Biomedical subjects

Denis Brunt

Publications and source records attributed to Denis Brunt.

16 recordsLinked to original sources

PubMed2006

Do people with Parkinson's disease change strategy during unplanned gait termination?

In light of the movement control problems reported for patients with Parkinson's disease (PD), we examined the lower extremity control strategies used by these subjects to stop walking in planned and unplanned situations. We compared how patients with PD and age and gender-matched control subjects modulated lower extremity muscular activity and ground reaction forces during planned and unplanned stoppings. The main findings were that control subjects did not alter muscle activation from planned to unplanned stopping, relative to stance limb kinetic events; they just increased the amplitude of the response (by approximately 800%). We speculate that these data provide preliminary evidence in support of a stereotypical sequence of muscle activation for gait termination whether planned or unplanned. In contrast, subjects with PD appeared to adopt a different strategy when stopping unexpectedly compared to planned stopping. Additional data show that subjects with PD required additional steps to stop walking when stopping unexpectedly as compared to control subjects.

Aged↗

PubMed2005

Changes in distal muscle timing may contribute to slowness during sit to stand in Parkinsons disease.

OBJECTIVE: To compare patterns of muscle activation in the lower extremity and subsequent forces during sit to stand in persons with Parkinsonism. BACKGROUND: There is an interruption of the tibialis anterior/soleus interaction during forward oriented movements in some subjects with Parkinsonism, including sit to stand. This task is a major determinant of independence and 44% of those with Parkinsonism report difficulty. METHODS: 41 subjects with Parkinsonism were asked to stand up from a bench. Peak acceleration and vertical ground reaction forces, the slopes to these peaks, and the timing of events were measured. Surface electrodes were placed on tibialis anterior and soleus. RESULTS: The slower group produced force at slower rate than the fast group. The slower group spent 64% of the time taken to stand to complete the flexion-momentum phase, and the fast group spent 56%. The slower group had a larger proportion of co-contraction trials than the other groups. CONCLUSIONS: Slower subjects took longer to perform the task due to a longer time for seat off. Deficits recruiting tibialis anterior may contribute to the decreased rate of production of the acceleration forces and the longer time required for seat off. Relevance Decreased rate of rise of force is used to identify fallers in the elderly and subjects with stroke. Decreased rates of force production may therefore assist in identifying those with Parkinsonism at risk of falls. Treatment strategies designed to facilitate tibialis anterior activation may improve the functional performance of this task.

Adaptation, Physiological↗

PubMed2005

Plantar feedback contributes to the regulation of leg stiffness.

BACKGROUND: Running and hopping involve moving in a bouncing fashion during which the limbs behave as springs. The ability to alter the stiffness of these leg springs is essential to maintaining an efficient gait. Since the plantar surface of the foot is the only part of the body to encounter the ground during bipedal locomotion, it would seem logical that some aspect of the neurological functioning of the foot is responsible for transmission of information about the surface characteristics to the central nervous system, resulting in changes in leg stiffness. METHODS: Ten subjects (9 males, 1 female) participated in this experiment. Lidocaine was injected inferior and posterior to the lateral malleolus in order to achieve tibial nerve block at the level of the ankle. Subjects hopped at 2.2 Hz on a force plate while data were collected at 1000 Hz. Data were analyzed for peak force and leg stiffness and compared using a repeated measures ANOVA. FINDINGS: Tactile sensation, deep pressure sensation, and abductor hallucis activity displayed significant decreases following the injection, as did postural stability. Subjects demonstrated a significantly decreased leg stiffness after the nerve block (P<.01). INTERPRETATION: Plantar sensation has an effect on regulating leg mechanics in hopping. A loss of sensation in this region can exert a significant impact on the properties of the leg in gait, and future research should determine the specific pathways by which plantar feedback exerts this effect.

Adult↗

PubMed2005

Initiation of movement from quiet stance: comparison of gait and stepping in elderly subjects of different levels of functional ability.

