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Biomedical subjects

G Sjøgaard

Publications and source records attributed to G Sjøgaard.

At least 55 records · Page 3Linked to original sources
PubMed1995

Intramuscular laser-Doppler flowmetry in the supraspinatus muscle during isometric contractions.

To study the regulation of microvascular blood flow in a compartment muscle, laser-Doppler measurements of muscle microcirculation were recorded in the supraspinatus muscle in eight volunteers during and following submaximal isometric muscle contractions. The subjects performed isometric shoulder abductions at five contraction levels from 5% to 50% maximal voluntary contraction for 1 min each and a sustained 30 degrees shoulder abduction for 20 min. The subjects' perceived exertion increased from "no perceived exertion" to "near maximal exertion" during the 20-min period with 30 degrees shoulder abduction. Microcirculation increased during all 1-min contractions. Following the contractions at 20%, 30% and 50% MVC post-exercise reactive hyperaemia was seen for a period of at least 1 min. The reactive hyperaemia increased in magnitude in response to increasing contraction level. The results showed the same time-history of the blood flow at microvascular level as previously seen in larger peripheral vessels in response to muscle contractions. During the 20-min contraction microcirculation increased in line with the findings during the brief contractions. However, in contrast to the brief contractions no postexercise reactive hyperaemia occurred following the prolonged contraction. Lack of postexercise reactive hyperaemia following the prolonged shoulder abduction would suggest insufficient regulation of the vascular resistance. Alternatively, lack of hyperaemia could be taken as an indication of sufficient microcirculation during the preceding contraction. From previous studies on intramuscular pressure and metabolism the latter alternative would seem unlikely.

Adult↗
PubMed1995

A national cross-sectional study in the Danish wood and furniture industry on working postures and manual materials handling.

Musculoskeletal disorders constitute a major problem in the wood and furniture industry and identification of risk factors is needed urgently. Therefore, exposures to different work tasks and variation in the job were recorded based on an observation survey in combination with an interview among 281 employees working in wood working and painting departments. A questionnaire survey confirmed high frequencies of symptoms from the musculoskeletal system: The one-year prevalence of symptoms from the low back was 42% and symptoms from the neck/shoulder was 40%. The exposure was evaluated based on: (1) classification of work tasks, (2) work cycle time, (3) manual materials handling, (4) working postures, and (5) variation in the job. Among the employees 47% performed feeding or clearing of machines, 35% performed wood working or painting materials, and 18% performed various other operations. Among the employees 20% had no variation in their job while 44% had little variation. Manual materials handling of 375 different burdens was observed, which most often occurred during feeding or clearing of machines. The weight of burdens lifted was 0.5-87.0 kg, where 2% had a weight of more than 50 kg. Among the lifting conditions 30% were evaluated as implying a risk of injury. An additional risk factor was the high total tonnage lifted per day, which was estimated to range from 132 kg to 58,800 kg. Working postures implied a risk of injury due to prolonged forward and lateral flexions of the neck, which was seen most frequently during wood working or painting materials. These data substantiate the finding that work tasks mainly during feeding or clearing of machines imply a risk of injury to the low back and a risk of injury to the neck and shoulder area mainly during wood working or painting materials. Optimal strategies for job redesign may be worked out by using these data in order to prevent occupational musculoskeletal disorders.

Adolescent↗
PubMed1995

Bone-on-bone forces during loaded and unloaded walking.

Joint moments and bone-on-bone forces in the ankle, knee and hip joint were studied in 7 healthy male subjects during unloaded and loaded walking. The subjects walked across a force platform while they were filmed at 200 Hz. Loaded walking was examined at 10 and 20 kg load carried symmetrically in the hands. Peak joint moments and peak bone-on-bone forces increased from unloaded to loaded walking for the ankle and hip joint (p < 0.05). The lowest bone-on-bone forces were found at the ankle joint (3,318 +/- 390 N) during unloaded walking and the highest at the hip joint (6,399 +/- 1,517 N) during 20 kg loading. Expressed relative to body weight (BW) these values corresponded to 4.2 +/- 0.50 and 8.0 +/- 1.78 BW). However, the individual values showed that 2 of the 7 subjects differed remarkably from the other 5, especially with respect to the hip joint loadings. During loaded walking (20 kg) these 2 subjects showed 14.4 and 15.1 BW peak compression force in the hip joint while the remaining subjects were all below 6.3 BW, which could be explained by the 2 subjects' low ankle joint moments and higher knee and hip joint moments. Apparently, a total 'leg moment' formed by the three major joints is required to support the body and maintain the locomotion, although the relative contribution from each joint can differ among individuals. The peak joint moments were the most dominant contributor to the peak bone-on-bone forces. Therefore, it is concluded that interindividual differences in walking style can lead to pronounced differences in peak bone-on-bone forces. It remains unclear how these interindividual differences are related to joint degradation.

