The influence of age on performance and muscle activity was studied during computer mouse tasks d... more The influence of age on performance and muscle activity was studied during computer mouse tasks designed to induce high demands on motor control. Eight young (mean age 25 years) and nine elderly (mean age 63 years) women participated. When the speed was self-determined, the elderly subjects performed 13%-18% slower than did the young. When speed was predefined, the error rate was higher in the elderly subjects than in the young ones (medium precision 7.8% compared to 2.5%, high precision 16.5% compared to 7.9%, respectively). The highest error rate was found for double-clicking (32.9% compared to 13.5%, respectively). The reduced performance in the elderly subjects was hypothesised to be a combined effect of deteriorated proprioception, increased motor unit size, and changes in the central nervous system. Electrical activity (EMG) was recorded from the forearm, shoulder and neck muscles. Higher levels of EMG activity were found in the elderly compared to the young. A likely explanation is that the impaired motor control necessitated an increased muscle activity. The highest levels of EMG activity and lack of EMG gaps were found for the forearm extensor muscles, especially the extensor digitorum muscle (mean EMG activity 10.4% compared to 8.1% of maximal electrical activity, EMGmax) whereas lower EMG activity levels were found for the shoulder region (e.g. right trapezius muscle mean EMG 2.8% compared to 1.1% EMGmax, respectively). The latter was possibly due to a relieving effect of the forearm support. Differences in muscle activity among the tasks were found, however they were minor for the shoulder and neck muscles. Consideration of the demands on motor control when designing user interfaces is recommended, to the benefit of both the young and the elderly.
The present study investigates the prevalence of sexual victimization and correlations between se... more The present study investigates the prevalence of sexual victimization and correlations between sexual victimization and indicators of poor health in two representative samples of men and women in Denmark. Specifically, the authors explore the prevalence of self-reported victimization among adolescents (N = 5,829) and adults (N = 3,932) and analyze differences in self-reported health outcomes between male and female victims
The aim of this study was to report the prevalence and nature of long-term diseases and their con... more The aim of this study was to report the prevalence and nature of long-term diseases and their consequences in children under the age of 16 in Denmark, and to identify the socio-demographic determinants of disease. Parents and stepparents participating in the Danish Health and Morbidity Survey, 2000, were interviewed at home about long-term diseases, including impairments and sequelae after injury and disease, in children under the age of 16 living at home. Answers were given for 7,670 children, and diseases were coded according to ICD-10 by two doctors. Logistic regression analysis was used to identify the determinants and consequences of disease. A total of 16.2% of children had one or more long-term diseases, boys (17.5%) more frequently than girls (14.8%). The prevalence increased through the first six years of life. A social gradient was seen: children of parents with low socioeconomic status or with little education had a higher prevalence. The most frequent disease was asthma ...
The Journal of Trauma: Injury, Infection, and Critical Care, 2010
Knowledge on long-term consequences of injury on health is vital when injury prevention policies ... more Knowledge on long-term consequences of injury on health is vital when injury prevention policies and emergency care are planned. However, few studies have described lasting health consequences associated with injury. This study analyses the relationship between injury and self-assessed health up to 10 years after the injury. The study makes use of a public health research database linking health interview survey information with data from national health registries. Using this database, the health of a group of Danish patients with injury events during 1995 to 2005 was compared with a noninjured group up to 10 years after the injury. The association between self-assessed general health and self-reported depression and injury-related factors were estimated using logistic regression analysis. When patients with injuries compared with noninjured, the odds ratios of poor self-assessed general health and self-reported depression were 1.83 (confidence level, 1.53-2.19) and 1.33 (confidence level, 1.14-1.54), respectively. Although decreasing with time, the effect of injury on general health was significant up to 10 years after the injury. The injury type was significantly related to health, and in particular, patients with back, head, and neck injuries reporting poor general health. No gender differences were found in the effect of injury on self-assessed health. Injuries have lasting consequences for physical and mental health up to 10 years after the injury event, in particular, for people sustaining head, neck, and back injuries. Sustaining an injury has the same effect on general health in men and women.
