Efeitos das combinações da prática constante e variada na aquisição de uma habilidade motora

Os efeitos de diferentes estruturas de prática na aquisição de uma habilidade motora foram investigados em um experimento em que a prática foi manipulada no que se refere à variabilidade. O delineamento constou de dois grupos de prática combinada (constante-por blocos e constante-aleatória) e de duas fases de aprendizagem (estabilização e adaptação). Sessenta estudantes universitários praticaram uma tarefa que consistia em tocar sensores de forma sequencial em integração a um estímulo visual. Para a realização da tarefa foi utilizado o aparelho de "timing" coincidente para tarefas complexas. O desempenho foi avaliado mediante três medidas de erro: absoluto, variável e de execução. O "timing" relativo e sua variabilidade foram utilizados para avaliar a macroestrutura do programa de ação da habilidade ao passo que a microestrutura foi avaliada pela variabilidade do tempo total de movimento. Os resultados mostraram que, ao variar a tarefa em seus aspectos perceptivo (velocidade do estímulo visual) e efetor (sequência de toques), a prática constante seguida de prática por blocos apresenta, na fase de adaptação, melhor desempenho em relação ao número de acertos de execução do que a prática constante seguida de prática aleatória, indicando, portanto, que a primeira proporciona mais condições de adaptação a uma nova tarefa motora.The effects of different practice schedules in the adaptive process of motor skill acquisition were investigated in an experiment involving different regimes of the variable practice. The experimental design consisted of two combined practice groups (constant-block and constant-random) and two learning phases (stabilization and adaptation). Sixty undergraduate students performed a task that consisted of touching response keys sequentially in integration with a visual stimulus. A coincident timing apparatus combined with a serial response device was used. The overall performance was evaluated using three measures: absolute error, variable error and number of correct trials. The relative timing and its variability were used to assess the macrostructure of the action program of the skill while its microstructure was evaluated by absolute movement time and its variability. The variable practice was manipulated both in terms of the visual stimulus velocities and the response patterns. The results showed a better performance for the constant-block practice group in the number of sequence errors in the adaptation phase. Overall results showed a superiority of constant-block practice group relative to the adaptation to the new task

Dietary fiber intake and risk of colorectal cancer: a pooled analysis of prospective cohort studies

Context Inconsistent findings from observational studies have continued the controversy over the effects of dietary fiber on colorectal cancer. Objective To evaluate the association between dietary fiber intake and risk of colorectal cancer. Design, Setting, and Participants From 13 prospective cohort studies included in the Pooling Project of Prospective Studies of Diet and Cancer, 725 628 men and women were followed up for 6 to 20 years across studies. Study- and sex-specific relative risks (RRs) were estimated with the Cox proportional hazards model and were subsequently pooled using a random-effects model. Main Outcome Measure Incident colorectal cancer. Results During 6 to 20 years of follow-up across studies, 8081 colorectal cancer cases were identified. For comparison of the highest vs lowest study- and sex-specific quintile of dietary fiber intake, a significant inverse association was found in the age-adjusted model (pooled RR=0.84; 95% confidence interval [CI], 0.77-0.92). However, the association was attenuated and no longer statistically significant after adjusting for other risk factors (pooled multivariate RR=0.94; 95% Cl, 0.86-1.03). In categorical analyses compared with dietary fiber intake of 10 t

Dietary fiber intake and risk of colorectal cancer: A pooled analysis of prospective cohort studies

Context: Inconsistent findings from observational studies have continued the controversy over the effects of dietary fiber on colorectal cancer. Objective: To evaluate the association between dietary fiber intake and risk of colorectal cancer. Design, Setting, and Participants: From 13 prospective cohort studies included in the Pooling Project of Prospective Studies of Diet and Cancer, 725 628 men and women were followed up for 6 to 20 years across studies. Study- and sex-specific relative risks (RRs) were estimated with the Cox proportional hazards model and were subsequently pooled using a random-effects model. Main Outcome Measure: Incident colorectal cancer. Results: During 6 to 20 years of follow-up across studies, 8081 colorectal cancer cases were identified. For comparison of the highest vs lowest study- and sex-specific quintile of dietary fiber intake, a significant inverse association was found in the age-adjusted model (pooled RR=0.84; 95% confidence interval [CI], 0.77-0.92). However, the association was attenuated and no longer statistically significant after adjusting for other risk factors (pooled multivariate RR=0.94; 95% CI, 0.86-1.03). In categorical analyses compared with dietary fiber intake of 10 to <15 g/d, the pooled multivariate RR was 1.18 (95% CI, 1.05-1.31) for less than 10 g/d (11% of the overall study population); and RR, 1.00 (95% CI, 0.85-1.17) for 30 or more g/d. Fiber intake from cereals, fruits, and vegetables was not associated with risk of colorectal cancer. The pooled multivariate RRs comparing the highest vs lowest study- and sex-specific quintile of dietary fiber intake were 1.00 (95% CI, 0.90-1.11) for colon cancer and 0.85 (95% CI, 0.72-1.01) for rectal cancer (P for common effects by tumor site=.07). Conclusions: In this large pooled analysis, dietary fiber intake was inversely associated with risk of colorectal cancer in age-adjusted analyses. However, after accounting for other dietary risk factors, high dietary fiber intake was not associated with a reduced risk of colorectal cancer. ©2005 American Medical Association. All rights reserved

