American Journal of Health Promotion, Oct 15, 2021
The COVID-19 pandemic has affected the sleep and dreams of many individuals. Some have experience... more The COVID-19 pandemic has affected the sleep and dreams of many individuals. Some have experienced improvements, while others have had more complaints. The changes to daily life such as working from home and spending more time indoors in confinement may have disturbed the circadian rhythms of some individuals. There were many reports of a shift towards a later bedtime during the pandemic, with several studies showing that in general, females experienced worse sleep than males, including more nighttime awakenings and nightmares. Increased dream and nightmare frequency during the pandemic has been shown in multiple studies. It has been postulated that because dreams are often guided by the dominant emotional state, that dreams and nightmares related to pandemic themes are a result of specific stressors related to COVID-19. Those experiencing unwanted sleep disturbances and nightmares could stand to benefit from mindfulness and relaxation practices that can ease stress and anxiety before bedtime. Striving to maintain a regular sleep schedule and enhance exposure to daylight–particularly during the first half of the day–may also be helpful.
BACKGROUND CONTEXT: There is relatively little known concerning the spectral profile of the cervi... more BACKGROUND CONTEXT: There is relatively little known concerning the spectral profile of the cervical muscles, despite the fact that neck injury and pain are quite prevalent. PURPOSE: The objective of the study was to calculate and study the power spectral characteristics of the sternocleidomastoids, splenii capitis and upper trapezii in anterolateral flexion and posterolateral extension in a ramp contraction. STUDY DESIGN/SETTING: In a laboratory setting experiments were conducted to record surface electromyographic (EMG) data from six cervical muscles and power spectral variables obtained. PATIENT SAMPLE: Forty normal and healthy young adults (21 men, 19 women). OUTCOME MEASURES: Power spectral of EMG signals. METHODS: EMG data for the left and right isometric anterolateral flexion and posterolateral extension were acquired from the sternocleidomastoids, splenii capitis and upper trapezius bilaterally. The subjects were seated in an upright posture and exerted left and right anterolateral flexor and posterolateral extensor efforts from rest to their maximal voluntary contraction in a gradual linear ramp fashion using visual feedback as a guide. The force exerted and the surface EMG data were sampled at 1 kHz at every 10th percentile grade of contraction and the EMG data were subjected to the Fast-Fourier transform analysis. The median frequency (MF), mean power frequency (MPF), peak power and total power of all six cervical muscles were analyzed. RESULTS: In the anterolateral flexion the ipsilateral sternocleidomastoid and splenius capitis had a wider band of frequency, which further widened with increasing grade of contraction. The trapezius did not engage in the same manner or to the same magnitude. The MF of the sternocleidomastoid in the anterolateral flexion in both genders progressively increased, the splenius capitis remained relatively unchanged, and the upper trapezius declined with the increasing grades of contraction. CONCLUSIONS: There is no significant difference between the genders in spectral profile. There is a bilateral symmetry in spectral profile with reference to activity; however, they are significantly different in different activities for the same muscles. With increasing magnitude of contraction power, spectral density distribution increases and the median frequency decreases. These results can serve as a useful reference for painful necks. Restoration of power spectral characteristics may indicate normalcy, which cannot be gleaned by other EMG or force variables.
This research project was approved by the Queen's University Faculty of Medicine Ethics Committee... more This research project was approved by the Queen's University Faculty of Medicine Ethics Committee on the use of Human Subjects. sistently produced lower peak moments than the reference axis. Males produced significantly greater peak moments than did females [P = 0.000]. Conclusions: Measurement axis alignment significantly effects the peak moment recorded. Furthermore, these results reinforce the need for accurate and consistent alignment between the subject and the dynamometer. The position of the subject [seated/standing] did not significantly affect the measured peak moment when using the Lido Active Back System in this study.
International Journal of Industrial Ergonomics, Nov 1, 2001
Industrial handwheel actuation through manual operation is a task common to numerous industries. ... more Industrial handwheel actuation through manual operation is a task common to numerous industries. Often, the task demand significantly exceeds the capacities and capabilities of the operator due to factors such as excessive strength and aerobic demands under both isometric and continuous efforts, as well as awkward postures necessitated by handwheels located above the shoulder or below the knee, or with limited workspace surrounding the handwheel. The lack of stable footing also contributes to the excessive task demand. There is little agreement among published research reports on acceptable ergonomic design guidelines for the task of industrial handwheel actuation, furthermore, existing guidelines do not address numerous factors known to affect the operator's ability to safely complete the task. The purpose of this article is to review the scientific literature concerning industrial handwheel actuation and the human operator, identify gaps in the knowledge and propose future research that will eventually lead to the adoption of industrial handwheel actuation tasks designed within the capacities and capabilities of the human operator. Relevance to industry Handwheel actuation is one of the most physically demanding tasks that workers in the process and rail industries are required to perform. Numerous injuries as well as production inefficiencies have been attributed to this task. Optimizing this control device actuation task in terms of operator safety and productivity is important for the long-term health of the industrial handwheel operator.
