Biomedical subjects

L D Abraham

Publications and source records attributed to L D Abraham.

At least 19 recordsLinked to original sources

PubMed2001

Quantitative EMG analysis to investigate synergistic coactivation of ankle and knee muscles during isokinetic ankle movement. Part 1: time amplitude analysis.

Synergy generally refers to the coordinated action of several motor elements to produce a specific motor task, either intentionally or automatically. One example is motor irradiation, a sudden spread of synergistic muscular coactivation resulting from a forceful single joint movement. To investigate this type of synergy pattern, a quantitative EMG approach was employed to characterize explicit neuromuscular synergy in the ankle-knee complex during maximal ankle isokinetic contraction. In the present study, isokinetic ankle contractions, both dorsiflexion and plantarflexion, at four different speeds (30, 60, 120, and 240 degrees/s) were studied in a normal adult population (N=11) to assess synergistic coactivation of the prime movers (tibialis anterior and gastrocnemius) and irradiated muscles (ipsilateral and contralateral rectus femoris and biceps femoris) of the ankle-knee complex. Electromyographic signals were collected with surface EMG electrodes and processed with traditional time-amplitude analysis to examine specific neural control strategies. The data generally supported several empirical assumptions common to neurological facilitation techniques. (1) Motor irradiation to the knee muscles due to ankle muscle isokinetic contraction was strongly directionally dependent. (2) Motor irradiation to the ipsilateral knee muscles due to ankle isokinetic contraction was speed dependent. (3) The prime movers demonstrated a similar control strategy, irrespective of different contraction speeds.

Adult↗

PubMed2001

Quantitative EMG analysis to investigate synergistic coactivation of ankle and knee muscles during isokinetic ankle movement. Part 2: time frequency analysis.

Fundamental to intralimb coordination in the lower extremity, ankle-knee synergy induced by motor irradiation has long been employed to secure facilitation of paralyzed muscles. This study, a companion research subsequent to the time amplitude analysis of surface electromyography in part 1, was to investigate the recruitment strategy of irradiated muscles and prime movers during ankle isokinetic contraction at different contraction speeds (30, 60, 120 and 240 degrees/s) with time frequency analysis. The results indicated the recruitment strategies of the major irradiated muscles (ipsilateral rectus femoris/ipsilateral biceps femoris) and prime movers (anterior tibialis/gastrocnemius) were time-dependent and significantly different in terms of the instantaneous median frequency. In general, the prime movers for ankle isokinetic concentric contraction demonstrated a similar recruitment strategy, irrespective of different contraction speeds. This finding is consistent with the idea of generalized motor programs that speed is one of the constraint parameters supplied to motor programs. Nevertheless, the recruitment strategies of the irradiated muscles were highly inconsistent, varying across trials at different contraction speeds, and were not relevant to those of the prime movers. In addition, the recruitment in the irradiated muscles seemly limited to motor units of low threshold, in spite of maximal voluntary contraction of the prime movers.

Adult↗

PubMed2001

Sensitivity of qualitative and quantitative spasticity measures to clinical treatment with cryotherapy.

This study examined the extent to which a battery of tests could detect a reduction of plantarflexor spasticity resulting from cryotherapy. The tests included a traditional qualitative spasticity scale, three potential quantitative spasticity measures and a measure of voluntary ankle muscle function. Twenty-six adult traumatic-brain-injured subjects were examined; these included 22 males and 4 females. The mean age was 28.15 years (range: 18-57, SD 10.78). The five tests were performed in random sequence on both ankles of each subject, before and after a 20 minute cold pack application to the calf. Tests were: modified Ashworth scale (MAS) scoring; H-reflex testing with and without dorsiflexor contraction (Hdf/Hctrl ratio); H-reflex testing with and without Achilles tendon vibration (Hvib/Hctrl ratio); reflex threshold angle (RTA) and timed toe tapping (TIT). Cryotherapy resulted in lowered MAS scores consistent with a reduction in spasticity. Doubly multivariate repeated measures ANOVA revealed a significant difference (F = 24.16, P < 0.001) in test scores between the pre- and post-cryotherapy test batteries. Significant pre- and post-cryotherapy differences (P < or = 0.03) for all dependent measures contributed to the main effect for cryotherapy. However, among the potential quantitative measures of spasticity only the RTA test demonstrated appropriate sensitivity to the reduction in spasticity. In spite of spasticity reduction, TIT performance was impaired following muscle cooling. Failure of the H-reflex ratios to show a reduction consistent with reduced spasticity was attributed to competing alpha and gamma motoneuron effects resulting from peripheral cooling.

