Effects of additional load at different heights on gait initiation: A statistical parametric mapping of center of pressure and center of mass behavior.

The purpose of this study was to investigate the effects of different vertical positions of an asymmetrical load on the anticipatory postural adjustments phase of gait initiation. Sixty-eight college students (32 males, 36 females; age: 23.65 ± 3.21 years old; weight: 69.98 ± 8.15 kg; height: 1.74 ± 0.08 m) were enrolled in the study. Ground reaction forces and moments were collected using two force platforms. The participants completed three trials under each of the following random conditions: no-load (NL), waist uniformly distributed load (WUD), shoulder uniformly distributed load (SUD), waist stance foot load (WST), shoulder stance foot load (SST), waist swing foot load (WSW), and shoulder swing foot load (SSW). The paired Hotelling's T-square test was used to compare the experimental conditions. The center of pressure (COP) time series were significantly different for the SUD vs. NL, SST vs. NL, WST vs. NL, and WSW vs. NL comparisons. Significant differences in COP time series were observed for all comparisons between waist vs. shoulder conditions. Overall, these differences were greater when the load was positioned at the shoulders. For the center of mass (COM) time series, significant differences were found for the WUD vs. NL and WSW vs. NL conditions. However, no differences were observed with the load positioned at the shoulders. In conclusion, only asymmetrical loading at the waist produced significant differences, and the higher the extra load, the greater the effects on COP behavior. By contrast, only minor changes were observed in COM behavior, suggesting that the changes in COP (the controller) behavior are adjustments to maintain the COM (controlled object) unaltered.

Effects of triceps surae fatigue and weight training level on gait variability and local stability in young adults.

Muscle fatigue negatively affects gait, and the changes in gait pattern due to muscle fatigue is influenced by which muscles are fatigued and pre-existing physical activity levels. However, how these factors alter gait stability and variability, measures related to risk of fall, remains unclear. To explore how muscular fatigue affects linear and nonlinear gait features in young adults, the effects of triceps surae fatigue and weight training level on gait variability and local stability, as well as a 12-min recovery time of post-fatigue period, were evaluated in young adults (trained and untrained groups). Some features were estimated, i.e., (i) step length (SL) and step frequency (SF), (ii) average standard deviation of trunk acceleration along strides (VAR), and (iii) local dynamic stability (LDS; maximum Lyapunov exponent). LDS presented a significant increase in the anterior-posterior direction with recovery to trained group. SL and SF changed immediately post-fatigue and recovered for both groups, while VAR increased significantly in all directions, with a recovery in the vertical direction for both groups and in the medial-lateral direction for trained group. Localized fatigue affected the analyzed gait variables independent of the participant's training condition, and an interval of 12 min does not seem to be enough for a complete recovery, suggesting a longer recovery period after tasks involving localized triceps surae fatigue to guarantee basal levels of gait variability and local stability. Graphical abstract Flow chart of the experimental protocol. A) Pre-fatigue: 4 min walking at PWS. B) Post-fatigue: first 4 min walking after fatigue protocol. C) Post-fatigue: second 4 min walking after fatigue protocol. D) Post-fatigue: third 4 min walking after fatigue protocol (PWS, preferred walking speed; AP, anterior-posterior; V, vertical; ML, medial-lateral).

Effects of inclined surfaces on gait variability and stability in unilateral lower limb amputees.