Journal of Electromyography and Kinesiology, Aug 1, 2001
The objective of the study was to determine the median frequency (MF) and mean power frequency (M... more The objective of the study was to determine the median frequency (MF) and mean power frequency (MPF) of the stermodeidomastorial, splenius capitis and trapezius in progressively and linearly increasing isometric cervical flexion and extension. There is a dearth of data on spectral parameters of cervical muscles. Such data have been generated from 40 young adult subjects (21 male and 19 female). The subjects were seated upright in an individually adjusted chair and stabilized with a 4-point Velcro restraint system to stabilize the torso. These subjects exerted isometric flexor and extensor forces in a random sequence on an instrumented resistance device (specifically designed for the study) in a gradual and linearly increasing manner with a visual feedback to their maximal voluntary contraction (MVC) within a 5 s period. Surface EMG was sampled from the sternocleidomastoid, the splenius capitis and the trapezius muscles bilaterally at 1 kHz. The EMG signals were subjected to Fast Fourier Transform (FFT) analysis. Spectral profiles of all muscles in the dimensions of frequency, power, and grade of contraction were plotted. The mean median frequency (MF), mean power frequency (MPF), peak power and total power were analyzed. In the sternocleidomastoid, and the splenius the MF increased with the grade of contraction, widening its bandwidth at higher grades. The trapezius maintained a narrow bandwidth and its MF declined with the grade of contraction.
International Journal of Industrial Ergonomics, 2000
This paper reviews the current state of the relationship between computer keyboard use and the de... more This paper reviews the current state of the relationship between computer keyboard use and the development of cumulative trauma disorders [CTDs] as found in the literature. Alternative keyboard designs using biomechanical evaluation methods as justi"cation for their use are also reviewed. Critical factors such as the repetitiveness of the keyboarding task, the tendency of users to type with excessive force and forcing users to maintain prolonged awkward and static postures are discussed in relation to CTD development. Suggestions for future research into this area and possible keyboard substitutes are also reviewed. Relevance to industry The increasing incidence of cumulative trauma disorders (CTDs) in the workplace has led to a search for possible contributing factors and ergonomic interventions. The computer keyboard input device has received much attention in the past and is believed by many to be a prime factor in the etiology of CTD occurrence. This paper reviews the scienti"c literature published thus far that explores the relationship between CTD development and keyboard use in the service industries.
Objectives. To measure the cervical isometric force generation capacity of men and women reliably... more Objectives. To measure the cervical isometric force generation capacity of men and women reliably while seated in upright neutral posture. Design. The cervical muscle isometric strength was determined in¯exion, extension, lateral¯exion, anterolateral¯exion and posterolateral extensions in an upright seated neutral posture. For this measurement a device was designed, fabricated and its reliability established. Background. To-date only a few studies on cervical strength data have been published. Of these, validity of some data is suspected due to the use of unstandardized methodology. No studies were identi®ed which reported cervical strengths in lateral and oblique planes. Methods. A testing device consisting of sturdy, stable and strong telescopic adjustable square metal tube was ®rmly bolted in thē oor. Another rotating metal tube was pivoted and adjustably counterweighted and attached to an immovable object with a load cell in its path. Using a horizontal bar upholstered at the terminal end attached to the rotating tube 40 young subjects were tested. They exerted their maximal voluntary isometric contraction in¯exion, extension, lateral¯exion, anterolateral¯exion, and posterolateral extension bilaterally. Results. Cervical muscle strength was maximum in extension and minimal in anterolateral¯exion (which was very close to¯exion strength). With progressive change in direction towards posterior region the strength progressively increased. There was a signi®cant dierence between male and female strengths P < 0:01. The¯exion/extension ratio of males was 1:1.37 and for females 1:1.79. There was a signi®cant dierence in strength values in dierent directions P < 0:01. Conclusions. The cervical strength is direction dependent. The extension generates maximum force and¯exion close to minimum. A progressive change from anterior to posterior direction generates increasing force. Relevance There is insucient information regarding cervical strength, which may at least indirectly and in part, indicate the force bearing capacity of cervical musculature. The present study furnishes some data to this end.
