Teddy Caderby

Does an additional load modify the Anticipatory Postural Adjustments in gait initiation

The objective of the study was to examine whether and how an additional load affects the Anticipatory Postural Adjustments (APA) in gait initiation in able-bodied individuals. Nineteen healthy participants initiated gait at a self-selected speed in two conditions: unloaded and with an overload of 15% body weight. The APA duration, the forward impulse of the APA and the duration of gait initiation increased significantly with the overload, while the other variables did not change. These results indicate that, during gait initiation with overload, able-bodied subjects modulate the APA duration to produce a higher forward impulse in order to achieve the steady-state gait at the end of the first step. These findings could have implications in clinical practice where overloading could be used to improve the gait initiation in pathologic patients. Further investigations are needed to confirm this suggestion.

Detection of swing heel-off event in gait initiation using force-plate data.

This study investigated the accuracy and reliability of four methods using force-plate data for detecting the swing heel-off (HO) time in gait initiation. Results of these methods were compared to those obtained by means of a reference method using a footswitch. Ten young healthy adults performed 18 forward gait initiation trials at self-selected speed and at maximal speed. Results showed that the method based on vertical impulse was the most accurate and reliable in determining HO in both speed conditions. The mean error obtained with this method was -8±10ms in the self-selected speed condition (-7±10ms in the maximal speed condition), with no significant effect of gait speed (P>0.05). These findings suggest that this method based on force-plate data is valid and reliable for detecting HO in forward gait initiation in the absence of additional hardware.

Influence of temporal pressure constraint on the biomechanical organization of gait initiation made with or without an obstacle to clear

AbstractMany daily motor tasks have to be performed under a temporal pressure constraint. This study aimed to explore the influence of such constraint on motor performance and postural stability during gait initiation. Young healthy participants initiated gait at maximal velocity under two conditions of temporal pressure: in the low-pressure condition, gait was self-initiated (self-initiated condition, SI); in the high-pressure condition, it was initiated as soon as possible after an acoustic signal (reaction-time condition, RT). Gait was initiated with and without an environmental constraint in the form of an obstacle to be cleared placed in front of participants. Results showed that the duration of postural adjustments preceding swing heel-off (“anticipatory postural adjustments”, APAs) was shorter, while their amplitude was larger in RT compared to SI. These larger APAs allowed the participants to reach equivalent postural stability and motor performance in both RT and SI. In addition, the duration of the execution phase of gait initiation increased greatly in the condition with an obstacle to be cleared (OBST) compared to the condition without an obstacle (NO OBST), thereby increasing lateral instability and thus involving larger mediolateral APA. Similar effects of temporal pressure were obtained in NO OBST and OBST. This study shows the adaptability of the postural system to temporal pressure in healthy young adults initiating gait. The outcome of this study may provide a basis for better understanding the aetiology of balance impairments with the risk of falling in frail populations while performing daily complex tasks involving a whole-body progression.

Effects of Changing Body Weight Distribution on Mediolateral Stability Control during Gait Initiation

During gait initiation, anticipatory postural adjustments (APA) precede the execution of the first step. It is generally acknowledged that these APA contribute to forward progression but also serve to stabilize the whole body in the mediolateral direction during step execution. Although previous studies have shown that changes in the distribution of body weight between both legs influence motor performance during gait initiation, it is not known whether and how such changes affect a person’s postural stability during this task. The aim of this study was to investigate the effects of changing initial body weight distribution between legs on mediolateral postural stability during gait initiation. Changes in body weight distribution were induced under experimental conditions by modifying the frontal plane distribution of an external load located at the participants’ waists. Fifteen healthy adults performed a gait initiation series at a similar speed under three conditions: with the overload evenly distributed over both legs; with the overload strictly distributed over the swing-limb side; and with the overload strictly distributed over the stance-leg side. Our results showed that the mediolateral location of center-of-mass (CoM) during the initial upright posture differed between the experimental conditions, indicating modifications in the initial distribution of body weight between the legs according to the load distribution. While the parameters related to the forward progression remained unchanged, the alterations in body weight distribution elicited adaptive changes in the amplitude of APA in the mediolateral direction (i.e., maximal mediolateral shift of the center of pressure (CoP)), without variation in their duration. Specifically, it was observed that the amplitude of APA was modulated in such a way that mediolateral dynamic stability at swing foot-contact, quantified by the margin of stability (i.e., the distance between the base of support boundary and the extrapolated CoM position), did not vary between the conditions. These findings suggest that APA seem to be scaled as a function of the initial body weight distribution between both legs so as to maintain optimal conditions of stability during gait initiation.