The present study investigates the prevalence of sexual victimization and correlations between se... more The present study investigates the prevalence of sexual victimization and correlations between sexual victimization and indicators of poor health in two representative samples of men and women in Denmark. Specifically, the authors explore the prevalence of self-reported victimization among adolescents (N = 5,829) and adults (N = 3,932) and analyze differences in self-reported health outcomes between male and female victims and corresponding controls. Gender differences are found in the reported prevalence of sexual victimization. Significantly more females than males reported forced sexual experiences in both samples. Associations between sexual victimization and poor health outcomes are found for both genders. Comparable patterns of association for men and women are found on a number of variables, particularly those pertaining to risk behavior.
To assess the diagnostic reliability of a new quantitative D-dimer assay (VIDAS New) and an estab... more To assess the diagnostic reliability of a new quantitative D-dimer assay (VIDAS New) and an established quick test (Nycocard D-dimer assay) in the diagnosis of deep vein thrombosis (DVT) compared with ultrasonography. A third assay (Auto Dimer) became available during sample collection and has been included in the final assessment. The diagnostic performance of the Auto Dimer assay was evaluated on three different coagulation analysers. A clinical prospective study of patients admitted to hospital for evaluation of DVT. Setting. The admission ward at Aalborg Hospital. Subjects. A total of 113 outpatients with suspected DVT. Main outcome measures. Compression ultrasonography was used as the reference method for a diagnosis of DVT and compared with different D-dimer assays. The results were expressed as sensitivity, specificity, positive predictive value and negative predictive value (NPV). Deep vein thrombosis was established in 49 patients (43%). Two D-dimer assays (VIDAS New and Auto Dimer) showed sensitivities of 90 and 88%, specificities of 42 and 44%, and NPV's of 85 and 83%, respectively. The Nycocard D-dimer assay showed a sensitivity of 63%, specificity of 67% and NPV of 71%. The diagnostic performance of VIDAS New and the Auto Dimer D-dimer assays is almost identical, but this study suggests that neither of the D-dimer assays is suitable as the only screening method for DVT, in a situation with a high pretest probability of DVT. This call for a differential strategy that distinguishes between cases of low and high clinical probability using either a D-dimer test or ultrasonography. Abbreviations DVT, deep venous thrombosis, NPV, negative predictive value, PPV, positive predictive value
To study the potentiality for developing an EMG-based model for the human shoulder, mapping of re... more To study the potentiality for developing an EMG-based model for the human shoulder, mapping of relations between static hand forces and electromyographic (EMG) activity of 13 shoulder muscles, were performed. The procedure was to perform by the hands slowly varying isometric forces up to 20% maximum voluntary force in the three-dimensional space. By combining these data with literature values on muscle physiological cross-sectional area and moment arm data, an EMG-based model was developed for estimating muscle forces in the glenohumeral joint. The model was validated for one standardized position by comparing joint moment, calculated from EMG by using the model, with moments from the external force. The highest correlation between these moments was found assuming a linear EMG/force calibration at low force level (< 20% MVC), giving correlations from 0.65 to 0.95 for the abduction/adduction moment and from 0.70 to 0.93 for the flexion/extension moment, for the six subjects. Moments calculated from EMG were for most subjects somewhat lower than the moments from the external force; the mean residual error ranged from 1.6 to 9.9 Nm. Taking this into account, the results can be used for assessment of muscle forces based on recordings of external forces at the hands during submaximal static work tasks without substantially elevated arms.
