxial accelerometer that has replaced the TriTrac. The aim of this study was to validate the RT3 against doubly labeled water (DLW) in a free-living, mixed weight sample of adults. Total energy expenditure (TEE) was measured over a 15-day period using DLW. Activity-related energy expenditure (AEE) was estimated by subtracting resting energy expenditure and thermic effect of feeding from TEE. The RT3 triaxial accelerometer was worn over 14 consecutive days. TEE and AEE were estimated using the RT3 proprietary equation. Thirty-six adults ages 18–56 years (56% women) with an average weight of 75.9 kg (SD = 14.8) completed all measurements. Compared to DLW, the RT3 underestimated TEE by 539 kJ (4%) and AEE by 485 kJ (15%) on average. The RT3 provided a relatively accurate assessment of free-living activity-related energy expenditure at the group level and generally underestimated total and activity-related energy expenditure compared to DLW.  相似文献   

Spontaneous recovery and ABC renewal from retroactive cue interference     

Miguez G  Cham HX  Miller RR 《Learning & behavior》2012,40(1):42-53

Two conditioned suppression experiments with rats were conducted to determine whether the spontaneous recovery and renewal that are commonly observed in retroactive outcome interference (e.g., extinction) also occur in retroactive cue interference. Experiment 1 showed that a long delay between Phase 2 (the interfering phase) and testing produces a recovery from the cue interference (i.e., the delay enhanced responding to the target cue trained in Phase 1), which is analogous to the spontaneous recovery effect observed in extinction and other retroactive outcome interference procedures. Experiment 2 showed that, when target and interfering cues are trained in separate contexts and testing occurs in a different but familiar context, a recovery from the cue interference is also observed (i.e., the context shift enhanced responding to the target), which is analogous to ABC renewal from extinction. The results are discussed in terms of the possibility that similar associative mechanisms underlie cue and outcome interference.  相似文献   

Performance factors in associative learning: Assessment of the sometimes competing retrieval model     

JE Witnauer  BM Wojick  CW Polack  RR Miller 《Learning & behavior》2012,40(3):347-366

Previous simulations revealed that the sometimes competing retrieval model (SOCR; Stout & Miller, Psychological Review, 114, 759-783, 2007), which assumes local error reduction, can explain many cue interaction phenomena that elude traditional associative theories based on total error reduction. Here, we applied SOCR to a new set of Pavlovian phenomena. Simulations used a single set of fixed parameters to simulate each basic effect (e.g., blocking) and, for specific experiments using different procedures, used fitted parameters discovered through hill climbing. In simulation 1, SOCR was successfully applied to basic acquisition, including the overtraining effect, which is context dependent. In simulation 2, we applied SOCR to basic extinction and renewal. SOCR anticipated these effects with both fixed parameters and best-fitting parameters, although the renewal effects were weaker than those observed in some experiments. In simulation 3a, feature-negative training was simulated, including the often observed transition from second-order conditioning to conditioned inhibition. In simulation 3b, SOCR predicted the observation that conditioned inhibition after feature-negative and differential conditioning depends on intertrial interval. In simulation 3c, SOCR successfully predicted failure of conditioned inhibition to extinguish with presentations of the inhibitor alone under most circumstances. In simulation 4, cue competition, including blocking (4a), recovery from relative validity (4b), and unblocking (4c), was simulated. In simulation 5, SOCR correctly predicted that inhibitors gain more behavioral control than do excitors when they are trained in compound. Simulation 6 demonstrated that SOCR explains the slower acquisition observed following CS-weak shock pairings.  相似文献   

The dual role of the context in postpeak performance decrements resulting from extended training     

Gonzalo P. Urcelay  James E. Witnauer  Ralph R. Miller 《Learning & behavior》2012,40(4):476-493

