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Biomedical subjects

S Knardahl

Publications and source records attributed to S Knardahl.

At least 19 recordsLinked to original sources
PubMed2005

Long-term repeatability of force, endurance time and muscle activity during isometric contractions.

We determined the repeatability and correlations between force, endurance and muscle activity during isometric contractions over three years. Twenty-six subjects, with and without complaints of the shoulder and neck, performed standardized maximal and submaximal shoulder-abduction contractions and wrist extension-contractions at yearly intervals from 1997 to 1999. Peak forces developed during maximal contraction and the endurance times of submaximal contractions during shoulder abduction and wrist extension were measured. Electromyography (EMG) of muscle activity was recorded bilaterally from the upper trapezius, middle deltoid, and forearm extensor muscles. Root mean square EMG amplitudes were calculated. We found statistically significant associations between peak forces developed during wrist extension and shoulder abduction, and between endurance times of submaximal wrist extension and shoulder abduction. No statistically significant changes in peak force and EMG(peak) were found over the measurement years. The responses were not statistically significantly influenced by gender, or neck and shoulder pain. However, we observed considerable intra-individual variation in the inter-year measurements particularly for the responses to submaximal contraction. Such large variations represent a challenge when attempting to use the responses to interpret the effects of therapies.

Adult↗
PubMed2005

Improved insulin-stimulated glucose uptake and glycogen synthase activation in rat skeletal muscles after adrenaline infusion: role of glycogen content and PKB phosphorylation.

AIM: Effects of in vivo adrenaline infusion on subsequent insulin-stimulated glucose uptake and glycogen synthase activation was investigated in slow-twitch (soleus) and fast-twitch (epitrochlearis) muscles. Furthermore, role of glycogen content and Protein kinase B (PKB) phosphorylation for modulation insulin sensitivity was investigated. METHODS: Male Wistar rats received adrenaline from osmotic mini pumps ( approximately 150 microg kg(-1) h(-1)) for 1 or 12 days before muscles were removed for in vitro studies. RESULTS: Glucose uptake at physiological insulin concentration was elevated in both muscles after 1 and 12 days of adrenaline infusion. Insulin-stimulated glycogen synthase activation was also improved in both muscles. This elevated insulin sensitivity occurred despite the muscles were exposed to hyperglycaemia in vivo. After 1 day of adrenaline infusion, glycogen content was reduced in both muscles; insulin-stimulated PKB ser(473) phosphorylation was increased in both muscles only at the highest insulin concentration. After 12 days of adrenaline infusion, glycogen remained low in epitrochlearis, but returned to normal level in soleus; insulin-stimulated PKB phosphorylation was normal in both muscles. CONCLUSION: Insulin-stimulated glucose uptake and glycogen synthase activation were increased after adrenaline infusion. Increased insulin-stimulated glucose uptake and glycogen synthase activation after adrenaline infusion cannot be explained by a reduction in glycogen content or an increase in PKB phosphorylation. The mechanisms for the improved insulin sensitivity after adrenaline treatment deserve particular attention as they occur in conjunction with hyperglycaemia.

Animals↗
PubMed2004

Work factors as predictors of intense or disabling low back pain; a prospective study of nurses' aides.

AIMS: To identify the work factors that predict intense low back pain (LBP) and LBP related sick leaves in nurses' aides. METHODS: The sample comprised 4266 randomly selected Norwegian nurses' aides, not bothered or only a little bothered by LBP during the previous three months, and not on sick leave when completing a mailed questionnaire in 1999. Of these, 3808 (89.3%) completed a second questionnaire 3 months later and 3651 (85.6%) completed a third questionnaire 15 months later. Intensity of low back symptoms and certified sick leaves attributed to LBP during the observation period were assessed by self reports at the follow ups. RESULTS: After adjustments for LBP during the three months prior to baseline, baseline health complaints, demographic and familial factors, and a series of physical, psychological, and social work factors, logistic regression analyses revealed the following associations: intense low back symptoms were predicted by frequent positioning of patients in bed, perceived lack of support from immediate superior, and perceived lack of pleasant and relaxing culture in the work unit. LBP related sick leaves were predicted by frequent handling of heavy objects, medium level of work demands, perceived lack of supportive and encouraging culture in the work unit, working night shifts, and working in a nursing home. Long term LBP related sick leaves were associated with changes of work or work tasks during the observation period that resulted in a perceived reduction of support and encouragement at work. CONCLUSIONS: Not only frequent mechanical exposures, but also organisational, psychological, and social work factors, such as night shift work, perceived lack of support from superior, and perceived lack of a pleasant and relaxing or supporting and encouraging culture in the work unit, are associated with an increased risk of intense low back symptoms and LBP related sick leaves in nurses' aides.