In this study, we present a case of late-puerperal onset of thrombohemorrhagic complications in a... more In this study, we present a case of late-puerperal onset of thrombohemorrhagic complications in a 33-yr-old woman with known antiphospholipid syndrome (APS) and heterozygosity for factor V Leiden gene mutation. Antithrombotic prophylaxis with low-molecular-weight (LMW) heparin was given since the 12th gestational week. Pregnancy and cesarean delivery were uncomplicated. Five weeks postpartum, the patient developed a severe hemorrhagic diathesis with marked thrombocytopenia accompanied by vaginal, nasal and cutaneous bleeding. A variety of autoimmune phenomena were also detected, partly at clinical presentation and partly later on, despite ongoing steroid treatment. Platelet counts recovered to normal values within a few weeks secondary to high-dose steroids and intravenous immunoglobulin administration. An ultrasound of both legs, performed because of persistent complaint of moderate calf pain, revealed bilateral deep venous thromboses (DVT). The clinical and biochemical findings were not consistent with thrombotic thrombocytopenic purpura (TTP), heparin-induced thrombocytopenia (HIT) or the 'hemolysis, elevated liver enzymes and low platelet syndrome' (HELLP). The diagnostic criteria for systemic lupus erythematosus (SLE) were not fulfilled either. The complex of thrombohemorrhagic complications and autoimmune phenomena seen in this case is unusual and not previously described in the late puerperal stage of APS-related pregnancies.
The influence of age on performance and muscle activity was studied during computer mouse tasks d... more The influence of age on performance and muscle activity was studied during computer mouse tasks designed to induce high demands on motor control. Eight young (mean age 25 years) and nine elderly (mean age 63 years) women participated. When the speed was self-determined, the elderly subjects performed 13%-18% slower than did the young. When speed was predefined, the error rate was higher in the elderly subjects than in the young ones (medium precision 7.8% compared to 2.5%, high precision 16.5% compared to 7.9%, respectively). The highest error rate was found for double-clicking (32.9% compared to 13.5%, respectively). The reduced performance in the elderly subjects was hypothesised to be a combined effect of deteriorated proprioception, increased motor unit size, and changes in the central nervous system. Electrical activity (EMG) was recorded from the forearm, shoulder and neck muscles. Higher levels of EMG activity were found in the elderly compared to the young. A likely explanation is that the impaired motor control necessitated an increased muscle activity. The highest levels of EMG activity and lack of EMG gaps were found for the forearm extensor muscles, especially the extensor digitorum muscle (mean EMG activity 10.4% compared to 8.1% of maximal electrical activity, EMGmax) whereas lower EMG activity levels were found for the shoulder region (e.g. right trapezius muscle mean EMG 2.8% compared to 1.1% EMGmax, respectively). The latter was possibly due to a relieving effect of the forearm support. Differences in muscle activity among the tasks were found, however they were minor for the shoulder and neck muscles. Consideration of the demands on motor control when designing user interfaces is recommended, to the benefit of both the young and the elderly.
Effects of speed and precision on electromyography (EMG) in human shoulder muscles were studied d... more Effects of speed and precision on electromyography (EMG) in human shoulder muscles were studied during a hand movement task where five points were marked repeatedly with a pencil. Six female subjects performed with three precision demands and at four speeds. Three of the speeds were predefined, while the last speed was performed as fast as possible. The EMG were recorded from 13 shoulder muscles or parts of muscles. Elbow velocity, acceleration and rectified EMG were calculated for each task. The mean elbow velocity and acceleration increased with speed and precision demands. There was an increase in EMG as the speed demand increased for all three precision demands (P < 0.001), and as the precision demand increased for the two highest predefined speed demands (P < 0.05). The combination of a high speed and a high precision demand resulted in the highest EMG. Different EMG levels were attained for the 13 muscles and the supraspinatus muscle always showed the highest normalized EMG. However, analysis of variance showed the same relative increase for all muscles with speed and precision demands. The EMG changes in response to precision demand can only be explained in part by the differences in movement velocity and acceleration, and other factors such as increased co-contraction must also be taken into account.
