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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
PubMed1998

Dynamic scapulohumeral rhythm: the effects of external resistance during elevation of the arm in the scapular plane.

The purpose of this study was to characterize the scapulohumeral rhythm in the normal shoulder during dynamic elevation of the arm in the scapular plane and to compare the scapulohumeral rhythm during three different states of loading: 1) arm completely unloaded and passively elevated, 2) light load consisting of active elevation against the weight of the limb, and 3) heavy loading against maximal resistance. Electromagnetic tracking was used to record three-dimensional scapular and humeral kinematics on 25 normal subjects. Cardan angles were calculated to assess the dynamic relationship of humeral elevation to scapular upward rotation. The results show that during dynamic humeral elevation the scapulohumeral rhythm changes depending on the phase of elevation and the external load on the arm. During passive range of motion, the scapulohumeral rhythm decreased from 7.9:1 to 2.1:1 as the arm was elevated. Light shoulder loads caused an increase of the scapulohumeral rhythm from 3.1:1 to 4.3:1 as the arm was elevated. Heavy shoulder loading resulted in an increasing scapulohumeral rhythm from 1.9:1 to 4.5:1 as the arm was elevated. The results suggest that the historical assumption of a simple linear 2:1 scapulohumeral rhythm ratio may be overly simplistic and may not accurately describe the scapulohumeral rhythm under varying dynamic conditions. Therapists need to understand the normal changing relationships of the scapulohumeral rhythm under different conditions for accurate interpretation of clinical observations.

Adolescent↗
PubMed1998

Scapulothoracic muscle fatigue associated with alterations in scapulohumeral rhythm kinematics during maximum resistive shoulder elevation.

Clinical examinations and biomechanical analysis of the shoulder often include an assessment of the scapulohumeral rhythm. It is important to understand factors which may affect the scapulohumeral rhythm so that optimal diagnostic and therapeutic strategies can be devised. The purpose of this study was to determine if the scapulohumeral rhythm, when assessed under dynamic conditions, is altered as a result of a fatigue-inducing exercise. Twenty-five subjects were required to elevate their arm against maximum resistance until they were no longer able to completely elevate their arm. Three-dimensional kinematics were measured using an electromagnetic tracking system. Electromyographic activity was recorded from the upper trapezius, lower trapezius, serratus anterior, and the middle deltoid muscles. Power frequency spectrum using the Fast Fourier Transform and the root mean square signal amplitudes were determined for each muscle. The scapulohumeral rhythm was determined using least squares regressions of humeral elevation to scapular upward rotation for 20% intervals (phases) of elevation for each subject. The results showed that during the midrange of elevation to maximum elevation [phases 3-5 (60-150 degrees)], the scapulohumeral rhythm decreased with fatigue, and that the decrease in the scapulohumeral rhythm was associated with myoelectric indicators of fatigue (median power frequency). The study suggests that shoulder fatigue affects the way in which the scapula moves concomitantly with the humerus. Fatigue tends to result in increased motion of the scapula, which alters the scapulohumeral rhythm.

Adolescent↗
PubMed1997

Sacroiliac motion for extreme hip positions. A fresh cadaver study.

STUDY DESIGN: This study placed fresh cadavers in different hip positions and obtained sacroiliac kinematics. The magnitudes and directions of angular and linear sacroiliac motion are reported. OBJECTIVES: To determine the three-dimensional motion at the left and right sacroiliac joints and to explore the mechanical structure of the sacroiliac joint. SUMMARY OF BACKGROUND DATA: Previous in vivo and in vitro studies have reported various amounts of motion at the sacroiliac joints, ranging from no motion to 18 degrees. The results of previous studies have typically not been reported as data in classic engineering terms, and three-dimensional analyses are sparse. Importantly, previous studies have not used external hip positions to elucidate the full range of sacroiliac motion. METHODS: Radiopaque markers were placed in the sacrum and each innominate bone before standardized performance of computed tomography scans at 3-mm intervals, with the fresh cadaver stabilized in the side-lying position on a specially constructed pallet. Computed tomography images were stored on magnetic tape, from which coordinates for centroids of the markers were obtained and subsequent mechanical analyses performed. The intersubchondral lines on the images were traced and reconstructed using computer technology to obtain the thickness of the intersubchondral joint space and the general configuration of the sacroiliac joints. RESULTS: The methods used in this study were validated. The largest amount of sacroiliac motion occurred in the sagittal plane (7 degrees on left and 8 degrees on the right, with a range of 3 degrees to 17 degrees). Definite trends in the direction of angular sacroiliac motion occurred with respect to both bilateral and reciprocal hip joint positions. The translation or linear motion of the posterior superior iliac spines with respect to the sacrum ranged from 4 to 8 mm. This motion tended to occur in all directions, with no detectable trends. The average intersubchondral thickness of the sacroiliac joint was 1.2 mm and the shape of the joint resembled that of an airplane propeller. CONCLUSIONS: Even though the subjects in this study were elderly, considerable angular and linear motion was in evidence. As such, it appears that extreme hip positions are necessary to elucidate full range of motion at the sacroiliac joint. The magnitude and direction of demonstrated sacroiliac motion appears to be sufficient to complement hip joint motion and influence motion at the lumbosacral junction and, thus, low back pain in both the direct and indirect sense.

