Biomedical subjects

Shrawan Kumar

Publications and source records attributed to Shrawan Kumar.

At least 19 recordsLinked to original sources

PubMed2006

Measures of localized spinal muscle fatigue.

The objective of this study was to determine the best variable, if any, to indicate the level of localized muscle fatigue. Six male and six female subjects were studied while they exerted their maximal voluntary contraction and 40% of maximal voluntary contraction of spinal extensors in an isometric lifting activity. The electromyography (EMG) of erectores spinae at thoracic and lumbar levels was measured bilaterally. Also, the muscle bed blood volume, level of blood oxygenation to erector spinae at L3 level and heart rate were measured. The initial and final values of subjective feelings of fatigue through visual analogue score, rate of perceived exertions and body part discomfort rating were recorded. The mean maximal voluntary contraction forces for males and females were 899 (238) N and 431 (135) N respectively. The mean durations of hold in maximal voluntary fatiguing contraction were 68.1 (39.9) s and 72.3 (37.0) s for men and women respectively. By the end of the hold the force declined to 52% for males and 62% for females. The EMG amplitudes and median frequencies also progressively declined (p < 0.01). ANOVA revealed that the task percentile values of all variables were significantly different (p < 0.01). Gender had a significant main effect (p < 0.01). The correlation coefficients between force and other individual variables were weak to modest, but significant (p < 0.001). None of the single variables predicted fatigue reliably for either gender and levels of contraction. The regression equations developed were highly significant (p < 0.01) and they explained 96 to 98% of variance in both genders and contractions.

Adult↗

PubMed2006

Torque and EMG in rotation extension of the torso from pre-rotated and flexed postures.

BACKGROUND: Back injury is a common place in our society. Up to two-thirds of back injuries have been associated with trunk rotation. However, the torque production ability with a rotated spine and electromyographic activity of trunk muscles in such efforts is poorly understood. Therefore, the objectives of this study are to study torque production capacity of variously rotated and flexed trunk and to measure the EMG of selected trunk muscles in these activities. METHODS: Nineteen normal young subjects (7 males and 12 females) were recruited. Subjects were stabilized on a posture-stabilizing platform and were instructed to assume a flexed and right rotated posture (20 degrees , 40 degrees and 60 degrees of rotation and 20 degrees , 40 degrees and 60 degrees of flexion) in a random order. The subjects were asked to exert their maximal voluntary contraction in the asymmetric plane of rotation-extension for a period of 5s. The surface EMG of the external and internal obliques, rectus abdominis, latissimus dorsi, erector spinae at the 10th thoracic and 3rd lumbar vertebral levels was recorded bilaterally along with the torque generated. FINDINGS: Whereas the torque generated was significantly affected by both rotation and extension in both genders (P<0.001), the EMG was independent of rotation but affected by flexion in females only (P<0.01). The torques produced by both genders in each of the nine postures was significantly different from each other (P<0.001). The EMG demonstrated a trend of increase with increasing rotation and flexion. The response surfaces of normalized peak EMG of the right external oblique and internal oblique was somewhat similar, indicating a rotator torque and a stabilizing effect. The left latissimus dorsi and right external oblique provided the rotational torque and the right erector spinae provided the extensor effort. Since the rotation-extension was performed in the plane of asymmetry, the effort required the recruitment of muscles involved in left rotation, stability of rotated spine and an extensor effort. INTERPRETATION: The torque production capacity of the human trunk is posture dependent and declines with increasing rotation. However, with increasing rotation and flexion, the magnitude of EMG increases. This implies that with increasing asymmetry, it requires more muscle effort (thus tissue stress) to generate less torque. Increasing asymmetry tends to weaken the system and may enhance chances of injury.

Abdomen↗

PubMed2006

Analysis of right anterolateral impacts: the effect of trunk flexion on the cervical muscle whiplash response.

