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Biomedical subjects

M D Grabiner

Publications and source records attributed to M D Grabiner.

At least 19 recordsLinked to original sources
PubMed1996

Measures of paraspinal muscle performance do not predict initial trunk kinematics after tripping.

The ability to limit the trunk flexion associated with an anteriorly directed trip is a determinant of successful recovery of recovering postural stability and is subservient to rapidly detecting and correcting the imposed trunk flexion in the available time. This experiment tested the hypothesis that subjects demonstrating greater eccentric trunk/hip extension strength, faster voluntary reaction times, shorter automatic response latencies, and larger automatic activation amplitudes of the paraspinal muscles, would demonstrate less trunk flexion following a trip. An isokinetic protocol was used to obtain measures of trunk extension strength, response latencies, and activation amplitudes. Motion analysis methods were used to quantify trunk kinematics during the positioning phase of recovery following an induced trip. Statistically significant and functionally meaningful relationships between eccentric strength of the trunk/hip extensors, voluntary-reaction time, automatic reaction time, activation amplitudes and trunk kinematics failed to emerge. Thus, although automatic and voluntary paraspinal muscle responses have the potential to limit trunk flexion during the positioning phase of recovery, the task may be achieved through intersegmental factors or other muscular sources such as the gluteus maximus and hamstrings.

Accidental Falls↗
PubMed1995

Visual guidance to force plates does not influence ground reaction force variability.

Gait analysis methods commonly require the subject to avoid visual guidance, that is, targeting, the force plate upon which a foot-strike is necessary. The putative rationale underlying the preference for not using targeting is the unsubstantiated contention that gait is altered. This study evaluated the influence of force plate targeting on the variability of ground reaction forces (GRF) in 15 normal subjects. Secondary factors of single vs multiple steps to the force plate and whether or not subjects were informed of the study's primary purpose were also examined. ANOVA main effects revealed that targeting did not significantly affect GRF variability (p > 0.05). A significant main effect of the number of steps required to reach the force plate on AP force variability was found (p = 0.002). Prior knowledge of the purpose of the study did not significantly affect GRF variability (p > 0.05). It was concluded that the variability of ground reaction forces is not significantly affected by targeting the force plate. Thus, targeting would not be expected to influence the variability of calculated kinetic variables that are subservient to GRF.

Adult↗
PubMed1995

On the assumption of bilateral lower extremity joint moment symmetry during the sit-to-stand task.

This study examined the validity of the assumption of bilateral lower extremity joint moment symmetry during the sit-to-stand motion for a group of young (n = 7) and a group of elderly (n = 7) female subjects. Two force plates and a motion analysis system were used to determine peak joint moments at the ankles, knees, and hips following liftoff from a chair. Statistically, bilateral asymmetries in peak joint moments were found at the knee joint in the young group [a right to left difference of 0.43% BW x BH (body weight x body height)] and at the hip joint in both subject groups (differences of 0.20% BW x BH and 1.09% BW x BH for the young and elderly subjects, respectively). Subsequent data analysis, using an algorithm that assumed bilateral ground reaction force (GRF) symmetry, was performed to determine whether the bilateral differences were a result of kinematic or GRF asymmetry. It was concluded from these results that both the kinematic and GRF data account for the bilateral asymmetry. The results of the subsequent analysis also showed that the method which assumed bilateral GRF symmetry underestimated the peak joint moments at the ankles, knees, and hips, with the greatest difference between methods being 0.10% BW x BH for the ankle joint. The results of this study suggest that the assumption of bilateral symmetry of lower extremity joint moments during the sit-to-stand is not valid. However, the biomechanical significance of the errors associated with assuming symmetry must also be taken into account.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Paraspinal precontraction does not enhance isokinetic trunk extension performance.