Adult↗
PubMed2004

Work factors as predictors of sickness absence attributed to airway infections; a three month prospective study of nurses' aides.

AIMS: To identify the work factors that are related to sickness absence attributed to airway infections (AAI) in nurses' aides. METHODS: The sample comprised 5563 Norwegian nurses' aides, not on sick leave when they completed a mailed questionnaire in 1999. Of these, 4931 (88.6%) completed a second questionnaire three months later. The outcome measure was the three month incidence proportion of certified AAI (>3 days), assessed by self reports at follow up. RESULTS: Working in a paediatric ward (odds ratio (OR) 2.42; 95% confidence interval (CI) 1.39 to 4.21), perceived lack of encouraging and supportive culture in the work unit (OR 1.78; 95% CI 1.21 to 2.61), and reporting medium (OR 1.52; 95% CI 1.09 to 2.12), and high levels (OR 1.60; 95% CI 1.13 to 2.26) of role conflicts at work were associated with an increased risk of AAI, after adjustments for baseline health complaints, demographic and familial factors, smoking, and a series of physical, psychological, and organisational work factors. The individual level factors male gender, smoking 10 cigarettes per day or more, having widespread pain, having had an accident related neck injury, and having long term health problems also predicted AAI. CONCLUSIONS: In nurses' aides, sickness absence attributed to airway infections seems to be related to the type of ward in which the aides are working, and to psychological and social work factors. Declaring airway infections as occupational diseases would have important consequences for the social security system.

Absenteeism↗
PubMed2003

Sympathetic nerve activity does not reduce proprioceptive acuity in humans.

AIM: Proprioception is essential in coordinating body segments and controlling muscles to perform movements. Animal studies have reported reduced muscle spindle sensitivity in jaw muscles during stimulation of sympathetic nerves. A stress-induced distortion of proprioception has been suggested that could lead to reduced fine control of movement and inefficient muscle use. The present study investigated whether increased muscle sympathetic activation alter human proprioception. METHOD: Movement detection thresholds of the right ankle were determined in eight healthy subjects, before and during two conditions known to increase muscle sympathetic activity (MSA); a cold pressor test (CPT) and oral glucose ingestion (GLUC). RESULTS: During a cold pressor test plasma noradrenaline (NA) and mean arterial pressure (MAP) increased significantly, compared with baseline (Ps<0.01), whereas the movement thresholds were unchanged (Ps>>0.05). After GLUC plasma NA and MAP increased significantly, compared with baseline (Ps<0.05). The movement threshold into flexion decreased (P=0.022), whereas into extension there was no change (P=0.28). The most prominent increase of plasma NA corresponded with a reduced movement detection threshold, suggesting increased muscle spindle sensitivity. CONCLUSION: The present findings contradict previous reports from animal studies and the hypothesis that sympathetic nerve activity reduces proprioceptive acuity.

Adult↗
PubMed2003

Work factors as predictors of sickness absence: a three month prospective study of nurses' aides.

AIMS: To identify the work factors that predict sickness absence in nurses' aides. METHODS: The sample comprised 5563 Norwegian nurses' aides, not on leave because of illness or pregnancy when they completed a mailed questionnaire in 1999. Of these, 4931 (88.6%) completed a second questionnaire three months later. The outcome measure was the three month incidence proportion of certified sickness absence (>3 days), as assessed by self reports at follow up. RESULTS: Perceived lack of encouraging and supportive culture in the work unit (odds ratio (OR) 1.73; 95% confidence interval (CI) 1.28 to 2.34), working in psychiatric and paediatric wards, having injured the neck in an accident, and health complaints were associated with higher risk of sickness absence, after adjustments for a series of physical, psychological, and organisational work factors, personal engagement in the work unit, demographic characteristics, and daily consumption of cigarettes. Having untraditional jobs (for nurses' aides) (OR 0.53; 95% CI 0.36 to 0.77), and engaging in aerobics or gym were associated with a lower risk of sickness absence. CONCLUSIONS: The study suggests that the three month effects of work factors on rates of certified sickness absence are modest in nurses' aides. The most important work factor, in terms of predicting sickness absence, seems to be perceived lack of encouraging and supportive culture in the work unit.

