Effects of backpack loads and positions on the variability of gait spatiotemporal parameters in young adults

Abstract Introduction: People carry backpacks of different weight in different positions every day. The effects of backpack wearing under different loads and positions were assessed according to the gait's spatiotemporal parameters and their variability in young adults. Methods Twenty-one subjects performed trials of 4 min in the conditions: control condition with no backpack; bilateral back load consisting of 10% body weight (BW); bilateral back load of 20% BW (B20); unilateral load of 10% BW; unilateral load with 20% BW (U20); bilateral frontal load with 10% BW; bilateral frontal load with 20% BW. Results Step length (SL) and step frequency (SF) show that frontal conditions differed from others as seen in B20. Gait cycle phases showed an increase in the B20 condition for double stance phase and stance phase, swing phase presented reduction in the B20 condition. There were significant main effects in position for SL, SF, and walk ratio, in load only for stride width. The highest variability of spatiotemporal parameters occurred in the U20 condition. All load conditions with 20% BW showed a greater variability when compared to the 10% BW counterpart. Conclusion We concluded that young adults can cope with up to a 15% BW load under a bilateral back position, but in the frontal position not even a 10% BW load was proven to be a safe limit. 20% BW loads should be avoided in any position. These recommendations may assure increased gait stability, decreased trunk forward lean and decreased muscle activation and fatigue reducing back pain occurrence.

Interações não lineares na arborização dendrítica de modelos de motoneurônios / Nonlinear interactions in the dendritic tree of motoneuron models

Este trabalho tem como objetivo verificar as diferenças funcionais entre sinapses proximais e distais e investigar as interações não line­ares de ativações sinápticas em modelos de motoneurônios em con­dições passivas. Os modelos utilizados, implementados em C++, são uma versão expandida dos desenvolvidos por Vieira e Kohn (2005), com uma arborização dendrítica mais detalhada: 5 ramos dendríti­cos equivalentes com 17 ou 19 compartimentos dendríticos cada um. Testes verificaram as diferenças funcionais de sinapses que ocorrem próximas ao soma e ao longo do dendrito além de avaliarem o grau de não linearidade de resposta da arborização dendrítica para dife­rentes ativações sinápticas em diferentes sítios. As diferenças funcio­nais entre as sinapses proximais e distais foram avaliadas pela injeção de senoides puras em diferentes compartimentos dendríticos. Os re­sultados mostraram atenuações mais intensas nas altas frequências e frequência de corte mais baixas em compartimentos dendríticos mais distantes do soma. As interações não lineares foram avaliadas apli­cando entradas sinápticas senoidais com frequências primas entre si, em dois ou mais ramos dendríticos equivalentes simultaneamente e em compartimentos dendríticos diferentes. O espectro de frequên­cia da corrente efetiva foi analisado, comparando a amplitude do pico das distorções harmônicas e por intermodulação com o pico da frequência fundamental de menor amplitude: quanto menores estas diferenças maior o grau de não linearidade entre as ativações sinápti­cas em compartimentos dendríticos distintos. Os resultados sugerem expressivo grau de não linearidade entre as entradas sinápticas nos dendritos. Notou­-se que, em todas as situações, quando se variou a condutância sináptica, maior foi o grau de não linearidade em relação aos casos em que se variou a corrente sináptica, bem como entradas sinápticas mais próximas eletrotonicamente apresentaram maior grau de não linearidade em...

The aim of this work was to verify the functional differences between proximal and distal synapses and to investigate the nonlinear interactions of synaptic activation in models of motoneurons in passive conditions. The models, implemented in C++, are an expanded version of that developed by Vieira and Kohn (2005), with a more detailed dendritic arborization: five equivalent dendrites with 17 or 19 dendritic compartments each one. Tests verified the functional differences of synapses that occur close to the soma and along the dendrite in addition to evaluating the degree of nonlinearity response from dendritic arborization for different synaptic activation at different sites. The functional differences between the proximal and distal synapses were evaluated by injection of pure sinusoids in different dendritic compartments. The results showed severe attenuation at high frequencies and a lower cut-off frequency in more distant dendritic compartments of the soma. The nonlinear interactions were evaluated by applying sinusoidal synaptic input at prime frequencies with each other in two or more dendritic branches simultaneously and at different dendritic compartments. The frequency spectrum of the effective current was analyzed by comparing the peak amplitude of harmonics and spurious rays with the peak amplitude of the fundamental frequency of smaller amplitude: the smaller these differences are, the greater the degree of nonlinearity between the synaptic activation of distinct dendritic compartments. The results suggest a high degree of nonlinearity between the dendrites. In all situations was noted that when the synaptic conductance was varied, the nonlinearities was greater in relation to the cases in which the synaptic current was varied, and nonlinear summation is expected for synapses located electrotonically close together in relation for electrotonically separated inputs, suggesting a dependence on membrane potential.