Bo Melin

Effects of experimentally induced mental and physical stress on motor unit recruitment in the trapezius muscle

Mental stress may induce muscle tension and it is thought to contribute to the development of musculoskeletal disorders. Prolonged activity of a muscles motor units (the smallest functional units) having low activation thresholds, may cause metabolic disturbances, degenerative processes and pain. The present experiment was aimed at investigating if the same motor units are activated by mental stress as by physical demands. Seventeen participants were exposed to mental stress tests (mental arithmetic, Stroop color word) and physical demands (standardized reference contraction, force ramp contraction) in the laboratory. In addition, they were exposed to the cold pressor test. Bipolar intramuscular electromyographic (EMG) activity was measured in the trapezius muscle, which covers the upper part of the back, the neck and the shoulder, and an automatic classification programme was used to separate the contributions of the individual motor units in the compex EMG signal. Overall muscle activity was measured by bipolar surface EMG and heart rate was recorded as an indicator of stress. The mental stress induced significant increases in muscle activity ( p < .05) and in heart rate ( p < .05). In 12 out of 14 participants, one or more motor units were found to be active in mentally as well as in physically induced muscle contraction. The results indicate that mentally induced stress may contribute to keeping low threshold motor units active, even in the absence of physical demands. Considering the health risks of prolonged motor unit activity, it was concluded that lack of mental rest is an important risk factor for the development of muscular pain.

Type A behavior in healthy males and females as related to physiological reactivity and blood lipids.

&NA; Type A behavior was assessed in 30 men and 30 women (ages 30–50) by a Videotaped Structured Interview (VSI). Scores for total Type A behavior as well as subcomponents (competitiveness, time urgency, hostility) were examined in relation to cardiovascular and neuroendocrine reactivity during a work day (change from a work‐free day) and during laboratory‐induced stress (change from resting condition). In addition, Type A and Type B males and females were compared with regard to total serum cholesterol, LDL and HDL cholesterol, and triglycerides. The results showed relationships between 1) competitiveness/hostility and physiological reactivity at work in men, 2) total Type A behavior (and hostility) and serum cholesterol in men, and 3) hostility and serum cholesterol in women. As expected, the association between Type A behavior and physiological measurements was more pronounced for “extreme” Type A and B men and women (upper and lower 10 subjects, respectively) than for the total groups of each sex.

Psychophysiological stress reactions, trapezius muscle activity, and neck and shoulder pain among female cashiers before and after introduction of job rotation

The aim of this study was to evaluate the effects of the introduction of a job rotation model on supermarket cashiers, with respect to psychophysiological stress reactions, muscle activity of the trapezius muscle (which covers the upper back, the neck and the shoulder), and musculoskeletal symptoms in the neck and shoulders. Thirty-one female cashiers were investigated before and after job rotation was introduced. Before the reorganization the participants were only performing cash register work at the checkout counters. After the reorganization they shifted between cash register work and work in different departments in the supermarket. At follow-up the participants, all right-handed, had a significantly lower diastolic blood pressure, and surface electromyography (EMG) showed a significantly decreased muscle activity in the trapezius muscle on the left side. Musculoskeletal symptoms of the neck and shoulders were only partly changed, and there was no change in prevalence of musculoskeletal pain, which was around 70%. From questionnaires, but not from self-ratings during work, it was found that the introduction of job rotation had been experienced as positive in several regards, although the perceptions of stress and hurry were the same at follow-up.

Physiological deactivation after two contrasting tasks at a video display terminal: learning vs repetitive data entry .

Two contrasting 90 min VDT work situations were simulated in the laboratory: (1) a machine-paced, repetitive data entry task; and (2) a stimulating, self-paced learning task with successive feedback. Thirty non-smoking male students (20-34 years), without previous experience of VDT work, participated individually in each condition on two consecutive days (balanced order) and in a task-free baseline condition. Self-reports and successive measurements (ambulatory recordings) of systolic and diastolic blood pressure and heart rate were obtained during work and during a subsequent 60 min period of deactivation. Urine samples were obtained after each period for the determination of catecholamines and cortisol. In the baseline condition, measurements were obtained at corresponding times of the day. As expected, the data entry task was associated with self-reports of boredom, irritation, and unpleasantness; the learning task wtih alertness, interest, and ability to concentrate. Similar elevations of physiological measurements occurred in both work situations. However, differences between conditions were found after work. Following data entry, deactivation was slower in five of the six variables (significant for epinephrine).

