High frequency tendon reflexes in the human soleus muscle

Tendon reflexes have been often used in studies of the human nervous system in health and disease. They have been investigated either in response to single tendon taps or to long duration vibrations. Tendon reflexes are described here in response to a high frequency vibration burst (3 cycles of a 100 Hz sine wave) applied to the Achilles tendon of standing subjects, either in quiet stance or during a forward leaning posture. The electromyogram from the soleus muscle usually showed three components separated by 10 ms which were interpreted as being three reflexes, each reflex induced by each of the three cycles in a burst. This result indicates that soleus tendon reflexes can respond in fast succession in a phasic manner when a brief high frequency vibration is applied to the Achilles tendon. This occurs in spite of possible depression of the la to motoneuron synapses and the long after hyperpolarization of the motoneurons. An interpretation of the results is that motoneurons from different subsets of the motoneuron pool respond to different cycles of the sinusoidal vibratory burst. (c) 2008 Elsevier Ireland Ltd. All rights reserved.

Neural influences on sprint running - Training adaptations and acute responses

Performance in sprint exercise is determined by the ability to accelerate, the magnitude of maximal velocity and the ability to maintain velocity against the onset of fatigue. These factors are strongly influenced by metabolic and anthropometric components. Improved temporal sequencing of muscle activation and/or improved fast twitch fibre recruitment may contribute to superior sprint performance. Speed of impulse transmission along the motor axon may also have implications on sprint performance. Nerve conduction velocity (NCV) has been shown to increase in response to a period of sprint training. However, it is difficult to determine if increased NCV is likely to contribute to improved sprint performance. An increase in motoneuron excitability, as measured by the Hoffman reflex (H-reflex), has been reported to produce a more powerful muscular contraction, hence maximising motoneuron excitability would be expected to benefit sprint performance. Motoneuron excitability can be raised acutely by an appropriate stimulus with obvious implications for sprint performance. However, at rest reflex has been reported to be lower in athletes trained for explosive events compared with endurance-trained athletes. This may be caused by the relatively high, fast twitch fibre percentage and the consequent high activation thresholds of such motor units in power-trained populations. In contrast, stretch reflexes appear to be enhanced in sprint athletes possibly because of increased muscle spindle sensitivity as a result of sprint training. With muscle in a contracted state, however, there is evidence to suggest greater reflex potentiation among both sprint and resistance-trained populations compared with controls. Again this may be indicative of the predominant types of motor units in these populations, but may also mean an enhanced reflex contribution to force production during running in sprint-trained athletes. Fatigue of neural origin both during and following sprint exercise has implications with respect to optimising training frequency and volume. Research suggests athletes are unable to maintain maximal firing frequencies for the full duration of, for example, a 100m sprint. Fatigue after a single training session may also have a neural manifestation with some athletes unable to voluntarily fully activate muscle or experiencing stretch reflex inhibition after heavy training. This may occur in conjunction with muscle damage. Research investigating the neural influences on sprint performance is limited. Further longitudinal research is necessary to improve our understanding of neural factors that contribute to training-induced improvements in sprint performance.

Alteration in neuromuscular function after a 5 km running time trial.

The aim of this study was to characterize the effect of a 5 km running time trial on the neuromuscular properties of the plantar flexors. Eleven well-trained triathletes performed a series of neuromuscular tests before and immediately after the run on a 200 m indoor track. Muscle activation (twitch interpolation) and normalized EMG activity were assessed during maximal voluntary contraction (MVC) of plantar flexors. Maximal soleus H-reflexes and M-waves were evoked at rest (i.e. H (MAX) and M (MAX), respectively) and during MVC (i.e. H (SUP) and M (SUP), respectively). MVC significantly declined (-27%; P < 0.001) after the run, due to decrease in muscle activation (-8%; P < 0.05) and M (MAX)-normalized EMG activity (-13%; P < 0.05). Significant reductions in M-wave amplitudes (M (MAX): -13% and M (SUP): -16%; P < 0.05) as well as H (MAX)/M (MAX) (-37%; P < 0.01) and H (SUP)/M (SUP) (-25%; P < 0.05) ratios occurred with fatigue. Following exercise, the single twitch was characterized by lower peak torque (-16%; P < 0.001) as well as shorter contraction (-19%; P < 0.001) and half-relaxation (-24%; P < 0.001) times. In conclusion, the reduction in plantar flexors strength induced by a 5 km running time trial is caused by peripheral adjustments, which are attributable to a failure of the neuromuscular transmission and excitation-contraction coupling. Fatigue also decreased the magnitude of efferent motor outflow from spinal motor neurons to the plantar flexors and part of this suboptimal neural drive is the result of an inhibition of soleus motoneuron pool reflex excitability.

