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Biomedical subjects

G L Smidt

Publications and source records attributed to G L Smidt.

At least 19 recordsLinked to original sources
PubMed1992

Human plantarflexor stiffness to multiple single-stretch trials.

The purpose of this investigation was to determine the influence of different stretch velocities, different rates of pre-stretch force development, and different pre-stretch muscle lengths on the intrinsic stiffness exhibited by the quasi-statically contracting active human plantarflexors during multiple single-stretch trials at 20-60% of maximum isometric contraction. Subjects were positioned prone, with the knee flexed 1.57 rad(90 degrees), shank stabilized, and foot secured in a hard plastic orthotic. Slowly increasing isometric plantarflexion force was produced until the plantarflexors were stretched by a rapid 0.2 rad (12 degrees) dorsiflexion movement. Plantarflexion forces and ankle positions were determined during these stretches as well as during resting stretches when the muscle was inactive. Resting forces were subtracted from the active trials, forces converted to torques, and stiffnesses determined for the first 62 ms of the stretch. The slope of the stiffness vs pre-stretch torque relationship averaged 4.30 +/- 0.34 Nm rad-1 Nm-1. Little difference was found between stiffness determined through the single-stretch method and the results of previous studies employing different mechanical inputs. Differences in stiffnesses with different stretching velocities were caused by computational artifact rather than by differences in intrinsic muscular reaction. Faster rates of pre-stretch force increase prior to the stretch resulted in slightly lower stiffnesses. Different pre-stretch muscle lengths apparently did not result in different stiffnesses. The shape of the torque vs displacement curve was remarkably insensitive to the planned manipulations of the testing conditions, responding in a stereotypical manner.

Adult↗
PubMed1992

The effect of high-intensity trunk exercise on bone mineral density of postmenopausal women.

The purpose of this study was to determine the effect of a 1-year trunk resistive exercise program on bone mineral density at the lumbar spine and hip in postmenopausal women. Forty-nine subjects were divided into exercise and control groups. Dual photon absorptiometry was used to measure bone mineral density and the Muscle Examination and Exercise Dosimeter 3000 system was used to assess trunk muscle strength. Resistive exercise target levels for the exercise group were based on the results of the trunk muscle strength tests. The exercise group performed 3 sets of 10 repetitions for each of the sit-up, prone trunk extension, and double leg flexion exercises. The subjects were seen once per month and performed the exercises a minimum of three times per week. The bone mineral density and strength tests were done at baseline, at 6 months and at 12 months. The results of the study showed that 1) the dual photon absorptiometry method and the Muscle Examination and Exercise Dosimeter 3000 system were highly reliable in measuring bone mineral density and trunk muscle strength, respectively; and 2) no significant differences were found between the exercise and control groups at lumbar vertebrae L2, L3, L4, L2-L4, and the femoral neck, Ward's triangle, and trochanteric region of the proximal femur at baseline, 6-month, and 12-month evaluation sessions.

Absorptiometry, Photon↗
PubMed1990

Relationship between trunk muscle torque and bone mineral content of the lumbar spine and hip in healthy postmenopausal women.

The purpose of the study was to determine the relationship between trunk muscle strength and bone mineral density (BMD). Fifty-six postmenopausal women, aged 38 to 73 years, were examined. The BMD of lumbar vertebrae L2-4, the femoral neck, the Ward's triangle, and the greater trochanter was measured with dual-photon absorptiometry. Isometric and isokinetic torque and work measurements obtained on a trunk testing unit were used to assess trunk flexor and extensor strength. Correlation analysis demonstrated a statistically significant relationship between most trunk torque and work measurements and BMD. The trunk extensors generally provided higher correlations with BMD than did the trunk flexors, and the isokinetic extension torque values demonstrated higher correlations than the isometric extension values in every case. Linear backward-regression models, based on the subjects' weight and trunk flexor and extensor torque and work measurements, demonstrated multiple-correlation coefficients of .67, .58, .43, and .65 in predicting the BMD of the L2-4 region, femoral neck, Ward's triangle, and greater trochanter region, respectively. Estrogen therapy status did not affect the linear regression models. These data suggest a positive relationship in postmenopausal women between flexor and extensor torque values and BMD at the lower lumbar spine and proximal femur.

Adult↗
PubMed1990

Relationship of extremity muscle torque and bone mineral density in postmenopausal women.

The purpose of this study was to examine the correlations between the torque of four extremity muscle groups and the bone mineral density (BMD) of the lumbar spine and hip in postmenopausal women. Fifty-six postmenopausal women (means age = 55.4 years, s = 7.1; means height = 162.6 cm, s = 6.4; means weight = 65.9 kg, s = 9.3) served as subjects. Bone mineral density was measured from the L2-L4 vertebral bodies, greater trochanter, femoral neck, and Ward's triangle using dual-photon absorptiometry. Hip abduction, knee extension, hip flexion, and grip force were assessed using the Spark Muscle Examination and Exercise Dosimeter (MEED) 3000 system. The Pearson product-moment correlations between muscle torque and BMD ranged from .07 to .42. The significant (p less than .05) correlations between torque and BMD (r = .27-.42) occurred in functionally and anatomically related areas. Results of this study demonstrate a statistically significant relationship between torque and BMD in anatomically related areas in postmenopausal women. This relationship, however, is not sufficiently strong to allow for prediction of BMD from the four muscle groups tested in this study. The relationship does suggest that strength may be a factor in the determination of BMD. Maintenance of strength in those muscle groups with anatomical or functional relationships to the hip and lumbar spine may play a role in the prevention and cessation of the osteoporotic changes that occur.