Adult↗
PubMed1995

Musculoskeletal symptoms among sewing machine operators.

OBJECTIVES: A longitudinal study was conducted to describe the prevalences and development of musculoskeletal symptoms among sewing machine operators in relation to age and exposure and among former sewing machine operators who changed exposure by changing occupation. METHODS: Musculoskeletal symptoms were assessed among 327 sewing machine operators in 1985 with the use of the standardized Nordic questionnaire. A follow-up study in 1991 showed that approximately one-third was still working as a sewing machine operator, one-third had changed occupation, and the rest were out of employment. The exposure was assessed by a questionnaire regarding the type of machine being operated, work organization, workplace design, units produced per day, and payment system. RESULTS: High prevalences of musculoskeletal symptoms of the neck and shoulders were found, with some associations to exposure variables such as efficiency. Initially symptom-free sewing machine operators were not at a higher risk of developing symptoms when they continued sewing during the six-year follow-up when compared with those who changed to other employment. However, symptomatic sewing machine operators who quit sewing were much more likely to be relieved of their symptoms than were symptomatic operators who continued sewing, odds ratio 3.26 [95% confidence interval (95% CI) 1.38-7.72] for 12-month symptoms and odds ratio 3.90 (95% CI 1.28-11.90) for 7-day symptoms. This trend also applied to long-lasting symptoms. CONCLUSIONS: The results demonstrate that, for many sewing machine operators, neck and shoulder symptoms are reversible and may be influenced by reallocation to other worktasks.

Adolescent↗
PubMed1995

Soft tissue architecture and intramuscular pressure in the shoulder region.

Soft tissue architecture including muscle insertions were studied in the shoulder region by dissecting three male cadavers. These dissections demonstrated that m. supraspinatus and mm. infraspinatus/teres minor were located in two separate, closed compartments limited by bony walls and tense stiff fascia. M. supraspinatus was composed of two parts which differed with respect to attachment site, fibre orientation, and muscle structure although they were similar with respect to muscle fibre length. Muscle structure, fascia and insertion sites should be taken into account in biomechanical modeling of the shoulder. Intramuscular pressures in the shoulder muscles were recorded in healthy females during voluntary isometric contractions performed in various arm positions, and at different contraction levels and measuring depths. Intramuscular pressure in m. supraspinatus during 30 degrees shoulder abduction: 58 (33-70) mmHg, exceeded the intramuscular pressure during 30 degrees flexion: 29 (7-40) mmHg. In m. infraspinatus lower values were registered. A simple relation between intramuscular pressure and measuring depth did not exist in the soft tissue above fossa supraspinata. During contractions a steep increase in intramuscular pressure was seen at a depth corresponding to the transition from m. trapezius to m. supraspinatus. The intramuscular pressure measurements showed wide regional heterogeneity at the same measuring depth during contractions, which is likely to be due to the complex anatomy found in this region. The results show the significance of the anatomy for the increase in intramuscular pressure during contractions. This in turn may impair muscle blood flow and thus affect muscle function over prolonged periods of time.

Aged↗
PubMed1994

The effect of prolonged isometric contractions on muscle fluid balance.

