Gait and electromyographic analysis of patients recovering after limb-saving surgery

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Modulation of cutaneous reflexes by load receptor input during human walking

To investigate the influence of load on the modulation of cutaneous reflexes, evoked by sural nerve stimulation, electromyographic activity in different leg muscles (tibialis anterior, gastrocnemius medialis (GM), biceps femoris, and soleus muscles (SO)) was recorded in healthy humans during treadmill walking with different body loads. Sural nerve stimulation was applied at two times perception threshold during different phases of the step cycle. Reflex amplitudes increased with body unloading and decreased with body loading. The reflex responses were not a simple function of the level of background activity. For example, in GM and SO, the largest reflex responses occurred during walking with body unloading, when background activity was de-creased. Hence, stable ground conditions (body loading) yielded smaller reflexes. It is proposed that load receptors are involved in the regulation of cutaneous reflex responses in order to adapt the locomotor pattern to the environmental condition

Estimation of flattening coefficient for absorption and circular dichroism using simulation

The absorbance and circular dichroism (CD) of suspensions is lower than if the same amount of chromophore were uniformly distributed throughout the medium. Several mathematical treatments of this absorption flattening phenomenon have been presented using various assumptions and approximations. This article demonstrates an alternative simulation approach that allows relaxation of assumptions. On current desktop computers, the algorithm runs quickly with enough particles and light paths considered to get answers that are usually accurate to better than 3%. Results from the simulation agree with the most popular analytical model for 0.01 volume fraction of particles, showing that the extent of flattening depends mainly on the absorbance through a particle diameter. Unlike previous models, the simulation can show that flattening is significantly lower when volume fraction increases to 0.1 but is higher when the particles have a size distribution. The simulation can predict the slope of the nearly linear relationship between flattening of CD and the absorbance of the suspension. This provides a method to correct experimental CD data where volume fraction and particle size are known

Control of roll and pitch motion during multi-directional balance perturbations

Does the central nervous system (CNS) independently control roll and pitch movements of the human body during balance corrections? To help provide an answer to this question, we perturbed the balance of 16 young healthy subjects using multi-directional rotations of the support surface. All rotations had pitch and roll components, for which either the roll (DR) or the pitch (DP) component were delayed by 150ms or not at all (ND). The outcome measures were the biomechanical responses of the body and surface EMG activity of several muscles. Across all perturbation directions, DR caused equally delayed shifts (150ms) in peak lateral centre of mass (COM) velocity. Across directions, DP did not cause equally delayed shifts in anterior-posterior COM velocity. After 300ms however, the vector direction of COM velocity was similar to the ND directions. Trunk, arm and knee joint rotations followed this roll compared to pitch pattern, but were different from ND rotation synergies after 300ms, suggesting an intersegmental compensation for the delay effects. Balance correcting responses of muscles demonstrated both roll and pitch directed components regardless of axial alignment. We categorised muscles into three groups: pitch oriented, roll oriented and mixed based on their responses to DR and DP. Lower leg muscles were pitch oriented, trunk muscles were roll oriented, and knee and arm muscles were mixed. The results of this study suggest that roll, but not pitch components, of balance correcting movement strategies and muscle synergies are separately programmed by the CNS. Reliance on differentially activated arm and knee muscles to correct roll perturbations reveals a dependence of the pitch response on that of roll, possibly due to biomechanical constraints, and accounts for the failure of DP to be transmitted equally in time across all limbs segments. Thus it appears the CNS preferentially programs the roll response of the body and then adjusts the pitch response accordingl

Rupture of a giant external iliac aneurysm six years after an aorto-bifemoral bypass

peer reviewedWe report the case of a patient operated on for an aorto-iliac aneurysm with an aorto-bifemoral bypass who presented a metachronous iliac aneurysm rupture, six years later, because of aneurysmal degeneration. We performed bipolar ligation of the external iliac artery and an end-to-end anastomosis of the prosthetic limb to the common femoral artery. We discuss aneurysms of the external iliac artery, characterised by their rarity, their specific morbidity and mortality

Neural regulation of rhythmic arm and leg movement is conserved across human locomotor tasks

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65152/1/jphysiol.2007.133843.pd

Attentional costs of walking are not affected by variations in lateral balance demands in young and older adults

Increased attentional costs of walking in older adults have been attributed to age-related changes in visuomotor and/or balance control of walking. The present experiment was conducted to examine the hypothesis that attentional costs of walking vary with lateral balance demands during walking in young and older adults. Twenty young and twenty older adults walked on a treadmill at their preferred walking speed under five conditions: unconstrained normal walking, walking on projected visual lines corresponding to either the participant’s preferred step width or 50% thereof (i.e. increased balance demand), and walking within low- and high-stiffness lateral stabilization frames (i.e. lower balance demands). Attentional costs were assessed using a probe reaction-time task during these five walking conditions, normalized to baseline performance as obtained during sitting. Both imposed step-width conditions were more attentionally demanding than the three other conditions, in the absence of any other significant differences between conditions. These effects were similar in the two groups. The results indicate that the attentional costs of walking were, in contrast to what has been postulated previously, not influenced by lateral balance demands. The observed difference in attentional costs between normal walking and both visual lines conditions suggests that visuomotor control processes, rather than balance control, strongly affect the attentional costs of walking. A tentative explanation of these results may be that visuomotor control processes are mainly governed by attention-demandingcortical processes, whereas balance is regulated predominantly subcortically