The aim of the study was to evaluate the effect of physical and mental demands on heart rate vari... more The aim of the study was to evaluate the effect of physical and mental demands on heart rate variability- (HRV-) derived indices of autonomic activity. Ten healthy, female subjects performed two computer tasks: one with combined mental and physical demands and a reference task primarily consisting of physical demands. The combined task, which was performed once with a keyboard and once with a computer mouse, was a computerized version of the colour word conflict task (CWT). The CWT is highly mentally demanding due to the inherent perceptual conflict between a word stimulus and a colour stimulus. In the reference task (REF) the physical demands were comparable to CWT, while the mental demands were low. Finally, the subjects rested at the workplace (REST). Data on performance, heart rate (HR), mean arterial blood pressure (MAP), HRV, and urinary concentrations of catecholamines were obtained. The following frequency bands were applied for HRV: very low frequency (VLF, 0.00-0.04 Hz), low frequency (LF, 0.05-0.15 Hz), high frequency (HF, 0.16-0.40 Hz) and total power (TP, 0.00-0.40 Hz). Indices of sympathetic nervous activity (I(SNS)) and parasympathetic nervous activity (I(PNS)) were estimated as normalized powers in LF and HF bands: I(SNS) = LF/(TP-VLF) and I(PNS) = HF/(TP-VLF). Values are expressed as normalised units (nu). There was an increase in I(SNS) during CWT [mouse: 0.490 (0.052) nu [ave (SEM)] and keyboard: 0.476 (0.039) nu] and REF [mouse: 0.453 (0.059) nu and keyboard: 0.489 (0.047) nu] compared to REST [0.397 (0.047) nu], but no difference between CWT and REF. Corresponding decreases were observed for I(PNS). HR and MAP were higher during CWT compared to REST. No effects were observed for excreted amounts of catecholamines. There were no differences between the computer mouse and the keyboard condition for I(SNS) and I(PNS). In conclusion, an increase in I(SNS) and a decrease in I(PNS) were found in response to a physically demanding reference computer task. Addition of mental demands did not elicit any further effect on I(SNS) and I(PNS), suggesting a significant influence of the physical rather than the mental demands during computer work.
Musculoskeletal symptoms among computer users are frequently found. The aim was to investigate th... more Musculoskeletal symptoms among computer users are frequently found. The aim was to investigate the musculoskeletal workload during computer work using speech recognition and traditional computer input devices (keyboard/mouse). Ten experienced computer users (nine female, one male) participated. They performed three different computer tasks: (1). text entry and (2). text editing of a standard text and (3). a self-selected work task. These tasks were performed twice using speech recognition and traditional computer input devices (keyboard/mouse). Additionally, a task consisting of reading aloud of the standard text was performed. Surface EMG from the forearm (m. extensor carpi ulnaris, m. extensor carpi radialis), the shoulder (m. trapezius) and the neck extensor muscles was recorded, in addition to the voice-related muscles (m. scalenii, m. cricothyroideus). Using speech recognition during text entry and text editing reduced the static muscle activity of the forearm, neck and to some extent the shoulder muscles. Furthermore, tendencies to longer periods of muscle activity pause (relative time with EMG gaps) in the forearm and shoulder muscles were found. This was seen at the expense of a tendency to an increased static activity and a decreased relative time with EMG gaps in m. cricothyroideus. Finally, during use of speech recognition the hand was tied to the keyboard/mouse for a shorter period of time, while the eyes were viewing the screen for a longer period of time compared to the condition with traditional computer input devices. It is recommended to use speech recognition as a supplementary tool to traditional computer input devices.
ABSTRACT Visually based point-and-click user interfaces have become very common. This increases t... more ABSTRACT Visually based point-and-click user interfaces have become very common. This increases the need to understand the mechanics in learning and using pointing devices in order to design appropriate human-computer interaction and thereby to help alleviate musculosketetal symptoms. The paper reports a study of preference, strategies and learning in using keyboard and mouse in a tracking task under time pressure. The keyboard was preferred by 11 out of 12 subjects due primarily to comfort, frustration, and visual strain. One of the most distinguishing features in favour of the keyboard was the opportunity to develop a working strategy facilitating learning.
