Frédéric Dierick

Energy cost, mechanical work, and efficiency of hemiparetic walking

The energy cost of walking (C) in nine chronic hemiparetic patients was calculated by measuring the total mechanical work (Wtot) done by the muscles and the efficiency of this work production (eta). The energy cost was twice normal in slow walkers and 1.3 times greater in fast walkers. The increase in C was proportional to the increase in Wtot and eta was normal at around 20%, despite an increase in muscle tone and muscle co-contractions. This type of approach gives a greater understanding into how segmental impairments increase Wtot and C and contribute to a patients disability.

Motion of the body centre of gravity as a summary indicator of the mechanics of human pathological gait

Abnormal movements of the body segments due to lowest level gait disorders such as musculoskeletal disorders, peripheral neuropathies and radiculopathies or middle-level disorders such as hemiplegia, paraplegia and dystonia influence the motion of the centre of gravity (CG) during walking. The translation of the CG can be studied by the work done by muscles (WExt) with respect to the ground. The efficacy of gaits mechanism can be quantified by the energy transferred between gravitational potential and kinetic energies (recovery). WExt and recovery were investigated in lowest and middle-level gait disorders during level walking. No statistical significant difference was observed between patients with lowest-level gait disorders and normal subjects. However, WExt was increased for the patients with middle-level gait disorders and recovery decreased up to 20%. The measurement of changes in mechanical energy of the CG might be a summary indicator for the mechanics of pathological gait.

Influence of gait pattern on the body's centre of mass displacement in children with cerebral palsy

We assessed the influence of digitigrade gait pattern, topographical types, severity of motor involvement, and locomotor experience on the bodys centre of mass (COM) displacement during gait in children with spastic cerebral palsy (CP). Three-dimensional COM displacements were computed from ground reaction forces in 51 independent digitigrade walkers (29 males, 22 females; mean age 10 years 6 months, SD 2 years 7 months, range 7 to 15 years). Results obtained from 10 participants without disabilities (five males, five females), in the same age range as the patients with CP, were used as a reference plantigrade group. Vertical and forward COM displacements were significantly different between the digitigrade and the plantigrade walkers. Neither the topographical type (quadriplegia, n=5; diplegia, n=20; right hemiplegia, n=13; left hemiplegia, n=13), nor the severity of motor involvement, nor the locomotor experience influenced COM displacements. We conclude that the COM displacement during gait in patients with CP was mainly influenced by the digitigrade gait pattern encountered in this neurological disorder rather than the different topographical types and motor involvements.

Execution time, kinetics, and kinematics of the mae-geri kick : comparison of national and international standard karate athletes

Abstract Little is known of the performance characteristics of the shotokan karate mae-geri kick. The aim of this study was to compare the execution time, the lower limb kinetics and kinematics, and their respective repeatability in the mae-geri kick of karate athletes of two different standards. Seventeen adult black belt karate competitors (9 national and 8 international athletes) performed six kicks with their dominant lower limb on a striking surface, combining maximum force impact and velocity. Execution time of movement and lower limb kinematics were recorded with a high-speed camera. Maximum force at impact and the forces exerted on the ground were measured using three force plates. The duration of the kick was significantly shorter for international than for national standard athletes. However, no significant difference in the maximum impact force of the kick was observed between the two groups. In addition, significant kinematic differences were observed between the groups, with two angles of motion and one velocity peak occurring sooner in the kick movement for the international athletes, specifically for the knee joint. International athletes also performed the kick with a significantly higher repeatability for duration and kinematics, specifically during the pre-loading phase that precedes the attack phase. We conclude that theduration of the kick and repeatability of lower limb kinematics could be useful in selecting top-level karate athletes and monitoring their training status.

Development of displacement of centre of mass during independent walking in children

The aims of this study were to assess the characteristics of three-dimensional displacement of the centre of mass of the body (CMb) during walking in healthy children and to compare it with those of young adults. Twenty-one children (11 males, 10 females; age range 1 to 9 years) were recruited from the nursery and school attached to the Université catholique de Louvain, Brussels, Belgium; and three young adults (one male two females; mean age 26 years 4 months) were recruited from the Rehabilitation and Physical Medicine Unit of the same university. Displacement of CMb was assessed at different walking velocities in the children and adults by two successive mathematical integrations of ground reaction forces, measured by a large strain-gauge force platform. Displacement of CMb was controlled for leg length of the participant to eliminate the scaling effect that is dependent on growth. Results showed that vertical and lateral amplitudes of the CMb when controlled for leg length were greater for children before 4 years of age and that the forward amplitude when controlled for leg length was greater for children before 7 years of age. We conclude that the development of mature human CMb displacement during independent walking is a gradual neural process, evolving until the age of 7 years.

Relationship between antagonistic leg muscles co-contractions and body centre of gravity mechanics in different level gait disorders.

Body centre of gravity (CG) mechanics and electromyographic activity of flexor-extensor antagonistic muscles of the lower limb were simultaneously recorded in lowest and middle-level gait disorders. Muscle co-contractions between tibialis anterior and triceps surae, and between rectus femoris and hamstrings were evaluated. CG mechanics was assessed by the external mechanical work (W(ext)) done to translate the CG with respect to the ground, and the recovery quantifying the efficacy of gait mechanism by the amount of energy transferred between gravitational potential and kinetic energies of the CG. The results showed a strong relationship between CG mechanics and the co-contractions of the main flexor-extensor ankle muscles. In middle-level gait disorders, our results suggest that the ankle antagonistic muscle co-contractions and the CG mechanics could provide information about gait mechanism and the integrity level of the locomotor program.