Aged↗
PubMed1996

Underwater forces produced by the hydro-tone bell.

Despite an increasing number of products available for therapeutic use, the prescription of such devices has a limited experimental foundation. The Hydro-Tone Bell is a product designed to be used as an upper body resistance device underwater. The purpose of this study was to devise a method and an apparatus to measure the force production capability of the Hydro-Tone Bell. It was tested in two different orientations and at water velocities varying from 31 to 152 cm/sec (1-5 ft/sec). The results of this study show that the Hydro-Tone Bell orientation and water velocity both have a considerable effect on force production. Approximately 50% more force is produced when the Hydro-Tone Bell is positioned at a 45 degree angle than when it is aligned at 0 degrees at a water velocity of 152 cm/sec (130 vs. 80 N or 29 vs. 19 lbs). However, at the slowest velocity tested, 31 cm/sec, the forces produced in the two orientations are nearly identical (approximately 5 N or 1.1 lbs). As expected, the forces produced in either orientation increase nonlinearly with increasing water velocity (eg., a two-fold increase in velocity causes approximately a four-fold increase in force production). Future clinical studies are needed to further investigate the orientations and movements most beneficial for actual therapeutic use. However, this study provides the necessary background information on the potential force production of the Hydro-Tone Bell over a range of functional velocities.

Exercise Therapy↗
PubMed1996

Interinnominate motion and symmetry: comparison between gymnasts and nongymnasts.

Some clinical approaches to the treatment of low back pain evaluate and treat observed asymmetries of pelvic posture and motion. Scientific evidence suggests the motion available between the innominate bones is small and variable in nature. The purposes of this investigation were 1) to determine if interinnominate motion of subjects without low back pain was symmetrical in reciprocal test posture combinations, 2) to assess innominate bone symmetry in standing, and 3) to determine if a difference in the magnitude of interinnominate motion was present between a subject group which performs more frequent flexibility activities compared with a subject group representing the general population. Thirty-four subjects (eight male gymnasts, nine female gymnasts, eight male nongymnasts, and nine female nongymnasts) were evaluated in standing and three other reciprocal postures (modified standing, modified sitting, and half-kneeling). In each posture, the Metrecom Skeletal Analysis System was used to obtain coordinates for the anterior and posterior iliac spines. Projection angles were used to determine the relative positions of the right and left innominate bones. Results suggest that stand to right modified standing and stand to left modified standing oblique sagittal interinnominate composite motions were symmetrical, stand to right modified sitting and stand to left modified sitting oblique sagittal interinnominate composite motions were asymmetrical, and stand to right half-kneel and stand to left half-kneel oblique sagittal interinnominate composite motions' symmetrical properties were mixed depending on the group. Gymnasts as a group were found to have asymmetrically positioned innominate bones while nongymnasts as a group had symmetrically positioned innominate bones.

Adolescent↗
PubMed1995

Sacroiliac kinematics for reciprocal straddle positions.

