Biomedical subjects

M Kjaer

Publications and source records attributed to M Kjaer.

At least 109 records · Page 6Linked to original sources

PubMed1999

The effect of supervised rehabilitation on strength, postural sway, position sense and re-injury risk after acute ankle ligament sprain.

The effect of an early rehabilitation program, including postural training, on ankle joint function after an ankle ligament sprain was investigated prospectively. Ninety-two subjects, matched for age, sex, and level of sports activity, were randomized to a control or training group. All subject received the same standard information regarding early ankle mobilization. In addition, the training group participated in supervised physical therapy rehabilitation (1 h, twice weekly) with emphasis on balance training. Postural sway, position sense and isometric ankle strength were measured 6 weeks and 4 months after the injury, and at 12 months re-injury data were obtained. In the training group, there was a significant difference between the injured and uninjured side for plantar flexion (P < 0.01), eversion (P < 0.01) and inversion (P < 0.05), but not for dorsiflexion at 6 weeks. In the control group, there was a significant difference between the injured and uninjured side for plantar flexion (P < 0.01), eversion (P < 0.01), inversion (P < 0.01), and dorsiflexion (P < 0.05) at 6 weeks. Postural sway, but not position sense, differed between the injured and uninjured side in both groups (P < 0.01) at 6 weeks. The side-to-side percent differences were similar in both groups for all variables (P > 0.05) at 6 weeks, and there were no side-to-side differences at 4 months in either group. In the control group, 11/38 (29%) suffered a re-injury, while this number was only 2/29 (7%) in the training group (P < 0.05). These data showed that an ankle injury resulted in reduced ankle strength and postural control at 6 weeks, but that these variables had normalized at 4 months, independent of the supervised rehabilitation. However, the findings also demonstrated that supervised rehabilitation may reduce the number of re-injuries, and therefore may play a role in injury prevention.

Adult↗

PubMed1999

Cardiovascular and neuroendocrine responses to exercise in hypoxia during impaired neural feedback from muscle.

Reflex mechanisms from contracting skeletal muscle have been shown to be important for cardiovascular, neuroendocrine, and extramuscular fuel-mobilization responses in exercise. Furthermore, because hypoxia results in exaggerated metabolic changes in contracting muscle, the present study evaluated whether enhancement of cardiovascular and neuroendocrine responses by hypoxia during exercise is influenced by neural feedback from contracting muscle. Seven healthy males cycled at 46% maximal O(2) uptake for 20 min both during normoxia and at 11.5% O(2), and both without and with epidural anesthesia (EA; 20 ml 0.25% bupivacain, resulting in cutaneous hypesthesia below T10-T12 and 25% reduction in maximal leg strength). Exercise to exhaustion was also performed at 7.8% O(2). The exercise-induced increases in heart rate; cardiac output; leg blood flow; plasma concentrations of growth hormone, adrenocorticotropin, cortisol, and catecholamines; renin activity; glucose production and disappearance; norepinephrine spillover [2, 190 +/- 341 ng/min (exercise at 11.5% O(2)) vs. 988 +/- 95 ng/min (exercise during normoxia)]; lactate release from and glucose uptake in the leg; and the decreases in plasma insulin and free fatty acids were exaggerated in hypoxia (P < 0.05). In muscle, concentrations of lactate, creatine, and inosine 5'-monophosphate were higher, and those of phosphocreatine were lower after exercise in hypoxia compared with normoxia. The exercise-induced increase in mean arterial blood pressure was not affected by hypoxia, but it was reduced by EA [108 +/- 4 mmHg (control) vs. 97 +/- 4 mmHg (EA); P < 0.05], and the reduction was more pronounced during severe hypoxia compared with normoxia. Apart from this, time to exhaustion at extreme hypoxia, circulatory responses, concentrations of neuroendocrine hormones, and extramuscular substrate mobilization were not diminished by EA. In conclusion, in essence the hypoxia-induced enhancement of systemic adaptation to exercise is not mediated by neural feedback from working muscle in humans.

Adult↗

PubMed1999

Heart rate during exercise with leg vascular occlusion in spinal cord-injured humans.