Determination of the vertical ground reaction forces acting upon individual limbs during healthy and clinical gait

In gait lab, the quantification of the ground reaction forces (GRFs) acting upon individual limbs is required for dynamic analysis. However, using a single force plate, only the resultant GRF acting on both limbs is available. The aims of this study are (a) to develop an algorithm allowing a reliable detection of the front foot contact (FC) and the back foot off (FO) time events when walking on a single plate, (b) to reconstruct the vertical GRFs acting upon each limb during the double contact phase (DC) and (c) to evaluate this reconstruction on healthy and clinical gait trials. For the purpose of the study, 811 force measurements during DC were analyzed based on walking trials from 27 healthy subjects and 88 patients. FC and FO are reliably detected using a novel method based on the distance covered by the centre of pressure. The algorithm for the force reconstruction is a revised version of the approach of Davis and Cavanagh [24]. In order to assess the robustness of the algorithm, we compare the resulting GRFs with the real forces measured with individual force plates. The median of the relative error on force reconstruction is 1.8% for the healthy gait and 2.5% for the clinical gait. The reconstructed and the real GRFs during DC are strongly correlated for both healthy and clinical gait data (R(2)=0.998 and 0.991, respectively).

Hemorrhagic versus ischemic stroke: Who can best benefit from blended conventional physiotherapy with robotic-assisted gait therapy?

Background Contrary to common belief of clinicians that hemorrhagic stroke survivors have better functional prognoses than ischemic, recent studies show that ischemic survivors could experience similar or even better functional improvements. However, the influence of stroke subtype on gait and posture outcomes following an intervention blending conventional physiotherapy with robotic-assisted gait therapy is missing. Objective This study compared gait and posture outcome measures between ambulatory hemorrhagic patients and ischemic patients, who received a similar 4 weeks’ intervention blending a conventional bottom-up physiotherapy approach and an exoskeleton top-down robotic-assisted gait training (RAGT) approach with Lokomat. Methods Forty adult hemiparetic stroke inpatient subjects were recruited: 20 hemorrhagic and 20 ischemic, matched by age, gender, side of hemisphere lesion, stroke severity, and locomotor impairments. Functional Ambulation Category, Postural Assessment Scale for Stroke, Tinetti Performance Oriented Mobility Assessment, 6 Minutes Walk Test, Timed Up and Go and 10-Meter Walk Test were performed before and after a 4-week long intervention. Functional gains were calculated for all tests. Results Hemorrhagic and ischemic subjects showed significant improvements in Functional Ambulation Category (P<0.001 and P = 0.008, respectively), Postural Assessment Scale for Stroke (P<0.001 and P = 0.003), 6 Minutes Walk Test (P = 0.003 and P = 0.015) and 10-Meter Walk Test (P = 0.001 and P = 0.024). Ischemic patients also showed significant improvements in Timed Up and Go. Significantly greater mean Functional Ambulation Category and Tinetti Performance Oriented Mobility Assessment gains were observed for hemorrhagic compared to ischemic, with large (dz = 0.81) and medium (dz = 0.66) effect sizes, respectively. Conclusion Overall, both groups exhibited quasi similar functional improvements and benefits from the same type, length and frequency of blended conventional physiotherapy and RAGT protocol. The use of intensive treatment plans blending top-down physiotherapy and bottom-up robotic approaches is promising for post-stroke rehabilitation.

Short-term increase in discs’ apparent diffusion is associated with pain and mobility improvements after spinal mobilization for low back pain

Pain perception, trunk mobility and apparent diffusion coefficient (ADC) within all lumbar intervertebral discs (IVDs) were collected before and shortly after posterior-to-anterior (PA) mobilizations in 16 adults with acute low back pain. Using a pragmatic approach, a trained orthopaedic manual physical therapist applied PA mobilizations to the participants’ spine, in accordance with his examination findings. ADCall was computed from diffusion maps as the mean of anterior (ADCant), middle (ADCmid), and posterior (ADCpost) portions of the IVD. After mobilization, pain ratings and trunk mobility were significantly improved and a significant increase in ADCall values was observed. The greatest ADCall changes were observed at the L3-L4 and L4-L5 levels and were mainly explained by changes in ADCant and ADCpost, respectively. No significant changes in ADC were observed at L5-S1 level. The reduction in pain and largest changes in ADC observed at the periphery of the hyperintense IVD region suggest that increased peripheral random motion of water molecules is implicated in the IVD nociceptive response modulation. Additionally, ADC changes were observed at remote IVD anatomical levels that did not coincide with the PA spinal mobilization application level.

Unstable footwear as a speed-dependent noise-based training gear to exercise inverted pendulum motion during walking

ABSTRACT Previous research on unstable footwear has suggested that it may induce mechanical noise during walking. The purpose of this study was to explore whether unstable footwear could be considered as a noise-based training gear to exercise body center of mass (CoM) motion during walking. Ground reaction forces were collected among 24 healthy young women walking at speeds between 3 and 6 km h−1 with control running shoes and unstable rocker-bottom shoes. The external mechanical work, the recovery of mechanical energy of the CoM during and within the step cycles, and the phase shift between potential and kinetic energy curves of the CoM were computed. Our findings support the idea that unstable rocker-bottom footwear could serve as a speed-dependent noise-based training gear to exercise CoM motion during walking. At slow speed, it acts as a stochastic resonance or facilitator that reduces external mechanical work; whereas at brisk speed it acts as a constraint that increases external mechanical work and could mimic a downhill slope.