The context??s role in Pavlovian conditioning depends on the trial spacing during training, with massed trials revealing a function akin to that of discrete stimuli, and spaced trials revealing a modulatory function (Urcelay & Miller, Journal of Experimental Psychology. Animal Behavior Processes, 36, 268?C280, 2010). Here we examined the contextual determinants of a common but largely ignored effect: attenuated conditioned responding with extended reinforced training (i.e., a postpeak performance deficit [PPD]). Contextual sources of PPDs were investigated in four fear-conditioning experiments with rats. In Experiment 1, as the number of reinforced trials increased, conditioned responding decreased, even when testing occurred outside the training context. Experiment 2 revealed opposing influences of context on the PPD based on trial spacing, which interacted with whether testing occurred in the training context. This finding reconciles Experiment 1??s results with previous data (Bouton, Frohardt, Sunsay, Waddell, & Morris, Journal of Experimental Psychology. Animal Behavior Processes, 34, 223?C236, 2008). Experiment 3 suggested that extended training with these parameters did not lead to habituation to conditioned or unconditioned stimuli. In Experiment 4, few or many massed training trials were followed orthogonally by context extinction or no context extinction. After many pairings, context extinction reduced the PPD (i.e., enhanced responding), suggesting a competitive role of the context. These results, together with prior data suggesting that context modulates expressions of the PPD, are consistent with the view that contexts can play two distinctly different roles.  相似文献   

Early detection of fungal biomass on library materials     

Nick R. Konkol  Christopher J. McNamara  Ethel Hellman  Ralph Mitchell 《Journal of Cultural Heritage》2012,13(2):115-119

Library materials are susceptible to fungal deterioration. The paper constituents of archival materials are subjected to harmful physical and chemical processes as they are slowly consumed by fungi. Remediation of fungal contamination can be costly and risk further damage to fragile or previously degraded materials. Early detection of fungal growth would permit the use of relatively noninvasive treatments to remediate fungal contamination of artifacts before visible or lasting damage has occurred. Current methods used for the detection of microbial biomass, such as colony counts, microscopic biovolume estimation, and ergosterol analysis are expensive, time consuming, or are inappropriate for use with fungi. Beta-N-acetylhexosaminidase (EC 3.2.1.52) activity provides a rapid and reliable means of fungal detection on a variety of cultural heritage materials. Adapted for use on archival materials, fluorogenic 4-Methylumbelliferyl (MUF) labeled substrate N-acetyl-Beta-D-glucosamine (NAG) was used to detect fungal beta-N-acetylhexosaminidase activity. The fluorescence generated by minute quantities of fungi was quickly detected at an early stage of growth. The sensitivity of the assay was comparable to other biochemical techniques. The fluorometric assay was well-suited for early detection of fungal biomass on paper and assessment of the effectiveness of common remediation practices.  相似文献   

Workshop report     

John Smyth  Ralph G. Straton 《The Australian Educational Researcher》1985,12(3):44-44

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The Appraisal of Academic Conduct: Are Norms an Adequate Moral Guide?     

Ralph Blunden 《高等教育研究与发展》1996,15(2):145-166

This paper examines the legitimacy of norms as a means of evaluating academic conduct. Section one provides a general overview of some issues involved. In section two the concept of norms is unpacked and, in section three, some problems with an adequate account of norms are identified. In section four the rationality of norms is examined and in the following section, section five, the concept of deviance is discussed. It is argued that deviance from rational academic norms is usually, but not always, unacceptable. However, it also is suggested that dissenting conduct is required of academics since it is a central professional norm, closely connected to the purposes of a university. The concept of academic freedom, whilst not examined in any detail in this paper, provides a general defence of dissenting–but, in general, not of deviant ‐conduct. Given the difficulties associated with the concept of norms, the importance of character over conduct is emphasised. It is concluded that the moral basis for evaluating academic conduct and, hence, attempts to improve university teaching, is seriously problematic.  相似文献   

A Method for Investigating College Student Peer Group Holding Power     

Ralph E. Prusok 《Journal of Experimental Education》2013,81(3):66-68

The interaction of group prestige among groups, dissonance of new member attitudes with those of the established group, and homogeneity of established group attitudes, were dependent variables studied. Groupattrition rate was the independent variable. The data consisted of attitude scores, group prestige ranks, and attrition statistics. Analysis was by the method of partial correlations. College fraternity chapters (N = 19) were the subject groups. It was concluded that no differences exist on the dimensions posited, however, trends of results seemed to support the theoretical notions. The method utilized should be explored further.  相似文献   

The nature of citizenship education provision: an initial study     

Ralph Leighton 《Curriculum Journal》2013,24(2):167-181

While compulsory citizenship education has apparently been accepted and, in some quarters, regarded as overdue, in schools there has been little opportunity to discuss the meaning of ‘citizenship’. This article reports an initial study of four schools, with a focus on one of them. From this study it was evident that teachers and students have different views about what they are offering and being offered. Some implications of the spaces between these differences are aired in the conclusion of the article.  相似文献