European Journal of Applied Physiology, May 1, 2003
The purpose of this study was to calculate electromyographic (EMG) power spectra of the sternocle... more The purpose of this study was to calculate electromyographic (EMG) power spectra of the sternocleidomastoid (SCM), the splenius capitis (SPL) and the trapezius (TRP) muscles from both sides of the body in bilateral lateral flexion and compare them with the EMG spectral characteristics of the same muscles in the sagittal and oblique planes recorded from the same subjects in the same experimental session but reported elsewhere in the literature. Forty normal and healthy young adults (21 males, 19 females) volunteered for the study. The subjects were prepared and positioned appropriately to exert linearly ramping isometric exertion aided by visual feedback against a rigid and load cell instrumental device. Exertions were carried out in a random order. The maximal voluntary contraction was reached within a 5-s test period. The torque and EMG from the SCM, SPL and TRP muscles were sampled bilaterally at a rate of 1 kHz. The EMG data were subjected to fast Fourier transform analysis. During lateral flexion, the torque generated by females was significantly lower than males ( P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.01) and represented at 75% of male torque. Contrary to flexion/extension and oblique plane activities, the ipsilateral SCM was most active with highest power and up to four dominant frequencies demonstrating four distinct peaks. The bandwidth of this muscle progressively increased with the grade of contraction up to 400 Hz, similar to flexion/extension with median frequency (MF) spread between 21 and 109 Hz for males and 78 and 99 Hz for females. The ipsilateral SPL was the second most active muscle, which maintained a narrow bandwidth (200 Hz) and one dominant frequency, rising in power with increasing grade of contraction. Flexion and extension caused symmetrical activity bilaterally. The results of MANOVA revealed a significant main effect of gender, activity direction, grade of contraction and individual muscles ( P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.001). There was a significant interaction between muscle and activity direction ( P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.001) implying significantly different MF and mean power frequency if the direction of exertion was changed. Male and female subjects responded to direction differently ( P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.001).
Study Design. Experimental analysis was performed to determine the effects of low-velocity rear-e... more Study Design. Experimental analysis was performed to determine the effects of low-velocity rear-end impacts on phasic and magnitudinal activity of the cervical muscles in expected and unexpected conditions. Objectives. To determine the phasic response of the cervical muscles to increasing low-velocity rear-end impacts, and to compare the quantitative effects of awareness and unawareness of impending impact. Summary of Background Data. The literature contains little information on the etiology of whiplash injuries. Animal and cadaver studies have yielded some insight into the phenomenon. However, in vivo studies of the cervical muscular response and head-neck kinematics to low-velocity impacts are rare. Methods. Seven healthy volunteers were subjected to rear-end impacts of 4.9, 8.8, 10.8, and 13.7 m/s 2 acceleration at two levels of expectation: expected and unexpected. Bilateral electromyograms of the sternocleidomastoids, trapezii, and splenii capitis were recorded. Triaxial accelerometers recorded the acceleration of the chair, torso at the shoulder level, and head of the participant. Results. At an acceleration of 13.7 m/s 2 , the sternocleidomastoids generated up to 179% of their maximal voluntary contraction electromyogram, whereas the splenii and trapezii did not exceed 35% of their maximal voluntary contraction in most of the experimental conditions. Electromyographic variables were significantly affected by the levels of acceleration and expectation (P Ͻ 0.001). The onset time and peak electromyogram time for the sternocleidomastoid progressively decreased with increasing levels of acceleration. The kinetic variables and the electromyographic variables regressed significantly on the acceleration (P Ͻ 0.01), explaining from 96% to 100% of the variability. Conclusions. Muscle responses were greater with higher levels of acceleration. Because the muscular component of the head-neck complex plays a central role in the abatement of higher acceleration levels, it may be a primary site of injury in the whiplash phenomenon.
The aim of the experiment was to determine the impact of axial trunk rotation and arm position on... more The aim of the experiment was to determine the impact of axial trunk rotation and arm position on upper extremity adduction force and muscle activity. Ten healthy male subjects performed graded maximum voluntary contractions under isometric conditions in seven upper extremity positions and three trunk postures (neutral and 90 degrees left/right rotated) in a simulated manual materials handling task. A custom built lightweight force-measuring device was held between the palmar surfaces of the hands and subjects compressed the lateral surfaces of the device. Muscle activity was recorded bilaterally over the muscle bellies of the anterior deltoid, the long head of the biceps brachii and over the flexor carpi radialis. The activity of the right pectoralis major was also recorded unilaterally. Descriptive, multivariate analysis of variance (MANOVA) and post-hoc Scheffé comparisons were performed on the mean and peak force as well as the EMG [electromyographic] data. Further analysis was performed on the force-EMG relationship at 20% intervals of maximum voluntary contraction (force). Both upper extremity adduction force and EMG were significantly affected by position (p&lt;0.01) but not by trunk rotation. The muscle activity increased and force decreased with flexion of the upper extremity. Pearson correlation coefficients between force and EMG were low. The biceps and flexors were the most active muscles depending upon upper extremity position, and the right pectoralis major muscle activity expressed the highest correlation with force. The present findings confirm earlier hypotheses that upper extremity adduction strength is not significantly affected by trunk rotation.
