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Biomedical subjects

M D Grabiner

Publications and source records attributed to M D Grabiner.

At least 37 records · Page 2Linked to original sources
PubMed1999

Peroneal motoneuron excitability increases immediately following application of a semirigid ankle brace.

STUDY DESIGN: Within-session, within-subject comparison of 2 conditions. OBJECTIVES: To determine the influence of application of a semirigid ankle brace on the excitability of the peroneus longus muscle motoneuron pool as measured by the H-reflex. BACKGROUND: The literature suggests that cutaneous mechanoreceptors can contribute to proprioception, especially during conditions in which skin experiences displacement. Further, skin displacement and stimulation of cutaneous mechanoreptors have been shown to increase motoneuron excitability. METHODS AND MEASURES: H-reflexes and M-waves of the peroneus longus muscle were acquired by stimulating the common peroneal nerve of 11 uninjured subjects during 2 randomly ordered conditions, with and without application of an Aircast Air-Stirrup. Five reflexes were collected at each of 12 stimulation voltages. The peak-to-peak amplitudes of the M-wave and H-reflex from each subject's ensemble-averaged data at each stimulation voltage was used to generate H-reflex and M-wave recruitment curves. The H-reflex amplitude was subsequently expressed as a percentage of the maximum M-wave amplitude. RESULTS: The normalized H-reflex amplitude increased by approximately 10% during the braced condition compared to the nonbraced condition. The peroneus longus H-reflex latency and M-wave amplitude were not affected by the bracing condition. CONCLUSIONS: Application of the ankle brace excited afferents possibly arising from a number of candidate mechanoreceptors, 1 of which is likely cutaneous. The findings raise questions as to whether the increased motorneuron excitability can be used for the purposes of rehabilitation from ankle injury.

Adult↗
PubMed1999

Peroneus longus can not be fully activated during ankle complex exercises by uninjured subjects.

This study characterized, for the first time, the extent to which the peroneus longus muscle can be voluntarily activated by uninjured subjects during common ankle rehabilitative exercises. Ten healthy subjects performed isometric maximum voluntary contractions (MVCs) of eversion and plantarflexion on a dynamometer and against manual resistance, and performed dynamic whole-body activities that place large loads on the ankle complex (vertical jumps and side-cuts). During these activities, surface EMG signals were collected from the peroneus longus and expressed as a percentage of the maximum motor responses elicited by electric stimulation. Voluntary activation levels of the peroneus longus during isometric MVCs performed on the dynamometer and performed against manual resistance were not significantly different. Side-cuts produced significantly larger activation levels than those maximum vertical jumps and the isometric exercises. Nevertheless, the activation levels were substantially lower than those reported for other lower extremity muscles. These results serve as the basis for further questions related to whether voluntary peroneus longus activation level can be affected by specific rehabilitative efforts, whether activation levels are influenced by acute and chronic ankle complex injuries and, if so, whether this effect influences the functional outcome of rehabilitation efforts following ankle injuries.

Adult↗
PubMed1998

EMG variability during maximum voluntary isometric and anisometric contractions is reduced using spatial averaging.

Electromyography (EMG) is a commonly used tool that can be plagued with poor signal-to-noise ratios. One result of poor signal-to-noise ratios is increased within- and between-subject variability of quantified EMG variables, for example, the integrated EMG. Methods that reduce within- and between-subject variability of quantified EMG variables can increase the statistical power of an experimental design and aid in the functional interpretation of experimental results. The purpose of this investigation was to determine the effectiveness of spatially averaging the surface EMG signal to reduce the variability of the quantified EMG obtained during maximum voluntary contractions (MVC). The present study extends the work of earlier investigators describing the enhanced signal characteristics obtained by spatially averaging the surface EMG measured during submaximum voluntary isometric contractions and stretch reflexes. Ten subjects performed maximum voluntary isometric and anisometric (concentric and eccentric) contractions of the elbow flexors. Four electrodes, forming two pairs of bipolar electrodes were placed over both the biceps brachii and brachioradialis muscles. Four rectified and integrated EMG signals from the electrode array were compared. Data from each subject's contraction condition and from each muscle were used to compute a coefficient of variation that was considered representative of the within-subject variability. These data were analysed with a multifactorial repeated measures analysis of variance (ANOVA). The results revealed a muscle-specific, statistically significant superiority of one of the methods in reducing the variability of the rectified and integrated EMG signal. Summing the rectified and integrate signals from each bipolar pair of electrodes in the array was shown to reduce significantly the within-subject variability.