Adolescent↗

PubMed2000

The effect of ankle joint position and effort on quadriceps reflex sensitivity.

OBJECTIVE: To investigate a possible ankle-knee synergy, experiments with normal subjects were performed to compare changes of the quadriceps motor pool excitability due to ankle position and effort. METHODS: Vastus medialis H reflex amplitude was examined during ankle isometric contractions conditioned by different ankle positions (dorsiflexion, neutral, and plantarfiexion) with or without voluntary effort (either in the dorsiflexion or plantarflexion direction). Repeated measures ANOVAs were performed on the mean and standard deviation of the H peak-to-peak amplitude. RESULTS: Mean vastus medialis H reflex amplitudes were significantly different among the trials of different ankle efforts (P<0.05), and significantly increased during plantarfiexion efforts. In contrast, mean vastus medialis H reflex amplitude did not vary with respect to changes of ankle position (P>0.05). CONCLUSIONS: The data suggest that (1) the position of the ankle joint did not significantly modify the excitability of the neuromotor pool of the VM muscle, in either static or active cases, and (2) the effort effect from the ankle joint on the VM neuromotor pool is most significant during ankle plantarfiexion effort. Possible mechanisms are central motor irradiation and peripheral force-dependent pathways from the ankle joint that influence the VM neuromotor pool.

Adult↗

PubMed1999

Muscle activity in rapid multi-degree-of-freedom elbow movements: solutions from a musculoskeletal model.

The activity of certain muscles that cross the elbow joint complex (EJC) are affected by forearm position and forearm movement during elbow flexion/extension. To investigate whether these changes are based on the musculoskeletal geometry of the joint, a three-dimensional musculotendinoskeletal computer model of the EJC was used to estimate individual muscle activity in multi-degree-of-freedom (df) rapid (ballistic) elbow movements. It is hypothesized that this model could reproduce the major features of elbow muscle activity during multi-df elbow movements using dynamic optimal control theory, given a minimum-time performance criterion. Results from the model are presented and verified with experimental kinematic and electromyographic data from movements that involved both one-df elbow flexion/extension and two-df flexion/extension with forearm pronation/supination. The model demonstrated how the activity of particular muscles is affected by both forearm position and movement, as measured in these experiments and as previously reported by others. These changes were most evident in the flexor muscles and least evident in the extensor muscles. The model also indicated that, for specific one- and two-df movements, activating a muscle that is antagonistic or noncontributory to the movement could reduce the movement time. The major features of muscle activity in multi-df elbow movements appear to be highly dependent on the joint's musculoskeletal geometry and are not strictly based on neural influences or neuroanatomical substrates.

Computational Biology↗

PubMed1996

Isolation and characterization of a subtilisin-like serine proteinase secreted by the sap-staining fungus Ophiostoma piceae.