The influence of age on performance and muscle activity was studied during computer mouse tasks d... more The influence of age on performance and muscle activity was studied during computer mouse tasks designed to induce high demands on motor control. Eight young (mean age 25 years) and nine elderly (mean age 63 years) women participated. When the speed was self-determined, the elderly subjects performed 13%-18% slower than did the young. When speed was predefined, the error rate was higher in the elderly subjects than in the young ones (medium precision 7.8% compared to 2.5%, high precision 16.5% compared to 7.9%, respectively). The highest error rate was found for double-clicking (32.9% compared to 13.5%, respectively). The reduced performance in the elderly subjects was hypothesised to be a combined effect of deteriorated proprioception, increased motor unit size, and changes in the central nervous system. Electrical activity (EMG) was recorded from the forearm, shoulder and neck muscles. Higher levels of EMG activity were found in the elderly compared to the young. A likely explanation is that the impaired motor control necessitated an increased muscle activity. The highest levels of EMG activity and lack of EMG gaps were found for the forearm extensor muscles, especially the extensor digitorum muscle (mean EMG activity 10.4% compared to 8.1% of maximal electrical activity, EMGmax) whereas lower EMG activity levels were found for the shoulder region (e.g. right trapezius muscle mean EMG 2.8% compared to 1.1% EMGmax, respectively). The latter was possibly due to a relieving effect of the forearm support. Differences in muscle activity among the tasks were found, however they were minor for the shoulder and neck muscles. Consideration of the demands on motor control when designing user interfaces is recommended, to the benefit of both the young and the elderly.
The present study investigates the prevalence of sexual victimization and correlations between se... more The present study investigates the prevalence of sexual victimization and correlations between sexual victimization and indicators of poor health in two representative samples of men and women in Denmark. Specifically, the authors explore the prevalence of self-reported victimization among adolescents (N = 5,829) and adults (N = 3,932) and analyze differences in self-reported health outcomes between male and female victims
The aim of this study was to report the prevalence and nature of long-term diseases and their con... more The aim of this study was to report the prevalence and nature of long-term diseases and their consequences in children under the age of 16 in Denmark, and to identify the socio-demographic determinants of disease. Parents and stepparents participating in the Danish Health and Morbidity Survey, 2000, were interviewed at home about long-term diseases, including impairments and sequelae after injury and disease, in children under the age of 16 living at home. Answers were given for 7,670 children, and diseases were coded according to ICD-10 by two doctors. Logistic regression analysis was used to identify the determinants and consequences of disease. A total of 16.2% of children had one or more long-term diseases, boys (17.5%) more frequently than girls (14.8%). The prevalence increased through the first six years of life. A social gradient was seen: children of parents with low socioeconomic status or with little education had a higher prevalence. The most frequent disease was asthma ...
The Journal of Trauma: Injury, Infection, and Critical Care, 2010
Knowledge on long-term consequences of injury on health is vital when injury prevention policies ... more Knowledge on long-term consequences of injury on health is vital when injury prevention policies and emergency care are planned. However, few studies have described lasting health consequences associated with injury. This study analyses the relationship between injury and self-assessed health up to 10 years after the injury. The study makes use of a public health research database linking health interview survey information with data from national health registries. Using this database, the health of a group of Danish patients with injury events during 1995 to 2005 was compared with a noninjured group up to 10 years after the injury. The association between self-assessed general health and self-reported depression and injury-related factors were estimated using logistic regression analysis. When patients with injuries compared with noninjured, the odds ratios of poor self-assessed general health and self-reported depression were 1.83 (confidence level, 1.53-2.19) and 1.33 (confidence level, 1.14-1.54), respectively. Although decreasing with time, the effect of injury on general health was significant up to 10 years after the injury. The injury type was significantly related to health, and in particular, patients with back, head, and neck injuries reporting poor general health. No gender differences were found in the effect of injury on self-assessed health. Injuries have lasting consequences for physical and mental health up to 10 years after the injury event, in particular, for people sustaining head, neck, and back injuries. Sustaining an injury has the same effect on general health in men and women.