Adult↗
PubMed2001

Cognitive performance and muscle activation in workers with chronic shoulder myalgia.

The present study determined whether workers with chronic shoulder myalgia exhibit impaired cognitive performance and elevated muscle activation. Ten workers with and 10 without shoulder myalgia performed three sessions, each consisting of three different cognitive tasks. Subjective pain was reported on visual analogue scales (VAS). Surface electromyography was recorded bilaterally from the trapezius and forearm extensor muscles. Speed and error rates of the cognitive work were almost the same in the two groups, but the myalgia subjects reported more stress during the work. In two of the cognitive tasks, both groups increased their speed of performance to the same extent from the first to the third session, despite pain increase in the myalgia subjects. In the biomechanically demanding task, the speed fell from the first to the third session in both groups. Muscle activation was equal in the two groups and constant throughout the protocol despite changes in speed of performance and pain. It is concluded that localized chronic muscle pain does not significantly alter cognitive performance, or muscle activation level during cognitive work. However, the perceived burden of work is larger, as indicated by the higher stress reported during cognitive work in the myalgia subjects compared with their pain-free controls.

Chronic Disease↗
PubMed2000

No difference in the lipolytic response to beta-adrenoceptor stimulation in situ but a delayed increase in adipose tissue blood flow in moderately obese compared with lean men in the postexercise period.

This study was undertaken to determine the effect of previous exercise on adipose tissue responsiveness to beta-adrenoceptor stimulation and on adipose tissue blood flow (ATBF). Eight lean and 8 obese men (body mass index [BMI], 23.6 +/- 2.1 [SD] v 29.0 +/- 1.9 kg x m(-2)) were investigated with abdominal subcutaneous microdialysis and 133Xe clearance. A stepwise isoprenaline infusion (10(-8), 10(-7), and 10(-6) mol x L(-1)) was administered in situ in the microdialysis catheter before and 2 hours after a submaximal exercise bout (90 minutes of cycling at 55% of maximal O2 uptake). No differences in the response (increase in interstitial glycerol v preinfusion level) to isoprenaline infusions were found between the 2 groups. In both groups, there was no difference in the response to postexercise versus preexercise infusion. When the vasodilating agent hydralazine (0.125 g x L(-1)) was infused into the microdialysis catheter to control for the vascular effects of isoprenaline, an interaction effect between exercise and isoprenaline dose was found. Analyses showed an attenuated response to the high isoprenaline dose after exercise (lean, 251 +/- 42 [SE] micromol x L(-1); obese, 288 +/- 77 micromol x L(-1)) versus before exercise (lean, 352 +/- 62 micromol x L(-1), P = .045 v after; obese, 380 +/- 94 micromol x L(-1), P = .021 v after), indicating a desensitization of lipolysis to beta-adrenoceptor stimulation. ATBF and arterial plasma glycerol increased after exercise in both groups, but the increase was delayed in obese subjects. Arterial plasma insulin was higher in the obese versus lean subjects at all times, and decreased during recovery in both groups. In conclusion, abdominal subcutaneous adipose tissue responsiveness to beta-stimulation is not enhanced postexercise in lean and obese men, whereas previous exercise increases ATBF. Furthermore, the data suggest slower lipid mobilization postexercise and resistance to the antilipolytic effect of insulin in the obese.

Adipose Tissue↗
PubMed2000

Cardiovascular psychophysiology.