Interference between work and outside-work demands relative to health: unwinding possibilities among full-time and part-time employees

Background: Demands from work and home may interfere with one another and the stress engendered by that can be detrimental to health. Purpose: To study the relationship between experienced interference and subjective health, and address the impact of unwinding on these associations. Method: Questionnaire data from a representative sample of the Swedish population are used considering full-time and part-time employed women and men aged 25–64. The associations between negative interference (either work-home or home-work) and sleep quality, self-rated health, and the use of sleeping pills/tranquillizers are analyzed by means of logistic regressions, compiling odds ratios (ORs) with 95% confidence intervals (CIs). The impact of adjustment for lack of unwinding on these associations is assessed. Results: Work-home interference is associated with suboptimal sleep quality and self-rated health for both women and men. The significance of this disappears among women after adjustment for lack of unwinding, regardless of work schedule. Among both sexes, home-work interference is associated with suboptimal sleep quality and self-rated health. When adjusting for lack of unwinding, the relationship to sleep quality disappears, but not the one to self-rated health, equally for women and men. Conclusion: Only among women, unwinding seems to buffer the association between work-home interference and health.

How Does Iq Affect Onset of Smoking and Cessation of Smoking—linking the Swedish 1969 Conscription Cohort to the Swedish Survey of Living Conditions

Objective: To examine the association between intelligence quotient (IQ) measured at ages 18 to 20 and onset of smoking, and the association between IQ and smoking cessation. Methods: Data on IQ, smoking, mental health, and social background among 49,321 Swedish men born 1949 to 51, collected at conscription for military service in 1969, were used. The association between IQ and smoking cessation was investigated among those 694 members of the full cohort also interviewed in the Swedish Level of Living Conditions study 1981 to 2002. Results: Lower IQ measured at ages 18 to 20 was weakly associated with increased prevalence of smoking, independently of indicators of mental illness and social misbehavior measured in late adolescence. By contrast, smoking cessation later in life among those who smoked at ages 18 to 20 was not associated with IQ. Among smokers, lower IQ was significantly associated with a lower level of smoking after adjusting for other factors. Conclusion: Low IQ was associated with an increased prevalence of smoking in adolescence. However, the main part of this association disappeared after adjustment for measures of mental health and social function in early life. IQ was not associated with likelihood of quitting smoking. IQ = intelligence quotient; CI = confidence interval; ICD-8 = International Classification of Diseases, 8th revision; ULF = Swedish Surveys of Living Conditions; OR = odds ratio.

Cognitive ability in adolescence and mortality in middle age—a prospective life course study

Background: An association between childhood cognitive ability measured by IQ tests and mortality has been reported recently. It is not clear from those studies to what extent the increased relative risk associated with lower IQ scores may be attenuated by adjustment for other risk factors. This study aims to investigate the association between cognitive ability measured at age 18–20 years and mortality among middle-aged men adjusting for risk factors for mortality over the life course. Methods: Data on cognitive ability, and other risk factors for premature mortality (indicators of mental health and social adjustment and behavioural factors), were collected among 49 321 men, born in 1949–51, at conscription for compulsory military training in 1969–70. Information on socioeconomic factors in childhood and adulthood, as well as information on mortality, was collected through national registers. Results: Cognitive ability showed an inverse and graded association with mortality between 40 and 53 years of age (1297 cases, crude hazard ratio (HR) 1.15, 95% CI 1.12 to 1.18, for one-point decrease on the nine-point IQ scale). Adjustment for indicators of social misbehaviour, mental health problems and behavioural risk factors, measured in late adolescence, and adult social circumstances strongly attenuated the increased risks of mortality, and it was no longer significantly increased (adjusted HR 1.02, 95% CI 0.99 to 1.06, for one-point decrease on the nine-point IQ scale). Conclusion: The association between IQ and mortality among men below 54 years of age was almost completely attenuated by adjustment for risk factors captured by our measures of achieved social positions.

Cognitive ability in early adulthood is associated with later suicide and suicide attempt: the role of risk factors over the life course.

