Christophe Gillet

Does lower limb preference influence gait initiation

Gait initiation (GI) has been the focus of many investigations in order to determine the kinematic and kinetic parameters associated with this process. In these studies, the parameters are observed during GI with the preferential lower limb. However, none of these studies have looked at the impact on GI parameters when the start is achieved with the non-preferential limb. This investigation focused on the effects of lower limb preference on the kinematic and kinetic parameters of GI. Upon display of a visual cue, subjects stepped with preferential limb or non-preferential limb at natural speed. The duration of GI phases, the medio-lateral component of the center of mass (CM) displacement, the medio-lateral distance between the center of pressure and the CM, the step width as well as the medio-lateral impulse, were observed. When subjects started with the non-preferential limb, the bodyweight transfer was facilitated by a greater impulse during the anticipatory postural adjustment (APA) phase. Conversely, a more lateral CM displacement during the execution phase and a more lateral step in preferential start were observed. Asymmetry in frontal plane body motion was observed during weight transfer following APA, as well as during assistive control of ballistic body motion during the execution phase of the first step. In both conditions, the non-preferential limb provided the greater lateral impulse on the ground. This may have clinical relevance especially in individuals with unilateral limb dyscontrol and postural asymmetry that may require rehabilitation.

Trunk's Natural Inclination Influences Stance Limb Kinetics, but Not Body Kinematics, during Gait Initiation in Able Men

The imposing mass of the trunk in relation to the whole body has an important impact on human motion. The objective of this study is to determine the influence of trunks natural inclination - forward (FW) or backward (BW) with respect to the vertical - on body kinematics and stance limb kinetics during gait initiation. Twenty-five healthy males were divided based on their natural trunk inclination (FW or BW) during gait initiation. Instantaneous speed was calculated at the center of mass at the first heel strike. The antero-posterior impulse was calculated by integrating the antero-posterior ground reaction force in time. Ankle, knee, hip and thoraco-lumbar (L5) moments were calculated using inverse dynamics and only peaks of the joint moments were analyzed. Among all the investigated parameters, only joint moments present significant differences between the two groups. The knee extensor moment is 1.4 times higher (P<0.001) for the BW group, before the heel contact. At the hip, although the BW group displays a flexor moment 2.4 times higher (P<0.001) before the swing limbs heel-off, the FW group displays an extensor moment 3.1 times higher (P<0.01) during the swing phase. The three L5 extensor peaks after the toe-off are respectively 1.7 (P<0.001), 1.4 (P<0.001) and 1.7 (P<0.01) times higher for the FW group. The main results support the idea that the patterns described during steady-state gait are already observable during gait initiation. This study also provides reference data to further investigate stance limb kinetics in specific or pathologic populations during gait initiation. It will be of particular interest for elderly people, knowing that this population displays atypical trunk postures and present a high risk of falling during this forward stepping.

Propulsion and braking in the study of asymmetry in able-bodied men's gaits.

The present study was designed to test functional differences between both lower limbs in able-bodied gait according to fore-aft force impulse analyses and to assess the existence of a preferential lower limb for forward propulsion and braking. The leg that did more of the braking (Most Braking Limb) and the leg that did more of the propulsion (Most Propulsive Limb) were defined by the higher negative and positive impulses calculated from the anterior-posterior component of the ground reaction force. 24 adult men free of pain and injury to their lower extremities (M age = 25.9 yr., SD = 4.5) performed 10 walking trials on a 10-m walkway with two force plates flush mounted in the middle. The anterior-posterior component of the velocity of the center of mass (VAP) was calculated with the VICON system. Results highlighted two forms of asymmetry behaviour: although significant bilateral differences between the legs concerning the propulsive and braking impulses were found in all participants, 70.8% of the participants displayed a different Most Braking Limb than Most Propulsive Limb, whereas 25% used the same leg to produce both more propulsion and braking. High consistency was found in the behavioural strategy. Bilateral differences in VAP according to the gait cycle (Most Propulsive Limb vs Most Braking Limb) suggested a functional division of tasks between the two lower limbs for 70.8% of the participants. The study provides support for the relevancy of a functional categorization to highlight different asymmetry strategies in able-bodied gait.