The present study investigates the prevalence of sexual victimization and correlations between se... more The present study investigates the prevalence of sexual victimization and correlations between sexual victimization and indicators of poor health in two representative samples of men and women in Denmark. Specifically, the authors explore the prevalence of self-reported victimization among adolescents (N = 5,829) and adults (N = 3,932) and analyze differences in self-reported health outcomes between male and female victims and corresponding controls. Gender differences are found in the reported prevalence of sexual victimization. Significantly more females than males reported forced sexual experiences in both samples. Associations between sexual victimization and poor health outcomes are found for both genders. Comparable patterns of association for men and women are found on a number of variables, particularly those pertaining to risk behavior.
To assess the diagnostic reliability of a new quantitative D-dimer assay (VIDAS New) and an estab... more To assess the diagnostic reliability of a new quantitative D-dimer assay (VIDAS New) and an established quick test (Nycocard D-dimer assay) in the diagnosis of deep vein thrombosis (DVT) compared with ultrasonography. A third assay (Auto Dimer) became available during sample collection and has been included in the final assessment. The diagnostic performance of the Auto Dimer assay was evaluated on three different coagulation analysers. A clinical prospective study of patients admitted to hospital for evaluation of DVT. Setting. The admission ward at Aalborg Hospital. Subjects. A total of 113 outpatients with suspected DVT. Main outcome measures. Compression ultrasonography was used as the reference method for a diagnosis of DVT and compared with different D-dimer assays. The results were expressed as sensitivity, specificity, positive predictive value and negative predictive value (NPV). Deep vein thrombosis was established in 49 patients (43%). Two D-dimer assays (VIDAS New and Auto Dimer) showed sensitivities of 90 and 88%, specificities of 42 and 44%, and NPV's of 85 and 83%, respectively. The Nycocard D-dimer assay showed a sensitivity of 63%, specificity of 67% and NPV of 71%. The diagnostic performance of VIDAS New and the Auto Dimer D-dimer assays is almost identical, but this study suggests that neither of the D-dimer assays is suitable as the only screening method for DVT, in a situation with a high pretest probability of DVT. This call for a differential strategy that distinguishes between cases of low and high clinical probability using either a D-dimer test or ultrasonography. Abbreviations DVT, deep venous thrombosis, NPV, negative predictive value, PPV, positive predictive value
To study the potentiality for developing an EMG-based model for the human shoulder, mapping of re... more To study the potentiality for developing an EMG-based model for the human shoulder, mapping of relations between static hand forces and electromyographic (EMG) activity of 13 shoulder muscles, were performed. The procedure was to perform by the hands slowly varying isometric forces up to 20% maximum voluntary force in the three-dimensional space. By combining these data with literature values on muscle physiological cross-sectional area and moment arm data, an EMG-based model was developed for estimating muscle forces in the glenohumeral joint. The model was validated for one standardized position by comparing joint moment, calculated from EMG by using the model, with moments from the external force. The highest correlation between these moments was found assuming a linear EMG/force calibration at low force level (< 20% MVC), giving correlations from 0.65 to 0.95 for the abduction/adduction moment and from 0.70 to 0.93 for the flexion/extension moment, for the six subjects. Moments calculated from EMG were for most subjects somewhat lower than the moments from the external force; the mean residual error ranged from 1.6 to 9.9 Nm. Taking this into account, the results can be used for assessment of muscle forces based on recordings of external forces at the hands during submaximal static work tasks without substantially elevated arms.