Objectives. The objectives of the study were to determine the phasic recruitment of cervical musc... more Objectives. The objectives of the study were to determine the phasic recruitment of cervical muscles with increasing magnitudes of low velocity frontal impacts, and to determine quantitative effects of awareness of impending impact in comparison to being impacted unawares. Background. Biomechanics of low velocity frontal impact is poorly understood and requires more work. Methods. Ten healthy young adults were subjected to frontal impacts causing accelerations of 5.3, 8.6, 11.0 and 14.0 m/s 2 (0.54, 0.88, 1.12 and 1.43 gs) while the subjects were unaware of the impending impact and after being told that they were going to be impacted. Electromyograph from sternocleidomastoids, splenius capitis and upper trapezius was recorded bilaterally. Triaxial accelerometers recorded the acceleration of the sled, torso and head of the subjects. Results. The normalized electromyograph magnitude progressively rose with the level of acceleration whereas the time to onset generally decreased. At 14 m/s 2 sled acceleration the trapezius muscle generated 79% of their maximal voluntary contraction whereas the sternocleidomastoids generated 32% of their maximum voluntary contraction. The normalized peak electromyograph, the time to onset, the time of the peak electromyograph were significantly affected by the level of acceleration ðP < 0:01Þ, the expectation of impact ðP < 0:01Þ and muscle group studied ðP < 0:01Þ. The subject gender did not have a significant effect. The kinematic variables and the electromyograph regressed significantly on acceleration ðP < 0:01Þ. Conclusions. The muscle responses were greater with higher levels of acceleration, particularly the trapezius in frontal impacts. Since the muscular components play a significant and central role in head/neck complex motion abatement at higher levels of acceleration, it may be a primary site of injury at low velocity whiplash phenomenon. Relevance An understanding of the pattern of biomechanical loading may assist in a more specific treatment of the patient injured in a low velocity frontal impact.
This research project was approved by the Queen's University Faculty of Medicine Ethics Committee... more This research project was approved by the Queen's University Faculty of Medicine Ethics Committee on the use of Human Subjects. sistently produced lower peak moments than the reference axis. Males produced significantly greater peak moments than did females [P = 0.000]. Conclusions: Measurement axis alignment significantly effects the peak moment recorded. Furthermore, these results reinforce the need for accurate and consistent alignment between the subject and the dynamometer. The position of the subject [seated/standing] did not significantly affect the measured peak moment when using the Lido Active Back System in this study.
The aim of the experiment was to determine the impact of axial trunk rotation and arm position on... more The aim of the experiment was to determine the impact of axial trunk rotation and arm position on upper extremity adduction force and muscle activity. Ten healthy male subjects performed graded maximum voluntary contractions under isometric conditions in seven upper extremity positions and three trunk postures (neutral and 90 degrees left/right rotated) in a simulated manual materials handling task. A custom built lightweight force-measuring device was held between the palmar surfaces of the hands and subjects compressed the lateral surfaces of the device. Muscle activity was recorded bilaterally over the muscle bellies of the anterior deltoid, the long head of the biceps brachii and over the flexor carpi radialis. The activity of the right pectoralis major was also recorded unilaterally. Descriptive, multivariate analysis of variance (MANOVA) and post-hoc Scheffé comparisons were performed on the mean and peak force as well as the EMG [electromyographic] data. Further analysis was performed on the force-EMG relationship at 20% intervals of maximum voluntary contraction (force). Both upper extremity adduction force and EMG were significantly affected by position (p&lt;0.01) but not by trunk rotation. The muscle activity increased and force decreased with flexion of the upper extremity. Pearson correlation coefficients between force and EMG were low. The biceps and flexors were the most active muscles depending upon upper extremity position, and the right pectoralis major muscle activity expressed the highest correlation with force. The present findings confirm earlier hypotheses that upper extremity adduction strength is not significantly affected by trunk rotation.