Body Weight↗
PubMed1989

Exploration of mechanical and electromyographic responses of trunk muscles to high-intensity resistive exercise.

The purposes of this study were to determine the effects of high intensity exercise on fatigue of the trunk muscles within a test session, and on multiple kinetic and electromyographic (EMG) variables over a 6-week training period. Fourty-five normal men and women (20-40 years of age) completed the study. The KIN/COM trunk testing unit (Chattecx Corporation, Chattanooga, Tennessee) was used for both testing and training. The results of the study follow: 1) The KIN/COM trunk testing system was very accurate, and the method used was highly reproducible for the kinetic variables. Reproducibility for the endurance variables was mixed, and isolated EMG variables were poor. 2) Kinetic and EMG decrements associated with fatigue did occur in the trunk muscles with ten continuous cycles of maximal concentric and eccentric contractions. 3) Trunk muscle strength gains were highest for the same mode of exercise used in training (specificity), but significant strength gains also were seen in different modes of muscle contraction (transfer of training). For the trunk extensors, the eccentric form of exercise was superior. 4) The rate of isometric torque development and decay was increased by exercise in men. 5) Trunk muscle endurance was retained when gains in strength occurred. 6) The majority of variables reflecting strength and endurance were retained. The methods and results can serve as guidelines for the evaluation of trunk muscle function and resistive exercise in the clinic.

Abdominal Muscles↗
PubMed1987

Comparison of clinical and objective methods of assessing trunk muscle strength--an experimental approach.

An objective method was used to evaluate the validity of the sit-up, prone trunk extension, and double leg lowering clinical tests. Normal men and women and patients with a history of backache served as subjects. The vast majority of the subjects were able to perform the Grade 1 level, which was the highest resistance imposed by the sit-up and prone extension tests. The double leg lower was superior to the other two clinical tests but was able to identify only broad differences in strength capability. In the main, the subjective clinical tests were poor discriminators and seemed to lack the range of resistance necessary to be definitively useful as methods of assessing trunk muscle strength and may not provide appropriate resistance for improving trunk muscle strength in most patients.

Adult↗
PubMed1987

Analysis of strength tests and resistive exercises commonly used for low-back disorders.

Using a modeling approach the conventional sit-up, the double straight-leg lowering, and prone trunk extension, the authors have shown these to have limitations as tests of maximum trunk flexion and extension strength and as modes of resistive exercise. These maneuvers are poor discriminators of trunk muscle strength, and they lack the range of resistance necessary to cover the spectrum of human trunk muscle strength capability. Use of manually handled weights can improve the above clinical tests and resistive exercise methods. As a result of selective positioning of the weights, variable resistance above and below that provided by the body segments alone can be achieved. The partial sit-up may be appropriate only for patients with significant trunk flexion weakness, and the straight head-trunk sit-up may be useful as a more strenuous test and resistive exercise. Rationale and derivations of the rigid-body equilibrium equations, as well as some of the limitations and assumptions associated with the modeling approach, are presented.

Adult↗
PubMed1977

Effect of cane on variables of gait for patients with hip disorders.

The purposes of this study were to determine the effect of a cane, used in the hand contralateral to the involved hip, on patients' floor reaction forces and on selected time and distance measurements of gait. An instrumented cane, force plate, dynograph recorder and footswitch were among the equipment items used. When the patients walked with a cane the stride length and swing times were increased, while the cadence and the vertical component of the floor reaction force were decreased. The average peak axial loading on the can was 11.6 kg and the average anterior bending moment on the cane was 67.3 kgcm.

Arthroplasty↗
PubMed1977

The influence of isometric exercise and passive stretch on hip joint motion.

A method was designed to compare the effects of isometric contractions and passive stretch on modifying joint range of motion in 30 normal men. Subjects were randomly assigned into a control group, a passive stretch group, or an isometric contraction group. Each subject assumed a left sidelying position on the force table. Stabilization was applied to the pelvis and left lower extremity. The cuff, to which the force cable was attached, was applied to the right lower extremity. Force measurements produced by the isometric contractions or passive stretch procedures were stored on computer tape. The results of the mean differences in pelvifemoral angle measurements indicated that both treatment groups significantly increased their range of passive hip flexion with the knee extended when compared to the control group. Comparisons between the two treatment groups indicated that the isometric contraction and passive stretch procedures had significant and similar effects.

Adult↗
PubMed1977

Accelerographic, temporal, and distance gait factors in below-knee amputees.

Gait characteristics of 19 patients with a unilateral below-knee amputation were studied. The accelerographic and foot placement method used in this study allowed for simultaneous acquisition of data commonly obtained in the experimental laboratory (acceleration) and data easily gathered in the physical therapy clinic (temporal and distance factors). The following results may be of interest to the clinician: 1) measures of cadence, stride length, and velocity were highly related and the magnitude of these measures was below commonly accepted values for normal; 2) the below-knee amputees spent more time in stance phase on their uninvolved lower extremity than on their involved (prosthetic) extemity; 3) the step length from heel strike of the uninvolved lower extremity to heel strike of the involved (prosthetic) lower extremity was greater and accomplished in less time than the opposite step; and 4) smoothness of the gait pattern and any single temporal and distance factor exhibited low statistical relationships.

Acceleration↗