Biomedical subjects

M J Lake

Publications and source records attributed to M J Lake.

6 recordsLinked to original sources

PubMed1998

Mechanical inputs related to perception of lower extremity impact loading severity.

PURPOSE: Human responses to repetitive locomotor loadings are likely dependent upon the perceived severity of the impact. Few researchers have attempted to identify the mechanical variables upon which perception of impact severity is based. This study examined the relationship of selected impact loading variables to the perception of impact severity by employing an established psychophysical test procedure. METHODS: A human pendulum apparatus was used to administer and measure impact loadings similar to those encountered during running. Nineteen subjects experienced over 100 right foot impacts which comprised nine different impact conditions presented in a random manner. The conditions represented combinations of three impact velocities and three interface materials covering a force platform. RESULTS: Group mean subjective ratings of impact severity were highly related to all measured biomechanical descriptors of impact severity. The variables of impact force rate of loading (FRA) and peak shank acceleration had correlation coefficients of 0.99 with perceived severity. When all individual results were combined to determine the relationship of impact loading variables to perception, correlations were generally 0.7 or above with FRA alone explaining 64% of the perceptual rating variability. CONCLUSIONS: These results indicate that impact perception was highly associated with the mechanical input variables commonly measured and that midsole materials such as those typically found in athletic footwear do not remove our ability to perceive the severity of impact loads.

Adult↗

PubMed1996

Six weeks of training does not change running mechanics or improve running economy.

Running technique and economy (VO2submax) were examined before and after a 6-wk period of running training. Fifteen males were filmed and performed 10-min economy runs at 3.36 m.s-1 on a treadmill. An incremental treadmill test was used to record running performance and maximal oxygen consumption (VO2max). Subjects were randomly assigned to a training group and a control group that did not participate in any running program. There were no significant changes in kinematic variables between pre- and post-training tests for either group. Neither were there any significant physiological changes over the 6 wk in the control group. However, the training group demonstrated a significantly (P < 0.01) increased VO2max (57.7 +/- 6.2 vs 61.3 +/- 6.3 ml.kg-1.min-1) and running performance. VO2submax in the training group was significantly (P < 0.05) worse (41.0 +/- 4.5 vs 42.4 +/- 4.3 ml.kg-1.min-1) post-training, although the percent utilization of VO2max (71.6 +/- 7.9 vs 69.3 +/- 6.9%) and submaximal heart rate (169 +/- 15 vs 161 +/- 15 beats.min-1) were significantly lower (P < 0.05). The training-induced improvements in running performance could be attributed to physiological rather than biomechanical modifications. There were no changes in biomechanical descriptors of running style that signaled changes in running economy.

Adolescent↗

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

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↗