Feed-forward and feedback mechanisms are both important for control of the heart rate response to muscular exercise, but their origin and relative importance remain inadequately understood. To evaluate whether humoral mechanisms are of importance, the heart rate response to electrically induced cycling was studied in participants with spinal cord injury (SCI) and compared with that elicited during volitional cycling in able-bodied persons (C). During voluntary exercise at an oxygen uptake of approximately 1 l/min, heart rate increased from 66 +/- 4 to 86 +/- 4 (SE) beats/min in seven C, and during electrically induced exercise at a similar oxygen uptake in SCI it increased from 73 +/- 3 to 110 +/- 8 beats/min. In contrast, blood pressure increased only in C (from 88 +/- 3 to 99 +/- 4 mmHg), confirming that, during exercise, blood pressure control is dominated by peripheral neural feedback mechanisms. With vascular occlusion of the legs, the exercise-induced increase in heart rate was reduced or even eliminated in the electrically stimulated SCI. For C, heart rate tended to be lower than during exercise with free circulation to the legs. Release of the cuff elevated heart rate only in SCI. These data suggest that humoral feedback is of importance for the heart rate response to exercise and especially so when influence from the central nervous system and peripheral neural feedback from the working muscles are impaired or eliminated during electrically induced exercise in individuals with SCI.

Adult↗

PubMed1999

Glucose production during exercise in humans: a-hv balance and isotopic-tracer measurements compared.

The present study compared the arteriohepatic venous (a-hv) balance technique and the tracer-dilution method for estimation of hepatic glucose production during both moderate and heavy exercise in humans. Eight healthy young men (aged 25 yr; range, 23-30 yr) performed semisupine cycling for 40 min at 50.4 +/- 1.5(SE)% maximal O(2) consumption, followed by 30 min at 69.0 +/- 2.2% maximal O(2) consumption. The splanchnic blood flow was estimated by continuous infusion of indocyanine green, and net splanchnic glucose output was calculated as the product of splanchnic blood flow and a-hv blood glucose concentration differences. Glucose appearance rate was determined by a primed, continuous infusion of [3-(3)H]glucose and was calculated by using formulas for a modified single compartment in non-steady state. Glucose production was similar whether determined by the a-hv balance technique or by the tracer-dilution method, both at rest and during moderate and intense exercise (P > 0. 05). It is concluded that, during exercise in humans, determination of hepatic glucose production can be performed equally well with the two techniques.

Adult↗

PubMed1999

Negative interstitial pressure in the peritendinous region during exercise.

In the present study, tissue pressure in the peritendinous area ventral to the human Achilles tendon was determined. The pressure was measured during rest and intermittent isometric calf muscle exercise at three torques (56, 112, and 168 Nm) 20, 40 and 50 mm proximal to the insertion of the tendon in 11 healthy, young individuals. In all experiments a linear significant decrease in pressure was obtained with increasing torque [e.g., at 40 mm: -0.4 +/- 0.3 mmHg (rest) to -135 +/- 12 mmHg (168 Nm)]. No significant differences were obtained among the three areas measured. On the basis of these observations, microdialysis was performed in the peritendinous region with a colloid osmotic active substance (Dextran 70, 0.1 g/ml) added to the perfusate with the aim of counteracting the negative tissue pressure. Dialysate volume was found to be fully restored (100 +/- 4%) during exercise. It is concluded that a marked negative tissue pressure is generated in the peritendinous space around the Achilles tendon during exercise in humans. Negative tissue pressure could lead to fluid shift and could be involved in the increase in blood flow previously noted in the peritendinous tissue during exercise (H. Langberg, J. Bülow, and M. Kjaer. Acta Physiol. Scand. 163: 149-153, 1998; H. Langberg, J. Bülow, and M. Kjaer. Clin. Physiol. 19: 89-93, 1999).

Achilles Tendon↗

PubMed1998

[Sports medicine].

Explore the source record for details and available documents.

Athletic Injuries↗

PubMed1998

Hormone-sensitive lipase (HSL) expression and regulation in skeletal muscle.

