Sheldon R. Simon

Biomechanical and metabolic effects of varying backpack loading on simulated marching

Twelve healthy, male Army recruits performed three, 40-min treadmill marches at 6 km/h, under three load carriage conditions: 0%-body weight (BW) backpack load, 15%-BW load and 30%-BW load. Kinematic and kinetic data were obtained, immediately before and after each treadmill march, for computing ankle, knee and hip joint rotations and moments. Metabolic data (oxygen uptake ([Vdot]O2), expired ventilation ([Vdot]E), respiratory exchange ratio (RER)), heart rate (HR) and ratings of perceived exertion (RPE) were collected continuously during marching. Significant differences (p⩽0.05) were observed between each load for [Vdot]O2, HR and [Vdot]E throughout the marches. At 40 min, relative energy costs for 0%-BW, 15%-BW and 30%-BW loads were 30, 36 and 41% [Vdot]O2max, respectively. RPE responses during marching significantly differed for only the 30%-BW load and were greater than responses at 0%-BW and 15%-BW loads. During load carriage trials prior to treadmill marches (pre-march), peaks in internal, hip extension, knee extension and ankle plantar flexion moments increased with increasing backpack load. Relative to 0%-BW load, percentage increases in knee moments, due to 15%-BW and 30%-BW loads, pre-march, were substantially larger than the percentage increases for hip extension and plantar flexion moments, pre-march. Pre-march and post-march peaks in hip extension and ankle plantar flexion moments were similar with all loads, while notable premarch to post-march declines were observed for knee extension moment peaks, at 15%-BW and 30%-BW load. Pre-march joint loading data suggests that the knee may be effecting substantial compensations during backpack loaded marching, perhaps to attenuate shock or reduce load elsewhere. Post-march kinetic data (particularly at 15%-BW and 30%-BW load), however, indicates that such knee mechanics were not sustained and suggests that excessive knee extensor fatigue may occur prior to march end, even though overall metabolic responses, at 15%BW and 30%-BW load, remained within generally recommended limits to prevent fatigue during prolonged work.

The effect of fatigue on multijoint kinematics and load sharing during a repetitive lifting test

Study Design. A repetitive lifting test in the sagittal plane was performed with a submaximal load at a maximal lifting rate to understand the effects of fatigue on kinematic and kinetic measures of performance. Objectives. To quantify the effect of fatigue during a highly repetitive lifting task, in terms of lifting force transmitted to the load, joint motion patterns, and internal joint load sharing. Summary of Background Data. Industrial surveillance and epidemiologic data suggest that repetitive lifting is a risk factor for low back pain. Previous studies examining the effect of fatigue have either been constrained to isolated trunk movement, or have not explored the internal load distribution and potential alteration in the loading patterns. Methods. Sixteen healthy male subjects performed repetitive lifting in the sagittal plane with a load equal to 25% of their maximal lifting capacity, at a maximal lifting rate. Changes in lifting performance were determined from the power transferred to the box, joint kinematics, and joint kinetics. Data from three cycles at the start and end of the exercise were tested for the effect of fatigue using repeated‐measures analysis of variance. Results. Fatigue was documented by a reduction in average lifting force and hip and spine torque generation, whereas internal joint load sharing was relatively unchanged. The fatigue was associated with decreased knee and hip motion, and increased lumbar flexion. Decreased postural stability also was evident. Conclusions. The significant decrease in postural stability and force generation capability because of the repetitive lifting task indicated a higher risk of injury in the presence of unexpected perturbation. Multijoint coordinated lifting tasks provide a more realistic protocol to study neuromuscular fatigue.

Spectral and temporal responses of trunk extensor electromyography to an isometric endurance test.

Study Design. This study investigated the effect of trunk extensor muscle location on the spectral and temporal electromyographic activity of the muscles during a fatiguing isometric extension of the torso against gravity. Objectives. To determine the spectral responses of the trunk extensor muscles at more locations than have been studied previously, to determine if fatigue in the knee flexors limits this test, and to quantify the recruitment patterns of the trunk extensor muscles in a group of healthy subjects. Summary of Background Data. Isometric endurance tests appear to have more value than strength tests in predicting the occurrence of low back pain. Electromyographic activity of trunk extensor muscles during these tests may provide clues to the etiology of neuromuscular‐based low back pain. Spectral electromyographic measures appear to be successful discriminators between low back pain patient and normal populations, although which muscles provide the best information is unclear. Likewise, the recruitment patterns of the trunk extensors during fatiguing isometric tasks is not well quantified. Methods. Ten healthy men performed an isometric trunk endurance test. Surface electromyography was recorded from the erector spinae medially and laterally at vertebral levels of L1 and L3, medially at L5, and from the biceps femoris and gastrocnemius. Spectral parameters were calculated from the Fast Fourier Transform, and temporal parameters were calculated from the root mean square of the raw data. Linear regression was used to determine their responses as a function of time. Results. There was a significant effect of vertebral level and medial‐lateral location on the initial median frequency and linear slope of the median frequency regressions. No significant evidence of fatigue in the lower extremities was observed. For most subjects, the temporal response of the surface electromyography was parabolic (concave‐down), peaking at 30–50% of the endurance time. Conclusion. Establishment of which muscle locations provide the best information and knowledge of the recruitment patterns are essential for the development of clinical diagnostic procedures and rehabilitation protocols.