Adult↗
PubMed1998

Normally aging older adults demonstrate the bilateral deficit during ramp and hold contractions.

The bilateral deficit results from the maximum voluntary force of a bilaterally performed task being smaller than the sum of the maximum voluntary force of the unilaterally performed tasks. It is underlain by the limitation of the neural drive during maximum bilateral contractions and has been hypothesized to reflect the inability to fully activate high threshold motor units. Because high threshold motor units atrophy in older adults, a smaller bilateral deficit in older adults compared to young adults would further support the hypothesis. Indeed, K. Häkkinen et al. in 1995 and 1996 reported no bilateral deficit in older adults performing rapid maximum contractions. The present study extends this investigation to slowly developed maximum contractions. The results demonstrated a bilateral deficit (p < .05). This result, combined with the age related decrease in the number of high threshold motor units, tends to refute the contention that selective restriction of high threshold motor units causes the bilateral deficit during maximum voluntary isometric ramp and hold contractions.

Aged↗
PubMed1998

Fatigue effects on the bilateral deficit are speed dependent.

PURPOSE: The bilateral deficit is characterized by a decrease in maximum voluntary contraction (MVC) force during bilateral activation of homologous muscles compared with sum of the forces produced during unilateral MVC of the muscles. A proposed relationship between the bilateral deficit and the ability to activate high threshold motor units was investigated. The effects of muscle fatigue, induced using two contraction speeds, on the size of the bilateral deficit were measured. Based on previously published findings, it was expected that fast velocity isokinetic contractions compared with slow velocity isokinetic contractions would produce a larger bilateral deficit. It was hypothesized that following a unilateral fatigue protocol, the size of the bilateral deficit at the fast and slow velocities would be comparable. METHODS: The bilateral deficit was measured for isokinetic knee extension in 20 men (age:25 +/- 3 yr) before and after a fatigue protocol performed at 30 and 150 degreesxs(-1). RESULTS: The size of the bilateral deficit was initially the same at both velocities. The fatigue protocol at each contraction speed significantly decreased the maximum voluntary knee extension moment. The size of the bilateral deficit was not influenced by the 150 degrees fatigue protocol (pretest: -14.0% post-test: -12.5%; P > 0.05). However, the size of the bilateral deficit increased following the 30 degreesxs(-1) fatigue protocol (pretest: -13.7%; post-test: -21.9%; P < 0.05). CONCLUSIONS: The failure of the size of the bilateral deficit to be comparable at 30 and 150 degreesxs(-1) following fatigue is contrary to previous published reports that suggested reduced activation of high threshold motor unit is the primary mechanism underlying the bilateral deficit.

Adult↗
PubMed1998

Smokeless tobacco, reaction time, and strength in athletes.

PURPOSE: This study investigated the effects of smokeless tobacco on reaction time and strength in a group of Division III athletes. METHODS: Athletes were tested for simple and choice reaction time, maximum voluntary force, and maximum rate of force generation of the knee extensors on a KinCom dynamometer at 250 degrees.s-1. Smokeless tobacco-using athletes (N = 20) were tested while both using and after abstaining from smokeless tobacco. Another group of athletes (N = 20) who did not use smokeless tobacco served as a control group. RESULTS: Simple and complex reaction times were not affected by smokeless tobacco use or abstention. In the simple reaction time test, maximum voluntary knee extensor force was higher in the smokeless tobacco-using group while abstaining (P < 0.05). Maximum rate of force generation in the simple reaction time test was not statistically different between the conditions. In the choice reaction test, both strength parameters (maximum force and maximum rate of force generation) were higher in the user group while abstaining (P < 0.05) compared with the using condition. The strength parameter measurements in the control group were not statistically different from the tobacco-using group, while either using or abstaining. CONCLUSIONS: We conclude that smokeless tobacco use has no effect on reaction time but may detrimentally influence maximum voluntary force and maximum rate of force generation.

Adolescent↗
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↗