Ultrasound scanning was performed at three sites above the fossa supraspinata on nine healthy subjects and five patients with myofascial shoulder pain. This method produced a well-defined depiction of the soft tissue layers above the fossa supraspinata and reproducible muscle thickness measurements. In the healthy subjects the average distance from the skin surface to the trapezius muscle was 7.7 mm and the average thickness of the trapezius muscle was 5.3 mm, and the average thickness of supraspinatus muscle was 20.0 mm. The supraspinatus muscle was thinner at the medial measuring site than at the other two sites. In contrast, a tendency towards a larger distance was seen from the skin to trapezius muscle at the medial measuring site than at the other two sites. No statistical differences were found between the two groups of subjects either at rest or during brief shoulder abductions. All the subjects performed a 30 degrees unilateral isometric shoulder abduction test to exhaustion. The median endurance time was 33 min for the healthy subjects and only 5 min for the patients. The ratings of perceived exertion (RPE) were in line with this, since the increment in RPE with time was larger for the patients than for the healthy group. The reduced shoulder abduction endurance time in the patient group may have been related to impaired muscle function and/or pain development. During the 33-min shoulder abduction in the healthy subjects, the thickness of supraspinatus muscle increased by 14%, indicating muscle swelling, whereas the thickness of trapezius muscle remained constant.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Shoulder muscle load and muscle fatigue among industrial sewing-machine operators.

Physiological responses to physical work were assessed for 29 female industrial sewing-machine operators during an 8-h working day under ordinary working conditions. During sewing-machine work, the average (left and right) static load in the trapezius muscle was 9% of the maximal electromyogram (EMG) amplitude (% EMGmax), while the average mean load was 15% EMGmax, and the average peak load was 23% EMGmax. The static load level was unrelated to the muscle strength of the sewing-machine operators, which for the group as a whole was within the normal range. The load levels remained unchanged during the working day, while changes in the EMG mean power frequency and zero crossing frequency rate occurred, both indicating the development of muscle fatigue in left and right trapezius muscle during the working day. In line with this, the rating of perceived exertion in the shoulder and neck region increased during the working day. Dividing the group of sewing-machine operators into two groups, those with the highest frequency and those with the lowest frequency of shoulder/neck troubles showed that the former group had significantly lower muscle strength, despite the fact that no differences in the surface EMG during sewing were found between the two groups. It was concluded that industrial sewing-machine work involves a pattern of shoulder muscle activity which induces fatiguing processes in the shoulder and neck regions. Furthermore, since the static shoulder muscle load was independent of muscle strength, factors other than working posture may be of significance for the static shoulder muscle load.

Adult↗
PubMed1993

Plasma potassium concentration and doppler blood flow during and following submaximal handgrip contractions.

The aim of the present study was to investigate the time-course of blood velocity in the forearm during and following isometric handgrip contractions and to reveal a possible temporal relationship between the circulatory response and venous effluent potassium concentration ([K]) not only during contractions but also during the post-exercise recovery period. Contractions of 15% maximal voluntary contraction (MVC) and 30% MVC with and without 3 min of arterial occlusion following the contractions were studied. All contractions induced a significant increase in venous plasma [K] from an average resting level of 4.0 to 5.0 mM during 15% MVC and 5.8 mM during 30% MVC. Blood velocity increased from a resting level of 0.07 to 0.22 m s-1 and 0.36 m s-1 during 15% and 30% MVC, respectively. MVC of 30% always elicited a larger blood velocity and [K] response than 15% MVC. Following the contractions hyperaemia was elicited. Recovery of the local blood velocity was markedly slower than the K recovery, since [K] remained significantly above resting level for only 25 s following 15% MVC and 45 s following 30% MVC, while blood velocity remained elevated for 2 min and more than 7 min following 15 and 30% MVC, respectively. Further, a larger hyperaemia following the occlusion was elicited as compared to the contraction without occlusion, in spite of [K] being lower immediately after the occlusion period than immediately after the contraction. Finally, [K] decreased below resting level in the recovery period while the blood velocity remained elevated. Therefore, the present study showed that the venous plasma [K] is not causally related to the prolonged post-exercise hyperaemia. The skin temperature remained unchanged during the contractions, while during the recovery period the skin temperature increased for several minutes. The major part of the temperature increase was likely to be due to conductance of heart from muscles to skin surface as a consequence of muscle hyperaemia.

Adult↗
PubMed1992

Role of potassium in the reflex regulation of blood pressure during static exercise in man.

