Biomedical subjects

C G Kukulka

Publications and source records attributed to C G Kukulka.

At least 19 recordsLinked to original sources

PubMed2001

The influence of stimulus cue on the initiation of stepping in young and older adults.

OBJECTIVES: To investigate the influence of different reaction stimulus cues on the characteristics of ground reaction forces during the initiation of rapid forward stepping, and to determine whether age-related differences in step initiation are influenced by the type of stimulus cue used to trigger stepping. DESIGN: Case-control study. SETTING: University-based research laboratory. PARTICIPANTS: Fifteen healthy younger adults and 35 community-dwelling older adult volunteers. MAIN OUTCOME MEASURES: Subjects performed forward step initiation in response to 3 different reaction stimulus cues (light, sound, electrocutaneous) during simple reaction-time conditions. Ground reaction force data were collected and used to characterize the timing and magnitude features of the postural (weight-transfer) and step components. RESULTS: In comparison with the light and sound stimuli, the nonnoxious electrocutaneous trigger cue was associated with an increase in the magnitude of the initial displacement of the center of pressure (COP) in the mediolateral direction. Overall, older subjects were slower to initiate the postural and step components, and displayed a reduction in the initial posterior displacement of the COP. CONCLUSIONS: The postural component for lateral weight transfer was augmented by the electrocutaneous trigger cue, suggesting its potential to enhance step initiation among clinical populations. Age-related changes in stepping were unaffected by the type of stimulus cue, but the older group had a slower response initiation time and less forward propulsion. The abilities of many older persons may be compromised in situations where rapid adjustments in the base of support through stepping are triggered by environmental stimuli.

Adult↗

PubMed2000

Reflex facilitation during the stretch-shortening cycle.

Maximal torque during the concentric phase of a movement has been shown to be enhanced by prior eccentric muscle actions, a movement strategy referred to as the stretch-shortening cycle. Although the mechanical basis for this enhancement is well established, the neural component is not. We hypothesized that brief high-frequency bursts of spindle afferent discharge during the eccentric phase of the stretch-shortening cycle could be one mechanism for facilitating the volitional drive. To test this hypothesis, three sets of experiments were done. In the first (N=15), we demonstrated that both the peak and mean EMG of the soleus (S) and lateral gastrocnemius (LG) muscles were considerably greater during a reciprocal hopping (RHOP) task than for maximum isometric contractions (MIVCs). In the second experiment, we tested whether the dynamic nature of the RHOP or the eccentric phase of the RHOP contributed to the EMG potentiation. Peak and mean EMG produced with a concentric hop (CHOP), in which the lengthening phase of the hop was eliminated, were compared with that produced with the RHOP and MIVCs conditions (N=7). The RHOP produced greater peak EMG than either the CHOP or the MIVCs while the mean EMG for both hopping conditions was considerably more than the MIVCs. In the final experiment, we attempted to mimic the brief high-frequency burst of spindle afferent activity during the lengthening phase of the stretch-shortening cycle in the absence of muscle length changes. High-frequency (100 Hz) afferent stimulation (HFS) was delivered during MIVCs. At rest, the HFS produced negligible EMG activity but when superimposed over MIVCs produced a marked potentiation of the S EMG over values obtained during MIVCs alone. Evidence that HFS synchronizes the EMG associated with volitional activation is also provided. We conclude that a substantial but brief facilitation and possible synchronization of the neural drive is provided by the spindle afferents during the eccentric phase of the stretch-shortening cycle.

Adolescent↗

PubMed1998

The effect of treadmill gait training on low-frequency depression of the soleus H-reflex: comparison of a spinal cord injured man to normal subjects.