BACKGROUND: The cervical muscles are considered a potential site of whiplash injury, and there is a need to understand the cervical muscle response under non-conventional whiplash impact scenarios, including variable body position and impact direction. There is no data, however, on the effect of occupant position on the muscle response to frontal impacts. Therefore, the objective of the study was to measure cervical muscle response to graded right anterolateral impacts. METHODS: Twenty volunteers were subjected to right anterolateral impacts of 4.3, 7.8, 10.6, and 12.8 m/s(2) acceleration with their trunk flexed forward 45 degrees and laterally flexed right or left by 45 degrees. Bilateral EMG of the sternocleidomastoids, trapezii, and splenii capitis and acceleration of the sled, torso, and head were measured. RESULTS AND DISCUSSION: With either direction of trunk flexion at impact, the trapezius EMGs increased with increasing acceleration (p < 0.05). Time to onset of the electromyogram and time to peak electromyogram for most muscles showed a trend towards decreasing with increasing acceleration. With trunk flexion to the left, the left trapezius generated 38% of its maximal voluntary contraction (MVC) EMG, while the right trapezius generated 28% of its MVC EMG. All other muscles generated 25% or less of this measure (25% for the left splenius capitis, 8% for the right splenius capitis, 6% for the left sternocleidomastoid, and 2% for the left sterncleidomastoid). Conversely, with the trunk flexed to the right, the right trapezius generated 44% of its MVC EMG, while the left trapezius generated 31% of this value, and all other muscles generated 20% or less of their MVC EMG (20% for the left splenius capitis, 14% for the right splenius capitis, 4% for both the left and right sternocleidomastoids). CONCLUSION: When the subject sits with trunk flexed out of neutral posture at the time of anterolateral impact, the cervical muscle response is dramatically reduced compared to frontal impacts with the trunk in neutral posture. In the absence of bodily impact, the flexed trunk posture appears to produce a biomechanical response that would decrease the likelihood of cervical muscle injury in low velocity impacts.

Journal Article↗

PubMed2006

The effect of a 3-point harness restraint and car seat in whiplash-type lateral impacts.

STUDY DESIGN: Seventeen healthy volunteers were subjected to right and left lateral impacts 5.0, 6.8, 9.2, and 16.8 m/s acceleration while positioned in a Volvo car seat with lap and shoulder seat belt restraint in laboratory setting. OBJECTIVES: The purpose of this study was to determine the effect of using a standard 3-point lap and shoulder seat belt and Volvo car seat on the response of the cervical muscles to increasing low-velocity lateral impacts. SUMMARY OF BACKGROUND DATA: A previous study of lateral impacts in a 5-point harness restraint with head and trunk in neutral posture suggests that the burden of impact is borne primarily by the splenius capitis muscle contralateral to the direction of impact. That study, however, used a nonstandard harness for automobiles, and other studies suggest that a lap-and-shoulder seat belt may increase the risk of whiplash injury. METHODS: Triaxial accelerometers recorded the acceleration of the 1) sled, 2) torso at the shoulder level, and 3) head of the participant, while bilateral electromyograms of the sternocleidomastoids, trapezii, and splenii capitis were also recorded. RESULTS: For participants experiencing a right or left lateral impact, the muscle responses increased with increasing levels of acceleration (P < 0.05). The time to onset and time to peak electromyogram for most muscles also showed a trend to progressively decrease with increasing levels of acceleration. The peak head accelerations relative to the sled ranged from 2.5 to 10.6 m/s. When the impact was a right lateral impact, at the highest sled acceleration, the left splenius capitis generated 47% of its maximal voluntary contraction (MVC), and the left trapezius also 46% of its MVC; the left and right sternocleidomastoid, right splenius capitis, and right trapezius generated 29% or less of their MVC. For the highest level of acceleration in a left lateral impact, the right splenius capitis generated 48% of its MVC and the right trapezius 57% of the MVC, the left and right sternocleidomastoid, left splenius capitis, and left trapezius generated 29% or less of their MVC. In both directions of impact, the contralateral splenius capitis and trapezius showed a statistically significant difference in the EMG response compared with other muscles (P < 0.05). For participants experiencing a frontal impact, whether straight-on, right or left anterolateral, the muscle responses increased with increasing levels of acceleration (P < 0.05). The time to onset and time to peak electromyogram for most muscles also showed a trend to progressively decrease with increasing levels of acceleration. In a straight-on frontal impact, the trapezii (TRPs) muscles showed the greatest EMG response compared with the remaining muscles (P < 0.05). CONCLUSIONS: Compared with previously reported impact studies with a 5-point harness and rigid seat, the use of a 3-point lap and shoulder seat belt with car seat does not appear to adversely affect the cervical muscle response. In very-low- and low-velocity impact experiments, seat belt and seat type may thus not be particularly relevant to cervical EMG and kinematics.

Acceleration↗

PubMed2006

An observational electromyography study of the effect of trunk flexion in low-velocity frontal whiplash-type impacts.

