Using standing postures as a practical alternative to gait analysis for assessing normal neuromotor activity variation of the ankle muscle antagonists: a soleus H-reflex and EMG activity study comparing patients with hemiplegia to healthy subjects / Uso de posturas erguidas como alternativa práctica al análisis de marcha para evaluar la actividad neuromotora normal de los antagonistas del tobillo: una comparación entre pacientes hemiplégicos y sujetos normales

The purpose of this study was to evaluate and compare the soleus H-reflex amplitudes recorded in three standing postures between a group of patients with stroke and a group of healthy subjects. Nine ambulatory patients were compared with 10 healthy subjects. Measures were recorded during quiet standing (QS), heels raised (PO) and with the foot of the measured leg held just off the ground while standing on the opposite leg (SW). The results showed that patients, as opposed to the healthy group, did not inhibit soleus H-reflex in the SW posture. As opposed to evaluating ankle motor control during gait, the PO and SW standing postures appeared to offer a practical and objective method to assess soleus H-reflex when the purpose is to determine impairment (or recovery) of ankle neuromotor control in stroke survivors.

El propósito de este estudio fue evaluar y comparar la amplitud de el reflejo H en el músculo sóleo en tres posturas en la posición de pie entre un grupo de pacientes con hemiplejia y un grupo de individuos sanos. Nueve pacientes ambulatorios fueron comparados con diez individuos sanos. Registros fueron obtenidos en la posición de pie bipedal (QS), bipedal con talones elevados (PO), y unipedal manteniendo el pie afectado ligeramente elevado sin contacto con el piso (SW). Los resultados mostraron que los pacientes, en contraste con el el grupo sano, no presentaron inhibición del reflejo H en la postura SW. Comparado a registros del reflejo H obtenidos durante la marcha, aquellos obtenidos con las posturas PO y SW aparecen como un método más práctico y objetivo para evaluar el reflejo H del soleus si el propósito es determinar nivel de pérdida (o recuperación) de el control neuromotor del tobillo en pacientes con hemiplejia.

Using standing postures as a practical alternative to gait analysis for assessing normal neuromotor activity variation of the ankle muscle antagonists: a soleus H-reflex and EMG activity study / Uso de posturas erguidas como alternativa al análisis de marcha para evaluar la variación en la actividad neuromotora de los músculos antagonistas del tobillo: un estudio utilizando el reflejo H del músculo sóleo y EMG

Soleus and tibialis anterior muscle EMG and soleus H-reflex are widely used to study ankle motor control during gait. Normally, the soleus H-reflex amplitude and EMG activity varies greatly through the course of walking. The examining of these events during walking requires space and resources that are generally found only in research oriented facilities, making difficult a more practical use. Earlier reports have suggested that normal variation of the soleus H-reflex and EMG could be determined from standing postures. Therefore, the main purpose of this study was to examine and determine which standing postures would reproduce the normal neuromotor variation of the ankle muscle antagonists. A total of five postures were investigated. The results of this study demonstrated that the normal variation in the soleus H-reflex amplitude and the associated EMG activity can be comparably reproduced from two selected standing postures (PO and SW). The described method presents a practical and functional alternative to gait analysis when the goal is determining normal ankle neuromotor control.

La actividad electromiográfica (EMG) de los músculos tibial anterior y sóleo junto al reflejo H del sóleo han sido extensamente usados en el estudio del control motor del tobillo durante la marcha. Normalmente, la amplitud del reflejo H del sóleo y EMG varía ampliamente durante el curso de la marcha. El estudio de estos eventos durante la marcha requiere de espacio y equipamiento generalmente sólo disponible en laboratorios de investigación, por lo que resulta difícil su aplicación práctica. Previos estudios han sugerido que la variación normal del reflejo H del sóleo y EMG pudiese ser obtenida utilizando posturas en la posición de pie. El propósito principal de este estudio fue examinar y determinar qué posturas reproducirían la variación neuromotora normal en los músculos antagonistas del tobillo. Un total de cinco posturas fueron investigadas. Los resultados de este estudio demostraron que la variación normal de la amplitud del reflejo H del sóleo y EMG asociada, puede ser similarmente reproducida a partir de dos posturas (PO y SW). El método descrito presenta una alternativa práctica y funcional a la marcha, cuando el objetivo es la determinación del control neuromotor normal en el tobillo.

Effects of visual and auditory cues on gait in individuals with Parkinson's disease.

