PubMed Health⌕ Search

Biomedical subjects

Gunter P Siegmund

Publications and source records attributed to Gunter P Siegmund.

15 recordsLinked to original sources
PubMed2007

Electromyography of superficial and deep neck muscles during isometric, voluntary, and reflex contractions.

Increasingly complex models of the neck neuromusculature need detailed muscle and kinematic data for proper validation. The goal of this study was to measure the electromyographic activity of superficial and deep neck muscles during tasks involving isometric, voluntary, and reflexively evoked contractions of the neck muscles. Three male subjects (28-41 years) had electromyographic (EMG) fine wires inserted into the left sternocleidomastoid, levator scapulae, trapezius, splenius capitis, semispinalis capitis, semispinalis cervicis, and multifidus muscles. Surface electrodes were placed over the left sternohyoid muscle. Subjects then performed: (i) maximal voluntary contractions (MVCs) in the eight directions (45 deg intervals) from the neutral posture; (ii) 50 N isometric contractions with a slow sweep of the force direction through 720 deg; (iii) voluntary oscillatory head movements in flexion and extension; and (iv) initially relaxed reflex muscle activations to a forward acceleration while seated on a sled. Isometric contractions were performed against an overhead load cell and movement dynamics were measured using six-axis accelerometry on the head and torso. In all three subjects, the two anterior neck muscles had similar preferred activation directions and acted synergistically in both dynamic tasks. With the exception of splenius capitis, the posterior and posterolateral neck muscles also showed consistent activation directions and acted synergistically during the voluntary motions, but not during the sled perturbations. These findings suggest that the common numerical-modeling assumption that all anterior muscles act synergistically as flexors is reasonable, but that the related assumption that all posterior muscles act synergistically as extensors is not. Despite the small number of subjects, the data presented here can be used to inform and validate a neck model at three levels of increasing neuromuscular-kinematic complexity: muscles generating forces with no movement, muscles generating forces and causing movement, and muscles generating forces in response to induced movement. These increasingly complex data sets will allow researchers to incrementally tune their neck models' muscle geometry, physiology, and feedforward/feedback neuromechanics.

Adult↗
PubMed2006

Interaction between acoustic startle and habituated neck postural responses in seated subjects.

Postural and startle responses rapidly habituate with repeated exposures to the same stimulus, and the first exposure to a seated forward acceleration elicits a startle response in the neck muscles. Our goal was to examine how the acoustic startle response is integrated with the habituated neck postural response elicited by forward accelerations of seated subjects. In experiment 1, 14 subjects underwent 11 sequential forward accelerations followed by 5 additional sled accelerations combined with a startling tone (124-dB sound pressure level) initiated 18 ms after sled acceleration onset. During the acceleration-only trials, changes consistent with habituation occurred in the root-mean-square amplitude of the neck muscles and in the peak amplitude of five head and torso kinematic variables. The subsequent addition of the startling tone restored the amplitude of the neck muscles and four of the five kinematic variables but shortened onset of muscle activity by 9-12 ms. These shortened onset times were further explored in experiment 2, wherein 16 subjects underwent 11 acceleration-only trials followed by 15 combined acceleration-tone trials with interstimulus delays of 0, 13, 18, 23, and 28 ms. Onset times shortened further for the 0- and 13-ms delays but did not lengthen for the 23- and 28-ms delays. These temporal and spatial changes in EMG can be explained by a summation of the excitatory drive converging at or before the neck muscle motoneurons. The present observations suggest that habituation to repeated sled accelerations involves extinguishing the startle response and tuning the postural response to the whole body disturbance.

Acceleration↗
PubMed2006

Startle responses elicited by whiplash perturbations.