1. The relationship between [K+] in venous effluent blood and alterations in mean arterial blood pressure was studied during static handgrip contractions at 15 and 30% of maximal voluntary contraction (MVC). 2. To further elucidate the importance of K+ in the reflex regulation of blood pressure a situation with normal recovery was compared with a situation in which 3 min of post-exercise occlusion was applied by arresting the circulation to the forearm just prior to the cessation of the contraction. 3. There was a temporal as well as quantitative correlation between venous [K+] and the blood pressure response during and after static exercise. During 30% MVC mean arterial blood pressure (MAP) attained 161.7 mmHg and venous [K+] 5.8 mM, while the corresponding values during 15% MVC were 121.5 mmHg and 5.0 mM. 4. In the occlusion period mean arterial blood pressure remained elevated above resting level and provided a measure of the magnitude of muscle chemoreflexes. In the same period venous [K+] was maintained at 5.3 mM and 4.6 mM following 30% MVC and 15% MVC respectively. This is indicative of interstitial concentrations of above 8-10 mM. This level is sufficiently high to stimulate type III and IV muscle afferents involved in the reflex regulation of blood pressure, and strengthens the notion that K+ may play an important role in eliciting the pressor reflex. 5. In contrast to [K+] the time course of venous blood concentrations of lactate and ammonia (NH3) exhibited a clear dissociation from the blood pressure recordings.

Adult↗
PubMed1991

Potassium homeostasis during and following exhaustive submaximal static handgrip contractions.

The aim of the present study was to follow local potassium homeostasis during and after exhaustive contractions. Eight subjects performed static handgrip with their right forearm at 10%, 25% and 40% maximal voluntary contraction. Blood flow (venous occlusion plethysmography) and the venous effluent plasma potassium concentration were followed during the contractions and during a 60-min recovery period. Electromyography was registered during exercise (frequency analysis). With all three protocols the blood flow increased significantly during the contractions and the same was true of the effluent plasma potassium concentrations. In the recovery period blood flow and the venous effluent plasma potassium concentration returned to base values within 30 min following 40% maximal voluntary contraction while following 10% and 25% maximal voluntary contraction, venous effluent plasma potassium concentration was still significantly below resting values one hour after the exercise had ceased, indicating a long-lasting uptake of potassium from the blood into the muscles. In line with this a significant potassium deficit was still seen after 1 hour of recovery following 10% and 25% maximal voluntary contraction. It is concluded that the recovery of potassium homeostasis following prolonged low-intensity contractions is a slow process. This may be due to either sequestration of potassium in other tissues with a subsequent slow release and/or insufficient sodium/potassium pump activation. The contraction induced potassium loss may play a major role in muscle performance since it may impair mechanical force production, and it is hypothesized that this may be the origin of low-frequency fatigue.

Adult↗
PubMed1991

Role of exercise-induced potassium fluxes underlying muscle fatigue: a brief review.

The site of exercise-induced muscle fatigue is suggested to be the muscle membrane, which includes the sarcolemma and T-tubule membrane; the excitability of the membrane is dependent on the membrane potential. Significant potassium flux from the intracellular space of contracting muscle may decrease the membrane potential to half its resting value. This is true for isolated muscle preparations as well as for the whole body exercise in humans. Specific K+ channels have been identified, that may account for the intracellular K+ loss. Calcium-sensitive K+ channels open when intracellular Ca2+ concentrations increase, as during excitation. ATP-sensitive K+ channels may be involved but may open only at ATP concentrations well below those attained at exhaustion. However, ATP may be compartmentalized and only the membrane-bound ATP concentration may be of significance. Ca2+ accumulation and ATP depletion cause cell destruction; these changes induce an increased K+ conductance, which may inactivate the membrane and consequently prevent tension development. It is hypothesized that such a safety mechanism is identical to the fatigue mechanism.

Animals↗
PubMed1991

Potassium regulation during exercise and recovery.