In this study, we present a case of late-puerperal onset of thrombohemorrhagic complications in a... more In this study, we present a case of late-puerperal onset of thrombohemorrhagic complications in a 33-yr-old woman with known antiphospholipid syndrome (APS) and heterozygosity for factor V Leiden gene mutation. Antithrombotic prophylaxis with low-molecular-weight (LMW) heparin was given since the 12th gestational week. Pregnancy and cesarean delivery were uncomplicated. Five weeks postpartum, the patient developed a severe hemorrhagic diathesis with marked thrombocytopenia accompanied by vaginal, nasal and cutaneous bleeding. A variety of autoimmune phenomena were also detected, partly at clinical presentation and partly later on, despite ongoing steroid treatment. Platelet counts recovered to normal values within a few weeks secondary to high-dose steroids and intravenous immunoglobulin administration. An ultrasound of both legs, performed because of persistent complaint of moderate calf pain, revealed bilateral deep venous thromboses (DVT). The clinical and biochemical findings were not consistent with thrombotic thrombocytopenic purpura (TTP), heparin-induced thrombocytopenia (HIT) or the 'hemolysis, elevated liver enzymes and low platelet syndrome' (HELLP). The diagnostic criteria for systemic lupus erythematosus (SLE) were not fulfilled either. The complex of thrombohemorrhagic complications and autoimmune phenomena seen in this case is unusual and not previously described in the late puerperal stage of APS-related pregnancies.
The influence of age on performance and muscle activity was studied during computer mouse tasks d... more The influence of age on performance and muscle activity was studied during computer mouse tasks designed to induce high demands on motor control. Eight young (mean age 25 years) and nine elderly (mean age 63 years) women participated. When the speed was self-determined, the elderly subjects performed 13%-18% slower than did the young. When speed was predefined, the error rate was higher in the elderly subjects than in the young ones (medium precision 7.8% compared to 2.5%, high precision 16.5% compared to 7.9%, respectively). The highest error rate was found for double-clicking (32.9% compared to 13.5%, respectively). The reduced performance in the elderly subjects was hypothesised to be a combined effect of deteriorated proprioception, increased motor unit size, and changes in the central nervous system. Electrical activity (EMG) was recorded from the forearm, shoulder and neck muscles. Higher levels of EMG activity were found in the elderly compared to the young. A likely explanation is that the impaired motor control necessitated an increased muscle activity. The highest levels of EMG activity and lack of EMG gaps were found for the forearm extensor muscles, especially the extensor digitorum muscle (mean EMG activity 10.4% compared to 8.1% of maximal electrical activity, EMGmax) whereas lower EMG activity levels were found for the shoulder region (e.g. right trapezius muscle mean EMG 2.8% compared to 1.1% EMGmax, respectively). The latter was possibly due to a relieving effect of the forearm support. Differences in muscle activity among the tasks were found, however they were minor for the shoulder and neck muscles. Consideration of the demands on motor control when designing user interfaces is recommended, to the benefit of both the young and the elderly.
Effects of speed and precision on electromyography (EMG) in human shoulder muscles were studied d... more Effects of speed and precision on electromyography (EMG) in human shoulder muscles were studied during a hand movement task where five points were marked repeatedly with a pencil. Six female subjects performed with three precision demands and at four speeds. Three of the speeds were predefined, while the last speed was performed as fast as possible. The EMG were recorded from 13 shoulder muscles or parts of muscles. Elbow velocity, acceleration and rectified EMG were calculated for each task. The mean elbow velocity and acceleration increased with speed and precision demands. There was an increase in EMG as the speed demand increased for all three precision demands (P < 0.001), and as the precision demand increased for the two highest predefined speed demands (P < 0.05). The combination of a high speed and a high precision demand resulted in the highest EMG. Different EMG levels were attained for the 13 muscles and the supraspinatus muscle always showed the highest normalized EMG. However, analysis of variance showed the same relative increase for all muscles with speed and precision demands. The EMG changes in response to precision demand can only be explained in part by the differences in movement velocity and acceleration, and other factors such as increased co-contraction must also be taken into account.