STUDY DESIGN: This study investigated the influence of isometric contraction of the trunk extensor muscles, immediately preceding maximum effort isokinetic trunk extension (precontraction), on isokinetic performance variables and activation levels of the paraspinal muscles. OBJECTIVES: To determine whether agonist precontraction significantly improved the concentric and eccentric isokinetic trunk extension contraction. SUMMARY OF BACKGROUND DATA: Agonist precontraction has been reported to enhance agonist neural drive and force output of the knee and ankle joints. METHODS: Subjects performed concentric and eccentric isokinetic trunk extension at 60, 90, and 120 deg/sec, each of which were preceded by isometric trunk extension precontraction force equal to 0%, 25%, and 50% body weight. RESULTS: Concentric and eccentric contractions showed general, but no statistically significant performance enhancement with paraspinal precontraction. Eccentric contractions tended to improve to a greater extent than concentric contractions. CONCLUSIONS: It is possible that the addition of agonist precontraction increased the complexity of the trunk extension task, thus requiring a learning period, as is the case with most novel motor skills. There may be meaningful rehabilitation-related implications of the qualitative tendencies observed in the data that merit further consideration.

Adult↗
PubMed1994

Maximum rate of force development is increased by antagonist conditioning contraction.

Nine subjects performed maximum contractions with the knee extensor muscles on an isokinetic device set at 4.36 rad/s. The knee extensions were preceded by isometric conditioning contractions of the antagonist knee flexor muscles. The conditioning contraction forces were 0, 25, 50, 75, and 100% of the maximum isometric force. The purpose of the study was to determine 1) the effects of graded conditioning contractions with the knee flexor muscles on the maximum performance of the quadriceps femoris and 2) whether the effects of the conditioning contractions are similarly distributed to components of the quadriceps femoris. The increased initial quadriceps femoris activation levels associated with the conditioning contractions were similarly distributed to quadriceps femoris components. In contrast with previously published research on exercise performed at substantially lower knee extension velocities, the maximum knee extension force and the work performed were not affected by the conditioning contractions. However, the maximum rate of force development increased significantly (P < 0.05). The intensity of the knee flexor conditioning contractions likely influences agonist motor unit activation variables, but this influence may be related to the speed of the agonist contraction.

Adult↗
PubMed1994

Neuromechanics of the patellofemoral joint.

Patellofemoral joint pain is one of the most common ailments associated with visits to sports medicine clinics and can be disabling, although conservative clinical treatment has a reportedly very high success rate. Patellofemoral joint pain is often associated with improper tracking of the patella within the femoral trochlear notch. Improper tracking of the patella can be associated with increased patellofemoral contact pressures that may be a mechanical stimulus underlying patellar cartilage degeneration. In those cases in which anatomic anomalies and trauma may be excluded as the basis for improper tracking, attention is directed toward possible disruptions to the central nervous system control and contractile potential of the knee joint extensor musculature that underlies proper patellofemoral mechanics. This paper presents a review of three seminal components related to the neuromechanics of patellofemoral function; patellofemoral tracking, patellofemoral contact pressures, and neuromotor control of patellofemoral agonists. It is the intent of the authors to illuminate areas requiring further basic and clinical research and provide a point of departure for this work.

Biomechanical Phenomena↗
PubMed1993

Evaluation of methods to minimize cross talk in surface electromyography.

