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Biomedical subjects

M A Lafortune

Publications and source records attributed to M A Lafortune.

10 recordsLinked to original sources
PubMed1996

Dominant role of interface over knee angle for cushioning impact loading and regulating initial leg stiffness.

For in vivo impact loadings administered under controlled initial conditions, it was hypothesized that larger initial knee angles (IKA) and softer impacting interfaces would reduce impact loading and initial leg stiffness. A human pendulum was used to deliver controlled impacts to the right foot of 21 subjects for three IKA (0, 20 and 40 degrees) and three interfaces (barefoot, soft and hard EVA foams). The external impact force and the shock experienced by the subjects' shank were measured simultaneously with a wall mounted force platform and a skin mounted accelerometer, respectively. Stiffness of the leg was derived using impact velocity and wall reaction force data. The results disproved the role of the knee joint in regulating initial leg stiffness and provided only partial support for the hypothesized improved cushioning. Larger knee flexion at contact reduced impact force but increased the shock travelling throughout the shank. Conversely, softer interfaces produced sizable reductions in both initial leg stiffness and severity of the impact experienced by the lower limb. Force rate of loading was found to be highly correlated (r = 0.95) to limb stiffness that was defined by the heel fat pad and interface deformations. These results would suggest that interface interventions are more likely to protect the locomotor system against impact loading than knee angle strategies.

Acceleration↗
PubMed1996

Differential shock transmission response of the human body to impact severity and lower limb posture.

The shocks imparted to the foot during locomotion may lead to joint-degenerative diseases and jeopardize the visual-vestibular functions. The body relies upon several mechanisms and structures that have unique viscoelastic properties for shock attenuation. The purpose of the present study was to determine whether impact severity and initial knee angle (IKA) could alter the shock transmission characteristics of the body. Impacts were administered to the right foot of 38 subjects with a human pendulum device. Combinations of velocities (0.9, 1.05 and 1.2 m s-1) and surfaces (soft and hard foams) served to manipulate impact severity in the first experiment. Three IKA (0, 20 and 40 degrees) were examined in the second experiment. Transmission between shank and head was characterized by measuring the shock at these sites with miniature accelerometers. Velocity and surface had no effect on the frequency profile of shock transmission suggesting a consistent response of the body to impact severity. Shank shock power spectrum features accounted for the lower shock ratio (head/shank) measured under the hard surface condition. IKA flexion caused considerable reduction in effective axial stiffness of the body (EASB), 28.7-7.9 kNm-1, which improved shock attenuation. The high correlation (r = 0.97) between EASB and shock ratio underscored the importance of EASB to shock attenuation. The present findings provide valuable information for the development of strategies aimed at protecting the joints, articular cartilage, spine and head against locomotor shock.

Acceleration↗
PubMed1995

Tibial shock measured with bone and skin mounted transducers.

The purpose of this study was to assess the value of superficial transducer mounting to measure tibial shock during locomotion. Surface (SMT) and bone mounted transducers (BMT) simultaneously recorded axial tibial acceleration in five subjects who ran at 4.5 m s-1. SMT produced inconsistent recording across the subjects both in the time and frequency domains. In two subjects, SMT signals provided close approximation of BMT signals, some distortion occurred in one subject while severe distortions were observed in the other two subjects. The present results established that SMT could not be used directly to quantify the shock transmitted through the tibia during running. However, frequency transformation of SMT recordings produced encouraging results; the transformed SMT signals mimicked the signals recorded with the bone mounted transducer.

Acceleration↗
PubMed1995

Human pendulum approach to simulate and quantify locomotor impact loading.

The understanding of impact mechanics during locomotion is important for research within the fields of injury prevention and footwear design. Instrumented missiles offer a worthy solution to the lack of control inherent in in vivo activities and to the isolated nature of tissue studies. However, missiles cannot mimic the magnitude and temporal characteristics of locomotion impacts. A human pendulum approach employed the subject's own body as the missile to impart controlled impacts to the lower extremity. The subject is swung toward a force platform instrumented wall while lying supine on a suspended lightweight bed. The ability of the pendulum to reproduce locomotor impact loading was assessed for heel-toe running. Axial reaction force and shank acceleration patterns recorded during pendulum tests in ten subjects were found to closely resemble running patterns and they were obtained without discomfort to the subjects. This new approach relies upon one's own body to impart impacts representative of locomotion. It should prove useful to study human impact loading in a controlled manner.