H-Reflex recruitment curves were obtained at 0.1 and 1 Hz in the right soleus of an incomplete SCI man before and after training and on 12 neurologically normal individuals. Low frequency depression (LFD) was calculated by the formula: 1 - (H-wave amplitude at 1 Hz/0.1 Hz) x 100. Training consisted of treadmill walking at the speed matching his overground fast walking. The subject trained for 30 min every other day for 10 days under supervision and then continued three times a week for 4 months at a health club. Maximum H/M ratio of the right soleus (78%) was greater than that of the normals (67%) and did not change following training (79%). The mean LFD of the SCI subject was 24% prior to training compared to 42% for the normal subjects. Following training, LFD increased to 35%. In addition, the reflex threshold appears to have increased following training. This was accompanied by 47 and 45% increases in the subject's self selected and fast gait velocities, respectively. We conclude that training adaptations enabled the SCI subject to increase his gait velocity due to an improved ability to gate peripheral afferent feedback during gait.

Adult↗

PubMed1995

Spatial differences in fatigue-associated electromyographic behaviour of the human first dorsal interosseus muscle.

1. Fatigue-associated electromyographic (EMG) reactions of intrinsic hand muscles were studied during maintained isometric voluntary contractions of normal subjects. Most measurements concerned actions of the first dorsal interosseus (FDI). In a smaller number of subjects, complementary measurements were obtained for adductor pollicis (AP). 2. Measurements were made of isometric force (thumb adduction, index finger abduction and flexion) and of surface EMG amplitudes (AP and FDI) after rectification and smoothing (rsEMG). 3. In the analysis of fatigue, the subjects were required to maintain a steady isometric force (index finger abduction or thumb adduction) of half their maximum voluntary contraction (1/2MVC test) for as long as possible. Average endurance times were 88 +/- 19 s (mean +/- S.D.) for FDI and 119 +/- 29 s for AP (Student's t test, P < 0.02). 4. Pronounced differences in fatigue-associated EMG behaviour were observed between AP and FDI. In AP the reaction was as expected: a rise of EMG during maintained force (mean rsEMG at end of fatigue test/mean rsEMG at start of test (rsEMG-FI): 181 +/- 64%). In FDI this reaction was seen in half of the recorded cases, the remainder displaying bidirectional changes or a more or less marked decrease of EMG during the endurance task (mean for all cases together: rsEMG-FI, 103 +/- 15%; difference between AP vs. FDI significant, P < 0.01). 5. The unexpected EMG variability of the FDI reactions was further analysed with multiple bipolar recordings of surface EMG. For all the four thoroughly studied subjects, recordings were obtained which showed simultaneously occurring EMG changes in opposite directions (decrease and increase) at different sites of FDI while force was kept constant at 50% of the maximum voluntary contraction (MVC). 6. Further observations on FDI showed that EMGs simultaneously obtained from different recording sites could show dramatic differences in their responses depending on 'synergistic context' (e.g. in relation to changes in index finger extension force during maintained abduction at 50% MVC). Evidence for 'task switching' (shift in rsEMG distribution, shift in hand muscle synergy) was frequently observed during the performance of the 1/2MVC test. 7. The results indicate that FDI is not handled in a topographically homogeneous manner during the execution of an isometric constant force endurance test. Furthermore, the results suggest that this seemingly simple motor performance can be executed in several alternative manners associated with the activation of different muscle synergies and with different distributions of activity within the FDI.

Adult↗

PubMed1994

The reflex effects of nonnoxious sural nerve stimulation on human triceps surae motor neurons.