The purposes of this study were to quantify the effectiveness of various methods to minimize cross talk in surface electromyography (EMG) using common recording equipment, and to compare the intra- and interday variabilities of signals recorded with these methods. Comparisons were made for signals recorded with the single differential (SD), double differential (DD) and branched electrode (BE) techniques with large and small electrodes and corresponding interelectrode distances. The amount of cross talk in tibialis anterior EMG signals during maximum voluntary effort (MVE) triceps surae excitation was estimated using a protocol involving electrical stimulation of the triceps surae via the tibial nerve. In SD signals, cross talk averaged 12.2 and 10.2 percent MVE, for the large and small interelectrode distances, respectively. DD and BE signals contained significantly less cross talk (approximately 5 percent MVE for both techniques and interelectrode distances) than SD signals. The intra- and interday variabilities associated with these methods were estimated by recording tibialis anterior EMG signals during maximum voluntary isometric dorsiflexion (3 trials on each of 2 days) and calculating coefficients of variation for average-rectified values and median frequencies. EMG signals recorded with the small interelectrode distance showed greater interday amplitude variability than those recorded with the large interelectrode distance. Intra- and interday amplitude variabilities were similar across SD, DD and BE recording techniques. Intra- and interday frequency variabilities were similar across all experimental conditions. Thus, the DD and BE techniques, in conjunction with the large interelectrode distance (and large electrodes), provide a signal which contains significantly less cross talk than the SD technique without sacrificing intra- and interday amplitude and frequency stability.

Adult↗
PubMed1993

Kinematics of recovery from a stumble.

BACKGROUND: Injuries most frequently related to accidents in elderly persons are falls during locomotion and stair ascent and descent. Although numerous risk factors have been related to falling behavior, effective strategies to predict and prevent falls have not evolved. The rationale underlying this study was that systematic experimental and analytical investigation of the effects of perturbations during locomotion and the subsequent requisites for recovery could lead to the development of clinically relevant evaluation(s) capable of identifying a predisposition to falling. The present study is the first biomechanical investigation of recovery from an anteriorly directed stumble. METHODS: Seven healthy, young males participated in this study. While the subjects walked along a walkway in the laboratory, stumbles were unexpectedly induced using a mechanical obstacle. Videotape records of these trials were analyzed and selected sagittal plane kinematics extracted. RESULTS: The perturbation caused an increase in the maximum trunk flexion angle from 4.3 degrees (control) to 18.3 degrees (p = .057), and this change was significantly associated with preperturbation walking velocity (p = .036). The maximum hip and knee flexion angles increased from 26 to 47 degrees (p = .039) and from 60 to 89 degrees (p = .009), respectively. The increases in maximum hip flexion velocity (79%) and maximum knee extension velocity (36%) were not significant. CONCLUSIONS: Identification of the principal elements of control during perturbed locomotion can contribute to understanding the relationship between specific age-related performance deficits and some types of falling behavior. The results suggest that recovery from a stumble is dependent upon lower extremity muscular power and the ability to restore control of the flexing trunk.

Accidental Falls↗
PubMed1993

Converting Chattecx Balance System vertical reaction force measurements to center of pressure excursion measurements.

BACKGROUND AND PURPOSE: The purpose of this study was to determine the precision with which the postural stability data generated by the Chattecx Balance System could be converted to center of pressure displacement measurements. SUBJECTS: Two men and one woman were selected to represent a broad range of body sizes (age = 23-33 years, height = 154-175 cm, weight = 45-80 kg). METHODS: The Balance System load cells were placed on a force plate, and data were collected simultaneously from the Balance System and the force plate while the subjects performed standardized postural tasks. Linear regression analysis was used to characterize the relationship between the estimated center of pressure from the Balance System and the calculated center of pressure from the force plate. RESULTS: Significant linear relationships between the center of pressure estimated from the Balance System and the center of pressure calculated from the force plate were determined (all R2 values = > .90). CONCLUSION AND DISCUSSION: System data can be converted, and the methods recommended for use with the Balance System are described.

Adult↗
PubMed1993

Bilateral deficit is larger for step than for ramp isometric contractions.