The purpose of this study was to determine if combining visual and auditory cues has a greater effect on the gait pattern of patients with Parkinson's disease (PD) than the cues applied individually. Twenty-four individuals with idiopathic PD were recruited. Patients, while off antiparkinsonian medications, were measured on a 7.62-m walkway during two trials for each of four conditions performed in random order: without cues, with a visual cue, with an auditory cue and with both cues simultaneously. The auditory cue consisted of a metronome beat 25% faster than the subject's fastest gait speed. Brightly colored parallel lines placed along the walkway at intervals equal to 40% of a subject's height served as the visual cue. Average gait speed, cadence and stride length were calculated for each condition. Gait velocity, cadence and stride length significantly improved (p<005) when cues were used. Visual and auditory cues improved gait performance in patients with PD, but they did so in different ways. Auditory cueing significantly improved cadence, but visual cueing improved stride length. The simultaneous use of auditory and visual cues did not improve gait significantly more than each cue alone.

Methods of H-reflex evaluation in the early stages of Parkinson's disease.

Differentiating the early stages of Parkinson's disease from the normal consequences of aging or from other common neurologic conditions can be diagnostically problematic. The purpose of this study was to compare methodologies for measuring motor neuron excitability of Parkinson's disease patients with a control group. H-reflexes were monitored in 16 patients diagnosed in the early stages of Parkinson's disease (Hoehn & Yahr stages I and II) compared with 30 subjects who were disease free. Methods of measurement included H-reflex latencies, the relative values of maximum H-reflexes to maximum direct motor responses (H-to-M ratio), the relative values of H-reflex amplitudes during vibration compared with control H-reflex amplitudes (Hv-to-Hc ratio), and double-stimulation H-reflex recovery curves using different interstimulus interval parameters. No significant differences were observed for the H-to-M or Hv-to-Hc ratios, or for the H-reflex latencies. The H-reflex recovery curves for the patients with Parkinson's disease demonstrated significantly greater ratio amplitudes than the control group during the double-stimulus responses between the 150-msec and 700-msec interstimulus intervals. Although comparisons of simple H-reflexes and H-reflexes during vibration did not differentiate the patients in the early stages of Parkinson's disease from the control group, the double-stimulation paradigm was a sensitive method for detecting early diagnoses of this disease.

A test of a dual central pattern generator hypothesis for subcortical control of locomotion.

This study was designed to examine the nature of neural circuits involved in subcortical inter-limb coordination and reflex modulation mechanisms of locomotion. These circuits, called central pattern generators (CPGs), are believed to receive tonic input and generate rhythmically alternating sets of commands. Although CPGs have been theorized to exist in humans, their potential dual role in inter-limb coordination and reflex modulation is unclear. In the present study, nine participants walked on a treadmill, timing their heel-strikes to a metronome which varied the phase lag from 0.5 to 1.0 pi radians (0.1 pi intervals). A stimulus was delivered to the sural nerve and reflexes were measured in the ipsilateral and contralateral lower extremities through electromyography. The similarity between phase lag conditions for both temporal coordination (i.e., relative timing aspects between muscles and/or limbs) and reflex intensities suggested that they may be controlled by the same subcortical circuitry. Two plausible explanations exist: (1) a single CPG coordinates muscular contractions and phasically alters proprioceptive reflex modulation, as well as cutaneous input, using feed-forward control; (2) two separate circuits are strongly entrained, producing synchronous outputs for inter-limb coordination and reflex modulation. The out-of-phase task used in this study was limited in discerning such a difference, if it exists.

The H-reflex modulation in lying and a semi-reclining (sitting) position.

OBJECTIVE: The purpose of this study was to compare motor pool excitability as measured by the H-reflex during lying prone and sitting in a semi-reclining position. DESIGN AND METHOD: Twelve volunteer subjects were measured for maximum M-wave and H-wave during sitting and prone lying to determine an H/M ratio. Latency of each H-reflex was also measured. H-reflex responses were recorded during a control and a vibration condition in the two positions. A double-stimuli H-reflex recovery curve was also plotted for each subject in each relaxed position of sitting and lying. RESULTS: No significant differences were observed between the prone lying and sitting positions for the any of the variables measured. CONCLUSIONS: The present results showed no difference in H-reflex responses between sitting or lying and it is suggested that the subject/patient should be tested in a position which is most comfortable.

Accuracy characteristics of throwing as a result of maximum force effort.