The human startle response produces muscle contractions throughout the body but the most brisk and synchronized contractions appear in the neck muscles. This response, which is greatest with the first exposure to a startling stimulus, could produce excessive and inappropriately directed muscle contractions that could explain the higher incidence of whiplash injuries in people who are unprepared for the collision. This study seeks neurophysiological evidence of startle responses in the neck muscles of 120 healthy subjects exposed to between 1 and 16 rear-end impacts or forward perturbations of different speeds. Startle responses were quantified by the synchronous electromyographic (EMG) activity between 10 and 20 Hz in bilaterally homologous sternocleidomastoid, scalene and cervical paraspinal neck muscles. Coherence analyses of EMGs from the left and right muscles were used to estimate synchrony for: (i) the first unexpected trial, (ii) subsequent habituated trials, and (iii) the superposition of habituated trials and a loud acoustic stimulus (40 ms, 124 dB sound). The peak in coherent EMG activity between contralateral muscle pairs in the 10-20 Hz bandwidth was related to startle. Synchrony in this bandwidth was observed between the left and right muscles during the first impact or whiplash-like perturbation. This synchrony decreased significantly in the habituated trials, but reappeared when the loud acoustic stimulus was introduced. Its presence in the first trial indicates that startle is part of the neuromuscular response to an unexpected rear-end impact. This startle component of the neuromuscular response could play a role in the aetiology of whiplash injuries.

Acceleration↗
PubMed2006

Auditory startle alters the response of human subjects exposed to a single whiplash-like perturbation.

STUDY DESIGN: Human volunteers were exposed to a single whiplash-like perturbation. OBJECTIVE: To determine how muscle and kinematic responses are affected by the superposition of a rear-end collision and loud startling noise. SUMMARY OF BACKGROUND DATA: Many whiplash studies use forward perturbations without reproducing the sound of a car crash. Loud sounds are known to evoke startle responses in the neck muscles and therefore could affect whiplash injuries. METHODS: Sixty-five subjects (30 female, 35 male) were exposed to a single forward horizontal perturbation. Head and torso kinematics, and electromyographic activity in the sternohyoid, sternocleidomastoid, scalenus, and cervical paraspinal muscles were measured. Two awareness conditions (deceived and unaware subjects) nested in two startle conditions (with or without a 40 milliseconds, 124 dB sound) were tested. RESULTS: Startle and gender affected the amplitude and timing of numerous kinematic and muscle variables. Awareness affected only one muscle variable. Startled individuals exhibited greater peak head and trunk accelerations, increased activity of the cervical paraspinal muscles, and a reduced head retraction and trunk angle. CONCLUSIONS: An acoustic startle alters the neck muscle and kinematic responses and may be as important as gender in the genesis of whiplash injury.

Acoustic Stimulation↗
PubMed2005

Adaptations to normal human gait on potentially slippery surfaces: the effects of awareness and prior slip experience.

Prior knowledge of potentially slippery conditions has been shown to alter normal human gait in slip and fall experiments. Here we quantify the effects of two aspects of prior knowledge - awareness of a possible slip and prior slip experience - on normal gait. Sixty-eight subjects (40F, 28M) each walked over 48 high-friction surfaces (control trials) and 12 low-friction surfaces. Within- and between-subject changes in lower limb muscle activation, gait kinematics and ground reaction forces were analyzed in three non-slip control trials: one before and one after the first unexpected slip exposure, and a third after repeated slip exposures. Subjects knew they might slip in the latter two trials but not the first trial. Twenty subjects slipped during their first low-friction exposure (early slip group), 32 in later low-friction exposures (late slip group), and 16 subjects did not slip at all. Simultaneous changes in awareness and experience between the first two analyzed trials of the early slip group altered the muscle activity in both limbs, reduced the foot and knee angles at heel strike in the slip limb and reduced the ground reaction forces, impulses and utilized friction after heel strike in the slip limb. A change in only awareness between the first two analyzed trials of the late slip group produced the same kinematic changes seen in the early slip group, but only small muscle activity change and no kinetic changes. Subsequent slip experience in the late slip group produced the muscle activation and kinetic changes observed in the early slip group, but no further kinematic changes. These results showed that awareness of a potential slip primarily alters how the slip-limb approaches the floor, whereas prior slip experience primarily alters the anticipatory muscle activation and how the foot interacts with the floor. These muscle, kinematic and kinetic changes were consistent with a more cautious "normal" gait, and can reduce the external validity of slip and fall experiments.

Adolescent↗
PubMed2005

The effect of subject awareness and prior slip experience on tribometer-based predictions of slip probability.