Identification of key enzymes of sapstain fungi which cause wood discoloration is necessary for targeted inhibition strategies. Therefore proteinases involved in the nitrogen pathway have been characterized. The sap-staining fungus Ophiostoma piceae strain 387N produced proteolytic enzymes when grown on wood and protein-supplemented media. Proteolytic activity in culture filtrates was inhibited by PMSF and EDTA. The major protein in culture filtrates was a proteinase with a pI of 5.6 and a molecular weight of 33 kDa. This was the major proteinase produced by O. piceae and it was purified from culture filtrates by hydrophobic interaction chromatography. The proteinase was susceptible to autolytic degradation during chromatographic separations when ammonium sulfate was not present. When azocoll was used as a substrate, the proteolytic activity of the purified proteinase was determined to be optimal at pH 7-9 and 40 degrees C. Similar pH and temperature optima were obtained using succinyl-ala-ala-pro-phe-p-nitroanilide as the substrate. The N-terminal sequence of the protein showed a high degree of homology with fungal alkaline serine proteinases classified as subtilisin class II enzymes. Agreement in inhibition patterns and electrophoretic and catalytic properties suggested the secretion of the same proteinase during growth on wood. Understanding the role of this proteinase during fungal colonization is an important step toward disrupting fungal growth on wood.

Amino Acid Sequence↗

PubMed1996

Reliability of the Modified Ashworth Scale in the assessment of plantarflexor muscle spasticity in patients with traumatic brain injury.

Although the Modified Ashworth Scale (MAS) is commonly used to assess the severity of muscle spasticity for ankle plantarflexors, its reliability has only been established for elbow muscles. Interrater reliability, intrarater reliability and temporal (between-days) reliability were examined in this study. Also, interrater reliability for use of the scale with plantarflexors was compared with reported results from the measurement of elbow flexors. Thirty adult volunteers with traumatic brain injuries participated. There were 20 men and 10 women; the mean age was 28.3 years (SD = 10.8). Two physical therapists used the MAS to score the subjects independently. Measurements were repeated to yield multiple scores for intrarater reliability assessment. Twenty-one of the subjects returned individually on separate days to be measured again, so that temporal reliability could be assessed. Spearman's correlation coefficients were 0.73 for interrater reliability 0.74 and 0.55 for intrarater reliability, and 0.82 for temporal reliability. Overall, reliability of the MAS for assessing plantarflexor spasticity in patients with traumatic brain injury was found to be minimally adequate to support its continued use. However, interrater reliability was less than that which has been reported for elbow flexors, and intrarater reliability findings were mixed.

Adolescent↗

PubMed1996

Development and evaluation of a musculoskeletal model of the elbow joint complex.

This paper describes the development and evaluation of a musculoskeletal model that represents human elbow flexion-extension and forearm pronation-supination. The length, velocity, and moment arm for each of the eight musculotendon actuators were based on skeletal anatomy and joint position. Musculotendon parameters were determined for each actuator and verified by comparing analytical moment-angle curves with experimental joint torque data. The parameters and skeletal geometry were also utilized in the musculoskeletal model for the analysis of ballistic (rapid-directed) elbow joint complex movements. The key objective was to develop a computational model, guided by parameterized optimal control, to investigate the relationship among patterns of muscle excitation, individual muscle forces, and to determine the effects of forearm and elbow position on the recruitment of individual muscles during a variety of ballistic movements. The model was partially verified using experimental kinematic, torque, and electromyographic data from volunteer subjects performing both isometric and ballistic elbow joint complex movements. This verification lends credibility to the time-varying muscle force predictions and the recruitment of muscles that contribute to both elbow flexion-extension and forearm pronation-supination.

Adult↗

PubMed1995

Characterization of the cleavage specificity of a subtilisin-like serine proteinase from Ophiostoma piceae by liquid chromatography/mass spectrometry and tandem MS.

A proteinase secreted by the sapstaining fungus Ophiostoma piceae is thought to be necessary for the primary retrieval of nitrogen from wood proteins. By using mass spectrometry (MS) techniques, we have established the cleavage specificity of this subtilisin-like serine proteinase. This work demonstrated the potential of MS in determining cleavage specificities of newly isolated proteinases in a relatively short time frame, and determined that the O. piceae proteinase showed a substrate specificity similar to that of proteinase K. Primary cleavage of the insulin B-chain occurred between Leu15 and Tyr16. In addition numerous secondary cleavage sites occurred after hydrophobic, polar, and charged amino acids indicating a broad specificity.