Chronic low back pain sufferers exhibit freezing-like behaviors when asked to move their trunk as fast as possible

BACKGROUND CONTEXT The effect of chronic low back pain (CLBP) on the kinematic parameters of trunk motion has received much more interest in this last decade. However, there are no descriptions of the motor strategies that occur when patients perform trunk movements in the three anatomical planes at different pace conditions. PURPOSE To investigate motor strategies used by CLBP patients and asymptomatic people while performing different go and back trunk movements in an upright standing position. STUDY DESIGN A comparative study. PATIENT SAMPLE The control group (CG, n=33) included 14 men and 19 women with no history of low back pain, and the chronic low back pain group (CLBPG, n=49) included 21 men and 28 women. OUTCOME MEASURES Kinematic data were analyzed during six trunk movements: flexion, extension, left and right lateral bendings, and rotations under two pace conditions (preferred and fast paces). METHODS A three-dimensional optoelectronic motion analysis system was used to assess static (trunk inclinations and base of support) and dynamic (range of motion [ROM] and mean angular velocity of the trunk) parameters during the go and back phases of trunk movements. RESULTS In the initial position, CLBPG showed a more forward-tilted trunk inclination (2.1°±1.1°, p=.013) compared with CG. The base of support was significantly higher in CG (+22.7 cm2, p=.009) during the fast pace when compared with the preferred pace. Regardless of the pace condition, ROM and mean angular velocity of the trunk were significantly lower in CLBPG for all examined movements and the pace condition did not significantly alter ROM. At the preferred pace, both groups displayed the same motor strategy: they all went faster during the second phase of movement than during the first phase. However, at the fast pace, while CG was going faster during the first phase than during the second, CLBPG maintained the same motor strategy as at the preferred pace. CONCLUSIONS Contrary to CG who changed its motor behavior from a preferred pace to a fast pace, CLBPG exhibited freezing-like behaviors. This original result highlights the importance of studying the velocity. The use of this parameter may improve the diagnosis of CLBP patients and could be a key indicator for treatment progress and long-term monitoring.

Designing a camera placement assistance system for human motion capture based on a guided genetic algorithm

In multi-camera motion capture systems, determining the optimal camera configuration (camera positions and orientations) is still an unresolved problem. At present, configurations are primarily guided by a human operator’s intuition, which requires expertise and experience, especially with complex, cluttered scenes. In this paper, we propose a solution to automate camera placement for motion capture applications in order to assist a human operator. Our solution is based on the use of a guided genetic algorithm to optimize camera network placement with an appropriate number of cameras. In order to improve the performance of the genetic algorithm (GA), two techniques are described. The first is a distribution and estimation technique, which reduces the search space and generates camera positions for the initial GA population. The second technique is an error metric, which is integrated at GA evaluation level as an optimization function to evaluate the quality of the camera placement in a camera network. Simulation experiments show that our approach is more efficient than other approaches in terms of computation time and quality of the final camera network.

The influence of shoe drop on the kinematics and kinetics of children tennis players

Abstract This study investigated the immediate effects of reducing the shoe drop (i.e. the difference between the heel and the forefoot height) on the kinematics and kinetics of the lower extremities of children tennis players performing a tennis-specific movement. Thirteen children tennis players performed a series of simulated open stance forehands wearing 3 pairs of shoes differing only in the drop: 0 (D0), 6 (D6) and the control condition of 12 mm (D12). Two embedded forceplates and a motion capture system were used to analyse the ground reaction forces and ankle and knee joint angles and moments of the leading lower limb. In D6 compared with D12, the peak impact force was reduced by 24% (p = .004) and the ankle was less dorsiflexed at foot strike (p = .037). In D0 compared with D12, the peak impact force was reduced by 17% (p = .049), the ankle was less dorsiflexed at foot strike (p = .045) and the knee was more flexed at foot strike (p = .007). In addition, 4 out of 13 participants (31%) presented a forefoot strike pattern for some of the trials in D0. No difference was observed across shoe conditions for the peak knee extensor moment (p = .658) or the peak ankle plantarflexor moment (p = .071). The results provide preliminary data supporting the hypothesis that for children tennis players, using a 6-mm lower shoe drop might reduce heel impact forces and thus limit potentially impact-related injuries.