Prior knowledge of potentially slippery conditions has been shown to alter normal human gait in slip and fall experiments. We sought to quantify how the empirical relationship between slip probability and available floor friction was affected by subject awareness and prior slip experience. Sixty-eight subjects (40 females, 28 males) walked over three different low-friction surfaces inserted periodically between non-slip control trials. Three increasing levels of prior knowledge were used: deceived (unaware of the slippery surface), aware (20% chance of a slippery surface, but no prior slip experience) and experienced (aware with prior slip experience). Available friction was measured using a drag sled and a variable incidence tribometer. Of 620 low-friction trials, 124 generated slips greater than 27mm. The proportion of slips, the slip distance and the required friction (taken from the control trial immediately before a low-friction trial) generally decreased with increasing levels of prior knowledge. These adaptations were accommodated by logistically regressing slip outcome (yes/no) against the normalized friction (available friction minus required friction) rather than against available friction alone. The regressions showed that subject awareness biased the slip probability curve toward a lower slip risk for a given normalized friction, but that the subsequent addition of slip experience generated a slip risk curve that was not significantly different from that of deceived (and presumably unprepared) subjects. These findings suggest that data to validate a tribometer's ability to predict the risk of slipping (but not falling) can be acquired from subjects with prior slip experience.

Accidental Falls↗
PubMed2005

The effect of collision pulse properties on seven proposed whiplash injury criteria.

Recent epidemiological and biomechanical studies have suggested that whiplash injury is related to a vehicle's average acceleration rather than its speed change during a rear-end collision. To further explore this phenomenon, the effect of various kinematic properties of the collision pulse on seven proposed whiplash injury criteria was quantified. A BioRID II rear-impact dummy was seated on a programmable sled and exposed six times to each of 15 different collision pulses. Five properties of the collision pulse were varied: peak acceleration (1.3-4.4 g), speed change (3-11 km/h), duration (52-180 ms), displacement (2-26 cm) and shape (square, sine and triangular). Linear and angular accelerations and displacements of the head, and linear accelerations of the T1 and pelvis were measured in the sagittal-plane. Upper neck loads in the sagittal-plane were also measured. Variations within the proposed injury criteria between the different pulses were compared using analyses of variance. Six criteria--peak upper neck shear force, peak upper neck moment, peak retraction, the neck injury criterion (NIC) and two normalized neck injury criteria (Nij and Nkm)--exhibited graded responses that were most sensitive to the average acceleration of the collision pulse. Peak extension angle between the head and T1 decreased with both increasing speed change and peak acceleration, and was, therefore, deemed unsuitable as a whiplash injury criterion for the BioRID dummy. Of the seven criteria, Nij and Nkm were best able to distinguish between the 15 pulses. If the six graded injury criteria are related to the risk of whiplash injury, then the results of this study indicate that the risk of whiplash injury can be reduced by bumper and seat designs that prolong the collision pulse and thereby reduce the average vehicle and occupant accelerations for a given speed change.

Acceleration↗
PubMed2005

Variations in occupant response with seat belt slack and anchor location during moderate frontal impacts.

Both seat belt slack and anchor location are known to affect occupant excursion during high-speed frontal collisions, but their effects have not been studied at moderate collision severities. The goal of this study was to quantify how seat belt slack and anchor location affect occupant kinematics and kinetics in moderate severity frontal collisions. A Hybrid III 50th percentile male dummy was seated on a programmable sled and exposed to frontal collisions with a speed change of 17.5 km/h. The seat belt was adjusted either snugly or with 10 cm slack (distributed 60/40 between the shoulder and lap portions) and the anchor location was varied by adjusting the seat position either fully forward or rearward (seat travel = 13 cm). Accelerations and displacements of the head, T1 and pelvis were measured in the sagittal plane. Upper neck loads and knee displacements were also measured. Five trials were performed for each of the four combinations of belt adjustment (snug, slack) and anchor location (seat forward, seat rearward). For each trial, kinematic and kinetic response peaks were determined and then compared across conditions using ANOVAs. Peak displacements, accelerations and loads varied significantly with both seat belt slack and anchor location. Seat belt slack affected more parameters and had a larger effect than anchor location on most peak response parameters. Head displacements increased a similar amount between the snug/slack belt conditions and the rearward/forward anchor locations. Overall, horizontal head displacements increased from 23.8 cm in the snug-belt, rearward-anchor configuration to 33.9 cm in the slack-belt, forward-anchor configuration. These results demonstrated that analyses of occupant displacements, accelerations and loads during moderate frontal impacts should consider potential sources of seat belt slack and account for differences in seat belt anchor locations.

Acceleration↗
PubMed2005

Variability in vehicle and dummy responses in rear-end collisions.