Fitts' law predicts the accuracy of movement to a target decreases as the velocity of the movement increases. This speed-accuracy tradeoff has been examined under numerous conditions. During some tasks, however, increased force to nearly maximal level decreases the variability of the movement (Sherwood & Schmidt, 1980). This condition apparently produced results different from what would be predicted by Fitts' law. The purpose of the present study was to examine the effects of maximal force on dart throwing accuracy and variability. 54 subject were categorized into groups based upon their experience with dart throwing: Advanced, Intermediate, or Beginners. Each subject performed two sessions of 15 trials. Subjects were instructed to "throw normally" for one session and "throw as hard as you can" for the other session Distances from the target (triple-20 area) on the regulation dart board were measured and recorded after each of three darts was thrown. Average Error and Variable Error were calculated for each condition for each subject. The Average Error and Variable Error were greatest for the Beginner group and least for the Advanced group. For all three experience categories both Average Error and Variable Error were significantly greater when subjects performed with maximal force. The greater average error for the maximal force for all subjects suggested that the speed-accuracy tradeoff applied to this aiming task. The greater variability in accuracy with maximal force suggested a ceiling effect, which reduced variability in previous studies, was not achieved.

Characteristics of motor performance, learning, warm-up decrement, and reminiscence during a balancing task.

Warm-up decrement and reminiscence effects have been primarily attributed to methods of distribution of practice. The present study investigated the effects of different amounts of practice on a balancing task and observed the differences in individual learning. Subjects were randomly assigned to a 5- or 10-trial practice group and performed a retention session on a stabilometer 1 wk. after the first set of trials. Subjects were given the same amount of rest between trials and sessions. Following the retention session subjects were assigned by retention performance into a warm-up decrement or reminiscence group for further comparison. The group with more practice had higher over-all performance. The warm-up decrement group showed more time-on-balance during the first practice session than the reminiscence group. The second session performance curves were nearly identical for the 5- and the 10-trial groups whether warm-up decrement or reminiscence occurred. These results suggested the importance of considering individual differences in retention of learning.

Timing of anticipatory responses following an isometric contraction.

The effects on timing of anticipation following an isometric contraction were investigated. Using a Bassin timer, 35 subjects performed 10 trials for each of 4 forewarning periods at 3 stimulus speeds resulting in 120 trials for the control condition. An additional 120 trials were performed by all subjects following an isometric contraction for each trial. Over all trials, average responses indicated early anticipation of the timing target. The shortest forewarning period and slowest speed of stimulus produced the earliest responses and the longest forewarning period and fastest speed of stimulus produced responses closest to temporal coincidence. Subjects responded faster after the isometric contraction. Significant differences were observed for the main effects of forewarning period and speed of the stimulus. A significant interaction resulted for condition by forewarning periods. The postcontraction condition produced a significantly earlier average response than the control condition for all but the shortest forewarning period. The findings supported the concept that the time needed to respond during postcontraction effects is reduced. With prior contraction, anticipatory timing gradually diminished over time following the contraction.

Preoperative and postoperative assessment of surgical intervention for equinus gait in children with cerebral palsy.

We compared the effects of different methods of surgical correction of equinus gait in children with spastic cerebral palsy (CP) using pre- and postoperative measurements of gait, electromyography (EMG), range of motion (ROM), and dynamic ankle motion. Operative results significantly improved all variables that produced more normal ankle motion in subjects, although no differences were observed between surgical methods. We conclude that preoperative gait analysis can assist in surgical planning regardless of surgical method for Achilles lengthening and can provide an objective measure of results after surgical correction of equinus deformity.

Post-contraction variations in motor pool excitability.

Previous evidence has shown a marked increase in motoneuronal excitability during muscle contraction and decreased post-contraction excitability. This post-contraction inhibition has been shown to persist up to 800 msec following the end of contraction (Gottlieb and Agarwal, 1973) and apparently continues with gradual recovery up to one minute (Enoka, Hutton and Eldred, 1980). These effects have been attributed in part to influences of muscle receptors on the homonymous motor pool. The purpose of the present study was to observe the time course of short term post-contraction effects, following a maximum isometric contraction, on excitability of the homonymous motoneuronal pool as measured by the Hoffmann reflex. Each of five subjects lay supine on a table with shoulder blocks to prevent movement during resisted plantar flexion. The subject's preferred foot was placed in a stirrup attached to a force gauge which measured tension. Recording electrodes were applied over the soleus muscle, and M- and H-responses were evoked by percutaneous electrical stimulation of the tibial nerve at the popliteal fossa. The stimulus strength was set to elicit a control H-reflex at rest of half the magnitude of the maximum H-reflex value. For each trial the subject performed a 6 s maximum contraction of the triceps surae muscle group, beginning on one visual signal and ending on a second visual signal. The H-reflex was elicited at semi-random intervals prior to and after the visual signal to relax. Increased H-reflex excitability was observed during muscle contraction followed by a marked decrease in evoked amplitudes with gradual recovery following the end of contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Electromyographic analysis of movement following a maximal isometric contraction.