This study describes how elderly subjects initiate gait, and step from a position of quiet stance. Based on scores from selected standardized tests subjects were placed in either a high (HFL) or low functional level (LFL) group and were asked to initiate gait, step onto a 10 cm high, 1.22 m wide curb and step over a 10 cm high, 9 cm wide obstacle at a self paced speed. Stepping conditions affected the velocity of movement. It was clear that all subjects decreased initiation velocity for both curb and obstacle compared to gait initiation. Swing and stance limb acceleration ground reaction forces and EMG amplitude were modulated according to initiation velocity. Toe clearance was greater for obstacle than curb and gait initiation. Swing toe-off was significantly earlier and there was a trend for obstacle clearance to be greater for the HFL group. Those in the LFL group appear to be at a greater risk for falling due to the possible effect of slower rate of toe-off that could influence toe clearance over the obstacle.

Accidental Falls↗

PubMed2005

Lower extremity coupling parameters during locomotion and landings.

During ballistic locomotion and landing activities, the lower extremity joints must function synchronously to dissipate the impact. The coupling of subtalar motion to tibial and knee rotation has been hypothesized to depend on the dynamic requirements of the task. This study was undertaken to look for differences in the coupling of 3-D foot and knee motions during walking, jogging, and landing from a jump. Twenty recreationally active young women with normal foot alignment (as assessed by a licensed physical therapist) were videotaped with high-speed cameras (250 Hz) during walking, jogging, hopping, and jumping trials. Coupling coefficients were compared among the four activities. The ratio of eversion to tibial rotation increased from the locomotion to the landing trials, indicating that with the increased loading demands of the activity, the requirements of foot motion increased. However, this increased motion was not proportionately translated into rotation of the tibia through the subtalar joint. Furthermore, the ratio of knee flexion to knee internal rotation increased significantly from the walking to landing trials. Together these findings suggest that femoral rotation may compensate for the increase in tibial rotation as the force-dissipating demands of the task increase. The relative unbalance among the magnitude of foot, tibial, and knee rotations observed with increasing task demands may have direct implications on clinical treatments aimed at reducing knee motion via controlling motion at the foot during landing tasks.

Adult↗

PubMed2005

Knee biomechanics during landings: comparison of pre- and postpubescent females.

PURPOSE: The purpose of this investigation was to examine lower-extremity biomechanical differences between prepubescent and postpubescent female recreational athletes during three drop jump-landing sequences (static landing, vertical landing, and lateral landing) to determine whether maturation influenced injury risk. METHODS: Sixteen recreationally active postpubescent women (18-25 yr of age) and 16 recreationally active girls (8-11 yr of age) participated in this study. High-speed three-dimensional videography and force plate data were recorded for each subject's performance of the landing tasks and an inverse dynamics procedure was used to estimate knee joint resultant moments and forces. Kinematic and kinetic dependent variables were analyzed in three separate mixed-design 2 x 3 (maturation level x landing sequence) repeated measures multivariate analysis of variance. RESULTS: Statistical analyses indicated significant maturation level x landing sequence interactions for postpubescent participants who exhibited reduced knee flexion (4.5 degrees ) at initial contact, increased mediolateral knee joint forces [prepubescent: -0.63 +/- 0.21 N.(kg. radicalLH)(-1), postpubescent: 0.55 +/- 0.21 N.(kg. radicalLH)(-1)], and reduced knee extensor moments [prepubescent: -0.0124 +/- 0.001 N.m.(kg.BH. radicalLH)(-1), postpubescent: -0.0079 +/- 0.001 N.m.(kg.BH. radicalLH)(-1)] compared with their prepubescent counterparts. CONCLUSION: These findings suggest that developmental changes influence knee mechanics during landings in female athletes and highlight the need to examine multiple landing patterns when investigating landing strategies.

Adolescent↗

PubMed2004

Sural nerve evoked responses in human hip and ankle muscles while standing.