OBJECTIVE: The objective of this study was to quantify the occupant response variability due to differences in vehicle and seat design in low-speed rear-end collisions. METHODS: Occupant response variability was quantified using a BioRID dummy exposed to rear-end collisions in 20 different vehicles. Vehicles were rolled rearward into a rigid barrier at 8 km/h and the dynamic responses of the vehicle and dummy were measured with the head restraint adjusted to the up most position. In vehicles not damaged by this collision, additional tests were conducted with the head restraint down and at different impact speeds. RESULTS: Despite a coefficient of variation (COV) of less than 2% for the impact speed of the initial 8 km/h tests, the vehicle response parameters (speed change, acceleration, restitution, bumper force) had COVs of 7 to 23% and the dummy response parameters (head and T1 kinematics, neck loads, NIC, N(ij) and N(km)) had COVs of 14 to 52%. In five vehicles tested multiple times, a head restraint in the down position significantly increased the peak magnitude of many dummy kinematic and kinetic response parameters. Peak head kinematics and neck kinetics generally varied linearly with head restraint back set and height, although the neck reaction moment reversed and increased considerably if the dummy's head wrapped onto the top of the head restraint. CONCLUSIONS: The results of this study support the proposition that the vehicle, seat, and head restraint are a safety system and that the design of vehicle bumpers and seats/head restraint should be considered together to maximize the potential reduction in whiplash injuries.

Acceleration↗
PubMed2004

Vehicle speed affects both pre-skid braking kinematics and average tire/roadway friction.

Vehicles decelerate between brake application and skid onset. To better estimate a vehicle's speed and position at brake application, we investigated how vehicle deceleration varied with initial speed during both the pre-skid and skidding intervals on dry asphalt. Skid-to-stop tests were performed from four initial speeds (20, 40, 60, and 80 km/h) using three different grades of tire (economy, touring, and performance) on a single vehicle and a single road surface. Average skidding friction was found to vary with initial speed and tire type. The post-brake/pre-skid speed loss, elapsed time, distance travelled, and effective friction were found to vary with initial speed. Based on these data, a method using skid mark length to predict vehicle speed and position at brake application rather than skid onset was shown to improve estimates of initial vehicle speed by up to 10 km/h and estimates of vehicle position at brake application by up to 8 m compared to conventional methods that ignore the post-brake/pre-skid interval.

Automobile Driving↗
PubMed2004

Gradation of Neck Muscle Responses and Head/Neck Kinematics to Acceleration and Speed Change in Rear-end Collisions.

Recent epidemiological evidence shows that the potential for whiplash injury varies with both the average acceleration and speed change of a rear-end collision. The goal of this study was to examine the gradation of neck muscle responses and the head and neck kinematics to rear-end collision pulses in which the acceleration and speed change were independently varied. Thirty subjects (15F, 15M) underwent 36 consecutive rear-end collisions consisting of three different average accelerations (ā = 0.5, 0.9 and 1.3 g) and three different speed changes (Deltav = 0.25, 0.50 and 0.75 m/s). Onset and amplitude of the sternocleidomastoid (SCM) and cervical paraspinal (PARA) muscle responses were measured using surface electromyography. Kinematic measures included linear and angular accelerations and displacements of the head and torso. The results showed that the amplitude of the muscle and kinematics responses was graded to both collision acceleration and speed change. The magnitude of early peaks in the head/neck kinematics correlated more strongly with collision acceleration (r(2) = 0.63 to 0.69), whereas the magnitude of later kinematic peaks correlated more strongly with collision speed change (r(2) = 0.59 to 0.95). Onset of the SCM muscle response correlated only weakly with collision acceleration and speed change (r(2) </= 0.07). A collision pulse descriptor obtained by multiplying average acceleration and speed change (āDeltav) yielded the strongest and most consistent correlations with neck muscle (r(2) = 0.48 to 0.58) and head/neck kinematic responses (r(2) = 0.78 to 0.94). This measure of collision severity is also consistent with the recent epidemiological evidence that whiplash symptom intensity and duration increases with both average acceleration and speed change.

Journal Article↗
PubMed2003

Awareness affects the response of human subjects exposed to a single whiplash-like perturbation.