Energy Expenditure in People with Diabetes Mellitus: A Review

Physical activity (PA) is an important non-therapeutic tool in primary prevention and treatment of diabetes mellitus (DM). To improve activity-based health management, patients need to quantify activity-related energy expenditure and the other components of total daily energy expenditure. This review explores differences between the components of total energy expenditure in patients with DM and healthy people and presents various tools for assessing the energy expenditure in subjects with DM. From this review, it appears that patients with uncontrolled DM have a higher basal energy expenditure (BEE) than healthy people which must be considered in the establishment of new BEE estimate equations. Moreover, studies showed a lower activity energy expenditure in patients with DM than in healthy ones. This difference may be partially explained by patient with DMs poor compliance with exercise recommendations and their greater participation in lower intensity activities. These specificities of PA need to be taken into account in the development of adapted tools to assess activity energy expenditure and daily energy expenditure in people with DM. Few estimation tools are tested in subjects with DM and this results in a lack of accuracy especially for their particular patterns of activity. Thus, future studies should examine sensors coupling different technologies or method that is specifically designed to accurately assess energy expenditure in patients with diabetes in daily life.

Balance control during gait initiation: State-of-the-art and research perspectives

It is well known that balance control is affected by aging, neurological and orthopedic conditions. Poor balance control during gait and postural maintenance are associated with disability, falls and increased mortality. Gait initiation - the transient period between the quiet standing posture and steady state walking - is a functional task that is classically used in the literature to investigate how the central nervous system (CNS) controls balance during a whole-body movement involving change in the base of support dimensions and center of mass progression. Understanding how the CNS in able-bodied subjects exerts this control during such a challenging task is a pre-requisite to identifying motor disorders in populations with specific impairments of the postural system. It may also provide clinicians with objective measures to assess the efficiency of rehabilitation programs and better target interventions according to individual impairments. The present review thus proposes a state-of-the-art analysis on: (1) the balance control mechanisms in play during gait initiation in able bodied subjects and in the case of some frail populations; and (2) the biomechanical parameters used in the literature to quantify dynamic stability during gait initiation. Balance control mechanisms reviewed in this article included anticipatory postural adjustments, stance leg stiffness, foot placement, lateral ankle strategy, swing foot strike pattern and vertical center of mass braking. Based on this review, the following viewpoints were put forward: (1) dynamic stability during gait initiation may share a principle of homeostatic regulation similar to most physiological variables, where separate mechanisms need to be coordinated to ensure stabilization of vital variables, and consequently; and (2) rehabilitation interventions which focus on separate or isolated components of posture, balance, or gait may limit the effectiveness of current clinical practices.

Influence of temporal pressure constraint on the biomechanical organisation of gait initiation made with or without an obstacle to clear.

Many daily motor tasks have to be performed under a temporal pressure constraint. This study aimed to explore the influence of such constraint on motor performance and postural stability during gait initiation made with or without an obstacle to be cleared. Gait initiation, which corresponds to the transient period from an upright stance to steady-state walking, is a classical paradigm for studying the coordination between posture, equilibrium and movement. It is composed of a postural phase ending at swing heel-off, during which dynamic phenomena called ‘anticipatory postural adjustments’ (APA) are developed, followed by step execution phase ending at the time when the swing foot touches the ground (Brenière et al. 1987). These APA are manifested as a backward and lateral center-ofpressure (CoP) shift towards the swing-leg side, which promotes centre-of-mass acceleration in the opposite direction, i.e. forwardly and towards the stance-leg side. APA dynamics along the mediolateral (ML) direction is known to be predictive of postural stability reached at the end of gait initiation (Caderby et al. 2014), while APA dynamics along the anteroposterior direction is predictive of motor performance, in term of peak centreof-mass velocity (Brenière et al. 1987). Recent studies have shown that temporal pressure constraint influences the temporo-spatial features of APA associated with leg flexion from the erect posture tasks (Yiou et al. 2012, 2014; Hussein et al. 2013). Specifically, APA duration was shorter in the condition with a high temporal pressure (the leg flexion was triggered in a reaction-time [RT] condition) as compared to condition with a low temporal pressure (the leg flexion was self-initiated [SI]); this shortening was compensated by Influence of temporal pressure constraint on the biomechanical organisation of gait initiation made with or without an obstacle to clear