Alteration in neuromuscular function after a 5 km running time trial

The aim of this study was to characterize the effect of a 5 km running time trial on the neuromuscular properties of the plantar flexors. Eleven well-trained triathletes performed a series of neuromuscular tests before and immediately after the run on a 200 m indoor track. Muscle activation (twitch interpolation) and normalized EMG activity were assessed during maximal voluntary contraction (MVC) of plantar flexors. Maximal soleus H-reflexes and M-waves were evoked at rest (i.e. H (MAX) and M (MAX), respectively) and during MVC (i.e. H (SUP) and M (SUP), respectively). MVC significantly declined (-27%; P < 0.001) after the run, due to decrease in muscle activation (-8%; P < 0.05) and M (MAX)-normalized EMG activity (-13%; P < 0.05). Significant reductions in M-wave amplitudes (M (MAX): -13% and M (SUP): -16%; P < 0.05) as well as H (MAX)/M (MAX) (-37%; P < 0.01) and H (SUP)/M (SUP) (-25%; P < 0.05) ratios occurred with fatigue. Following exercise, the single twitch was characterized by lower peak torque (-16%; P < 0.001) as well as shorter contraction (-19%; P < 0.001) and half-relaxation (-24%; P < 0.001) times. In conclusion, the reduction in plantar flexors strength induced by a 5 km running time trial is caused by peripheral adjustments, which are attributable to a failure of the neuromuscular transmission and excitation-contraction coupling. Fatigue also decreased the magnitude of efferent motor outflow from spinal motor neurons to the plantar flexors and part of this suboptimal neural drive is the result of an inhibition of soleus motoneuron pool reflex excitability.

Enhanced D1 And D2 Inhibitions Induced By Low-frequency Trains Of Conditioning Stimuli: Differential Effects On H- And T-reflexes And Possible Mechanisms.

Mechanically evoked reflexes have been postulated to be less sensitive to presynaptic inhibition (PSI) than the H-reflex. This has implications on investigations of spinal cord neurophysiology that are based on the T-reflex. Preceding studies have shown an enhanced effect of PSI on the H-reflex when a train of ~10 conditioning stimuli at 1 Hz was applied to the nerve of the antagonist muscle. The main questions to be addressed in the present study are if indeed T-reflexes are less sensitive to PSI and whether (and to what extent and by what possible mechanisms) the effect of low frequency conditioning, found previously for the H-reflex, can be reproduced on T-reflexes from the soleus muscle. We explored two different conditioning-to-test (C-T) intervals: 15 and 100 ms (corresponding to D1 and D2 inhibitions, respectively). Test stimuli consisted of either electrical pulses applied to the posterior tibial nerve to elicit H-reflexes or mechanical percussion to the Achilles tendon to elicit T-reflexes. The 1 Hz train of conditioning electrical stimuli delivered to the common peroneal nerve induced a stronger effect of PSI as compared to a single conditioning pulse, for both reflexes (T and H), regardless of C-T-intervals. Moreover, the conditioning train of pulses (with respect to a single conditioning pulse) was proportionally more effective for T-reflexes as compared to H-reflexes (irrespective of the C-T interval), which might be associated with the differential contingent of Ia afferents activated by mechanical and electrical test stimuli. A conceivable explanation for the enhanced PSI effect in response to a train of stimuli is the occurrence of homosynaptic depression at synapses on inhibitory interneurons interposed within the PSI pathway. The present results add to the discussion of the sensitivity of the stretch reflex pathway to PSI and its functional role.