The concentrations of extracellular and intracellular potassium (K+) in skeletal muscle influence muscle cell function and are also important determinants of cardiovascular and respiratory function. Several studies over the years have shown that exercise results in a release of K+ ions from contracting muscles which produces a decrease in intracellular K+ concentrations and an increase in plasma K+ concentrations. Following exercise there is a recovery of intracellular K+ concentrations in previously contracting muscle and plasma K+ concentrations rapidly return to resting values. The cardiovascular and respiratory responses to K+ released by contracting muscle produce some changes which aid exercise performance. Increases in the interstitial K+ concentrations of contracting muscles stimulate CIII and CIV afferents to directly stimulate heart rate and the rate of ventilation. Localised K+ release causes a vasodilatation of the vascular bed within contracting muscle. This, together with the increase in cardiac output (through increased heart rate), results in an increase in blood flow to isometrically contracted muscle upon cessation of contraction and to dynamically contracting muscle. This exercise hyperaemia aids in the delivery of metabolic substrates to, and in the removal of metabolic endproducts from, contracting and recovering muscle tissues. In contrast to the beneficial respiratory and cardiovascular effects of elevations in interstitial and plasma K+ concentrations, the responses of contracting muscle to decreases in intracellular K+ concentrations and increases in intracellular Na+ concentrations and extracellular K+ concentrations contribute to a reduction in the strength of muscular contraction. Muscle K+ loss has thus been cited as a major factor associated with or contributing to muscle fatigue. The sarcolemma, because of changes in intracellular and extracellular K+ concentrations and Na+ concentrations on the membrane potential and cell excitability, contributes to a fatigue 'safety mechanism'. The purpose of this safety mechanism would be to prevent the muscle cell from the self-destruction which is evident upon overload (metabolic insufficiency) of the tissues. The net loss of K+ and associated net gain of Na+ by contracting muscles may contribute to the pain and degenerative changes seen with prolonged exercise. During exercise, mechanisms are brought into play which serve to regulate cellular and whole body K+ homeostasis. Increased rates of uptake of K+ by contracting muscles and inactive tissues through activation of the Na(+)-K+ pump serve to restore active muscle intracellular K+ concentrations towards precontraction levels and to prevent plasma K+ concentrations from rising to toxic levels. These effects are at least partially mediated by exercise-induced increases in plasma catecholamines, particularly adrenaline.(ABSTRACT TRUNCATED AT 400 WORDS)

Exercise↗
PubMed1990

Cardiovascular and metabolic responses to static contraction in man.

There is substantial controversy regarding muscle blood flow and its regulation during static exercises. Major issues include (1) the relationship between developed force and muscle blood flow, (2) the ability of metabolic vasodilation to overcome neurally mediated vasoconstriction, (3) the time course and magnitude of hyperaemic flow following static exercise and (4) blood flow to the contralateral inactive limb. At rest, 15, 25 and 50% maximal voluntary contractions (MVC) femoral venous flow in four healthy young men (LBF; mean +/- 1 SD) was 0.4 +/- 0.3, 1.76 +/- 0.65, 0.90 +/- 0.32 and 1.06 +/- 0.59 1 min-1, and mean arterial pressures (MAP) were 104 +/- 13, 140 +/- 14, 160 +/- 17 and 161 +/- 11 mmHg. Thus, LBF does not increase proportionally with increasing levels of MVC, despite increased arterial pressure. Further, during both 25 and 50% MVC, which were held to exhaustion, an elevated limb vascular resistance was encountered towards the end of contraction, which suggests that neurally mediated vasoconstrictor activity overrides local vasodilation. Femoral venous effluent documented perfusion of active muscle during contractions of 15 and 25% MVC, but less so at 50% MVC. Immediately in recovery LBF reached levels of 3-3.5 1 min-1, which corresponded to 150 ml 100 g-1 min-1. When both O2 uptake and lactate release during the contractions and in recovery were taken into account, a close correlation between rate of energy turnover and exerted force was found. When MAP was raised by static contraction of the opposite quadriceps, LBF in the inactive leg increased momentarily. Within 1 min vascular resistance became elevated and the blood flow became reduced.

Adult↗
PubMed1990

Beta 2-adrenergic stimulation does not prevent potassium loss from exercising quadriceps muscle.