The objective of this study was to investigate the influence of background EMG, as manipulated by changes in limb loading, and electrical stimulus intensity on sural nerve evoked EMG responses in proximal hip (ipsilateral gluteus medius and contralateral adductor longus) and distal ankle (ipsilateral soleus) muscles during quiet standing. We studied 14 healthy subjects who were instructed to stand on a force platform and load the right leg to 20, 30, 60, and 80% body weight. Trains of stimuli were delivered to the right sural nerve at three different intensities (1.5, 2, and 3 perception threshold). Average evoked responses from each of the three muscles were obtained for each combination of body weight and stimulus intensity. Reflex responses were consistently seen in gluteus medius and soleus but not adductor longus. The responses in gluteus medius and soleus consisted of complex inhibitory and excitatory responses with the primary effect in gluteus medius being a short latency excitation (mean latency of 57 ms) and in soleus, a short latency inhibition-excitation (latencies of 47 and 58 ms, respectively). The amplitudes of the responses were influenced primarily by background EMG. The results demonstrate consistent sural nerve evoked EMG responses in both a hip (gluteus medius) and ankle (soleus) muscle. While the findings for soleus generally corroborate and extend previous studies, the responses observed for the lateral hip muscle have not been previously reported.

Adolescent↗

PubMed2004

Spine-board transfer techniques and the unstable cervical spine.

STUDY DESIGN: A repeated-measures design using a cadaveric model was used in this preliminary investigation on the effectiveness of spine-board transfer techniques. OBJECTIVES: To compare the amount of angulation (flexion-extension) motion that results at the cervical spine during the execution of the log-roll maneuver and the lift-and-slide technique; and to examine how changes to the integrity of the cervical spine impacts the amount of motion generated during the transfer process. SUMMARY OF BACKGROUND DATA: Very little research has been performed to establish the efficacy of spine-board transfer techniques. Early studies have indicated that the log-roll maneuver may not be appropriate for transferring victims with thoracolumbar injuries. Also, there has not been a single study that has reported the impact of transfer techniques on the unstable cervical spine. This lack of data necessitated the present study. METHODS: Four groups (with six participants each) were asked to execute the log-roll maneuver and the lift-and-slide technique on five cadavers. An electromagnetic motion analysis device was used to assess the amount of angulation motion generated at the C5-C6 segment during the execution of these transfer techniques. To examine how changes to the integrity of the cervical spine impacts the amount of motion that is produced during the transfer process, flexion-extension motion was assessed under various conditions: across a stable C5-C6 segment, after the creation of a posterior ligamentous injury, and after a complete segmental injury. RESULTS: No significant differences in angulation motion were noted between transfer techniques. However, significant differences were noted between all three injury conditions. That is, as the severity of the injury increased, the average amount of angulation motion produced at the site of the lesion also increased, regardless of technique. CONCLUSION: The participants of this study were able to restrict flexion-extension motion equally well with thelog-roll maneuver as with the lift-and-slide technique. However, more research is needed to fully ascertain the effectiveness of spine-board transfer techniques.

Aged↗

PubMed2004

The effect of velocity on the strategies used during gait termination.

The purpose of this study was to examine the changes that occur in gait termination (GT) as cadence increases. Five healthy volunteers walked at three cadences in time to a metronome under the following conditions: normal walking, planned stopping and unplanned stopping. Electromyography and force plate data were collected at 1000 Hz. Peak posterior ground reaction force (deceleration force) was greatest for the lead limb in unplanned stopping and, in general, deceleration force increased as cadence increased. Duration of muscle activity relative to the time to peak loading was unchanged by cadence and was always longest in the lead limb during planned stopping. As cadence increases, the signal to stop must occur earlier during stance phase if a person is to stop in the subsequent step.

Adult↗

PubMed2004

Effect of botulinum toxin type A on gait of children who are idiopathic toe-walkers.

The purpose of this study was to determine the effects of botulinum toxin type A treatment on ankle muscle activity during gait of children who are idiopathic toe-walkers. Five children who were idiopathic toe-walkers with a mean age was 4.34 years participated. Gait of the subjects was evaluated prior to, 20 days following, and 12 months following bilateral botulinum toxin type A injection of the gastrocnemius and soleus muscles. Subjects received physical therapy following the 20-day evaluation. Dependent variables were type of foot contact pattern and duration of swing-phase tibialis anterior activity and onset of stance-phase gastrocnemius relative to ground contact. Prior to treatment 51% of foot contacts were with the toe (heel just off the ground) or were digitigrade, while the remaining contacts were flat foot or heel strike. At approximately 20 days following treatment, only 8% of foot contacts were toe contact or digitigrade. Prior to treatment, mean gastrocnemius onset was 30 ms prior to foot contact and the duration of swing-phase tibialis anterior was only 345 ms. Following treatment (and a more normal foot contact pattern), mean gastrocnemius onset followed ground contact by 36 ms and tibialis anterior duration increased through terminal swing and into the loading response. The posttreatment improvement was maintained at 12-month follow-up. It appears that botulinum toxin type A treatment normalizes the ankle EMG pattern during gait and a more normal foot-strike pattern is obtained. These data are discussed in terms of a neuromotor rationale for the rehabilitation of children who are idiopathic toe-walkers to maintain posttreatment improvements.