The “backpack effect” on ground reaction forces during gait

Today, backpack is often used during common leisure activities as mountaineering or trekking. Nevertheless, the majority of studies on the subject have investigated the effects of backpacking on physical performance during military carrying. Holewijn and Lotens (1992) have thus investigated the influence of different backpack designs on physical performance. On the other hand the effects of backpacking, in the role of a perturbing task more than in a mass carriage, have never been studied. Regarding to previous considerations, the present preliminary study sough to explore the carrying mode on the ground reaction forces (GRF) during gait.

Influence of a New Backpack Design on Kinematics and Dynamics of Walking

The backpacks influence the posture of the walkers. The object of this study is to quantify the modifications of the posture but also the modifications during gait, in differs configurations load: (a) without backpack, (b) with a commercial backpack, and with a prototype of which it is possible to make move part of the load, (c) behind of the trunk and (d) in front of the trunk. To evaluate this new design, 13 subjects were asked to walk, in straight line at their natural walking speed. Kinematics and dynamics data were recorded by a Vicon optoelectronic system and 2 force platforms (Kistler). The results show that the forward load condition (d) allows the raising of the walker trunk. Consequently, the postural attitude of the walker is closer to normal walk attitude (without load). For the dynamic data, no significant difference was noted between the 3 conditions of walk with backpack.

Quantify dynamic balance control in balance beam: measure of 3-D forces applied by expert gymnasts to the beam

Women gymnasts have to perform acrobatic skills in balance beam. The extremely reduced base of support (0.10 m), its height above the ground level (1.25 m) and the fact that acrobatic displacements require on this apparatus both foot standing and hand standing balances, are among the most important factors which determined the body’s balance vulnerability. However, few studies on gymnast’s balance control on beam have been conducted. The aim of the paper was to present the instrumentation of a balance beam that allowed to study the dynamic of reaction forces acting during the different supporting phases while acrobatic skill. The reliability of the results of external forces calculated from force plates and kinematic measurements (Gillet, 2003; Kingma, 1996) was evaluated by the mechanical equality of the Newton’s second law. We focused on the basic movement of back walkover.

Reorganization of motor cortex and impairment of motor performance induced by hindlimb unloading are partially reversed by cortical IGF-1 administration

HighlightsSensorimotor restriction affects organization of motor cortex.Sensorimotor restriction induces a degradation of motor performance.IGF‐1 partially reverses cortical shrinkage and decrease in cortical excitability.IGF‐1 prevents the degradation of spontaneous activity.IGF‐1 has only a weak effect on challenged and overground locomotion. ABSTRACT Immobilization, bed rest, or sedentary lifestyle, are known to induce a profound impairment in sensorimotor performance. These alterations are due to a combination of peripheral and central factors. Previous data conducted on a rat model of disuse (hindlimb unloading, HU) have shown a profound reorganization of motor cortex and an impairment of motor performance. Recently, our interest was turned towards the role of insulin‐like growth factor 1 (IGF‐1) in cerebral plasticity since this growth factor is considered as the mediator of beneficial effects of exercise on the central nervous system, and its cortical level is decreased after a 14‐day period of HU. In the present study, we attempted to determine whether a chronic subdural administration of IGF‐1 in HU rats could prevent deleterious effects of HU on the motor cortex and on motor activity. We demonstrated that HU induces a shrinkage of hindlimb cortical representation and an increase in current threshold to elicit a movement. Administration of IGF‐1 in HU rats partially reversed these changes. The functional evaluation revealed that IGF‐1 prevents the decrease in spontaneous activity found in HU rats and the changes in hip kinematics during overground locomotion, but had no effect of challenged locomotion (ladder rung walking test). Taken together, these data clearly indicate the implication of IGF‐1 in cortical plastic mechanisms and in behavioral alteration induced by a decreased in sensorimotor activity.