During exercise K+ is released from contracting muscle and plasma K+ concentration rises. Because beta 2-adrenergic agonists stimulate K+ uptake by skeletal muscle in vitro, we tested whether terbutaline, a selective beta 2-agonist, would reduce the loss of K+ from working muscle. Dynamic quadriceps muscle exercise was performed by 12 healthy male volunteers for 50 or 80 min at an average workload of 38 W. A steady K+ loss estimated at 0.16 +/- 0.02 mmol.min-1.kg working muscle-1 and a 0.30 +/- 0.05 mM elevation of arterial plasma K+ concentration were observed. The addition of terbutaline during exercise caused leg blood flow to increase 13% from 5.10 +/- 0.16 to 5.75 +/- 0.13 l/min and arterial K+ concentration to fall monoexponentially by 0.90 +/- 0.05 mM with a rate constant of 0.26 min-1. Terbutaline increased, rather than decreased, the washout of K+ from working quadriceps by 40% to an average value of 0.23 +/- 0.02 mmol.min-1.kg muscle-1. In an additional subject who exercised to exhaustion, terbutaline failed to diminish muscle K+ loss. We conclude that terbutaline does not augment Na(+)-K+ pump activity to a degree sufficient to prevent K+ loss from exercising muscle in humans. On the other hand, the rapid reduction in plasma K+ concentration observed with beta 2-adrenergic stimulation is compatible with an uptake of K+ by nonexercising tissue at an estimated maximal rate of 0.5 micromol.g-1.min-1.

Adrenergic beta-Agonists↗
PubMed1988

Muscle blood flow during isometric activity and its relation to muscle fatigue.

The effect of isometric exercise on blood flow, blood pressure, intramuscular pressure as well as lactate and potassium efflux from exercising muscle was examined. The contractions performed were continuous or intermittent (5 s on, 5 s off) and varied between 5% and 50% maximal voluntary contraction (MVC). A knee-extensor and a hand-grip protocol were used. Evidence is presented that blood flow through the muscle is sufficient during low-level sustained contractions (less than 10% MVC). Despite this muscle fatigue occurs during prolonged contractions. One mechanism for this fatigue may be the disturbance of the potassium homeostasis. Such changes may also play a role in the development of fatigue during intermittent isometric contractions and even more so in the recovery from such exercise. In addition the role of impaired transport of substances within the muscle, due to long-lasting daily oedema formation, is discussed in relation to fatigue in highly repetitive, monotonous jobs.

Adult↗
PubMed1988

Muscle energy metabolism and electrolyte shifts during low-level prolonged static contraction in man.

Seven men performed one-legged isometric knee extension at 5% MVC for 1 h. Total body oxygen uptake amounted to 451 (420-471) ml min-1 and oxygen uptake over the contracting leg to 200 (172-216) ml min-1, with no changes occurring during the 1 h contraction. Venous O2 tension decreased from 29.4 mmHg at rest to 23.1 mmHg with contraction and CO2 tension tended to increase from a resting value of 50.5 mmHg to 57.2 mmHg (n.s.). No similar changes occurred in arterial O2 and CO2 tensions. There was a small but continuous glucose uptake at both rest and throughout the contraction, whereas a lactate release occurred only in the early phase (2 min) of contraction. Muscle glycogen content was 312 mmol kg-1 dry wt at rest, no significant changes had occurred following 30 min or 1 h of contraction. Arterial and venous Hct and Hb values indicated that a flux of water occurred from the vascular bed to the contracting muscle, in which H2O increased from 3.06 l kg-1 dry wt at rest to 3.30 l kg-1 dry wt after 1 h at 5% MVC. Simultaneously potassium (K), was released from the muscle throughout contraction with a mean venous-arterial difference of 0.25 mmol l-1. With a plasma flow of 335 ml min-1 kg-1 wet wt the K loss amounted to 5 mmol kg-1 wet wt or roughly 5% of the total muscle K content.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

A magnesium load test in the diagnosis of magnesium deficiency.

The concentration of magnesium in muscle was determined and a standardized magnesium load test was performed in 21 patients, who 4 to 10 years previously had undergone intestinal bypass operations for severe obesity. The plasma concentration and 24-h urinary excretion of magnesium were also studied. Basic urinary excretion of magnesium and muscle magnesium were significantly lower in patients compared to healthy controls, while no differences were found in plasma magnesium. A slight negative correlation between muscle magnesium and retained magnesium was demonstrated (r = -0.51, P less than 0.05). Patients with magnesium retention greater than 20 per cent showed a significant decrease of magnesium retention after treatment with magnesium chloride mixture. Four patients with primarily low muscle magnesium all demonstrated an increment in the amount of magnesium in muscle after treatment. The load test described can be applied as a screening test in diagnosing magnesium deficiency.

Adult↗