OBJECTIVE: To examine the effect of forward and lateral trunk flexion on the cervical electromyogram and head kinematic response to whiplash-type frontal impacts. DESIGN: Observational study of sled impacts. SETTING: Laboratory. PARTICIPANTS: Twenty healthy volunteers. INTERVENTION: Twenty volunteers were subjected to increasing low-velocity (<8km/h) frontal impacts of 4.4, 7.6, 10.3, and 13.3m/s(2) acceleration with trunk forward flexed by 45 degrees and laterally flexed to the right and left by 45 degrees . MAIN OUTCOME MEASURES: Bilateral electromyography of the sternocleidomastoids, trapezii, and splenii capitis and acceleration of the sled, torso, and head were recorded. RESULTS: With either direction of lateral trunk flexion at impact, the trapezii electromyographic activity increased with increasing acceleration (P<.05). With the trunk flexed to the left, the left trapezius generated 39% of its maximal voluntary contraction (MVC) electromyographic activity, while the right trapezius generated 31% of its MVC electromyographic activity. The left splenius (ipsilateral to leftward trunk flexion) generated 24% of its MVC electromyographic activity, with all other muscles generating 15% or less of this measure. With the trunk flexed to the right, the right trapezius generated 38% of its MVC electromyographic activity, while the left trapezius generated 32% of this value. Again, the ipsilateral (to trunk flexion) splenius capitis generated 27% of its MVC electromyographic activity, and all other muscles 11% or less of this measure. CONCLUSIONS: When subjects sit with trunk flexed out of neutral posture at the time of frontal impact, the cervical muscle response is low and unlikely to be injurious.

Acceleration↗

PubMed2006

The effect of seat belt use on the cervical electromyogram response to whiplash-type impacts.

OBJECTIVE: The objective of this study was to determine the effect of a standard 3-point lap-and-shoulder seat belt and car seat on the electromyogram (EMG) response of the cervical muscles to increasing low-velocity impacts in comparison with that of a rigid seat and 5-point restraint. METHODS: Seventeen healthy volunteers were subjected to rear, frontal, right and left lateral and bilateral anterolateral, and posterolateral impacts with an acceleration varying from 4.4 to 16.8 m/s(2) while in a car seat with lap-and-shoulder seat belt. RESULTS: For rear-end impacts, whether straight on, right posterolateral, or left posterolateral, all muscles generated 50% or less of the maximal voluntary contraction (MVC) EMG. In straight-on rear impacts, the sternocleidomastoid was symmetrically the most active; however, in posterolateral impacts, the sternocleidomastoid contralateral to impact direction was more active than its counterpart. For a right lateral impact, at the highest acceleration, the left splenius capitis generated 47% of its MVC and the left trapezius did 46% of its MVC. In a left lateral impact, the right splenius capitis generated 48% of its MVC and the right trapezius did 57% of its MVC. In a straight-on frontal impact, the left trapezius generated 35% of its MVC and the right trapezius did 48% of its MVC. In a left anterolateral impact, the right splenius generated 60% of its MVC and the right trapezius did 66% of its MVC. Similarly, in a right anterolateral impact, the contralateral splenius muscle increased its activity to 52% of its MVC and the left trapezius was at 52% of its MVC. CONCLUSIONS: Compared with previously reported impact studies with a rigid seat and 5-point harness, the use of a 3-point lap-and-shoulder seat belt with a standard car seat did not appear to adversely affect cervical muscle response. In very-low-velocity and low-velocity impact experiments, seat belt and seat type may not significantly alter cervical EMG and kinematics.

Acceleration↗

PubMed2006

Low back problems and possible improvements in nursing jobs.