American Journal of Health Promotion, Oct 15, 2021
The COVID-19 pandemic has affected the sleep and dreams of many individuals. Some have experience... more The COVID-19 pandemic has affected the sleep and dreams of many individuals. Some have experienced improvements, while others have had more complaints. The changes to daily life such as working from home and spending more time indoors in confinement may have disturbed the circadian rhythms of some individuals. There were many reports of a shift towards a later bedtime during the pandemic, with several studies showing that in general, females experienced worse sleep than males, including more nighttime awakenings and nightmares. Increased dream and nightmare frequency during the pandemic has been shown in multiple studies. It has been postulated that because dreams are often guided by the dominant emotional state, that dreams and nightmares related to pandemic themes are a result of specific stressors related to COVID-19. Those experiencing unwanted sleep disturbances and nightmares could stand to benefit from mindfulness and relaxation practices that can ease stress and anxiety before bedtime. Striving to maintain a regular sleep schedule and enhance exposure to daylight–particularly during the first half of the day–may also be helpful.
BACKGROUND CONTEXT: There is relatively little known concerning the spectral profile of the cervi... more BACKGROUND CONTEXT: There is relatively little known concerning the spectral profile of the cervical muscles, despite the fact that neck injury and pain are quite prevalent. PURPOSE: The objective of the study was to calculate and study the power spectral characteristics of the sternocleidomastoids, splenii capitis and upper trapezii in anterolateral flexion and posterolateral extension in a ramp contraction. STUDY DESIGN/SETTING: In a laboratory setting experiments were conducted to record surface electromyographic (EMG) data from six cervical muscles and power spectral variables obtained. PATIENT SAMPLE: Forty normal and healthy young adults (21 men, 19 women). OUTCOME MEASURES: Power spectral of EMG signals. METHODS: EMG data for the left and right isometric anterolateral flexion and posterolateral extension were acquired from the sternocleidomastoids, splenii capitis and upper trapezius bilaterally. The subjects were seated in an upright posture and exerted left and right anterolateral flexor and posterolateral extensor efforts from rest to their maximal voluntary contraction in a gradual linear ramp fashion using visual feedback as a guide. The force exerted and the surface EMG data were sampled at 1 kHz at every 10th percentile grade of contraction and the EMG data were subjected to the Fast-Fourier transform analysis. The median frequency (MF), mean power frequency (MPF), peak power and total power of all six cervical muscles were analyzed. RESULTS: In the anterolateral flexion the ipsilateral sternocleidomastoid and splenius capitis had a wider band of frequency, which further widened with increasing grade of contraction. The trapezius did not engage in the same manner or to the same magnitude. The MF of the sternocleidomastoid in the anterolateral flexion in both genders progressively increased, the splenius capitis remained relatively unchanged, and the upper trapezius declined with the increasing grades of contraction. CONCLUSIONS: There is no significant difference between the genders in spectral profile. There is a bilateral symmetry in spectral profile with reference to activity; however, they are significantly different in different activities for the same muscles. With increasing magnitude of contraction power, spectral density distribution increases and the median frequency decreases. These results can serve as a useful reference for painful necks. Restoration of power spectral characteristics may indicate normalcy, which cannot be gleaned by other EMG or force variables.
This research project was approved by the Queen's University Faculty of Medicine Ethics Committee... more This research project was approved by the Queen's University Faculty of Medicine Ethics Committee on the use of Human Subjects. sistently produced lower peak moments than the reference axis. Males produced significantly greater peak moments than did females [P = 0.000]. Conclusions: Measurement axis alignment significantly effects the peak moment recorded. Furthermore, these results reinforce the need for accurate and consistent alignment between the subject and the dynamometer. The position of the subject [seated/standing] did not significantly affect the measured peak moment when using the Lido Active Back System in this study.
International Journal of Industrial Ergonomics, Nov 1, 2001
Industrial handwheel actuation through manual operation is a task common to numerous industries. ... more Industrial handwheel actuation through manual operation is a task common to numerous industries. Often, the task demand significantly exceeds the capacities and capabilities of the operator due to factors such as excessive strength and aerobic demands under both isometric and continuous efforts, as well as awkward postures necessitated by handwheels located above the shoulder or below the knee, or with limited workspace surrounding the handwheel. The lack of stable footing also contributes to the excessive task demand. There is little agreement among published research reports on acceptable ergonomic design guidelines for the task of industrial handwheel actuation, furthermore, existing guidelines do not address numerous factors known to affect the operator's ability to safely complete the task. The purpose of this article is to review the scientific literature concerning industrial handwheel actuation and the human operator, identify gaps in the knowledge and propose future research that will eventually lead to the adoption of industrial handwheel actuation tasks designed within the capacities and capabilities of the human operator. Relevance to industry Handwheel actuation is one of the most physically demanding tasks that workers in the process and rail industries are required to perform. Numerous injuries as well as production inefficiencies have been attributed to this task. Optimizing this control device actuation task in terms of operator safety and productivity is important for the long-term health of the industrial handwheel operator.