Botulinum Toxins, Type A↗

PubMed2003

Braking impulse and muscle activation during unplanned gait termination in human subjects with parkinsonism.

Persons with parkinsonism (PD) are known to have difficulty with both rapid force production and declination, and may not be able to adjust force levels during bimanual tasks in the upper extremity. We proposed that these deficits might underlie the problems experienced by those with PD when attempting to rapidly terminate locomotor activity. Rapid gait termination requires concomitant increases in braking impulse and decreases in propulsion impulse. We hypothesized that those with PD would be less able to modulate muscle activity and the associated braking impulse during gait termination. Muscular activity of soleus, tibialis anterior and gluteus medius, and braking impulse were compared between a group of subjects with PD and age and gender matched control subjects. Subjects with PD had similar patterns of muscular activation to control subjects although at dramatically reduced levels of amplitude. Consequently, PD subjects were unable to generate sufficient net braking impulse under time-critical conditions.

Aged↗

PubMed2002

Spinal cord modulation associated with isometric contractions.

OBJECTIVE: The dual-strategy hypothesis explains single-joint voluntary movement by dividing movements into two different strategies and suggesting that different excitation pulses modulate these movements. The existence of this excitation pulse was evaluated by quantifying magnitude and timing changes in the H-reflex (changes in spinal excitability) prior to a voluntary contraction. These changes in spinal excitability were assessed during a ballistic plantar flexion isometric contraction, where both the target size and force level was manipulated. METHODS AND MATERIALS: Subjects were seated in a modified chair with a force transducer placed under the metatarsal heads to measure ankle force output. Following a visual stimulus subjects were trained to produce a plantar flexion force of 25% and 50% of a maximum voluntary contraction, within target sizes of 5% and 15% of the selected force level. Soleus motor neuron reflex excitability was analyzed by measuring changes in the H/M ratio. The H-reflex was randomly elicited by tibial nerve stimulations at 15, 30, 45, 60, 75 and 90 ms prior to the recorded average soleus premotor time for each of the force and target size conditions. RESULTS: A two-way repeated-measures analysis of variance indicated a significant effect among target sizes for the time of change in spinal excitability, slope of facilitation (rate of rise of spinal excitability), and peak facilitation. A significant difference was also established between force levels for the slope and peak facilitation, but there was no difference with time of facilitation. CONCLUSIONS: These results indicate that changes in both target size and force level can influence slope and peak of facilitation. However, only target size appears to affect the time of facilitation. Results clearly support the existence of an excitation pulse that is regulated by the type of movement.

Adult↗

PubMed2002

Does postural instability affect the initiation of human gait?

During gait initiation (GI), decoupling of the center of mass and center of pressure allows the center of mass to fall forwards. Subjects initiated gait rapidly before and after tibial nerve block of the tibial nerve. Static single limb stability, stance limb ground reaction forces, electromyogram and temporal data were measured. It was hypothesized that postural stability would decrease post-block and that this would affect the kinetic and temporal properties of GI. Subjects had significantly decreased postural stability post-block and changes in normal gait kinetics, however, no changes were noted in ground reaction forces or relative temporal data of the GI task. The finding that GI was unaffected by diminished single leg postural instability suggests that GI is a pre-programmed task.

Adaptation, Physiological↗

PubMed2002

The interaction between leading and trailing limbs during stopping in humans.