1. The effects of low-intensity electrical stimulation of the ipsilateral sural nerve on the reflex response of human triceps surae motor neurons were examined in 169 motor units recorded in 11 adult volunteers: 69 units from soleus (SOL), 48 units from lateral gastrocnemius (LG), and 52 units from medial gastrocnemius (MG). The reflex effects were assessed by the peristimulus time histogram (PSTH) technique, categorized according to onset latencies, and the magnitudes of effects were calculated as percent changes in baseline firing rates. 2. Sural stimulation evoked complex changes in motor-unit firing at onset latencies between 28 and 140 ms. The two most common responses seen in all muscles were a short-latency depression (D1) in firing (mean onset latency = 40 ms) in 42% of all units studied and a secondary enhancement (E2) in firing (mean onset latency = 72 ms) in 43% of all units. In LG, the D1 effect represented a mean decrease in firing of 52% which was statistically different from the changes in MG (42% decrease) and SOL (38% decrease). The magnitudes of E2 effects were similar across muscles with an average of 47% increase in firing. 3. No differences were found in the frequencies of occurrence for the enhancements in firing among the muscles studied. The main difference in reflex responses was the occurrence of an intermediate latency depression (D2) in 27% of the LG units with a mean onset latency of 72 ms. 4. Based on estimates of conduction times for activation of low-threshold cutaneous afferents, the short-latency D1 response likely represents an oligosynaptic spinal reflex with transmission times similar to the Ia reciprocal inhibitory pathway. These findings raise the question as to the possibility of low-threshold cutaneous afferents sharing common interneurons with low-threshold muscle afferent reflexes that have identical onset latencies. The complex reflex effects associated with low-level stimulation of a cutaneous nerve indicate a rich assortment of peripheral responses that may influence a given movement. The predominance of a specific effect is most likely determined by the interaction of this input with other peripheral signals and descending commands specific to a given motor task.

Adult↗

PubMed1993

Motor unit recruitment in human medial gastrocnemius muscle during combined knee flexion and plantarflexion isometric contractions.

Previous work on multifunctional muscle has suggested that motor unit recruitment during a combined force task is the result of an interactive effect of weighted inputs acting simultaneously on the motoneuron pool. The present study shows that a similar effect describes motor unit activation in a two-joint muscle as forces are combined at both proximal and distal attachments. The recruitment thresholds of single motor units in medial gastrocnemius muscle were determined during combined knee flexion and plantarflexion isometric contractions. Slow isometric ramp contractions in knee flexion were produced while maintaining various background levels of plantarflexion force. The combination of knee flexion and plantarflexion forces at which a motor unit initially discharged was used to characterize recruitment as represented by the slope of the regression line fit to the individual data points. Each subject completed two experiments; one at each of two knee joint angles, with the ankle joint fixed at 90 degrees. The effect of knee angle was assessed by comparing the slopes of the regression lines that characterized motor unit recruitment at each knee angle. Motor units in medial gastrocnemius were recruited when the linear sum of the forces exerted in plantarflexion and knee flexion exceeded a certain threshold of combined force. Specifically, the apparent force threshold of recruitment in knee flexion decreased as the level of force maintained in plantarflexion increased. Further, evidence is provided indicating that the linear relationship describing recruitment in two-joint muscle is dependent upon joint angle.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

Human flexor reflex modulation during cycling.

1. Human flexor reflex (HFR) responses were elicited during ergometer cycling in neurologically intact humans with the objective of understanding the influence of lower limb muscle activity on phase-dependent reflex modulation during movement. The experimental setup permitted control over background muscle activity and stimulus intensity without significantly interfering with the cycling motion. 2. All experiments involved cycling on an ergometer at a set rate and workload. A 333-Hz, 15-ms pulse train of electrical stimulation was randomly delivered to the skin over the tibial nerve at the ankle at selected lower limb positions. In the first group of experiments, subjects were stimulated at six cycling phases while pedaling with normal, phasic ankle activity (free-form cycling). The second and third group of experiments involved stimulation under static limb positioning conditions and during active pedaling while subjects were asked to maintain a consistent background level of isolated tibialis anterior (TA) or soleus (SOL) electromyographic (EMG) activity. 3. Control criteria were established to assure similar isolated muscle EMG levels and sensory stimulation intensities throughout the experiments. With the aid of the application of a lower extremity brace and visual EMG feedback, SOL and TA activity were confined by the subject to a narrow range during the task of cycling. Stimulus consistency was achieved through maintenance of flexor hallucis brevis M-waves to within an envelope encompassing the mean value +/- 5% of the maximum M-wave amplitude in all experimental conditions. 4. When the subject's limb was statically positioned, the HFR responses in the SOL muscle showed no significant changes in pattern when compared at various limb positions. During cycling with consistent SOL activity, a response waveform pattern of early-latency-long-duration depression was followed by a later-latency facilitation response in all positions except the initial power phase. The initial power phase was characterized by an additional early-latency facilitation in all but one subject. 5. In the TA muscle response, no change in onset latency (57.5 +/- 0.8 ms, mean +/- SD), waveform pattern, or response amplitude (7.9 +/- 1.1% maximal voluntary contraction, mean +/- SD) was observed during static limb positioning. Significant increases in response amplitude (P < 0.05) coupled with significant increases (9.2 ms, P < 0.05) in onset latency were seen during the transition from the recovery phase to the power phase during cycling. In addition, there was no correlation between the prestimulation baseline level and the onset latency during controlled TA cycling activity conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1992