Both environmental and predispositional factors are of importance in the pathogenesis of cardiovascular (CV) disease. In humans, it is difficult to characterize the pathogenic environmental factors (exposures) because of the long time-span of pathogenesis. Perceived effort, control, social isolation, and absence of reward seem to increase the risk of CV diseases. It is methodologically easier to measure predispositional factors at one point in time and then record disease after some years; and there are several reports of associations between personality traits or behaviour patterns and CV disease. Recent psychophysiological research has focused on CV hyper-reactivity to challenge. Hyperreactivity seems to be common in the offspring of hypertensives. This relation may be psychophysiological rather than physiological. Several questions remain regarding the validity and reliability of the hyper-reactivity construct. Studies of social hierarchies in animals have shown that social interactions produce pronounced psychophysiological responses. The existence of several differentiated CV response patterns may explain the contradictory findings of studies that only measure one or few physiological parameters. Predisposition to behaviours and reactivity of physiological systems may be accentuated by dominance-subordinate interactions. The availability of control and the perception of mastery is crucial in terminating responding to stressors. The presence of relatively constant response patterns to social interactions suggests that social interactions must be taken into account. Focus of CV psychophysiology should shift to studies of behavioural and somatic responses during social interactions.

Animals↗
PubMed1999

The influence of experimental muscle pain on the human soleus stretch reflex during sitting and walking.

OBJECTIVES: The stretch reflex is functionally important during human locomotion. Muscle pain has been found to increase the stretch reflex amplitude during sitting, possibly due to an altered fusimotor drive. To further study the importance of altered fusimotor activity due to muscle pain we investigated the combined effect of muscle pain and motor task on the soleus stretch reflex. METHODS: Stretch reflexes were elicited before, during and after experimentally induced muscle pain in soleus (i.m. infusion of 6% saline) in 3 experiments: (1) in the relaxed soleus muscle and before, during and after an isometric ramp contraction (500 ms, 0-10 Nm), (2) at 3 different time periods during walking, and (3) at matched pain intensity and soleus activity during sitting and walking. RESULTS: Infusion of hypertonic saline into the soleus muscle caused a significant facilitated stretch reflex in the relaxed muscle (P<0.01), but not during walking or during sitting and walking at matched soleus EMG and matched pain levels. The infusion of isotonic saline (non-painful) did not cause any changes (P = 0.75). CONCLUSIONS: The main findings of the present study were that experimental muscle pain facilitated the stretch reflex during pain in the relaxed muscle, but caused no changes in stretch reflex amplitude during sitting and walking at higher "functional" background EMG levels.

Adolescent↗
PubMed1999

Short-term effects of exercise on plasma very low density lipoproteins (VLDL) and fatty acids.

PURPOSE: In the fasted state the lipid fuels for muscle metabolism are free fatty acids (FFA) released either from intramuscular triglycerides (TG), plasma albumin, or TG in circulating very low density lipoproteins (VLDL). The purposes of this study were to determine the influence of acute exercise of moderate intensity on 1) plasma total concentration of TG and VLDL components, 2) the plasma concentration and distribution of individual albumin-bound long-chain FFA, and 3) lipid peroxidation as measured by thiobarbituric acid reactive substances (TBARS). METHODS: Eight healthy male subjects each participated in one exercise (EX) and one rest (RE) experiment. In EX the subjects exercised for 90 min at 58+/-5% (mean +/- SD) of maximal O2 uptake on a cycle ergometer followed by 4.5 h bedrest. RE followed the same protocol, but without exercise. RESULTS: In EX there was no immediate change in VLDL concentration during the exercise. After exercise there was a decrease in VLDL, VLDL-TG, -cholesterol, -protein and -phospholipids compared with those after RE. There was no change in percentage composition of VLDL as result of exercise. Total plasma FFA concentration increased appreciably during exercise and remained elevated for several hours postexercise. There was no correlation between the change in FFA concentration and VLDL-TG. There was a significant positive correlation between the exercise-related increments in the various long-chain FFA, but the effect varied so that the relative abundance of oleic acid increased and that of stearic and arachidonic acid decreased during exercise. Plasma TBARS concentration increased during the day in both experiments. CONCLUSION: The results indicate that there is a delay in the effect of an exercise bout on plasma VLDL and confirm that exercise affects various FFA in plasma differentially.

Adult↗
PubMed1999

Job characteristics as predictors of neck pain. A 4-year prospective study.

