Paula L. Silva

Stretching versus strength training in lengthened position in subjects with tight hamstring muscles: A randomized controlled trial

Stretching is used to modify muscle length. However, its effects seem to be temporary. There is evidence in animal models that strengthening in a lengthened position may induce long lasting changes in muscle length. The objective of this study was to compare changes in hamstrings flexibility, peak torque angle and stretch tolerance after two training programs: stretching and strengthening in a lengthened position. Forty-five subjects with tight hamstrings were randomly assigned into three groups: control, stretching and strength training in lengthened position. The interventions were performed three times a week for eight weeks. The subjects were assessed before and after the end of the programs. Data provided by an isokinetic dynamometer were used to assess hamstrings flexibility, peak torque angle, and stretch tolerance. The data analysis demonstrated that strengthening in lengthened position changed peak torque angle in the direction of knee extension (p=0.001). No change in flexibility was observed (p=0.449). Both experimental groups showed an increase in stretch tolerance (p=0.001). The results demonstrated that strengthening in a lengthened position produced a shift of the torque-angle curve, which suggests an increase in muscle length. Conversely, stretching did not produce modification of torque-angle curve and flexibility; its effects appear restricted to increases in stretch tolerance.

Muscle-based perception: theory, research and implications for rehabilitation

INTRODUCAO: A percepcao muscular das propriedades espaciais dos membros restringe o padrao, periodo e magnitude das forcas exercidas durante a execucao de atividades motoras. A importância central da percepcao muscular, tanto para acoes rotineiras quanto para acoes especializadas, merece atencao da comunidade envolvida na area de reabilitacao, uma vez que alteracoes em suas funcoes podem estar relacionadas a importantes limitacoes funcionais. Nesta revisao, os autores apresentam um resumo da pesquisa que pode ser utilizada para guiar o desenvolvimento de ferramentas de avaliacao eficazes bem como programas de reabilitacao que sejam especificamente direcionados para estas disfuncoes. OBJETIVOS: Quatro pontos especificos foram incluidos: primeiro, a apresentacao da abordagem com base em informacoes relativas a percepcao muscular de acordo com as leis da fisica; segundo, a identificacao dos principios centrais determinantes da percepcao muscular que vem sendo revelada e apoiada por trabalhos empiricos; terceiro, um resumo dos relatos que investigaram e se os principios identificados poderiam ser generalizados para a percepcao muscular dos individuos com alteracoes motoras e sensitivas; e quarto, uma discussao preliminar sobre as implicacoes potenciais da pesquisa aqui apresentada, no tocante aos assuntos relacionados a reabilitacao.

Changes in lower limb co-contraction and stiffness by toddlers with Down syndrome and toddlers with typical development during the acquisition of independent gait.

During gait acquisition, children learn to use their changing resources to meet the requirements of the task. Compared to typically developing toddlers (TD), toddlers with Down syndrome (DS) have functionally different musculoskeletal characteristics, such as hypotonia, and joint and ligament laxity, that could produce a reduced passive stiffness. The interplay between this inherently lower passive stiffness and the demands of walking may result in different strategies during gait acquisition. This study compared normalized global stiffness and lower limbs co-contraction indices (CCI) used by toddlers with TD (n=12) and with DS (n=12), during the early stages of gait acquisition. Stiffness and CCI were normalized by gravitational torque (mLg) in both phases of gait (stance, swing). Five longitudinal evaluations were conducted from the onset of locomotion until three months post-acquisition. All children were video taped and had electromyographic (EMG) recordings from muscle pairs of one leg, which were used to calculate CCI of hip, knee, ankle, and total leg CCI. Body and lower limb stiffness were calculated according to a hybrid pendulum resonance equation. Results from ANOVAs revealed no group differences on stiffness or on CCIs during stance but children with DS showed greater CCI during swing. Despite the structural musculoskeletal differences between toddlers with TD and with DS, the similarities observed in their processes of gait development suggest functional equivalences.

An Empirical Illustration and Formalization of the Theory of Direct Learning: The Muscle-Based Perception of Kinetic Properties

The theory of direct learning portrays learning as specificity between higher order informational quantities, referred to as information for learning, and change in performance that occurs with practice (Jacobs & Michaels, 2007). The focus of the theory is on the lawful generation and possible use of information for learning. This study illustrates and further develops the theory. Participants in the study were asked to judge the mass of unseen handheld objects. In Experiment 1, different participants received feedback on different mechanical properties of the objects, and in Experiment 2, different participants practiced with different sets of objects. The practice led to changes in performance that, in the present portrayal, show up as movements through manifolds. As predicted by the theory, these movements are specific to information for learning, the most precise description of which is obtained with difference equations. A second and more theoretical part of the article provides a tentative formalization of the theory.

Haptic selective attention by foot and by hand

Nonvisual perceptions of a wielded objects spatial properties are based on the quantities expressing the objects mass distribution, quantities that are invariant during the wielding. The mechanoreceptors underlying the kind of haptic perception involved in wielding - referred to as effortful, kinesthetic, or dynamic touch - are those embedded in the muscles, tendons, and ligaments. The present experiments focus was the selectivity of this muscle-based form of haptic perception. For an occluded rod grasped by the hand at some intermediate position along its length, participants can attend to and report selectively the rods full length, its partial lengths (fore or aft of the hand), and the position of the grip. The present experiment evaluated whether participants could similarly attend selectively when wielding by foot. For a given rod attached to and wielded by foot or attached to (i.e. grasped) and wielded by hand, participants reported (by magnitude production) the rods whole length or fractional length leftward of the point of attachment. On measures of mean perceived length, accuracy, and reliability, the degree of differentiation of partial from full extent achieved by means of the foot matched that achieved by means of the hand. Despite their neural, anatomical, and experiential differences, the lower and upper limbs seem to abide by the same principles of selective muscle-based perception and seem to express this perceptual function with equal facility.