Age-related changes in postural responses preceding rapid self-paced and reaction time arm movements.

The electromyographic responses in postural (thigh and trunk) and primary agonist (shoulder) muscles were examined in standing young and older adults prior to rapid self-paced (SP) and simple reaction time (RT) arm flexion movements. In contrast to younger subjects, older adults demonstrated significantly lower frequencies of trials for self-paced movements in which thigh muscle responses preceded the activation of the shoulder muscle. Furthermore, younger adults showed more frequent early lower limb postural responses for SP versus RT movements, whereas older subjects retained comparable frequencies between task conditions. Overall, a significantly shorter intermuscular timing interval between leg and arm muscle onsets was also found for the older group.

Adult↗

PubMed1991

The effect of muscle length on motor unit discharge characteristics in human tibialis anterior muscle.

Muscle length influences the contractile properties of muscle in that when muscle is lengthened the relaxation phase of the muscle twitch is prolonged and when muscle is shortened, the relaxation phase is shorter in duration. As a result, the force exerted by active motor units varies with muscle length during voluntary contractions. To determine if motoneuron spike trains were adjusted to accommodate for changes in the contractile properties imposed by shortened and lengthened muscle, motor unit action potentials were recorded from the tibialis anterior muscle at different muscle lengths. Twenty subjects performed isometric ramp contractions at ankle angles of 20 degrees dorsiflexion, neutral between dorsiflexion and plantar flexion, and 30 degrees plantar flexion, which put the tibialis anterior muscle in a shortened, neutral, or lengthened condition, respectively. During isometric contractions where torque increased at 5% MVC/s, motor unit discharge rate at recruitment was greater in shortened muscle than in lengthened muscle (P less than 0.05). Brief initial interspike intervals (less than 40 ms) occurred more frequently in shortened muscle than in either neutral length or lengthened muscle. During steady contractions, motor unit discharge rate was greater per unit torque (N.m) in shortened muscle than in neutral length or lengthened muscle (P less than 0.05). These findings indicate that muscle length does influence the discharge pattern of motor unit spike trains during isometric ramp contractions.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1991

An objective method for assessing graded electrically evoked afferent activity in humans.

A problem arises in human sensorimotor studies when attempts are made to equate the intensity of electrical stimulation of a peripheral nerve with the amount of afferent activity generated. Results presented here reveal that sural recruitment curves exhibit large session to session differences both within and among subjects. These differences hinder the prediction of afferent activation based solely upon stimulus intensity. An alternative method based upon measurement of the evoked potentials is described for improving on these predictions. Sural nerve stimulation is used to demonstrate this method, but the method should be applicable wherever a peripheral nerve is accessible for electrical stimulation and evoked recordings.

Adult↗

PubMed1991

Depression of Hoffmann reflexes following voluntary contraction and implications for proprioceptive neuromuscular facilitation therapy.