A Simple Method for Measuring Lower Limb Stiffness in Hopping

Lower limb stiffness is of great of interest to the scientific and sporting communities, given its implication in sporting performance and in musculoskeletal injury risk. In the literature, lower limb stiffness has been extensively studied during hopping, as it constitutes a simple bouncing gait. Characterization of lower limb stiffness in hopping is commonly based on a biomechanical model called the “spring-mass model”. This model assimilates the whole-body to an oscillating system consisting of a mass supported by a single spring, which represents the mechanical behaviour of the lower limbs during the ground contact phase of hopping. The stiffness of the spring, referred to as “leg spring”, represents an overall stiffness of the musculoskeletal system of the lower limbs. In this chapter, we will describe the biomechanical aspects related to this concept of leg stiffness in hopping and we will present a simple method for measuring it. This method enables the calculation of leg stiffness from just the body mass of the individual and the contact and flight times during hopping, both of which may be obtained with simple technical equipment. This simple method may be particularly advantageous for assessing leg stiffness in a field environment, as well as in laboratory conditions.

Shoulder loading reliability in seated able-bodied subjects

Shoulder performance and sensorimotor control assessments help to identify shoulder instabilities and document the rehabilitation progress. Testing seated subjects in a position of hand prehension requires less controlled adjustments to maintain body balance in a clinically relevant situation. The objective of this work was to determine the test-retest repeatability of a novel shoulder stability test in seated subjects with the ipsi-lateral hand in prehension during four arm loading conditions. Able-bodied subjects were seated on a rigid chair fixed to a force plate. A horizontally and posteriorly directed force was applied to the hand for four 4 loading conditions ranging from 0 to 3 kg. Ten postural balance parameters were calculated from the center of pressure displacements and its corresponding free moments. Intra-class correlation coefficients were calculated for three consecutive trials and for four loading conditions. Generally, the intra-class correlations values increased gradually with the load and varied from 0.727 to 0.948. Tz values increased non-linearly with the applied load. The test-retest reliability of a new shoulder stability test in seated able-bodied subjects was high with sufficient loading (3 kg) and 3 trials.

Influence of gait speed on free vertical moment during walking

Free vertical moment (FVM) of ground reaction is recognized to be a meaningful indicator of torsional stress on the lower limbs when walking. The purpose of this study was to examine whether and how gait speed influences the FVM when walking. Fourteen young healthy adults performed a series of overground walking trials at three different speeds: low, preferred and fast. FVM was measured during the stance phase of the dominant leg using a force platform embedded in a 10 m-long walkway. Transverse plane kinematic parameters of the foot and pelvis were measured using a motion capture system. Results showed a significant decrease in peak abduction FVM (i.e., resisting internal foot rotation) and an increase in peak adduction FVM (i.e., resisting external foot rotation), together with an increase in gait speed. Concomitantly, we observed a decrease in the foot progression angle and an increase in the peak pelvis rotation velocity in the transverse plane with an increase in gait speed. A significant positive correlation was found between the pelvis rotation velocity and the peak adduction moment, suggesting that pelvis rotation influences the magnitude of adduction FVM. Furthermore, we also found significant correlations between the peak adduction FVM and both the step length and frequency, indicating that the alterations in FVM may be ascribed to changes in these two key variables of gait speed. These speed-related changes in FVM should be considered when this parameter is used in gait assessment, particularly when used as an index for rehabilitation and injury prevention.