The force produced by a muscle group during a maximum effort bilateral task has been reported to be less than that produced during a maximum effort unilateral task. It was hypothesized that if decreased activation of primarily fast motor units is responsible for this bilateral deficit, 1) the bilateral deficit would be larger in step than in ramp isometric contractions and 2) the rate of torque generation in step contractions would be slower in bilateral than in unilateral tasks. Twelve healthy male subjects performed unilateral and bilateral isometric knee joint extension tasks in which maximum torque was generated under ramp and step conditions. The maximum torques produced in the bilateral tasks were 17.0 and 24.6% less than those produced in the unilateral tasks during the ramp and step conditions, respectively (both P < 0.001). The bilateral torque deficit for the step condition was significantly greater than that for the ramp condition (P = 0.012). The rate of torque generation in the step condition was 19.7% slower in the bilateral than in the unilateral task (P = 0.010). Thus the results from these torque measurements support the notion that decreased activation of primarily fast motor units may be responsible for the bilateral deficit.

Adult↗
PubMed1993

Effect of the aircast on unilateral postural control: amplitude and frequency variables.

Little objective data exist regarding the effect of the Aircast Air-Stirrup on motor performance. Thus, the effect of the Aircast on the amplitude and frequency of postural sway during unilateral stance was evaluated for 15 uninjured male subjects. Postural sway during static and dynamic tests was measured using the Chattecx Balance System. Use of the Aircast improved unilateral postural control as evidenced by decreases in some of the components of postural sway. Previously, a link was made between a large amplitude of unilateral sway and a high probability of ankle injury (14). Thus, since Aircast use was found to decrease the amplitude of unilateral sway, it may also be beneficial in reducing the probability of injury. Although the scope of this study did not allow for differentiation among the complex systems involved in postural control, the possibility of the Aircast enhancing afferent feedback was proposed. The restricted inversion-eversion range of motion associated with the Aircast, in conjunction with the present observation that unilateral stability was enhanced with its use, suggests that the Aircast may provide a valuable prophylactic role in helping to reduce the incidence of ankle injuries.

Adult↗
PubMed1992

Cross talk in surface electromyograms of human hamstring muscles.

Signals generated from muscles other than the muscle(s) of interest (cross talk) can confound the interpretation of surface electromyograms (EMGs). In this study, the amount of cross talk in surface EMGs of human hamstring muscles was estimated using a protocol in which the quadriceps femoris was electrically stimulated via the femoral nerve. EMGs were recorded from the vastus lateralis and the medial and lateral hamstring muscle groups. The amplitude of the EMG response of the vastus lateralis to electrical stimulation was adjusted to match that of its maximum voluntary effort (MVE) under isometric conditions. Subsequent power density spectrum analysis showed that the median frequencies of the signals generated by electrical stimulation and MVE were not significantly different. In conventional bipolar recordings, cross talk in lateral hamstring EMGs averaged 17.1% MVE and in medial hamstring EMGs 11.3% MVE (average-rectified values). The double differential technique significantly reduced cross talk to 7.6% MVE for the lateral hamstrings, and to 4.2% MVE for the medial hamstrings. The double differential technique appears to be more selective than the bipolar technique when recording EMGs from muscles with highly active neighbors and thus should be used in such situations. Software simulations of the double differential technique also appear to be more selective than the bipolar technique and may be used when the number of amplifiers available is limited.

Adult↗
PubMed1992

In vivo tracking of the human patella.

The purpose of this study was to describe the dynamic, in vivo, three-dimensional tracking pattern of the patella for one normal male subject. Intracortical pins were inserted into the patella, tibia, and femur. The subject performed seated and squatting knee flexion/extension, and maximum voluntary quadriceps contractions. In addition, the vastus medialis oblique was subjected to maximal electrical stimulation. Motions of the markers attached to the intracortical pins were analyzed using an automated video system. Patellar and tibial motions were determined relative to a femoral reference system. While the tibia flexed 50 degrees from full extension (seated condition), the patella flexed 30.3 degrees, tilted laterally 10.3 degrees, and shifted laterally 8.6 mm. In general, these results show qualitative agreement with the data collected from cadaveric specimens [van Kampen and Huiskes, J. orthop. Res. 8, 372-382 (1990)]. The differences present may reflect different passive constraints to patellar motions, and different relative loading of the individual quadriceps components, in our study compared to the cadaveric study. Only small differences were found between patellar motions in the seated and squatting conditions. Differences in patellar displacements produced by (1) maximal electrical stimulation of the vastus medialis oblique, and (2) maximum voluntary quadriceps contraction, at 30 degrees knee flexion and full extension, may reflect the dominant influence of passive constraints, and the vastus lateralis, on normal patellar motions. Further in vivo study of patellar tracking seems warranted to evaluate surgical and conservative interventions for patellofemoral disorders.