Postcontraction depression of Hoffmann-reflex (H-reflex) amplitudes was examined to study the rationale underlying proprioceptive neuromuscular facilitation relaxation techniques. The time course of H-reflex amplitude depression was used to assess postcontraction changes in motoneuron reflex excitability. Sixteen healthy female subjects performed voluntary isometric plantar-flexion contractions (65%-75% of maximal voluntary contraction) in a prone position. H-reflex stimulation began at a postcontraction delay of 0.05, 0.1, 0.5, 1, or 5 seconds and continued every 10 seconds for 1 minute. Reflexes were depressed (mean = 67% decrease) by 0.05 second postcontraction, reached maximal depression (mean = 83.3% decrease) from 0.1 to 1 second postcontraction, recovered to 70% of control amplitudes (mean = 30% decrease) by 5 seconds postcontraction, and reached 90% control amplitudes (mean = 10% decrease) by 10.05 seconds postcontraction. The results indicate that proprioceptive neuromuscular facilitation techniques (eg, hold-relax) purported to produce a phase of relaxation following voluntary contraction do appear to produce a strong, but brief, neuromuscular inhibition that may be clinically useful for applying stretch.

Adult↗

PubMed1988

Effects of tendon pressure on alpha motoneuron excitability in patients with stroke.

The purpose of this study was to evaluate the effects of two intensities (5 and 10 kg) of continuous and intermittent Achilles tendon pressure on the H-reflex in eight hemiparetic subjects. A decrease in the H-reflex was interpreted as a depression in motoneuron excitability, a condition conducive for reducing muscle tone. The H-reflex measurements were obtained before, during, immediately after, and 2.5 minutes after tendon pressure application. Piecewise linear regression equations were used to evaluate the effects of four pressure conditions. The mean of the midpoints of the lines for each pressure condition was compared with prepressure baseline values by t tests and with the other pressure conditions by an analysis of variance. All four pressure conditions demonstrated H-reflexes less than prepressure baseline values, with three of the four conditions (5 and 10 kg of intermittent pressure and 5 kg of continuous pressure) being significantly less than prepressure baseline values (p less than .05). The analysis of variance revealed a significant difference among pressure conditions. Scheffé post hoc contrast comparisons revealed significant differences between intermittent and continuous pressure but not between 5 and 10 kg of pressure. The results of this study indicate that in these hemiparetic subjects, the H-reflex was depressed during both continuous and intermittent tendon pressure. Intermittent pressure was more effective then continuous, but 10 kg of pressure had no greater effect than 5 kg of pressure. The effects of pressure lasted only as long as the stimulus was present.(ABSTRACT TRUNCATED AT 250 WORDS)

Achilles Tendon↗

PubMed1987

Postural adjustments preceding rapid arm movements in parkinsonian subjects.

The electromyographic (EMG) responses in postural (thigh and trunk) and agonist (shoulder) muscles were examined in standing parkinsonian subjects and healthy controls prior to visual reaction time and self-paced rapid arm flexion movements. Recruitment of postural muscles typically preceded arm displacement in normals, but was less frequent, of shorter duration, and characterized by multiple EMG bursts which extended to the agonist in parkinsonians. Moreover, parallel delays in EMG recruitment times relative to the visual signal for both postural and agonist muscles were observed in akinetic patients. These abnormalities suggest that the basal ganglia may serve a preparatory motor function, by linking synergistic muscles through a common selection process.

Aged↗

PubMed1987

Muscle pressure effects on motoneuron excitability. A special communication.

The purpose of this communication is to report on the analysis of the effects of muscle pressure on altering motoneuron excitability. Motoneuron excitability was assessed by measuring changes in the H-reflex in 30 neurologically healthy individuals. The results indicate that muscle pressure is excitatory, but of such low intensity as to be of dubious therapeutic benefit. Methodological limitations specific to muscle pressure stimulation limit the interpretation of our results. These limitations are discussed, and a suggestion is made for an alternative approach to evaluate the effects of muscle pressure on motoneuron excitability.

Adult↗

PubMed1986

Changes in human alpha-motoneuron excitability during sustained maximum isometric contractions.