Amino Acid Sequence↗

PubMed1995

Factors affecting autolysis of a subtilisin-like serine proteinase secreted by Ophiostoma piceae and identification of the cleavage site.

The extracellular serine proteinase secreted by Ophiostoma piceae was degraded by autoproteolysis under certain conditions. At elevated temperatures the mature protein of 33 kDa was rapidly degraded without any accumulation of protein breakdown products. Glycerol, calcium ions and ammonium sulfate raised the heat stability of the enzyme, increasing its half-life at 45 degrees C from 1.9 min to 9.4 min, 40.4 min and 2 h, respectively. Thermal unfolding of the proteinase also occurred at higher temperatures in the presence of calcium ions and ammonium sulfate. Under conditions of heating, altered pH or partial depletion of protein-bound ions by EDTA, the structure of the proteinase was more susceptible to proteolysis. The major hydrolytic fragments of 19 kDa and 14 kDa, had N-terminal sequences of Ala1-Tyr2-Thr3-Thr4-Gln5-Thr6-Gly7-Ala8-Pro9-and Ser170-Glu171-Pro172-Se173-Val174-X-Thr 176-Val177-Gly178-Ala179-, respectively. Since the former sequence was identical to the N-terminus of the native protein, the major autoproteolytic cleavage site for a class II subtilase appeared to be the N-side of Ser170 using numbering based on the sequence of proteinase K. The secondary structure of the proteinase from O. piceae was similar to that of proteinase K based on circular dichroic spectra in the far ultraviolet region. This cleavage site was in a similar region to that identified for class I subtilases, which was located in an outer exposed loop of the tertiary structure of subtilisin-like serine proteinases.

Amino Acid Sequence↗

PubMed1995

Correlation of quantitative measures with the modified Ashworth scale in the assessment of plantar flexor spasticity in patients with traumatic brain injury.

This study of plantar flexor spasticity describes relationships among a traditional qualitative spasticity scale, three potential quantitative spasticity measures and a measure of voluntary ankle muscle function. Thirty-four volunteer adult patients with traumatic brain injuries participated. There were 28 males and 6 females; the mean age was 30.3 years. A battery of five randomly sequenced tests was performed for each subject on one ankle. Tests were: modified Ashworth scale (MAS) scoring; H-reflex testing with and without Achilles tendon vibration; H-reflex testing with and without dorsiflexor contraction; reflex threshold angle and timed toe tapping (TTT). Twenty-six subjects returned to have the second ankle tested, resulting in 60 ankles for the analyses. Spearman's coefficients for correlation of quantitative spasticity measures with MAS scores ranged from 0.39 to 0.49 with associated probabilities < or = 0.002. Pearson coefficients for correlation of quantitative spasticity measures with TTT scores were lower but also significant (P < or = 0.07). Multiple correlation for the set of quantitative measures yielded R = 0.614 (P < 0.001) with MAS scores and R = 0.365 (P = 0.045) with TTT scores. These findings reveal statistically significant relationships of low to moderate strength among potential quantitative spasticity measures, a traditional qualitative spasticity scale and a simple measure of voluntary ankle muscle function. Understanding these relationships is an essential part of the ongoing search for quantitative spasticity measures.

Adolescent↗

PubMed1993

Comparison of experimental and predicted muscle activation patterns in ballistic elbow joint movements.

The human elbow joint complex (EJC) is an intricate joint which produces combinations of movements that are unique within the human body and that are involved in performing many important tasks. This paper discusses an on-going study to predict muscle force patterns in elbow flexion-extension. Four musculotendon actuators are included in this preliminary musculoskeletal model for the analysis of ballistic elbow flexion-extension movements. The key objective is to develop a computational model, guided by optimal control, to investigate the relationship among patterns of muscle excitation, individual muscle forces, and movement kinematics. Model verification is attempted using experimental data from volunteer subjects performing a ballistic elbow flexion movement.