The aim of the study was to evaluate the effect of physical and mental demands on heart rate vari... more The aim of the study was to evaluate the effect of physical and mental demands on heart rate variability- (HRV-) derived indices of autonomic activity. Ten healthy, female subjects performed two computer tasks: one with combined mental and physical demands and a reference task primarily consisting of physical demands. The combined task, which was performed once with a keyboard and once with a computer mouse, was a computerized version of the colour word conflict task (CWT). The CWT is highly mentally demanding due to the inherent perceptual conflict between a word stimulus and a colour stimulus. In the reference task (REF) the physical demands were comparable to CWT, while the mental demands were low. Finally, the subjects rested at the workplace (REST). Data on performance, heart rate (HR), mean arterial blood pressure (MAP), HRV, and urinary concentrations of catecholamines were obtained. The following frequency bands were applied for HRV: very low frequency (VLF, 0.00-0.04 Hz), low frequency (LF, 0.05-0.15 Hz), high frequency (HF, 0.16-0.40 Hz) and total power (TP, 0.00-0.40 Hz). Indices of sympathetic nervous activity (I(SNS)) and parasympathetic nervous activity (I(PNS)) were estimated as normalized powers in LF and HF bands: I(SNS) = LF/(TP-VLF) and I(PNS) = HF/(TP-VLF). Values are expressed as normalised units (nu). There was an increase in I(SNS) during CWT [mouse: 0.490 (0.052) nu [ave (SEM)] and keyboard: 0.476 (0.039) nu] and REF [mouse: 0.453 (0.059) nu and keyboard: 0.489 (0.047) nu] compared to REST [0.397 (0.047) nu], but no difference between CWT and REF. Corresponding decreases were observed for I(PNS). HR and MAP were higher during CWT compared to REST. No effects were observed for excreted amounts of catecholamines. There were no differences between the computer mouse and the keyboard condition for I(SNS) and I(PNS). In conclusion, an increase in I(SNS) and a decrease in I(PNS) were found in response to a physically demanding reference computer task. Addition of mental demands did not elicit any further effect on I(SNS) and I(PNS), suggesting a significant influence of the physical rather than the mental demands during computer work.
Musculoskeletal symptoms among computer users are frequently found. The aim was to investigate th... more Musculoskeletal symptoms among computer users are frequently found. The aim was to investigate the musculoskeletal workload during computer work using speech recognition and traditional computer input devices (keyboard/mouse). Ten experienced computer users (nine female, one male) participated. They performed three different computer tasks: (1). text entry and (2). text editing of a standard text and (3). a self-selected work task. These tasks were performed twice using speech recognition and traditional computer input devices (keyboard/mouse). Additionally, a task consisting of reading aloud of the standard text was performed. Surface EMG from the forearm (m. extensor carpi ulnaris, m. extensor carpi radialis), the shoulder (m. trapezius) and the neck extensor muscles was recorded, in addition to the voice-related muscles (m. scalenii, m. cricothyroideus). Using speech recognition during text entry and text editing reduced the static muscle activity of the forearm, neck and to some extent the shoulder muscles. Furthermore, tendencies to longer periods of muscle activity pause (relative time with EMG gaps) in the forearm and shoulder muscles were found. This was seen at the expense of a tendency to an increased static activity and a decreased relative time with EMG gaps in m. cricothyroideus. Finally, during use of speech recognition the hand was tied to the keyboard/mouse for a shorter period of time, while the eyes were viewing the screen for a longer period of time compared to the condition with traditional computer input devices. It is recommended to use speech recognition as a supplementary tool to traditional computer input devices.
ABSTRACT Visually based point-and-click user interfaces have become very common. This increases t... more ABSTRACT Visually based point-and-click user interfaces have become very common. This increases the need to understand the mechanics in learning and using pointing devices in order to design appropriate human-computer interaction and thereby to help alleviate musculosketetal symptoms. The paper reports a study of preference, strategies and learning in using keyboard and mouse in a tracking task under time pressure. The keyboard was preferred by 11 out of 12 subjects due primarily to comfort, frustration, and visual strain. One of the most distinguishing features in favour of the keyboard was the opportunity to develop a working strategy facilitating learning.
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