Data from a community-based 4-year prospective study were used to investigate job characteristics as predictors of neck pain. Of 1791 working responders who completed a questionnaire in 1990, 1429 (79.8%) returned a second questionnaire 4 years later (1994). In responders without neck pain during the previous 12 months in 1990, the "little influence on own work situation" factor predicted neck pain during the previous 12 months (odds ratio = 2.21; 95% confidence interval, 1.18 to 4.14) and previous 7 days in 1994 (OR = 2.85; 95% confidence interval, 1.21 to 6.73) after adjustment for a series of potential confounders. In responders with neck pain in 1990, the little influence on own work situation factor was associated with persistent neck pain 4 years later. The study indicates that having little influence on one's own work situation is a predictor of neck pain.

Adult↗
PubMed1999

Chronic carbon monoxide exposure in vivo induces myocardial endothelin-1 expression and hypertrophy in rat.

Smoking is associated with endothelial dysfunction and increased plasma levels of endothelin-1. The component of tobacco smoke inducing these effects is unknown. Carbon monoxide induces hypoxia, and there is evidence of carbon monoxide acting as a local mediator in both endothelial and smooth muscle cells. The purpose of this study was to determine whether chronic carbon monoxide exposure similar to that experienced by smokers affects myocardial endothelin-1 expression. Sprague-Dawley female rats were exposed to carbon monoxide 100 ppm for one week or to 100 ppm for one week and 200 ppm for a second week. Carboxyhaemoglobin was 12+/-0.9% in the low and 23+/-1.1% in the high carbon monoxide exposure group. Endothelin-1 expression was measured by competitive reverse transcriptase polymerase chain reaction. High carbon monoxide exposure increased endothelin-1 mRNA by 54+/-12% (P<0.001) in the left ventricle and by 53+/-12% (P<0.001) in the right ventricle. In the low carbon monoxide exposure group corresponding changes were 43+/-14% (P=0.06) and 12+/-16%(P=0.29). Right ventricular weight increased by 18+/-7% (P=0.02) after high and by 16+/-5% (P=0.02) after low exposure. Left ventricular weight was elevated by 5+/-2% (P=0.05) when both exposure groups were compared to controls. We conclude that chronic carbon monoxide exposure leading to carboxyhaemoglobin levels similar to those observed in smokers increases endothelin-1 gene expression and induces myocardial hypertrophy in the rat.

Animals↗
PubMed1998

Effect of beta-adrenoceptor blockade on postexercise oxygen consumption and triglyceride/fatty acid cycling.

In the recovery period after strenuous exercise, there is increased O2 uptake, termed the excess postexercise O2 consumption (EPOC). One of the mechanisms suggested to explain EPOC is activation of the triglyceride/fatty acid (TG/FA) cycle by catecholamines. The purpose of this study was to determine the effect of selective beta1- and nonselective beta-adrenoceptor blockade on EPOC and the TG/FA cycle. Seven healthy young men each participated in three control and three exercise experiments in a randomized and balanced sequence. In the exercise experiments, subjects exercised for 90 minutes at 58% +/- 2% (mean +/- SD) of maximal O2 uptake on a cycle ergometer, followed by a 4.5-hour bedrest. The control experiments followed the same protocol, but without exercise. In one control and one exercise experiment, the selective beta1-adrenoceptor antagonist atenolol (0.062 mg.kg(-1) body weight) was administered intravenously immediately after the exercise (EXAT) and at the corresponding time in the rest-control experiment (REAT). In a second set of control and exercise experiments, the nonselective beta-adrenoceptor antagonist propranolol (0.15 mg.kg(-1) body weight) was administered (REPRO and EXPRO). In a third set of rest and exercise experiments, an injection of saline was given instead of beta-antagonist (RE and EX). TG/FA cycling was calculated by combining results obtained with a two-stage glycerol infusion and indirect calorimetry. O2 uptake was significantly increased above control levels throughout the recovery period after exercise with the nonselective beta-adrenoceptor antagonist, beta1-adrenoceptor antagonist, and saline. However, there was no difference between the time course or magnitude of EPOC in the three situations. After 4.5 hours of bedrest, the mean increase in O2 uptake was 8% to 9% in all three conditions. TG/FA cycling was increased after exercise, but no effects of beta-antagonists were observed. We conclude that EPOC and the rate of TG/FA cycling are not attenuated by selective beta1- or nonselective beta-adrenoceptor blockade after an acute prolonged exercise protocol.