Biomechanical Phenomena↗

PubMed1991

Interactions between automatic postural adjustments and anticipatory postural patterns accompanying voluntary movement.

In order to examine interactions between centrally initiated postural activity preceding voluntary arm movements and compensatory postural activity, we studied patterns of postural muscle activity preceding a vigorous bilateral reach and grasp task or triggered by support surface motion. The reaching task required movement onset to be coincident with a predictable stimulus, and in some trials a brief backward platform perturbation was timed to occur before, during, or after the reach onset. Centrally initiated anticipatory postural activity was subject-specific and was very often absent when perturbation-induced postural activity was elicited just prior to movement onset. Likewise, compensatory postural activity patterns elicited by the platform perturbation did not occur when they would have coincided with the anticipatory postural activity. These data support the idea that the central neural processes which determine the specific activation pattern of the supporting limb musculature are influenced by both the intended dynamic outcome and the current dynamic status of the body.

Adult↗

PubMed1991

Physiological and biomechanical factors associated with elite endurance cycling performance.

In this study we evaluated the physiological and biomechanical responses of "elite-national class" (i.e., group 1; N = 9) and "good-state class" (i.e., group 2; N = 6) cyclists while they simulated a 40 km time-trial in the laboratory by cycling on an ergometer for 1 h at their highest power output. Actual road racing 40 km time-trial performance was highly correlated with average absolute power during the 1 h laboratory performance test (r = -0.88; P less than 0.001). In turn, 1 h power output was related to each cyclists' VO2 at the blood lactate threshold (r = 0.93; P less than 0.001). Group 1 was not different from group 2 regarding VO2max (approximately 70 ml.kg-1.min-1 and 5.01 l.min-1) or lean body weight. However, group 1 bicycled 40 km on the road 10% faster than group 2 (P less than 0.05; 54 vs 60 min). Additionally, group 1 was able to generate 11% more power during the 1 h performance test than group 2 (P less than 0.05), and they averaged 90 +/- 1% VO2max compared with 86 +/- 2% VO2max in group 2 (P = 0.06). The higher performance power output of group 1 was produced primarily by generating higher peak torques about the center of the crank by applying larger vertical forces to the crank arm during the cycling downstroke. Compared with group 2, group 1 also produced higher peak torques and vertical forces during the downstroke even when cycling at the same absolute work rate as group 2. Factors possibly contributing to the ability of group 1 to produce higher "downstroke power" are a greater percentage of Type I muscle fibers (P less than 0.05) and a 23% greater (P less than 0.05) muscle capillary density compared with group 2. We have also observed a strong relationship between years of endurance training and percent Type I muscle fibers (r = 0.75; P less than 0.001). It appears that "elite-national class" cyclists have the ability to generate higher "downstroke power", possibly as a result of muscular adaptations stimulated by more years of endurance training.

Adolescent↗

PubMed1988

Antagonist muscle activity during stretching: a paradox re-assessed.

The purpose of this investigation was to examine and compare the simultaneous electromyographic activity from surface and implanted wire electrodes of an antagonist pair of muscles during a reversal stretching technique. Previous studies reported increased electromyographic activity of a muscle being stretched during antagonist muscle activation. Five male subjects performed a stretching method which consisted of active plantarflexion, followed by active dorsiflexion. Adjacent surface and implanted wire electrodes were applied to the soleus and tibialis anterior muscles. Comparison of the surface electrode recordings showed apparent cocontraction during dorsiflexion. However, no activity was observed on the soleus wire electrode trace during the dorsiflexion phase of the stretching method. Power spectral analysis showed a significant (P less than 0.001) frequency shift between plantarflexion (91.9 V2.Hz-1) and dorsiflexion (66.1 V2.Hz-1) from the surface electrode recordings. Cross-correlation between tibialis anterior and surface soleus activity during dorsiflexion provided strong evidence that the apparent electromyographic soleus signal originated in the tibialis anterior muscle with an average of 8.7 ms delay of the surface soleus signal. Although not generalizable to other studies, it was concluded that in this study the tracings from the surface electrodes, which gave the appearance of co-contraction between antagonist muscles, were actually cross-talk between the electrodes. The rationale for antagonist contraction during stretching in order to inhibit contraction of the muscle being stretched is supported with this evidence and is consistent with those studies which show greater range of motion gains using the reversal technique.