Because the enzymatic regulation of muscle triglyceride metabolism is poorly understood we explored the character and activation of neutral lipase in muscle. Western blotting of isolated rat muscle fibers demonstrated expression of hormone-sensitive lipase (HSL). In incubated soleus muscle epinephrine increased neutral lipase activity by beta-adrenergic mechanisms involving cyclic AMP-dependent protein kinase (PKA). The increase was paralleled by an increase in glycogen phosphorylase activity and could be abolished by antiserum against HSL. Electrical stimulation caused a transient increase in activity of both neutral lipase and glycogen phosphorylase. The increase in lipase activity during contractions was not influenced by sympathectomy or propranolol. Training diminished the epinephrine induced lipase activation in muscle but enhanced the activation as well as the overall concentration of lipase in adipose tissue. In agreement with the in vitro findings, in adrenalectomized patients an increase in muscle neutral lipase activity was found at the end of prolonged exercise only if epinephrine was infused. In accordance with feedforward regulation of substrate mobilization in exercise, our studies have shown that HSL is present in skeletal muscle cells and is stimulated in parallel with glycogen phosphorylase by both epinephrine and contractions. HSL adapts differently to training in muscle compared with adipose tissue.

Animals↗

PubMed1998

Adrenal medulla and exercise training.

The adrenaline release from the adrenal medulla increases during exercise, but at a given absolute work intensity the magnitude of this response is less pronounced in endurance trained vs sedentary individuals most likely due to a lower sympathetic stimulation of the adrenal medulla. However, when trained and untrained subjects are compared at identical relative work loads as well as in response to numerous non-exercise stimuli. endurance trained athletes have a higher epinephrine secretion capacity compared to sedentary individuals. This indicates a development of a so-called "sports adrenal medulla" as a result of a long term adaptation of an endocrine gland to physical training. Such an adaptation is parallel to adaptations taking place in other tissues like skeletal muscle and the heart. and can be advantageous in relation to both exercise performance in the competing athlete and cause a biological rejuvenation in relation to aging.

Adrenal Medulla↗

PubMed1998

The natural killer cell response to exercise in spinal cord injured individuals.

In order to evaluate exercise-induced changes in natural killer (NK) and other immunocompetent cells in spinal cord injured individuals, immunological competent blood cells and stress hormones were followed in five paraplegic and six quadriplegic subjects in relation to 30 min electrically stimulated cycling exercise. The leukocyte and lymphocyte concentrations increased during exercise. In the recovery period, the concentration of neutrophils increased, whereas the lymphocytes decreased. The percentage and concentration of NK cells increased during exercise in the paraplegic group and returned to pre-exercise level 2 h after, whereas no changes were seen in these measures for the quadriplegic group. No changes in activated CD38+ NK cells appeared. Unstimulated and interferon-alpha or interleukin-2 stimulated NK cell activity increased during exercise and returned to pre-exercise level 2 h after with no distinction between paraplegics and quadriplegics. The concentrations of plasma growth hormone and catecholamines increased during exercise, with the rise in epinephrine being more pronounced in paraplegic than in quadriplegic subjects, indicating a difference between the groups in sympathetic nervous system integrity. The sympathoadrenal activity is concluded to be responsible for recruitment of NK cells to the blood during exercise.

Adult↗

PubMed1998

Bone fracture during electrical stimulation of the quadriceps in a spinal cord injured subject.

We report a fracture through the lateral femoral condyle of a paraplegic subject caused by electrical stimulation (ES). The subject was a 50-year-old man who 4 years earlier had sustained a complete spinal cord injury (SCI) at level T6. The fracture occurred during ES-induced measurement of maximal isometric torque of the quadriceps with the knee flexed at an angle of 90 degrees. ES was delivered through surface electrodes with biphasic square wave pulses from a constant current stimulator. The torque was calculated to be 93Nm, corresponding to 20.8kg at the ankle. The regional bone mineral density of the entire lower extremities was .83g/cm2, corresponding to 60% of sex- and age-matched able-bodied reference values. Several factors are suspected to have contributed to the fracture: maximal ES in combination with a muscle spasm, severe osteoporosis, increased muscular strength induced by regular ES cycling (twice a week), and testing position with the knee locked in 90 degrees flexion. The risk of fracture as well as various precautions are discussed and should be taken into consideration in future studies.

Biomechanical Phenomena↗

PubMed1998

Bolus injection (2-4 min) versus short-term (10-20 min) infusion of 5-fluorouracil in patients with advanced colorectal cancer: a prospective randomised trial. Nordic Gastrointestinal Tumour Adjuvant Therapy Group.