Adrenergic beta-Antagonists↗
PubMed1998

Effect of beta-adrenoceptor stimulation on oxygen consumption and triglyceride/fatty acid cycling after exercise.

The purpose of this study was to characterize the effects of prolonged beta-adrenoceptor stimulation on O2 uptake and triglyceride/fatty acid (TG/FA) cycling during rest with and without previous exercise. Eight men performed two exercise (90 min cycling at 56 +/- 3 (SD)% of maximal O2 uptake, followed by 4.5 h bed rest) and two rest-control experiments. In one rest and one exercise experiment a bolus dose (5 micrograms) of the beta-adrenoceptor agonist isoprenaline was given immediately after exercise, followed by a continuous infusion (20 ng kg-1 min-1), and at the corresponding time in the rest experiment. In the other experiments saline was given instead. The O2 uptake increased in the post-exercise period both with and without beta-stimulation. The total excess post-exercise oxygen consumption (EPOC) was not different between saline (8.1 +/- 1.8 (SE) L) and isoprenaline administration (10.8 +/- 1.8 L, P = 0.40). Also, the total accumulated increase in O2 uptake for the 4.5 h period after isoprenaline infusion was not different between the rest (12.5 +/- 2.0 L) and the exercise experiments (15.2 +/- 1.7 L, P = 0.40). The rate of TG/FA cycling increased after both exercise and isoprenaline treatment, but no interaction effect was found. In conclusion, the increases observed in O2 uptake and the rate of TG/FA cycling during beta-adrenoceptor stimulation were not increased by a previous exercise bout.

Adrenergic beta-Agonists↗
PubMed1998

Adrenergic control of post-exercise metabolism.

After strenuous exercise there is a sustained increase in resting O2 consumption. The magnitude and duration of the excess post-exercise O2 consumption (EPOC) is a function of exercise intensity and exercise duration. Some of the mechanisms underlying the rapid EPOC component (<1 h) are well defined, while the mechanisms causing the prolonged EPOC component (>1 h) are not fully understood. It has been suggested that beta-adrenergic stimulation is of importance for the prolonged component. There is an increased level of plasma adrenaline and noradrenaline during exercise, and it is shown that catecholamines stimulate energy expenditure through beta-adrenoceptors. After exercise an increased fat oxidation and an increased rate of triglyceride fatty acid (TG-FA) cycling may account for a significant part of the prolonged EPOC component. These processes may be stimulated by catecholamines. However, the return of plasma concentration of catecholamines to resting levels after exercise is more rapid than the return of O2 uptake. But plasma concentration of catecholamines may be an insensitive indicator of sympathetic activity, since the clearance rate of catecholamines is high. Also, the sensitivity to catecholamines may be increased after exercise. A decreased post-exercise O2 uptake has been shown when beta-blockade is administered in dogs before the exercise bout. In a pilot study in humans, administration of beta-antagonist after exercise did not seem to change EPOC.

Animals↗
PubMed1996

Low-dose hypertonic saline (NaCl 8.0%) treatment of uncontrolled abdominal hemorrhage: effects on arterial versus venous injury.

The present study compared hemodynamic response to hypertonic saline (HTS; NaCl 8.0%) treatment of uncontrolled hemorrhage from a stab injury in the abdominal aorta (A) or vena cava (V), respectively. The hypothesis was challenged that adverse effects of HTS treatment is dependent on the pressure load in the lesioned vessel. Uncontrolled hemorrhage was produced in anesthetized rats by vessel puncture with a syringe needle. After 10 min of hemorrhage, subjects were randomized to HTS infusion, 2.0 mL/kg i.v. given at .4 mL/min (AHTS, n = 10 and VHTS, n = 10), or to no treatment (AC, n = 12 and VC, n = 7). mean arterial pressure (MAP), heart rate, plasma electrolytes, protein, and hematocrit were recorded continuously for 240 min. HTS treatment produced MAP elevation but did not influence the final outcome in either A or V lesions. Thus, evidence of worsened outcome related to HTS treatment was not confirmed. However, one-half of all subjects with arterial hemorrhage died, compared to only 1 of 17 subjects with venous hemorrhage. Spontaneous MAP recovery during hemorrhage, and MAP response to HTS treatment, were shown to have predictive value for survival.

Abdomen↗