Interferência contextual e nível de habilidade na aprendizagem do serviço do voleibol

Este estudo investigou o efeito da interferência contextual (IC) na aquisição do serviço do voleibol em adolescentes com diferentes níveis de habilidade, considerando os testes de transferência imediato e retardado. A amostra foi composta por 56 meninas com idade entre 14 e 16 anos, distribuídas em quatro grupos de prática: aleatório com nível superior de habilidade (GAS), blocos com nível superior de habilidade (GBS), aleatório com nível inferior de habilidade (GAI) e blocos com nível inferior de habilidade (GBI). A tarefa motora consistiu dos serviços por baixo e por cima direcionados a alvos na quadra. Os resultados mostraram que o efeito da IC não foi observado nos grupos GAI e GBI, por outro lado, os grupos GAS e GBS apresentaram melhor desempenho no teste de transferência imediato. A ausência de diferenças significativas no teste de transferência retardado sugere que o efeito da IC pode ser temporário.Este estudio investigó el efecto de la interferencia contextual (IC) en la adquisición del servicio de voleibol en adolescentes con diferentes niveles de habilidad, teniendo en cuenta las pruebas de transferencia inmediata y retardada. La muestra estuvo conformada por 56 niñas de edades comprendidas entre 14 y 16 años, divididas en cuatro grupos de práctica: al azar con mayor nivel de habilidad (GAS), por bloques con mayor nivel de habilidad (GBS), al azar con menor nivel de habilidad (GAI ) y por bloques con menor nivel de habilidad (GBI). La tarea motora consistió de servicios por abajo y por encima dirigidos a objetivos en la cancha. Los resultados mostraron que no se observó el efecto de la IC en los grupos GAI y GBI, por otra parte, los grupos GAS y GBS presentaron mejor rendimiento en la prueba de transferencia inmediata. La ausencia de diferencias significativas en la prueba de transferencia de retraso sugiere que el efecto de la IC puede ser temporario.The purpose of this study was to investigate the effect of contextual interference on acquiring the volleyball serve in adolescents with different skill levels, considering then immediate and delayed transfer tests. Participants were 56 schoolgirls separated in four practice groups: random practice with higher level skill subjects (GAS), blocked practice with higher level skill subjects (GBS), random practice with lower level skill subjects (GAI) and blocked practice with lower level skill subjects (GBI). The acquisition task consisted in performing underhand and overhead services directed at two targets affixed to the ground. The results showed no effect of contextual interference on the lower level skill subjects. However when comparing the types of practice between the higher level skill subjects, the effect was observed in the immediate transfer test. The absence of significant differences between groups in the delayed transfer test suggest that the contextual interference effect may be temporary

Ventilatory function and winter fresh fruit consumption in a random sample of British adults.

The relation between ventilatory function and the reported frequency of consumption of fresh fruit and fruit juice was studied among 1502 lifelong non-smokers and 1357 current smokers aged 18-69 with no history of chronic respiratory disease. Forced expiratory volume in one second (FEV1) was assessed by turbine spirometry. As winter fruit consumption was more widely dispersed than summer consumption and few subjects ate fruit more frequently in the winter, winter fruit consumption was taken as an indicator of habitual (year round) consumption. After adjustment for sex, age, height, cigarette consumption, region of residence, and household socioeconomic group, FEV1 was associated with winter fruit consumption. The mean adjusted FEV1 among those who never drank fresh fruit juice and ate fresh fruit less than once a week during the winter was 78 ml lower (95% confidence interval 24-132 ml) than the mean for the other subjects. A similar difference was found in all age-sex groups and among both current smokers and lifelong non-smokers. Antioxidant and other actions of vitamin C may protect against pulmonary emphysema, or reduce bronchoconstrictor responses to environmental pollutants

Breast cancer hypothesis: a single cause for the majority of cases

STUDY OBJECTIVE—The main cause of breast cancer remains unknown. Numerous causal factors or predisposing conditions have been proposed, but account for only a small percentage of the total disease. The current search for multiple causes is unavailing. This report explores whether any single aetiological agent may be responsible for the majority of cases, and attempts to define its properties.
METHODS—Examination of all relevant epidemiological and biological evidence.
MAIN RESULTS—Genetic inheritance is not the main cause of breast cancer because most cases are sporadic, there is a low prevalence of family history, and genetically similar women have differing rates after migration. Environmental exposure, such as pollution by industrialisation, is not a major cause, as deduced from a spectrum of epidemiological data. The possibility of infection as cause is not persuasive as there is no direct biological evidence and no epidemiological support. Oestrogen status is closely related to breast cancer risk, but there are numerous inconsistencies and paradoxes. It is suggested that oestrogens are not the proximate agent but are promoters acting in concert with the causal agent. Dietary factors, and especially fat, are associated with the aetiology of breast cancer as shown by intervention and ecological correlation studies, but the evidence from case-control and cohort studies is inconsistent and contradictory.
CONCLUSIONS—The hypothesis that best fits the epidemiological data is that dietary fat is not itself the causal agent, but produces depletion of an essential factor that is normally protective against the development of breast cancer. Many of the observed inconsistencies in the epidemiology are explainable if deficiency of this agent is permissive for breast cancer to develop. Some properties of the putative agent are outlined, and research investigations proposed.


Keywords: breast cance