AIM: This paper reports a study that aimed to evaluate the workload, to identify problems leading to the higher incidence rate of work-related low back injury among nurses in the orthopaedic and intensive care unit departments of the hospital, and to gather information about improvements that the nurses would like in the workplace. BACKGROUND: The literature shows that low back injuries are common among nurses, and intervention programmes are needed to address this problem. METHOD: The hospital injury records were examined in a retrospective study. In addition, a validated questionnaire was administered between January and May 2005 to 47 nurses (23 orthopaedic and 24 intensive care nurses). The questionnaire contained questions on workload, history of back injuries, problems, possible solutions and psychophysical measures of exertion. FINDINGS: The life-time incidence and point prevalence of low back pain were 65% and 30%, respectively, in orthopaedic nurses, and 58% and 25%, respectively, in the intensive care nurses. The mean weight handled was reported to be 47 +/- 30 kg by the orthopaedic nurses and 26 +/- 10 kg by the intensive care nurses. The low back scored highest for body-part discomfort - 4.6 and 4.0, respectively, on a 10-point scale. The rate of perceived job exertion was 6.7 +/- 1.8 (very strong), and 5.8 +/- 1.9 (strong) on Borg's 10-point scale. The total effort required by the job, rated on Visual Analogue Scales, was 67 +/- 14% and 68 +/- 15% of the maximum, respectively. The Borg scores and the total effort according to the Visual Analogue Scale, and the Borg scores and force effort on the Visual Analogue Scale were moderately correlated (r = 0.53, P < 0.01 for both comparisons). CONCLUSION: The methodology proposed here is practical for job evaluation and to design a participatory ergonomic intervention aiming at reducing low back injuries in nursing jobs. There are workload differences between nursing jobs. Lifting devices, biomechanical training, bigger rooms, adequate set-up and additional staff are suggested improvements.

Adult↗

PubMed2006

Cut-points to prevent low back injury due to force exertion at work.

Force exertion is related to low back injuries (LBI). This paper critically reviews the literature concerning cut-points for back force exertion, presents available guidelines in a concise manner, and identifies areas that need further research. The studies reviewed were grouped according to the criteria used to set the cut-point values. Most often cut-points differ than concur. The approach considering physiological, psychophysical, epidemiological, and biomechanical aspects of back force exertion meets the most known criteria and presents the lowest common denominator of instantaneous load for lifting tasks. Further experimental and epidemiological studies in peak load and cumulative exposure are necessary. Compound indices should also be developed for pushing, pulling, and carrying. Future indices should consider electromyographically determined fatigue, differential viscoelastic properties of tissues, aging, and the cross sectional area of back muscles. We hope that this paper contributes to a more systematic appraisal of back force exertion at work.

Alberta↗

PubMed2006

Musculoskeletal symptoms in support staff in a large telecommunication company.

PRIMARY OBJECTIVE: The primary objective of this study was to determine the extent and severity of the musculoskeletal problems in office workers in a telecommunication company. RESEARCH DESIGN: A questionnaire survey was conducted to assess the prevalence of musculoskeletal disorders' symptoms, their perceived intensity and interaction with ability to work among office workers. METHODS AND PROCEDURES: The Cornell Musculoskeletal Discomfort Questionnaire and Cornell Hand Discomfort Questionnaire developed by the Human Factors and Ergonomics Laboratory at Cornell University were used on a sample of 140 office workers in a telecommunication company. MAIN OUTCOMES AND RESULTS: Discomfort/pain/ache at the wrist level was reported by 86.5% for the left side and 95.5% for the right side. Additionally, discomfort/pain/ache was reported by 77.5% of the sample for neck and 31% of the sample for the left and 50% for the right shoulder region. At the hand site, the area in the distal proximity of the wrist was the most affected site being indicated in 90% of cases for left side and 95% of cases for the right side. CONCLUSIONS: An overview of problems associated with the body parts in office work may allow targeted prevention and intervention.

Adult↗

PubMed2005

The effect of trunk flexion in healthy volunteers in rear whiplash-type impacts.

STUDY DESIGN: Twenty young, healthy volunteers in a laboratory were subjected to rear-end impacts 4.4, 7.9, 10.9, and 13.1 m/s acceleration with head rotation to right and left. OBJECTIVES: The purpose of this study was to determine the response of the cervical muscles to increasing low-velocity rear impacts when the head is rotated at the time of impact. SUMMARY OF BACKGROUND DATA: A previous study of rear impacts with head in neutral posture suggests that the burden of impact is borne primarily by the sternocleidomastoid muscles bilaterally. To improve automobile designs to prevent whiplash injury, we need to understand the response of the cervical muscles to whiplash-type perturbations in other conditions that mimic road collisions, such as when the head is rotated to the right and left at the time of rear-end impact. METHODS: Triaxial accelerometers recorded the acceleration of the sled, torso at the shoulder level, and head of the participant, while bilateral electromyograms (EMGs) of the sternocleidomastoids, trapezii, and splenii capitis were also recorded on 20 subjects (10 males and 10 females, mean age of 23.6 +/- 3 years) RESULTS: For participants experiencing a rear-end impact, whether having the head rotated to the left or right at the time of impact, the muscle responses increased with increasing levels of acceleration (P < 0.01). The time to onset and time to peak EMG for all muscles progressively decreased with increasing levels of acceleration (P < 0.01). Which muscle responded most to a whiplash-type neck perturbation was determined by the direction of head rotation. With the head rotated to the left, the right sternocleidomastoid generated 88% of its maximal voluntary contraction EMG (at least triple the response of other muscles). In comparison, the left sternocleidomastoid, both trapezii, and the splenii capitis generated on average only 10 to 30% of their maximal voluntary contraction EMG with head rotated to the left. On the other hand, with the head rotated to the right, the left sternocleidomastoid generated 94% of its maximal voluntary contraction EMG (again, at least triple the response of other muscles). CONCLUSIONS: If the head is rotated out of neutral posture at the time of rear impact, the injury risk tends to be greater for the sternocleidomastoid muscle contralateral to the side of rotation. Measures to prevent whiplash injury may have to account for the asymmetric response because many whiplash victims are expected to be looking to the left or right at the time of collision.