Contributions of Cocontraction and Eccentric Activity to Stiffness Regulation

Individuals commonly adjust joint stiffness in response to changes in environmental and task demands. The objective of the present study was to evaluate the contribution of muscular cocontraction and eccentric activity to this adjustment. In all, 30 healthy volunteers participated in the present study. The authors indirectly manipulated elbow stiffness by modifying (a) the frequency of forearm movements (frequency conditions) and (b) the kinetic properties of the forearm through the addition of external mass (mass conditions). Multilevel regression models identified muscular cocontraction and eccentric activity as predictors of joint stiffness in the frequency conditions but not in the mass conditions. Results indicated that cocontraction is not the sole mechanism for stiffness regulation. Rather, the mechanisms that different participants used varied as a function of the demands of the task.

Steady-state stress at one hand magnifies the amplitude, stiffness, and non-linearity of oscillatory behavior at the other hand.

Stress at one body segment can influence rhythmic movements of non-neighboring body segments. The nervous, circulatory, and fascia (connective tissue) systems are potential mediators of such remote effects. Assessing them begins with a detailed description of the remote effects. Precisely, how do the rhythmic movements change? In our experiment with seven participants, left-hand oscillations of held pendulums at self-selected frequencies were examined as a function of right-hand tonic forces of 0, 10 or 20% of the maximum voluntary contraction. We evaluated the effect of the right hands tonic force on the amplitude and frequency, and the stiffness and friction functions of the left hands oscillations. Our results suggest that (a) amplitude and stiffness (both linear and non-linear) increased with tonic force but frequency and friction (both linear and non-linear) did not, and (b) the stiffness increases due to right hand 10 and 20% stress were indifferent to the initial (0%) left-hand stiffness values. Discussion took note of how the nervous system and architectural features of the body (e.g., its network of connective tissue) may produce such effects.

The role of haptic information in shaping coordination dynamics: Inertial frame of reference hypothesis

Current research suggests that non-visual perception of the spatial orientation of body segments is tied to vectors representative of their mass moment distribution (v(mm)). Our question was whether the relative orientation of v(mm) of right and left hands (Δv(mm)=v(mm) left-v(mm) right) constitutes haptic information supporting bimanual coordination and, if so, how it contributes to coordination dynamics. Blindfolded participants coordinated the motions of a pair of cross-shaped, hand-held pendulums that were either symmetrically loaded (Δv(mm)=0) or asymmetrically loaded (Δv(mm)≠0). The sign and magnitude of Δv(mm), in particular of the first moment vector, systematically affected the pattern of coordination (indexed by mean relative phase ϕ), but not its stability. These results suggest that (1) Δv(mm) specifies a frame of reference about which coordination is organized; and (2) that the changes in pattern were a function of the experimentally induced biases in this perceptual frame of reference and not a function of a functional asymmetry akin to detuning. The implications of the findings to the understanding of perceptual regulation of interlimb coordination were discussed.

Women With Early Stages of Knee Osteoarthritis Demonstrate Lower Mechanical Work Efficiency at the Knee

The purpose of this study was to investigate the mechanical work of the hip, knee, and ankle in females with mild and moderate levels of knee osteoarthritis (OA). Thirty-nine women with knee OA and 39 healthy women participated in the study. Mechanical work expenditures at the hip, knee, and ankle were computed using data obtained during gait. Knee total and absorptive mechanical work was lower for the OA group. Muscle weakness and pain may have contributed to the lower mechanical efficiency of the knee, which may help explain the lower level of physical function demonstrated by women with knee OA.

The Effect of Walking Speed on Foot Kinematics is Modified When Increased Pronation is Induced

BACKGROUND The relation between walking speed and foot kinematics during gait is not well established, and neither is it clear whether this relation is modified in the presence of factors expected to increase pronation (eg, abnormal foot alignment). Understanding how foot kinematics is affected by walking speed under varying conditions could contribute to our understanding of stresses to the musculoskeletal system during walking. We evaluated the effect of walking speed on foot kinematics in the frontal plane during gait and determined whether this effect is modified by using medially inclined insoles that force the foot into increased pronation. METHODS Twenty-six healthy young adults were assessed while walking on a treadmill wearing flat insoles and wearing medially inclined insoles. Foot kinematics in the frontal plane was measured with a three-dimensional motion analysis system. Data were analyzed during the stance phase of gait. RESULTS There was no main effect of speed on average calcaneal position. However, there was a significant insole type × walking speed interaction effect. In the flat insole condition, increased walking speed was associated with a less inverted average calcaneal position (or greater magnitudes of eversion), whereas in the inclined insole condition, higher speeds were associated with a less everted average calcaneal position (or increased magnitudes of inversion). CONCLUSIONS The magnitude of foot eversion increases at faster gait speeds under typical conditions. In the presence of factors that induce excessive pronation, however, this effect is reversed. Results suggest that individuals use greater active control of foot motion at faster speeds in the presence of excessive pronation to improve push-off efficiency. Potential clinical consequences of this functional strategy are discussed.