Adult↗
PubMed1992

Decoupling of bilateral paraspinal excitation in subjects with low back pain.

This study compared bilateral paraspinal excitation in normal subjects and subjects with low back pain. Comparison was made between six control subjects and seven low back pain subjects who performed maximum-effort isometric trunk extension in minimum elapsed time at two trunk angles. Electromyographic signals were collected bilaterally from the paraspinal musculature. The time- and amplitude-normalized electromyographic data were analyzed using a repeatability criterion sensitive to temporal and amplitude differences. This analysis showed that low back pain subjects demonstrated temporal and amplitude decoupling of the paraspinal musculature bilaterally. Low back pain subjects also demonstrated clinically meaningful disruptions between paraspinal excitation and isometric trunk extension moment. This method may be useful in quantifying neuromotor control in low back pain for initial and follow-up clinical evaluation for static and dynamic functional tests.

Adult↗
PubMed1992

Modeling recovery from stumbles: preliminary data on variable selection and classification efficacy.

OBJECTIVE: The primary purpose of this preliminary investigation was to determine the functional relationship between selected information processing time and response execution variables and measures of postural stability in elderly women. A secondary purpose was to explore the efficacy of a neuromotor model using selected variables to retrospectively identify subjects with a self-reported history of falling. DESIGN: Descriptive, retrospective, cohort. SETTING: General community. SUBJECTS: Convenience sample of 17 community-dwelling females with a mean age of 72.2 years. MAIN OUTCOME MEASURES: Postural stability variables included the amplitude and frequency of postural sway during static vision-aided no-vision conditions. Information processing and response execution variables were collected using a simple-choice reaction time paradigm for an isometric knee extension task. RESULTS: Postural stability and information processing variables were functionally independent. Based upon significant intergroup differences, simple and choice pre-motor reaction time and non-vision aided anterior posterior sway amplitude were selected for inclusion in a discriminant analysis. The resulting discriminant function was significant (P = 0.01), correctly categorizing all of the subjects with a self-reported history of falling and identifying six out of seven of the non-fallers. CONCLUSIONS: These preliminary results suggest that it is feasible to identify a predisposition to falling by detecting an inability to respond successfully to a postural disturbance.

Accidental Falls↗
PubMed1992

Further evidence against a direct automatic neuromotor link between the ACL and hamstrings.

The purpose of this experiment was to determine whether reflexive, or more broadly, automatic hamstrings excitation could be elicited during isometric, maximum effort, step increases in knee extension torque. Eight healthy subjects without lower extremity dysfunction or injury performed maximum effort isometric knee extension at 15 and 85 degrees of knee flexion in minimum elapsed time. Surface electromyography was used to record medial (semimembranosis and semitendinosis) and lateral (biceps femoris--long head) hamstrings excitation that was subsequently normalized to the excitation during maximum isometric knee flexion. To assess whether automatic hamstrings excitation was elicited, the amplitude of the EMG signals was analyzed and compared for 50 ms prior to peak knee extension torque, and three consecutive 50 ms windows following peak knee extension torque. The amplitude of the EMG subsequent to the peak knee extension torque failed to support the contention of an automatic hamstrings excitation mediated by neural circuitry from the ACL. The present results, in conjunction with previous work, suggest that a protective automatic hamstrings contraction is not normally elicited in response to conditions subjecting the anterior cruciate ligament to strain.

Adult↗