STUDY DESIGN: A descriptive and correlation approach was used to assess joint motion. OBJECTIVES: Magnitudes and directions of sacroiliac motion were examined from three different upright postural conditions. SUMMARY OF BACKGROUND DATA: Evidence and clinical views suggest that sacroiliac motion available in the normal case is extremely small to nonexistent. METHODS: Systems for standardizing the three postures and the Metrecom skeletal analysis system (Metrecom, Faro Technologies, Inc., Lake Mary, FL) for acquiring coordinate data for selected skeletal landmarks. RESULTS: The complete sacroiliac oblique-sagittal motion that occurred between the right forward and left forward stride positions was 9 degrees (SD 6.5). The composite oblique-transverse motion was 5 degrees (SD 3.9). The motions in each plane were significantly different from zero. A joint mobility relationship existed between the hip and sacroiliac joints. CONCLUSION: The results demonstrate that substantial angular motion is possible at the sacroiliac joints.

Adult↗
PubMed1995

Effects of local muscle fatigue on three-dimensional scapulohumeral rhythm.

The relationship of scapulothoracic motion to glenohumeral motion, commonly referred to as the scapulohumeral rhythm, has been the subject of numerous investigations. The purpose of this study was to assess the effects of localized muscular fatigue on three-dimensional scapulothoracic motion and the resulting scapulohumeral rhythm during elevation of the humerus in the plane of the scapula. A six-degree-of-freedom digitizing system (Metrecom(TM)) was used to define scapular and trunk reference frames, and three-dimensional Eulerian angles were determined for scapular motion for 0-135 degrees of humeral elevation before and after fatigue of the upper and lower trapezius muscles. Local muscle fatigue was determined using spectral analysis of electromyographic signals for the upper and lower trapezius muscles. The results demonstrated an average of 22% decrease in the median frequencies of the muscles sampled following resistive exercise, suggesting a state of local muscle fatigue. Concomitant with the fatigue was a selective decrease in scapulothoracic motion about two of the three scapular axes. RELEVANCE: Occupational and recreational conditions often require repetitive overhead elevations of the arms, resulting in muscular fatigue and various pathologies. During repetitive arm elevations the scapulohumeral rhythm or synchronization between the humerus and the scapula is balanced to allow the most efficient elevation of the arm. A better understanding of this much-discussed scapulohumeral rhythm and the changes induced by muscular fatigue may provide insight into the pathomechanics associated with shoulder dysfunction.

Journal Article↗
PubMed1993

The difference in stiffness of the active plantarflexors between young and elderly human females.

The purpose of this investigation was to determine the difference in the intrinsic stiffness of the active plantarflexor muscles between young and elderly human females, and to determine changes in this stiffness associated with a 6-week strengthening exercise program. Intrinsic muscle stiffness was determined by measuring the resistance in the first 62 milliseconds offered by the muscle to multiple single stretch trials at 20% to 60% of maximal isometric contraction. Stiffnesses were related to pre-stretch torque (K/PST) by a linear fit. The K/PST relationship of the elderly subjects exhibited a steeper slope, indicating a greater increase in stiffness with an increase in pre-stretch torque. The effect of testing subjects at identical relative, but different absolute pre-stretch torque levels precluded definitive conclusions on possible stiffness differences between the age groups. After the strengthening exercise program, the plantarflexors showed an increase in maximum produced torque, and a decrease in stiffness as well as a decrease in the slope of the K/PST relationship.

Adult↗
PubMed1993

Three-dimensional joint range of motion measurements from skeletal coordinate data.

Frequently, joint range of motion is reported for a single plane (eg., sagittal, coronal, or transverse). However, the arc of joint motion during functional activities and many clinical tests encompasses motion in all three planes simultaneously. The purposes of this paper are to discuss a method to obtain relative joint three-dimensional angular displacement measurements using coordinates from skeletal landmarks and provide an analytical example of the method using three-dimensional angular displacement of the knee joint as a model. In order to calculate the three-dimensional relative motion, an orthogonal reference frame for each bone needs to be established. To establish the local reference frame, three noncollinear points are used to define unit vectors that are mutually perpendicular. Three-dimensional angles can be determined to describe the magnitude of the moving body rotation angles about the X, Y, and Z axes. These angles indicate the relative motion of body segments for abduction/adduction, flexion/extension, and internal/external rotation. The technique provides a more vigorous biomechanical understanding of joint motion and may have implications for measuring patient progress and evaluating joint mobilization treatment. This technique may also serve as a basis for developing new evaluation and treatment techniques.

Biomechanical Phenomena↗
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↗