Experiments were conducted to evaluate the change in alpha-motoneuron excitability during sustained maximum isometric contractions of human triceps surae. A test H-reflex was used to assess motoneuron excitability 10 ms after a conditioning reflex was generated. The test reflex was compared to a reference H-reflex; both test and reference reflexes were of approximately equal amplitudes at the onset of the sustained maximum efforts. Both reflexes were assumed to be influenced by similar descending and peripheral inputs. In addition, the test reflex was influenced by the conditioning reflex. For the 4 subjects tested, the test reflex decreased in amplitude within the first 30-40 s of effort, while the reference reflex remained roughly constant or increased in amplitude. The decline of the test reflex relative to the reference was indicative of an inhibitory effect due to the conditioning reflex. In that the conditioning reflex was always generated 10 ms prior to the test reflex, the two factors most likely responsible for the inhibition would be recurrent inhibition and summation of motoneuron afterhyperpolarization. A combination of these two factors could also account for the associated slowing of motoneuron firing during sustained maximum efforts.

Action Potentials↗

PubMed1986

Electrical and mechanical changes in human soleus muscle during sustained maximum isometric contractions.

Experiments were designed to evaluate changes in the electrical activation and force generating capabilities of human soleus muscle during sustained, maximum isometric contractions. Eighteen experiments were conducted on 7 healthy subjects. Surface EMG, and in select cases, intramuscular fine wire EMG recordings, were made to assess the electrical activation of soleus. Subjects performed maximum isometric plantarflexion contractions of 1-3 min during which time supramaximal electrical pulses were delivered to the tibial nerve at 5-s intervals to elicit maximum M waves. M wave areas were assessed for evidence of neuromuscular junction failure. The results revealed that, on average, maximum force declined to 80% of unfatigued maximum by 60 s of effort, 74% by 90 and 120 s, and 70% by 180 s. M waves were stable for efforts up to 3 min, thereby providing little evidence for neuromuscular junction failure. In 3 experiments, total spike counts from intramuscular recordings displayed a 50% reduction in firing by 30 s of effort, with little additional slowing for up to 3 min. Although all of the fatigue-induced electrical and mechanical alterations in muscle activation reported earlier for intrinsic hand and foot muscles were verified in these experiments on soleus, the magnitudes and time courses of these changes were quite different. All changes were consistent with a muscle designed to optimally resist fatigue.

Action Potentials↗

PubMed1986

Effects of intermittent tendon pressure on alpha motoneuron excitability.

The purpose of this study was to test the effectiveness of intermittent tendon pressure on the depression of alpha motoneuron excitability. The excitability changes of the motoneurons were assessed by measuring changes in H-reflex amplitudes before, during, and after intermittent tendon pressure application. Twenty-six of 28 subjects with no known neurological deficit displayed an immediate decrease in H-reflex amplitudes during tendon pressure (X = 73% of control values), which reached a maximum depression (45% of controls) within 20 to 30 seconds of application. The analysis of variance revealed significant differences (p less than .05), and post-hoc t tests indicated that these differences were between control values (prepressure and postpressure) and those values obtained at times 0, 5, 10, 20, and 30 seconds of pressure application. These results suggest that a maintained reduction in muscle tone might be induced through intermittent tendon pressure. Because we found no carry-over effects after pressure application, the usefulness of this technique is limited to the time during which the stimulus is presented.

Adult↗

PubMed1985

Effect of tendon pressure on alpha motoneuron excitability.

The purpose of this study was to test the effect of tendon pressure on muscle activity by evaluating changes in the excitability of the motoneurons supplying the muscle. The excitability changes of the motoneurons were assessed by measuring changes in H-reflex amplitudes before, during, and after tendon-pressure application. Twenty-eight of 32 subjects with no known neurological deficit displayed an initial decrease in H-reflex amplitude during tendon pressure (mean = 60% of control values) but returned to 85 percent of control values within the first 5 seconds of pressure and reached 93 percent of control values within 30 seconds of application. The ANOVA revealed significant differences (p less than .05) and the post hoc t test showed these differences to be between control values and those obtained during the first 10 seconds of pressure. These findings support the clinical impression of reduced muscle tone resulting from tendon pressure. If these results are applied to a patient group, the transient behavior of the tendon-pressure response would limit the applicability of the technique to situations demanding an immediate, short-term reduction in muscle activity.

Adult↗