O ensino de línguas para crianças no contexto educacional brasileiro: breves reflexões e possíveis provisões

This article aims at discussing about the foreign language teaching to young learners, taking the principles of the Sociocultural Theory (Vygotksy, 1978) and of the Communicative Approach (Almeida Filho, 1993, 2005) related to Primary English teaching (Cameron, 2001; Brewster, Ellis & Girard, 2002) as a theoretical references. Considerations about the importance of language learning in childhood will be made, as well as about the role of the grammar, oral language and mother tongue in the process. Likewise, the importance of Teacher Education will be briefly approached. This work is ended with the discussion about some possible procedures in the language teaching processes followed by a brief presentation of possible guidelines based on the bakhtinian notion of discourse genres.

Medalhistas de ouro nas Paraolimpiadas de Atenas 2004 : reflexões de suas trajetorias no desporto adaptado

Universidade Estadual de Campinas . Faculdade de Educação Física

Reflexões acerca do brincar na educação infantil

Universidade Estadual de Campinas . Faculdade de Educação Física

Metodologia de ensino em educação fisica : contribuições de Vygotsky, para as reflexões sobre um modelo pedagogico

Universidade Estadual de Campinas. Faculdade de Educação Física

Da natureza do espaço ao espaço da natureza : reflexões sobre a relação corpo-natureza em parque publicos urbanos

Universidade Estadual de Campinas. Faculdade de Educação Física

As diferentes interfaces da aventura na natureza : reflexões sobre a sociabilidade na vida contemporanea

Universidade Estadual de Campinas . Faculdade de Educação Física

Reflexões sobre a Educação Fisica para portadores de necessidades educacionais especiais a luz da individualização

Universidade Estadual de Campinas . Faculdade de Educação Física

Da busca pela natureza aos ambientes artificiais : reflexões sobre a escalada esportiva

Universidade Estadual de Campinas . Faculdade de Educação Física

Exposições em museus de ciências: reflexões e critérios para análise

Hoje, no que diz respeito à sua interface direta com o público, os museus são considerados, em teoria, instituições com objetivos variados, como educação, lazer, informação e inclusão social. Neste contexto, as exposições aparecem como elemento fundamental da relação entre museus e sociedade, e a expografia torna-se, portanto, ferramenta de comunicação essencial para a efetividade do processo de divulgação. Mas, como se dá a comunicação nestes espaços? Trata-se o presente, de uma reflexão acerca das estratégias de comunicação nas exposições em museus de ciências e sua eficácia. Foram selecionadas três temáticas, a primeira delas é a dos tipos de exposição, e entre as numerosas possibilidades de categorização, optou-se por aquelas descritas por Dean (2003) e Davallon (1986 e 1989). Outra questão discutida é a do uso do objeto, tido, dentre as diferentes mídias a que se pode recorrer em uma exposição, como o diferencial do museu. Por fim, discute-se a questão da interatividade, por vezes reduzida à manipulação, a partir dos níveis propostos por Wagensberg (2000). Apontam-se exemplificações dessas temáticas na exposição de longa duração Pesquisa em Zoologia: a biodiversidade sob o olhar do zoólogo, inaugurada pelo Museu de Zoologia da Universidade de São Paulo em setembro de 2002.

A experiência de uma formadora de professores de Química: analisando suas ações e reflexões num curso de educação continuada

Objetivou-se analisar a experiência de uma formadora num curso de formação continuada para professores de Química, ocorrido numa universidade pública do estado de São Paulo, em 2004. Os dados apresentados surgiram da observação da prática da formadora e de suas reflexões, nas quais ela própria evidencia ideias, conflitos, angústias e impressões sobre suas ações durante o curso. Entre a prática da formadora e suas reflexões, surgem contrastes que irão se tornar nosso foco de investigação. Interpretamos esses contrastes como a atuação de elementos inconscientes que ora favorecem ora dificultam a sua prática e nos mostram que nem sempre a reflexão e a ação atuam na mesma direção. Defendemos uma prática reflexiva mais profunda e questionadora dos sujeitos como possibilidade para produzir melhores efeitos na formação e na atividade docente. Conceitos do referencial teórico psicanalítico de Freud e Lacan serviram de base para a análise dos dados.