A post-contraction sensory discharge effect following an isometric contraction is commonly cited as the explanation for perception of movement or distortion of limb proprioception during post-contraction movements. The purpose of this study was to compare motor output of agonist neuromuscular activity between a control positioning movement and a post-contraction movement. Terminal positioning accuracy and electromyographic (EMG) data of the triceps brachii during rapid elbow extension were recorded during normal movements and during movements following a maximal isometric contraction. Separate t-tests revealed the post-contraction positioning resulted in significant undershooting of the target position, and also the integrated EMG (IEMG) for the post-contraction conditions was significantly less than the control condition. No difference was observed in mean peak frequencies between the control and post-contraction conditions. Apparently, the post-contraction target undershooting is a result of less total motor output rather than a change in neuromuscular frequency firing rates.

Flexibility characteristics of elite female and male volleyball players.

It is a common assumption that increased range of motion is related to high level performance, however it is difficult to provide conclusive evidence for this assumption due to the many variables contributing to skilled performance. The purpose of this study was to compare shoulder and hip flexibility to jumping height of members of the men's and women's United States Olympic Festival volleyball teams. Twenty-four men and 22 women were measured for standing vertical jump (SVJ) and approach vertical jump (AVJ), as well as range of shoulder extension (SHO) and hip flexion (HIP). A significant and positive correlation was revealed between AVJ and HIP for the men r = 0.42, p less than 0.03). For the women, significant and negative correlations resulted between SVJ and HIP (r = -0.54, p = 0.009) and between AVJ and HIP (r = -0.47, p = 0.03). Although a positive correlation between flexibility and AVJ observed for the men supported the assumption that greater flexibility is related to greater skilled performance, the opposite results occurred for the women. The negative correlations for the women indicate that the players with the greatest vertical jumps had the least hip flexibility. It was concluded that greater hip flexibility may benefit men more than women for jumping ability.

Contribution of arm movement to the force components of a maximum vertical jump.

Vertical jump is used commonly as a measure of leg power for evaluation prior to participation in sports activities (RK Gray, KB Start, DJ Glencross, Res Q 33:230-235, 1962; DO Klotz, Doctoral dissertation, University of Iowa, 1948). Unless vertical jump meets the definition of mechanical leg power, it should not be used as a measure of leg power. Measurement of leg power in a vertical jump should not be started with a countermovement of the arms prior to jumping. The purpose of this research was to investigate the kinetic and kinematic contributions of arm movement to the vertical jump. Eighteen subjects performed three vertical jumps on a force platform with arm movement and three jumps without arm movement. The contribution of arm movement to maximum force, work done, power, and the release velocity was found as 6, 14, 15, and 6%, respectively, for this population. The contribution of the arm action to reduce the impact force was 12%. The contribution of arm movement to vertical jump maximum force in this study was less than reported in previous studies. J Orthop Sports Phys Ther 1989;11(5):198-201.

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.

Effects of electromyographic biofeedback on reaction time and movement time.

The effects of electromyographic (EMG) biofeedback on reaction time (RT) and movement time (MT) were investigated utilizing 42 right-handed, male subjects from a university population. Subjects were randomly divided into three groups, a control group and two experimental groups. Both experimental groups were exposed to their EMG signals from their triceps brachii during the task, one experimental group received written information explaining the purpose of the EMG was to improve performance through biofeedback. Reaction times of the first block of 25 trials were significantly faster than those on the subsequent three blocks of trials for all groups. This provided evidence of learning. No other significant effects for reaction times were observed. Mean movement time for the EMG-only group was significantly slower than the means of either the Control group or EMG-Biofeedback group, with no difference between the latter two. The differences between experimental groups may have been related to alteration of strategy, anxiety, motivation.

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.

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).