This study aims to analyze gait variability and stability of individuals with amputation walking on upward (8%), horizontal (0%), and downward (- 8%) inclines, by using linear and nonlinear descriptors. Trunk linear variability and gait spatiotemporal parameters were evaluated. Nonlinear variability (local dynamic stability-LDS), was estimated by the maximum Lyapunov exponent (λ) computed from a trunk marker velocity. The gait descriptors were compared among three distinct groups (N participants): unilateral transtibial amputees (TTA, N = 12); unilateral transfemoral amputees (TFA, N = 13); control group (CT, N = 15). For step width and support phase, the effect of inclination was greater for TFA group, especially in the DOWN condition. Linear variability was higher for amputees (TFA and TTA) especially in the UP condition in the medial-lateral and anterior-posterior directions. TTA and TFA groups presented greater λ values than CT group in medial-lateral direction indicating decreased LDS, but TFA group presented smaller λ values than TTA and CT groups in the V direction. Our findings showed that inclination introduced significant changes in the estimated parameters for all groups, with greater changes for amputee groups. Furthermore, the level of amputation directly affects the analyzed gait parameters being the TFA group the one which presents greater changes. Graphical abstract The objective of this study was to analyze gait variability of individuals with amputation walking on (A) upward (+ 8%), (B) horizontal (0%), and (C) downward (- 8%) inclines, by using linear and nonlinear biomechanical descriptors. Linear measures of variability, such trunk variability and gait spatiotemporal parameters were evaluated. Nonlinear variability was estimated by the exponent of divergence (maximum Lyapunov exponent) of the velocity of a marker fixed in the subject's trunk while walking on inclined surfaces.

Effects of backpack load and positioning on nonlinear gait features in young adults.

Overloaded backpacks can cause changes in posture and gait dynamic balance. Therefore, the aim of this study was to assess gait regularity and local dynamic stability in young adults as they carried a backpack in different positions, and with different loads. Twenty-one healthy young adults participated in the study, carrying a backpack that was loaded with 10 and 20% of their body weight (BW). The participants walked on a level treadmill at their preferred walking speeds for 4 min under different conditions of backpack load and position (i.e. with backpack positioned back bilaterally, back unilaterally, frontally or without a backpack). Results indicate that backpack load and positioning significantly influence gait stability and regularity, with the exception of the 10% BW bilateral back position. Therefore, the recommended safe load for school-age children and adolescents (10% of BW) should also be considered for young adults. Practitioner summary: Increase in load results in changes in posture, muscle activity and gait parameters, so we investigated the gait adaptations related to regularity and stability. Conditions with high backpack loads significantly influenced gait stability and regularity in a position-dependent manner, except for 10% body weight bilateral back position.

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.

A simple, reliable method to determine the mean gait speed using heel markers on a treadmill.

Gait speed is an essential parameter of gait analysis. Our study proposed a simple and accurate method to extract a mean gait speed during walking on a treadmill using only kinematic data from markers placed on the heels of the participants' feet. This method provided an attractive, simple method that remains resistant to errors in treadmill calibration. In addition, this method required only two markers, since heel markers are essential to gait analysis, and the proposed method is robust enough to differentiate among various gait speeds (mean error <1%).

Linear and Nonlinear Gait Features in Older Adults Walking on Inclined Surfaces at Different Speeds.

This study evaluated linear and nonlinear gait features in healthy older adults walking on inclined surfaces at different speeds. Thirty-seven active older adults (experimental group) and fifty young adults (control group) walked on a treadmill at 100% and ±20% of their preferred walking speed for 4 min under horizontal (0%), upward (UP) (+8%), and downward (DOWN) (-8%) conditions. Linear gait variability was assessed using the average standard deviation of trunk acceleration between strides (VAR). Gait stability was assessed using the margin of stability (MoS). Nonlinear gait features were assessed by using the maximum Lyapunov exponent, as a measure of local dynamic stability (LDS), and sample entropy (SEn), as a measure of regularity. VAR increased for all conditions, but the interaction effects between treadmill inclination and age, and speed and age were higher for young adults. DOWN conditions showed the lowest stability in the medial-lateral MoS, but not in LDS. LDS was smaller in UP conditions. However, there were no effects of age for either MoS or LDS. The values of SEn decreased almost linearly from the DOWN to the UP conditions, with significant interaction effects of age for anterior-posterior SEn. The overall results supported the hypothesis that inclined surfaces modulate nonlinear gait features and alter linear gait variability, particularly in UP conditions, but there were no significant effects of age for active older adults.

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.