Adult↗

PubMed1986

H-reflex changes during static stretching and two variations of proprioceptive neuromuscular facilitation techniques.

The effects of 3 stretching methods on the motor pool excitability of the soleus muscle as measured by the Hoffmann reflex have been compared with the objective of revealing central nervous system influences promoting muscle compliance to lengthening. The H-wave was reduced slightly throughout the static stretch method. The contract-relax (CR) method produced profound inhibition during the first several hundred milliseconds following contraction, but gradually increased to values similar to static stretch (SS) values 2 sec following contraction. Hoffmann reflex values for the contract-relax-antagonist-contract (CRAC) method were greatly depressed throughout the stretching phase with a slight increase after 2 sec. It was concluded that several inhibitory neural influences can have an additive effect in profoundly reducing motor pool excitability. Under the assumption that greater motor pool inhibition reduces muscle contractibility and therefore allows more muscle compliance, it is suggested that the proprioceptive neuromuscular facilitation (PNF) methods, particularly those involving reciprocal activation, provide the greatest potential for muscle lengthening. This is supported by previous studies which compared gains in range of motion using these 3 stretching methods (Holt et al. 1970; Moore and Hutton 1980; Etnyre and Abraham 1985).

Adult↗

PubMed1986

Gains in range of ankle dorsiflexion using three popular stretching techniques.

Among modern stretching techniques none has clearly been shown to be the most effective for increasing range of motion. The most common stretching method comparisons are between static stretching (SS) and one or more Proprioceptive Neuromuscular Facilitation (PNF) technique(s). The two most frequently implemented PNF techniques are: contract-relax (CR); and contract-relax-antagonist-contract (CRAC). Previous comparative investigations among stretching methods have primarily observed changes in straight-leg hip flexion as a result of lengthening the hamstrings, a two-joint muscle. The present study observed gains in range of motion among three stretching methods (SS, CR, CRAC) of a joint limited by a single joint muscle, the soleus. Twelve subjects performed each of the three methods on separate days. Significant differences were observed among all methods (p = .001). Further analysis revealed the CRAC method was superior to the CR method (p less than .01), and the CR method was superior to the SS method (p less than .01). Significant pre-post-treatment gains in range of motion were observed as a result of the CR and CRAC methods, but not the SS method. The results of this study support the findings of those previous investigations for two-joint muscles in which PNF techniques were more effective than static stretching for increasing range of motion. Also, a reciprocal activation (CRAC in the present study) was the most effective for increasing range of motion.

Adult↗

PubMed1985

The distal hindlimb musculature of the cat. Cutaneous reflexes during locomotion.

In order to better understand the organization of the locomotor control system, we examined the temporal patterns of distal hindlimb muscle responses to brief electrical stimulation of cutaneous nerves during walking on a treadmill. Electromyographic recordings were made from twelve muscles; stimuli were applied individually to three nerves at random times throughout the step cycle. A new graphical technique was developed to assist detailed examination of the time course and gating of complex reflex patterns. The short latency reflexes were of two primary types: inhibition of extensors and excitation of flexors; these responses were only evident during locomotor phases in which the respective motoneuron pools were active. Longer-latency response components were gated in a similar but not identical manner, suggesting some independence from the basic locomotory influence on the motoneuronal pool. The phase-dependent gating of reflexes appeared to be consistent with a functional role for reflex responses during locomotion. The reflex responses of muscles with complex anatomical actions were often correspondingly complex.

Animals↗