Journal of Electromyography and Kinesiology, Aug 1, 2001
The objective of the study was to determine the median frequency (MF) and mean power frequency (M... more The objective of the study was to determine the median frequency (MF) and mean power frequency (MPF) of the stermodeidomastorial, splenius capitis and trapezius in progressively and linearly increasing isometric cervical flexion and extension. There is a dearth of data on spectral parameters of cervical muscles. Such data have been generated from 40 young adult subjects (21 male and 19 female). The subjects were seated upright in an individually adjusted chair and stabilized with a 4-point Velcro restraint system to stabilize the torso. These subjects exerted isometric flexor and extensor forces in a random sequence on an instrumented resistance device (specifically designed for the study) in a gradual and linearly increasing manner with a visual feedback to their maximal voluntary contraction (MVC) within a 5 s period. Surface EMG was sampled from the sternocleidomastoid, the splenius capitis and the trapezius muscles bilaterally at 1 kHz. The EMG signals were subjected to Fast Fourier Transform (FFT) analysis. Spectral profiles of all muscles in the dimensions of frequency, power, and grade of contraction were plotted. The mean median frequency (MF), mean power frequency (MPF), peak power and total power were analyzed. In the sternocleidomastoid, and the splenius the MF increased with the grade of contraction, widening its bandwidth at higher grades. The trapezius maintained a narrow bandwidth and its MF declined with the grade of contraction.
International Journal of Industrial Ergonomics, 2000
This paper reviews the current state of the relationship between computer keyboard use and the de... more This paper reviews the current state of the relationship between computer keyboard use and the development of cumulative trauma disorders [CTDs] as found in the literature. Alternative keyboard designs using biomechanical evaluation methods as justi"cation for their use are also reviewed. Critical factors such as the repetitiveness of the keyboarding task, the tendency of users to type with excessive force and forcing users to maintain prolonged awkward and static postures are discussed in relation to CTD development. Suggestions for future research into this area and possible keyboard substitutes are also reviewed. Relevance to industry The increasing incidence of cumulative trauma disorders (CTDs) in the workplace has led to a search for possible contributing factors and ergonomic interventions. The computer keyboard input device has received much attention in the past and is believed by many to be a prime factor in the etiology of CTD occurrence. This paper reviews the scienti"c literature published thus far that explores the relationship between CTD development and keyboard use in the service industries.
Objectives. To measure the cervical isometric force generation capacity of men and women reliably... more Objectives. To measure the cervical isometric force generation capacity of men and women reliably while seated in upright neutral posture. Design. The cervical muscle isometric strength was determined in¯exion, extension, lateral¯exion, anterolateral¯exion and posterolateral extensions in an upright seated neutral posture. For this measurement a device was designed, fabricated and its reliability established. Background. To-date only a few studies on cervical strength data have been published. Of these, validity of some data is suspected due to the use of unstandardized methodology. No studies were identi®ed which reported cervical strengths in lateral and oblique planes. Methods. A testing device consisting of sturdy, stable and strong telescopic adjustable square metal tube was ®rmly bolted in thē oor. Another rotating metal tube was pivoted and adjustably counterweighted and attached to an immovable object with a load cell in its path. Using a horizontal bar upholstered at the terminal end attached to the rotating tube 40 young subjects were tested. They exerted their maximal voluntary isometric contraction in¯exion, extension, lateral¯exion, anterolateral¯exion, and posterolateral extension bilaterally. Results. Cervical muscle strength was maximum in extension and minimal in anterolateral¯exion (which was very close to¯exion strength). With progressive change in direction towards posterior region the strength progressively increased. There was a signi®cant dierence between male and female strengths P < 0:01. The¯exion/extension ratio of males was 1:1.37 and for females 1:1.79. There was a signi®cant dierence in strength values in dierent directions P < 0:01. Conclusions. The cervical strength is direction dependent. The extension generates maximum force and¯exion close to minimum. A progressive change from anterior to posterior direction generates increasing force. Relevance There is insucient information regarding cervical strength, which may at least indirectly and in part, indicate the force bearing capacity of cervical musculature. The present study furnishes some data to this end.