While the initiation of gait has been well studied, the mechanisms of stopping the forward progression of the center of mass have received less attention. The purpose of this current experiment was to examine the effects of constraining cadence on how the body is brought to a stop. Lower limb electromyogram (gluteus medius, hamstrings and soleus (SOL)) and force plate data were compared between two gait conditions, walking and planned stopping, at three different cadences (100, 125 and 150% of normal cadence). As cadence increased, the onset of muscle activity prior to heel-strike decreased for all muscles except SOL. SOL activity was evident prior to heel-strike during stopping and after heel-strike during walking. As cadence increased, onset times before heel-strike were shorter in stopping and SOL became active more rapidly after heel-strike in walking. The normalized duration of muscle activity remained invariant as cadence increased. This activity was always longer under the lead limb during stopping at each cadence. This was reflected by increases in the braking forces produced by the leading limb. The rate at which force was generated was not different between gait conditions but increased with increasing cadence. Thus, subjects relied less on the trailing limb and more on the leading limb as cadence increased.

Adult↗

PubMed2002

The effect of foot placement on sit to stand in healthy young subjects and patients with hemiplegia.

OBJECTIVE: To determine the effect of altering the foot placement of the dominant limb in young healthy subjects and the uninvolved limb of subjects with hemiplegia on their ability to perform sit to stand (STS). DESIGN: Controlled biomechanical experiment. SETTING: Research laboratory of a university health science center. PARTICIPANTS: Nonrandom convenience sample of 10 healthy and 10 subjects with hemiplegia. Respective mean ages were 26 and 59 years. All patients with hemiplegia could ambulate and STS independently. The mean time since the stroke was 3.6 years. INTERVENTIONS: Subjects came from a sitting to a standing position under 3 different conditions: (1) normal condition, where both limbs were placed in 100 degrees of knee flexion; (2) limb extended condition, where the dominant or uninvolved limb was extended to 75 degrees of knee flexion; and (3) limb elevated condition, where the dominant or uninvolved limb was placed on a dense foam support equal to 25% of the subject's knee height. MAIN OUTCOME MEASURES: Vertical and anteroposterior ground reaction forces (GRFs) and bilateral tibialis anterior and quadriceps electromyogram (EMG) activity. RESULTS: In the young subjects, the normally placed nondominant limb compensated for the extended or elevated position of the dominant limb. Peak GRFs and EMG amplitudes were all significantly greater for the nondominant limb. In patients with hemiplegia, the EMG of the involved limb increased 39% in the limb-elevated and -extended conditions compared with the normal condition. Respective values for the uninvolved limb decreased. GRFs were significantly greater for the uninvolved limb except for the vertical force in the limb-extended position. CONCLUSIONS: Muscle activity and GRFs can be influenced by altering the initial foot placement of the dominant or uninvolved limb during STS. These initial data have positive implications for the rehabilitation of patients with hemiplegia who could be taught to overcome a reduced ability to use their impaired limb after stroke.

Adolescent↗

PubMedDate not supplied

Intrinsic pedal musculature support of the medial longitudinal arch: an electromyography study.

Much of the work describing support of the medial longitudinal arch has focused on the plantar fascia and the extrinsic muscles. There is little research concerning the function of intrinsic muscles in the maintenance of the medial longitudinal arch. Ten healthy volunteer adults served as subjects for this study, which was approved by the University Investigational Review Board. The height of the navicular tubercle above the floor was measured in both feet while subjects were seated with the foot in a subtalar neutral position and then when standing in a relaxed calcaneal stance. Subtalar neutral was found by palpating for talar congruency. Recordings of muscle activity from the abductor hallucis muscle were performed while the subjects maintained a maximal voluntary contraction in a supine position by plantarflexing their great toes. An injection of lidocaine (1% with epinephrine) was then administered by a Board-certified orthopedic surgeon in the region of the tibial nerve, posterior and inferior to the medial malleolus. Measurements were repeated and compared by using a paired t test. After the nerve block, the muscle activity was 26.8% of the control condition (P =.011). This corresponded with an increase in navicular drop of 3.8 mm. (P =.022). The observation that navicular drop increased when the activity of the intrinsic muscles decreased indicates that the intrinsic pedal muscles play an important role in support of the medial longitudinal arch.

Adult↗