Sébastien Leteneur

Effect of trunk inclination on lower limb joint and lumbar moments in able men during the stance phase of gait

BACKGROUND Though the effect of imposed trunk posture affects walking patterns little is known about the effect of natural orientation of the trunk on gait. The objectives of this study are to test if the lower limb joint and thoraco-lumbar moments are similar in subjects who maintain an average natural forward or backward trunk inclination during gait and verify if the lower limbs are equally affected. METHODS Twenty-five young men were divided according to their natural backward or forward trunk inclination during level walking. Ankle, knee, hip and thoraco-lumbar moments were calculated by an inverse dynamic approach for the two limbs. A two-way ANOVA was performed on peak lower limb moments. A one-way ANOVA was performed on thoraco-lumbar peak moments. FINDINGS There was a main effect for both trunk inclinations and lower limb sides but no interaction. For the forward leaners, the duration of hip extension moment was longer (P<0.001) while the hip flexion moment was 1.3 times smaller (P<0.001). Differences between the lower limb sides were noted in all joints but at push-off of the stance phase only. The two thoraco-lumbar extension moments were, respectively, 1.4 times higher for the forward leaners while the two flexion moments were approximately 1.4 times higher for the backward leaners. INTERPRETATIONS The backward leaners propel themselves with a strong hip flexor activity at push-off while the forward leaners use their hip muscles throughout stance. These results support the idea that trunk inclinations and moment variations are associated with the type of walking patterns.

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.

Bilateral Strength Deficit Is Not Neural in Origin; Rather Due to Dynamometer Mechanical Configuration.

During maximal contractions, the sum of forces exerted by homonymous muscles unilaterally is typically higher than the sum of forces exerted by the same muscles bilaterally. However, the underlying mechanism(s) of this phenomenon, which is known as the bilateral strength deficit, remain equivocal. One potential factor that has received minimal attention is the contribution of body adjustments to bilateral and unilateral force production. The purpose of this study was to evaluate the plantar-flexors in an innovative dynamometer that permitted the influence of torque from body adjustments to be adapted. Participants were identically positioned between two setup configurations where torques generated from body adjustments were included within the net ankle torque (locked-unit) or independent of the ankle (open-unit). Twenty healthy adult males performed unilateral and bilateral maximal voluntary isometric plantar-flexion contractions using the dynamometer in the open and locked-unit mechanical configurations. While there was a significant bilateral strength deficit in the locked-unit (p = 0.01), it was not evident in the open-unit (p = 0.07). In the locked-unit, unilateral torque was greater than in the open-unit (p<0.001) and this was due to an additional torque from the body since the electromyographic activity of the agonist muscles did not differ between the two setups (p>0.05). This study revealed that the mechanical configuration of the dynamometer and then the body adjustments caused the observation of a bilateral strength deficit.

Effect of natural trunk inclination on variability in soleus inhibition and tibialis anterior activation during gait initiation in young adults

BACKGROUND Anticipatory postural adjustments (APAs) of gait initiation (GI) permit first step execution. APAs are characterized by a structured pattern of soleus (SOL) inhibition followed by tibialis anterior (TA) activation. This pattern shows variability among young adults where SOL is not always inhibited before TA activation. Initial posture preceding GI could explain a part of this variability. The aim of the study was to investigate the effect of natural trunk inclination on APAs during GI. METHODS Two groups of twelve subjects divided by natural trunk inclination angle performed five gait initiation trials. A regression model was computed to predict SOL inhibition and TA activation. RESULTS Backward leaners showed less SOL inhibition in stance leg (25.8% of trials) compared to forward leaners (55.6% of trials). Regression model revealed that high tonic EMG activity in SOL in the stance leg is the variable that best explains SOL inhibition variation within trials but not TA activation. CONCLUSION Slight variations in APAs are due to natural trunk inclination but more contribution in APAs is due to initial posture, future step speed and initial tonic soleus activity. Absence of SOL inhibition could be in part explained by natural trunk inclination, where the backward inclination leads to lower tonic SOL activity in quiet standing. These effects could be due to inherent and functional variability, which depend on postural variation, muscular coordination and limb roles.

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.

When motor simulation of disequilibrium increases postural stability

L.P. Heurley*, E.M. Simoneau, S. Leteneur and D. Brouillet LAMIH UMR CNRS 8201 ‘Laboratory of Industrial and Human Automation, Mechanics and Computer Science’, Université Nord de France, Université de Valenciennes et du Hainaut-Cambrésis, Le Mont Houy, 59313 Valenciennes Cedex 9, France; Laboratory EPSYLON EA 4556 ‘Dynamics of Human Abilities and Health Behaviors’, Université Montpellier III, Paul Valéry, Route de Mende, 34199 Montpellier Cedex 5, France

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.

Effect of natural sagittal trunk lean on standing balance in untreated scoliotic girls

Background: Generally, scoliotic girls have a tendency to lean further back than a comparable group of non‐scoliotic girls. To date, no study has addressed how standing balance in untreated scoliotic girls is affected by a natural backwardly or forwardly inclined trunk. Methods: 27 able‐bodied young girls and 27 young girls with a right thoracic curve were classified as leaning forward or backward according to the median of their trunk sagittal inclination. Participants stood upright barefoot. Trunk and pelvis orientations were calculated from 8 bony landmarks. Upright standing balance was assessed by 9 parameters calculated from the excursion of the center of pressure and the free moment. Findings: In the anterior‐posterior direction, backward scoliotic girls had a greater center of pressure range (P = 0.036) and speed (P = 0.015) by 10.4 mm and 2.8 mm/s respectively than the forward scoliotic group. Compared to their matching non‐scoliotic group, the backward scoliotic girls stood more on their heels by 14.6 mm (P = 0.017) and display greater center of pressure speed by 2.5 mm/s (P = 0.028). Medio‐lateral center of pressure range (P = 0.018) and speed (P = 0.008) were statistically higher by 8.7 mm and 3.6 mm/s for the backward group. Only the free moment RMS was significantly larger (P = 0.045) for the backward scoliotic group when compared to the forwardly inclined scoliotic group. Interpretation: Only those with a backward lean displayed statistically significant differences from both forward scoliotic girls and non‐scoliotic girls. Untreated scoliotic girls with an exaggerated back extension could profit more from postural rehabilitation to improve their standing balance. HIGHLIGHTS27 able‐bodied and 27 scoliotic girls were classified as leaning forward or backward.Backward scoliotic girls displayed a greater standing imbalance than the forward ones.Backward scoliotic girls stood more on their heels than backward able‐bodied girls.Backward scoliotic girls could profit more from postural rehabilitation.

Low additional thickness under the toes could change upright balance of healthy subjects

The purpose of the study was to evaluate the effect of an additional thickness placed under the toes (TUT) on the CoP measures and to determine the optimum thickness required to maximize the postural control performance. Four conditions were compared: TUT 0 (control), 0.8, 3, and 6mm and four variables were computed from the CoP displacements. These results suggest that the lowest TUT could contribute to changing balance control, and may have clinical interest. This brings perspectives in the management of patients with risk of falling or with chronic pain syndromes, complementing validated therapeutic strategies.