European Journal of Applied Physiology, May 1, 2003
The purpose of this study was to calculate electromyographic (EMG) power spectra of the sternocle... more The purpose of this study was to calculate electromyographic (EMG) power spectra of the sternocleidomastoid (SCM), the splenius capitis (SPL) and the trapezius (TRP) muscles from both sides of the body in bilateral lateral flexion and compare them with the EMG spectral characteristics of the same muscles in the sagittal and oblique planes recorded from the same subjects in the same experimental session but reported elsewhere in the literature. Forty normal and healthy young adults (21 males, 19 females) volunteered for the study. The subjects were prepared and positioned appropriately to exert linearly ramping isometric exertion aided by visual feedback against a rigid and load cell instrumental device. Exertions were carried out in a random order. The maximal voluntary contraction was reached within a 5-s test period. The torque and EMG from the SCM, SPL and TRP muscles were sampled bilaterally at a rate of 1 kHz. The EMG data were subjected to fast Fourier transform analysis. During lateral flexion, the torque generated by females was significantly lower than males ( P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.01) and represented at 75% of male torque. Contrary to flexion/extension and oblique plane activities, the ipsilateral SCM was most active with highest power and up to four dominant frequencies demonstrating four distinct peaks. The bandwidth of this muscle progressively increased with the grade of contraction up to 400 Hz, similar to flexion/extension with median frequency (MF) spread between 21 and 109 Hz for males and 78 and 99 Hz for females. The ipsilateral SPL was the second most active muscle, which maintained a narrow bandwidth (200 Hz) and one dominant frequency, rising in power with increasing grade of contraction. Flexion and extension caused symmetrical activity bilaterally. The results of MANOVA revealed a significant main effect of gender, activity direction, grade of contraction and individual muscles ( P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.001). There was a significant interaction between muscle and activity direction ( P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.001) implying significantly different MF and mean power frequency if the direction of exertion was changed. Male and female subjects responded to direction differently ( P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.001).
Study Design. Experimental analysis was performed to determine the effects of low-velocity rear-e... more Study Design. Experimental analysis was performed to determine the effects of low-velocity rear-end impacts on phasic and magnitudinal activity of the cervical muscles in expected and unexpected conditions. Objectives. To determine the phasic response of the cervical muscles to increasing low-velocity rear-end impacts, and to compare the quantitative effects of awareness and unawareness of impending impact. Summary of Background Data. The literature contains little information on the etiology of whiplash injuries. Animal and cadaver studies have yielded some insight into the phenomenon. However, in vivo studies of the cervical muscular response and head-neck kinematics to low-velocity impacts are rare. Methods. Seven healthy volunteers were subjected to rear-end impacts of 4.9, 8.8, 10.8, and 13.7 m/s 2 acceleration at two levels of expectation: expected and unexpected. Bilateral electromyograms of the sternocleidomastoids, trapezii, and splenii capitis were recorded. Triaxial accelerometers recorded the acceleration of the chair, torso at the shoulder level, and head of the participant. Results. At an acceleration of 13.7 m/s 2 , the sternocleidomastoids generated up to 179% of their maximal voluntary contraction electromyogram, whereas the splenii and trapezii did not exceed 35% of their maximal voluntary contraction in most of the experimental conditions. Electromyographic variables were significantly affected by the levels of acceleration and expectation (P Ͻ 0.001). The onset time and peak electromyogram time for the sternocleidomastoid progressively decreased with increasing levels of acceleration. The kinetic variables and the electromyographic variables regressed significantly on the acceleration (P Ͻ 0.01), explaining from 96% to 100% of the variability. Conclusions. Muscle responses were greater with higher levels of acceleration. Because the muscular component of the head-neck complex plays a central role in the abatement of higher acceleration levels, it may be a primary site of injury in the whiplash phenomenon.
The aim of the experiment was to determine the impact of axial trunk rotation and arm position on... more The aim of the experiment was to determine the impact of axial trunk rotation and arm position on upper extremity adduction force and muscle activity. Ten healthy male subjects performed graded maximum voluntary contractions under isometric conditions in seven upper extremity positions and three trunk postures (neutral and 90 degrees left/right rotated) in a simulated manual materials handling task. A custom built lightweight force-measuring device was held between the palmar surfaces of the hands and subjects compressed the lateral surfaces of the device. Muscle activity was recorded bilaterally over the muscle bellies of the anterior deltoid, the long head of the biceps brachii and over the flexor carpi radialis. The activity of the right pectoralis major was also recorded unilaterally. Descriptive, multivariate analysis of variance (MANOVA) and post-hoc Scheffé comparisons were performed on the mean and peak force as well as the EMG [electromyographic] data. Further analysis was performed on the force-EMG relationship at 20% intervals of maximum voluntary contraction (force). Both upper extremity adduction force and EMG were significantly affected by position (p&lt;0.01) but not by trunk rotation. The muscle activity increased and force decreased with flexion of the upper extremity. Pearson correlation coefficients between force and EMG were low. The biceps and flexors were the most active muscles depending upon upper extremity position, and the right pectoralis major muscle activity expressed the highest correlation with force. The present findings confirm earlier hypotheses that upper extremity adduction strength is not significantly affected by trunk rotation.