Adult↗

PubMed2005

Cervical muscle response to trunk flexion in whiplash-type lateral impacts.

The purpose of this study was to determine the response of the cervical muscles to increasing low-velocity, whiplash-type lateral impacts when the occupant is seated out of the recommended driving position (neutral posture). Twenty healthy volunteers were subjected to left lateral impacts of 4.1, 7.7, 10.5, and 13.7 m/s(2) acceleration, with their trunk flexed by 45 degrees and laterally flexed to the right and left also by 45 degrees at the time of impact. Bilateral electromyograms of the sternocleidomastoids, trapezii, and splenii capitis were recorded. Under these conditions of trunk-flexed postures, in a left lateral impact, muscle responses were of generally low magnitude with the trunk flexed to either the left or right. Even at the highest acceleration of 13.7 m/s(2), all muscles generated less than 37% of their known maximal voluntary contraction electromyogram. Also, in these left lateral impacts, the right splenius capitis showed a greater EMG response than the left splenius capitis regardless of whether the subject was flexed to the right or left at the time of impact. The right splenius capitis (the one contralateral to the left lateral impact direction) was more active than its counterpart. Compared to what is known for EMG responses with an occupant in the neutral posture, the right sternocleidomastoid (usually the most active muscle in a left lateral collision) was significantly less-active with trunk flexion than with neutral posture conditions (P<0.01). In the absence of bodily impact, the flexed trunk posture does not produce a biomechanical response that would increase the likelihood of cervical muscle injury in low velocity lateral impacts, and may lessen the risk of injury for some muscles.

Acceleration↗

PubMed2005

Analysis of right anterolateral impacts: the effect of head rotation on the cervical muscle whiplash response.

BACKGROUND: The cervical muscles are considered a potential site of whiplash injury, and there are many impact scenarios for whiplash injury. There is a need to understand the cervical muscle response under non-conventional whiplash impact scenarios, including variable head position and impact direction. METHODS: Twenty healthy volunteers underwent right anterolateral impacts of 4.0, 7.6, 10.7, and 13.0 m/s2 peak acceleration, each with the head rotated to the left, then the head rotated to the right in a random order of impact severities. Bilateral electromyograms of the sternocleidomastoids, trapezii, and splenii capitis following impact were measured. RESULTS: At a peak acceleration of 13.0 m/s2, with the head rotated to the right, the right trapezius generated 61% of its maximal voluntary contraction electromyogram (MVC EMG), while all other muscles generated 31% or less of this variable (31% for the left trapezius, 13% for the right spleinus. capitis, and 16% for the left splenius capitis). The sternocleidomastoids muscles also tended to show an asymmetric EMG response, with the left sternocleidomastoid (the one responsible for head rotation to the right) generating a higher percentage (26%) of its MVC EMG than the left sternocleidomastoid (4%) (p < 0.05). When the head is rotated to the left, under these same conditions, the results are reversed even though the impact direction remains right anterolateral. CONCLUSION: The EMG response to a right anterolateral impact is highly dependent on the head position. The sternocleidomastoid responsible for the direction of head rotation and the trapezius ipsilateral to the direction of head rotation generate the most EMG activity.

Journal Article↗

PubMed2005

Looking away from whiplash: effect of head rotation in rear impacts.