Acceleration↗
PubMed1995

Transfer function between tibial acceleration and ground reaction force.

The purpose of the present study was to capture the relationship between ground reaction force (GRF) and tibial axial acceleration. Tibia acceleration and GRF were simultaneously recorded from five subjects during running. The acceleration of the bone was measured with a transducer mounted onto an intracortical pin. The signals were analyzed in the frequency domain to characterize the relationship between GRF and tibial acceleration. The results confirmed that for each subject this relationship could be represented by a frequency transfer function. The existence of a more general relationship for all five subjects was also confirmed by the results. The transfer functions provided information about transient shock transmissibility for the entire impact phase of running.

Acceleration↗
PubMed1994

Foot inversion-eversion and knee kinematics during walking.

The purpose of this study was to monitor selected aspects of the three-dimensional kinematics of the knee during walking with regular shoes and with modified shoes that induced either pronation or supination of the foot. Steinmann traction pins were inserted into the right tibia and femur of five adult men who had apparently normal lower extremities. Target clusters mounted onto the pins were filmed by four cine cameras operating at 100 frames/sec. Two trials per subject were analyzed for each of the three experimental conditions: regular running shoes, running shoes with a 10 degree valgus wedge, and running shoes with a 10 degree varus wedge. The different types of footwear induced only minor kinematic changes at the knee during the stance phase of walking. The angular patterns of the tibiofemoral joint were modified by less than 1 degree, whereas the translatory patterns were altered by 2 mm. Immediately following foot-strike, the valgus-wedge shoes caused the tibia to rotate internally 4 degrees more than the varus-wedge shoes, but at the tibiofemoral joint no consistent differences in the pattern of internal-external rotation between normal and modified footwear were measureable. These findings suggest that, in the healthy lower extremity, increased internal and external tibial rotation is resolved at the hip joint, with changes at the tibiofemoral joint that barely are detectable with the techniques used in this study.

Adult↗
PubMed1992

Three-dimensional kinematics of the human knee during walking.

Three-dimensional kinematics of the tibiofemoral joint were studied during normal walking. Target markers were fixed to tibia and femur by means of intra-cortical traction pins. Radiographs of the lower limb were obtained to compute the position of the target markers relative to internal anatomical structures. High-speed cine cameras were used to measure three-dimensional coordinates of the target markers in five subjects walking at a speed of 1.2 m s-1. Relative motion between tibia and femur was resolved according to a joint coordinate system (JCS). The measurements have identified that substantial angular and linear motions occur about and along each of the JCS axes during walking. The results do not, however, support the traditional view that the so-called 'screw home' mechanism of the knee joint operates during gait.

Adult↗
PubMed1991

Three-dimensional acceleration of the tibia during walking and running.

Measurements of tibial acceleration during walking and running were obtained by means of a triaxial accelerometer. The accelerometer was fixed to the free end of a Steinmann pin inserted into the right tibia of one volunteer subject. The patterns of tibial acceleration showed little step-to-step variation within each experimental condition. Following foot strike and depending upon footwear, the resultant tibial acceleration reached between 2.7 and 3.7 g during walking. The tibia experienced maximal accelerations of 10.6 g during running. The high values of tibial acceleration recorded in the antero-posterior (AP) and medio-lateral (ML) directions clearly revealed the importance of measuring all three components of acceleration to quantify the magnitude of the shock experienced by the lower limbs during locomotor activities.

Acceleration↗
PubMed1991

Contribution of angular motion and gravity to tibial acceleration.

A bone-mounted accelerometer and high-speed cinematography were used to compare the axial tibial acceleration caused by ground impact with the total tibial axial acceleration as measured by a transducer. Due to the effects of gravity and tibial angular motion, the magnitude of the peak acceleration at foot strike was 43% below and 18% above the peak axial acceleration due to impact for running and walking, respectively. Depending on the distance of the accelerometer from the tibial center of rotation which is located at the ankle joint, different axial acceleration signals should be expected during comparable locomotor activities.

Acceleration↗