Objectives. The objectives of the study were to determine the phasic recruitment of cervical musc... more Objectives. The objectives of the study were to determine the phasic recruitment of cervical muscles with increasing magnitudes of low velocity frontal impacts, and to determine quantitative effects of awareness of impending impact in comparison to being impacted unawares. Background. Biomechanics of low velocity frontal impact is poorly understood and requires more work. Methods. Ten healthy young adults were subjected to frontal impacts causing accelerations of 5.3, 8.6, 11.0 and 14.0 m/s 2 (0.54, 0.88, 1.12 and 1.43 gs) while the subjects were unaware of the impending impact and after being told that they were going to be impacted. Electromyograph from sternocleidomastoids, splenius capitis and upper trapezius was recorded bilaterally. Triaxial accelerometers recorded the acceleration of the sled, torso and head of the subjects. Results. The normalized electromyograph magnitude progressively rose with the level of acceleration whereas the time to onset generally decreased. At 14 m/s 2 sled acceleration the trapezius muscle generated 79% of their maximal voluntary contraction whereas the sternocleidomastoids generated 32% of their maximum voluntary contraction. The normalized peak electromyograph, the time to onset, the time of the peak electromyograph were significantly affected by the level of acceleration ðP < 0:01Þ, the expectation of impact ðP < 0:01Þ and muscle group studied ðP < 0:01Þ. The subject gender did not have a significant effect. The kinematic variables and the electromyograph regressed significantly on acceleration ðP < 0:01Þ. Conclusions. The muscle responses were greater with higher levels of acceleration, particularly the trapezius in frontal impacts. Since the muscular components play a significant and central role in head/neck complex motion abatement at higher levels of acceleration, it may be a primary site of injury at low velocity whiplash phenomenon. Relevance An understanding of the pattern of biomechanical loading may assist in a more specific treatment of the patient injured in a low velocity frontal impact.
This research project was approved by the Queen's University Faculty of Medicine Ethics Committee... more This research project was approved by the Queen's University Faculty of Medicine Ethics Committee on the use of Human Subjects. sistently produced lower peak moments than the reference axis. Males produced significantly greater peak moments than did females [P = 0.000]. Conclusions: Measurement axis alignment significantly effects the peak moment recorded. Furthermore, these results reinforce the need for accurate and consistent alignment between the subject and the dynamometer. The position of the subject [seated/standing] did not significantly affect the measured peak moment when using the Lido Active Back System in this study.
The aim of the experiment was to determine the impact of axial trunk rotation and arm position on... more The aim of the experiment was to determine the impact of axial trunk rotation and arm position on upper extremity adduction force and muscle activity. Ten healthy male subjects performed graded maximum voluntary contractions under isometric conditions in seven upper extremity positions and three trunk postures (neutral and 90 degrees left/right rotated) in a simulated manual materials handling task. A custom built lightweight force-measuring device was held between the palmar surfaces of the hands and subjects compressed the lateral surfaces of the device. Muscle activity was recorded bilaterally over the muscle bellies of the anterior deltoid, the long head of the biceps brachii and over the flexor carpi radialis. The activity of the right pectoralis major was also recorded unilaterally. Descriptive, multivariate analysis of variance (MANOVA) and post-hoc Scheffé comparisons were performed on the mean and peak force as well as the EMG [electromyographic] data. Further analysis was performed on the force-EMG relationship at 20% intervals of maximum voluntary contraction (force). Both upper extremity adduction force and EMG were significantly affected by position (p&lt;0.01) but not by trunk rotation. The muscle activity increased and force decreased with flexion of the upper extremity. Pearson correlation coefficients between force and EMG were low. The biceps and flexors were the most active muscles depending upon upper extremity position, and the right pectoralis major muscle activity expressed the highest correlation with force. The present findings confirm earlier hypotheses that upper extremity adduction strength is not significantly affected by trunk rotation.
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