STUDY DESIGN: Twenty healthy volunteers in a laboratory were subjected to rear-end impacts 4.4, 7.9, 10.9, and 13.1 m/s acceleration, with head rotation to the right and left. OBJECTIVE: The purpose of this study was to determine the response of the cervical muscles to increasing low-velocity rear impacts when the head is rotated at the time of impact. SUMMARY OF BACKGROUND DATA: A previous study of rear impacts with head in neutral posture suggests that the burden of impact is borne primarily by the sternocleidomastoid muscles bilaterally. To improve automobile designs to prevent whiplash injury, we need to understand the response of the cervical muscles to whiplash-type perturbations in less-than-ideal conditions, such as when the head is rotated to the right and left at the time of rear-end impact. METHODS: Triaxial accelerometers recorded the acceleration of the sled, torso at the shoulder level, and head of the participant, while bilateral electromyograms of the sternocleidomastoids, trapezii, and splenii capitis were also recorded. RESULTS: For participants having a rear-end impact, whether having the head rotated to the left or right at the time of impact, the muscle responses increased with increasing levels of acceleration (P < 0.01). The time to onset and time to peak electromyogram for all muscles progressively decreased with increasing levels of acceleration (P < 0.01). Which muscle responded most to a whiplash-type neck perturbation was determined by the direction of head rotation. With the head rotated to the left, the right sternocleidomastoid generated 88% of the maximal voluntary contraction electromyogram (at least triple the response of other muscles). In comparison, the left sternocleidomastoid, both trapezii, and the splenii capitis generated on average only 10% to 30% of the maximal voluntary contraction electromyogram with head rotated to the left. On the other hand, with the head rotated to the right, the left sternocleidomastoid generated 94% of the maximal voluntary contraction electromyogram (again, at least triple the response of other muscles). CONCLUSIONS: If the head is rotated out of neutral posture at the time of rear impact, the injury risk tends to be greater for the sternocleidomastoid muscle contralateral to the side of rotation. Measures to prevent whiplash injury may have to account for the asymmetric response because many victims of whiplash are expected to be looking to the left or right at the time of collision.

Acceleration↗

PubMed2005

Kinematic and electromyographic response to whiplash-type impacts. Effects of head rotation and trunk flexion: summary of research.

Despite the fact that whiplash patients often report they had their head rotated or were in a twisted posture at the time of impact, the effect of these postures on the cervical muscle response to impact remains uninvestigated in impact studies. Prior impact studies have positioned the volunteers in the recommended driving position, for example, with head and trunk in a neutral posture. Using an approach of sled impacts with volunteers in very-low velocity impacts to describe the head kinematics and cervical muscle electromyography in response has provided a wealth of data. From this approach, the effect of varying impact direction and level of impact awareness can be discerned without subjecting the volunteers to injury. In part 1 of this review, a further series of results of impacts from eight directions is presented, revealing that the cervical electromyography response to whiplash-type impacts varies according to the presence and direction of head rotation. In part 2, additional data is summarised concerning whiplash-type impacts from 8 directions in the presence of trunk flexion. Contrary to a popular notion, head rotation or trunk flexion at the time of impact are factors that probably reduce injury risk. This data adds to attempts to approach an understanding of the human response to more complex scenarios of low-velocity road collisions.

Acceleration↗

PubMed2005

Cervical muscle response to head rotation in whiplash-type left lateral impacts.

STUDY DESIGN: Twenty healthy volunteers were subjected to left lateral impacts, randomly looking either left or right. OBJECTIVES: The purpose of this study is to determine the response of the cervical muscles to lateral impact whiplash-type perturbations when the head is rotated at the time of impact. SUMMARY OF BACKGROUND DATA: A previous study of left lateral impacts with head in neutral posture suggests that the burden of impact is borne primarily by the splenius capitis muscles. In order to improve automobile designs to prevent whiplash injury, we need to understand the response of the cervical muscles to whiplash-type perturbations in less-than-ideal conditions, such as when the head is rotated to the right and at the time of lateral impact. METHODS: Bilateral electromyograms of the sternocleidomastoids, trapezii, and splenii capitis were recorded. Triaxial accelerometers recorded the acceleration of the sled, torso, and head of the participant. RESULTS: For participants experiencing a left lateral impact, whether having the head rotated to the left or right at the time of impact, the muscle responses generally increased with increasing levels of acceleration (P < 0.05). The time of onset and peak electromyograph reading for most muscles progressively decreased with increasing acceleration. Overall, however, muscle responses were of low magnitude with the head rotated to the left or right. The sternocleidomastoid muscle responsible for head rotation (i.e., right sternocleidomastoid muscle when looking left) had a greater electromyograph response than its counterpart (P < 0.05). The contralateral splenius capitis and trapezius had the highest electromyograph responses. The remaining muscles showed similar levels of electromyograph responses, but even at the highest acceleration of 12.8 m/s, all generated less than 45% of their maximal voluntary contraction electromyograph reading. CONCLUSIONS: Compared to a lateral impact with the volunteer's head in the neutral position, a lateral impact with head rotation to either right or left may reduce the muscle response. Further studies are needed to determine whether or not head rotation at the time of lateral impact reduces overall injury risk.