STUDY DESIGN: Human subjects were exposed experimentally to a single whiplash-like perturbation. OBJECTIVE: To determine how awareness of the presence and timing of a whiplash-like perturbation affects the onset and amplitude of the neck muscle response and the peak magnitude of head and neck kinematics. SUMMARY OF BACKGROUND DATA: Although most whiplash injuries are sustained in rear-end collisions, which occur without warning, most studies of whiplash injury have used subjects aware of the imminent perturbation. METHODS: Seated subjects (35 women and 31 men) underwent a single forward horizontal perturbation (peak acceleration, 1.5 g). Surface electromyography measured the sternocleidomastoid and cervical paraspinal muscle activity. Three awareness conditions were tested: a countdown for subjects alerted to their perturbation, a perturbation without an alert for subjects who expected it within 60 seconds, and an unexpected perturbation for surprised subjects who were deceived. RESULTS: The muscle and kinematic responses of aware (alerted and unalerted) subjects were not significantly different. Sternocleidomastoid activation occurred 7 ms later in surprised subjects than in aware subjects (P < 0.0002). Cervical paraspinal amplitudes were 260% larger and angular head accelerations in flexion were 180% larger in surprised male subjects than in alerted male subjects. Surprised female subjects exhibited a 25% larger head retraction and a 30% lower forward acceleration of the mastoid process than aware female subjects. CONCLUSIONS: The larger retractions observed in surprised females likely produce larger tissue strains and may increase injury potential. Aware human subjects may not replicate the muscle response, kinematic response, or whiplash injury potential of unprepared occupants in real collisions.

Acceleration↗
PubMed2003

Rapid neck muscle adaptation alters the head kinematics of aware and unaware subjects undergoing multiple whiplash-like perturbations.

To examine whether habituation confounds the study of whiplash injury using human subjects, we quantified changes in the magnitude and temporal development of the neck muscle electromyogram and peak linear and angular head/torso kinematics of subjects exposed to sequential whiplash-like perturbations. Forty-four seated subjects (23F, 21M) underwent 11 consecutive forward horizontal perturbations (peak sled acceleration=1.5 g). Electromyographic (EMG) activity was recorded over the sternocleidomastoid (SCM) and cervical paraspinal (PARA) muscles with surface electrodes, and head and torso kinematics were measured using linear and angular accelerometers and a 3D motion analysis system. EMG onset occurred at reflex latencies (67-75 ms in SCM) and did not vary with repeated perturbations. EMG amplitude was significantly attenuated by the second perturbation in PARA muscles and by the third perturbation in SCM muscles. The mean decrement in EMG amplitude between the first trial and the mean of the last five trials was between 41% and 64%. Related kinematic changes ranged from a 21% increase in head extension angle to a 29% decrease in forward acceleration at the forehead, and were also significantly different by the second exposure in some variables. Although a wider range of perturbation intensities and inter-perturbation intervals need to be studied, the significant changes observed in both muscle and kinematic variables by the second perturbation indicated that habituation was a potential confounder of whiplash injury studies using repeated perturbations of human subjects.

Acceleration↗
PubMed2002

The effect of perturbation acceleration and advance warning on the neck postural responses of seated subjects.

The muscle and kinematic responses of subjects exposed to postural perturbations have been shown to vary with platform acceleration when this acceleration was covaried with platform velocity or displacement. The purpose of the current study was to isolate platform acceleration and examine its effect on the neck muscle response and head kinematics of seated subjects exposed to anterior perturbations. Thirty-six subjects (20 females, 16 males) underwent two blocks of 36 perturbations. Three different perturbations with peak accelerations of 7.7, 14.7, and 21.7 m/s(2) up to a common velocity of 0.5 m/s were used. In one block, subjects received an audible warning corresponding to the platform acceleration magnitude, and in the other block, no advance warning was given. Onset and amplitude of the sternocleidomastoid and cervical paraspinal muscle responses were measured using surface electromyography. Kinematic measures included linear and angular accelerations and displacements of the head. The results showed no differences in either the preperturbation posture or the muscle or kinematic responses between the warned and unwarned trials. Significant differences were observed in the onset and amplitude of the muscle and kinematic variables with perturbation acceleration, although these response differences were not linearly graded with perturbation acceleration. Gradation of muscle activation times has not been previously observed in postural perturbation studies, and their gradation with platform acceleration in the current study suggested that platform acceleration was a strong regulator of the reflex muscle response in postural perturbations.

Acceleration↗