Stability and control of a frontal four-link biped system

A conceptual model, for studying the involvement of the central nervous system (CNS) in the performance of lateral swaying movements is described. The model is based on a four-link planar biped that approximates gross human locomotion in the frontal plane. The viscoelastic function of the musculoskeletal system provides a linear controller for the system. Such an intrinsic controller can effectively duplicate simple well-learned tasks in the absence of higher level CNS feedback. This hypothesis is supported by comparing the proposed controller with two neurophysiologically involved linear decoupling schemes. Reference trajectories for swaying commands are recorded from experiments conducted in the Gait Analysis Laboratory of the Ohio State University Hospitals. These reference trajectories are inputs to all three controllers. The viability of intrinsic feedback scheme in the execution of swaying tasks is demonstrated via comparison of responses from the three controllers.<<ETX>>

The planning of orthopaedic reconstructive surgery using computer-aided simulation and design

Three-dimensional reconstructions from computed tomographic (CT) images are currently being used clinically in a wide variety of orthopaedic surgical applications. The computer may be used to select the optimum standard artificial joint replacement or to design a custom artificial joint replacement for a particular patient. Where large bony defects exist, the computer may be used to design bone allografts for joint reconstruction and to manufacture models of the bones for use in planning the surgery. In cases where osteotomies are performed to improve the mechanics of the joint, each proposed osteotomy may be simulated on the computer to identify the surgical plan that will optimally normalize the diseased joint.

A viscoelastic sphere model for the representation of plantar soft tissue during simulations

Simulations of human body during locomotion require a realistic representation of the foot which is the major interacting part of the body with the environment. Most simulation models consider the foot to be a rigid link, and impose unrealistic kinematic conditions. This study utilizes a viscoelastic sphere model with realistic properties, which can be used to represent the plantar surface of the foot during locomotion. The mechanical properties of the sphere are identified using experimental data on heel pads (Valiant, 1984). To check the validity of the model the results of the experimental study are reproduced by simulating the impact tests. Sensitivity analyses of the model parameters are carried out. The model is found to be insensitive to variations in stiffness and damping properties. The change in the thickness of the soft tissue, however, affected the maximum force of deformation proportionally. A symmetrical pressure distribution for the sphere during impact is calculated. It is concluded that the viscoelastic sphere model, presented here, can be incorporated into a foot model to represent the plantar surface of the foot.

Avascular necrosis of the femoral head: Early MRI detection and radiological correlation

Magnetic Resonance Imaging (MRI) and conventional radiographs were compared in 49 hips with Avascular Necrosis (AVN). MRI detected AVN in 25% of the hips during the preradiological stage of the disease. Both MRI and conventional radiographs accurately detected AVN in the remaining 75% of hips. Correlation between the patterns observed with the two techniques reflected the underlying histopathologic events. The reactive interface between infarcted bone and viable bone could be identified on MRI as a low signal intensity (SI) band. On conventional radiographs the reactive interface appeared as a sclerotic band. The adjacent hyperemic zone was seen on MRI as a high SI band and as a lucent zone on the plain films. Variations of this pattern occurred as related to the extend and duration of AVN and to the individuals ability to mount a healing response. Minor degrees of collapse of the femoral head were better identified with plain radiographs but MRI demonstrated small areas of hyperintensity probably corresponding to early subchondral fractures.

The effect of lifting belt use on multijoint motion and load bearing during repetitive and asymmetric lifting.

The evaluation of the effect of lifting belts on multijoint coordinated lifting performance has been limited. Thirteen subjects participated in two experiments: (a) fatiguing repetitive sagittal lifting and (b) asymmetric lifting. Both experiments were performed with and without the use of a common flexible lifting belt to determine the effect of belt use on the trunk and lower extremity motion and load sharing. During both tests, the use of the belt was observed to restrict the sagittal trunk range of motion and velocity, while the hip motion and velocity increased. Although one of the risk factors for acquisition of low back pain may be reduced while wearing the belt, the results also demonstrate a need for greater study of the consequences on the risk of injury to the other joints. More laboratory experiments and prospective epidemiological studies are needed before a conclusive recommendation could be made in favor of using the belt as a valid preventive measure.

Using causal reasoning in gait analysis

This paper describes a series of experiments in which expert diagnostic systems were constructed to analyze human pathologic gait. The difference between successive systems is the recognition of the need for both causal reasoning about the process of gait and experiential, associational knowledge that can control causal reasoning. The performance of the first system (DR. GAIT-1), which relies exclusively on associational knowledge, is quite limited. The second system (DR. GAIT-2), because it is based on a qualitative causal model of gait, overcame many of the difficulties faced by the first system, but its ability to diagnose cases is limited by the complexity of causal reasoning. The third system (QUAWDS), which we are currently developing, is an experiment in integrating causal reasoning with associational knowledge so that robust conclusions can be produced efficiently.

Postural stability of constrained three dimensional robotic systems

A Lyapunov-based approach for the design of a PD controller for robotic systems that are subject to multiple constraints is developed. A candidate Lyapunov function is proposed for the proof of stability using the mechanical energy equation for constrained systems. Sufficient conditions for local and global stability of the unconstrained system are given. An analysis is presented for the unconstrained case and extended to the constrained case. To check the effectiveness of the proposed controller, an eight-link 3D biped model is considered. The system dynamic equations are first derived. Constraint support forces are later added to the system. Simulation of the model motion when equipped with the proposed controller shows that it exhibits a stable response in the unconstrained case.<<ETX>>