Adult↗

PubMed2005

Kinematic and electromyographic response to whiplash loading in low-velocity whiplash impacts--a review.

Whiplash injury is a common injury, with a substantial health and economic burden. For five decades, researchers have been striving to discover the mechanisms of acute whiplash injury to develop methods of prevention through automobile design, and to develop treatment approaches. While earlier experiments with animals, cadavers, and military volunteers have provided some useful insights, it is only in recent years that research has progressed to reveal how neck muscles respond to collisions, particularly how they bear the burden of the forces of collision and how impact direction affects the neck muscle response which may determine the mechanism of injury. Initial volunteer experiments tended to focus on impact velocities (specifically differences in target and bullet vehicle velocities) and head acceleration, but gradually the focus has shifted to understanding the pattern of spinal segment motion and muscle contraction in response to the perturbation. An approach has been devised using sled impacts with healthy volunteers to elucidate in more detail various head kinematics and cervical muscle responses in low-velocity whiplash-type impacts. This approach involves the use of four levels of very-low to low velocity impacts to describe the kinematics of the head and the EMG response of cervical muscles in response to acceleration, but avoids any discernible risk of injury. This allows researchers to determine the cervical muscle response under many different scenarios, including varying direction of impact, awareness of impending impact, and others, without subjecting volunteers to any discernible risk. An initial series of results of impacts from eight directions is presented here, and these reveal that the cervical response to whiplash-type impacts is modified by impact awareness, muscles studied, and direction of impact. This will hopefully improve the understanding of the human response to low-velocity whiplash impacts.

Acceleration↗

PubMed2005

Physical demands analysis of occupational tasks in neighborhood pubs.

This paper describes a case study of a neighborhood pub in British Columbia, Canada. This case study is an examination of three common pub occupations-bartending, waitressing and cooking (n = 17). The aims of this study are to determine the biomechanical loads of job tasks identified as physically demanding for the three occupations analyzed, to assess the potential risk of musculoskeletal injury in these job tasks, and to recommend injury prevention measures. Risk of musculoskeletal injury was assessed with four validated methods (RULA, NIOSH lifting equation, Shoaf pulling model, 3D Static Strength prediction program). Tasks commonly and frequently performed were observed to pose some risk to the working populations and require investigation and changes soon as indicated by the upper extremity and low-back assessment procedures used. Mean combined compression at the lumbrosacral disc in common tasks have been demonstrated to exceed the action limit described by NIOSH. Ligament strain was observed to reach as high as 18% at the lumbosacral joint.

Adult↗

PubMed2005

Comparison of instantaneous and cumulative loads on the low back and neck in orthodontists.

BACKGROUND: Musculoskeletal disorders of back and neck among orthodontists are prevalent. Due to low instantaneous load they have not been investigated. The present study aimed to quantify and compare instantaneous and cumulative loads on low back and neck in orthodontists. METHODS: The sample included nine graduate orthodontic students from the University of Alberta and one practicing orthodontist to validate the generalization from student to professional group. The subjects were videotaped performing regular duties and the recorded postures were printed for biomechanical analysis of compression and shear loads and exposure time. Instantaneous loads were calculated using a biomechanical model developed specifically for this study and cumulative loads were calculated from the resultant loads. FINDINGS: The average instantaneous low back compression loads for men and women were found to be 1383 N and 936 N respectively. The average daily cumulative load on the other hand were found to be 16.2 MNs and 9.9 MNs for males and females respectively. INTERPRETATION: The study demonstrates that smaller loads cannot be ignored due to their magnitude if their duration is long because the time dependent properties of the tissues become modulating factor. Thus the measurement of instantaneous loads on tasks in orthodontists is not indicative of the amount of cumulative stress experienced by them.

Adult↗