BACKGROUND Cognitive ability/intelligence quotient (IQ) in youth has previously been associated with subsequent completed and attempted suicide, but little is known about the mechanisms underlying the associations. This study aims to assess the roles of various risk factors over the life course in explaining the observed relationships. METHOD The present investigation is a cohort study based on data on IQ test performance and covariates, recorded on 49 321 Swedish men conscripted in 1969-1970, at ages 18-20 years. Information on suicides and hospital admissions for suicide attempt up to the age of 57 years, childhood and adult socio-economic position, and adult family formation, was obtained from linkage to national registers. RESULTS Lower IQ was associated with increased risks of both suicide and suicide attempt during the 36 years of follow-up. The associations followed a dose-response pattern. They were attenuated by approximately 45% in models controlling for social background, mental ill-health, aspects of personality and behavior, adult socio-economic position and family formation. Based on one-unit decreases in IQ test performance on a nine-point scale, the hazard ratios between ages 35 and 57 years were: for suicide 1.19 [95% confidence interval (CI) 1.13-1.25], fully adjusted 1.10 (95% CI 1.04-1.18); and for suicide attempt 1.25 (95% CI 1.20-1.31), fully adjusted 1.14 (95% CI 1.09-1.20). CONCLUSIONS Cognitive ability was found to be associated with subsequent completed and attempted suicide. The associations were attenuated by 45% after controlling for risk factors measured over the life course. Psychiatric diagnosis, maladjustment and aspects of personality in young adulthood, and social circumstances in later adulthood, contributed in attenuating the associations.

Cognitive Ability in Late Adolescence and Disability Pension in Middle Age: Follow-Up of a National Cohort of Swedish Males

Low cognitive ability in late adolescence has previously been shown to be associated with disability pension (DP) in young adulthood. However, most DP’s are granted later in working life, and the mechanisms of the association are not fully understood. We aimed to investigate the association between cognitive ability in late adolescence and DP at ages 40-59, and investigate the role of individual and socioeconomic factors. Information on cognitive ability, health status, personality aspects and health behaviours at age 18-20 was obtained from the 1969-70 conscription cohort, comprising 49 321 Swedish men. Data on DP’s 1991-2008 was obtained from the Longitudinal Database of Education, Income and Employment. Information on socioeconomic and work-related factors in childhood and adulthood was obtained from national sociodemographic databases. Hazard ratios for DP during follow-up were estimated by Cox proportional hazards models. We found a graded relationship between cognitive ability in late adolescence and DP in middle age. One step decrease on the nine-point stanine scale of cognitive ability was associated with a crude hazard ratio of 1.26 (95 % CI 1.24-1.27). Socioeconomic and work-related circumstances in adulthood explained much of the association, but factors measured already in late adolescence also showed importance. The findings suggest an accumulation of risks over the life course. Although attenuated, the graded relationship remained after adjusting for all factors.

Neck/shoulder and back pain in new graduate nurses: A growth mixture modeling analysis

BACKGROUND Although it is well known that musculoskeletal disorders are common among registered nurses, little longitudinal research has been conducted to examine this problem from nursing education to working life. OBJECTIVES The aim was to investigate the prevalence and incidence of neck/shoulder and back pain in nursing students in their final semester, and one and two years after graduation. Furthermore, to identify common trajectories of neck/shoulder and back pain, and explore sociodemographic and lifestyle-related factors, contextual factors and health outcome that might be characteristic of individuals in the various trajectories. DESIGN Longitudinal study following nursing students from their final year of studies, with follow-ups one and two years after graduation. SETTINGS AND PARTICIPANTS Nursing students who graduated from the 26 universities providing undergraduate nursing education in Sweden 2002 were invited to participate (N=1700). Of those asked, 1153 gave their informed consent. METHODS The participants answered postal surveys at yearly intervals. Descriptive statistics were used to analyze prevalence and incidence of pain, and growth mixture modeling was applied to identify different homogeneous clusters of individuals following similar trajectories in pain development across time. RESULTS The prevalence of neck/shoulder and back pain remained constant over time (around 50% for neck/shoulder pain and just over 40% for back pain). Six different development trajectories for each symptom were found, reflecting patterns of stable pain levels or variation in levels over time: one symptom-free group, two decreasing pain groups, two increasing pain groups, and one chronic pain group. With few exceptions, the same factors (sex, children, chronic disease, working overtime, work absence, sickness presence, physical load, depression, self-rated health, sleep quality and muscular tension) were associated with neck/shoulder and back pain trajectories. Different types of physical load characterized new nurses with neck/shoulder pain and back pain respectively. CONCLUSIONS The high prevalence of pain among nursing students and among new graduate nurses, suggests that it would be effective to implement preventive strategies already during nursing education, but they should also preferably continue after graduation. Many factors associated with pain in the neck/shoulder and back seem to be modifiable, and thereby constitute targets for preventive strategies.