The use of bolus 5-fluorouracil (5-FU) as a short-term infusion over 10-30 min is increasing at the cost of a push injection, mainly due to practical advantages. Since even a short prolongation of the administration time results in lower 5-FU peak and area under the curve (AUC) levels, there might be a risk of decreased efficacy. The aim of this study was to compare a rapid intravenous (i.v.) 5-FU injection and a short-term 5-FU infusion with respect to objective responses and toxicity in patients with advanced colorectal cancer. 203 patients with measurable advanced colorectal cancer were randomised to bolus 5-FU either as an injection for 2-4 min or as a short-term infusion lasting 10-20 min. In both groups, the 5-FU dose was 500 mg/m2 and leucovorin 60 mg/m2 was given 40 min after the start of 5-FU. Treatment was given on two successive days every other week until progression. Objective tumour regression was seen in 27/100 (27%) in the injection group and in 13/103 (13%) in the infusion group (P = 0.02). Severe toxicity was rare and did not differ significantly between the groups. Progression-free survival tended to be longer in the injection group (P = 0.07), but overall survival did not differ between the groups. Bolus 5-FU should be administered as a rapid i.v. injection rather than as a short-term infusion, since the former rate of administration results in a higher response rate without being significantly more toxic.

Adult↗

PubMed1998

Blood flow in the peritendinous space of the human Achilles tendon during exercise.

This study evaluated blood flow in the peritendinous space of the human Achilles tendon during rest and 40-min dynamical contraction of m. triceps surae. In 10 healthy volunteers 133Xe was injected in to the peritendinous space just ventrally to the Achilles tendon 2 and 5 cm proximal to the calcaneal insertion of the tendon, respectively. Blood flow 5 cm proximal to the Achilles tendon insertion was found to increase 4-fold from rest to exercise whereas the exercise induced increase in blood flow was less pronounced, only 2.5-fold, when measured 2 cm proximal to the Achilles tendon insertion. Lymph drainage from the area was found to be negligible both during rest and exercise. We conclude that dynamical calf muscle contractions result in increased peritendinous blood flow at the Achilles tendon in humans.

Achilles Tendon↗

PubMed1998

Lactate/H+ transport in skeletal muscle from spinal-cord-injured patients.

In order to evaluate the effect of prolonged muscle inactivity on sarcolemmal lactate/H+ transport in humans, the lactate/H+ transport capacity was determined in the thigh muscle of spinal-cord-injured (SCI) individuals. The lactate transport rate was measured in sarcolemmal giant vesicles produced by collagenase treatment of muscle biopsies obtained from the vastus lateralis muscle. Six SCI subjects with total loss of motor and sensory functions of their lower limbs participated in the study. The duration of the injury ranged from 2 to 15 years. The total lactate transport rate in the muscle of SCI patients was 46.5 +/- 2.6 pmol.cm-2.s-1 (mean +/- SEM), which corresponds to a 17% lower (P < 0.05) transport rate than that found in healthy, untrained subjects. The estimated carrier-mediated lactate/H+ transport capacity was approximately 26% lower in the SCI patients than in healthy, untrained subjects. The observed muscle lactate/H+ transport capacity of SCI individuals is in accordance with a positive correlation between the capacity of the lactate/H+ transporters and the percentage occurrence of slow-twitch fibres in a muscle, although there seems to be a wide range of transport capacities within each fibre type. The present results show that the sarcolemmal lactate/H+ transport capacity is lower in SCI individuals than in normally physically active subjects, which indicates that prolonged muscle inactivity reduces the lactate/H+ transport capacity of human muscle.

Adult↗

PubMed1998

Isokinetic muscle strength and hiking performance in elite sailors.

The aim of the present study was to describe the isokinetic strength profile and its relation to hiking performance in male (SM, n = 15) and female (SF, n = 6) elite sailors compared to a group of male control subjects (CM, n = 8) similar in age, anthropometry and level of fitness. Eccentric knee extension strength was higher in SM compared to CM (P < 0.01). Furthermore, SM were stronger during trunk extension (P < 0.05), but not during trunk flexion compared to CM. Overall muscle strength was lower in SF compared to SM (P < 0.01) and CM (P < 0.05), except for eccentric knee extension strength, where SF and CM did not differ (P > 0.05). Hiking performance correlated to maximal eccentric and isometric knee extensor strength in SF (rs = 0.83-0.88, P < 0.05) and in CM (rs = 0.73-0.77, P < 0.05) and to maximal eccentric knee extensor strength at high velocity in SM (rs = 0.46-0.54, P < 0.05). For a subgroup of hikers in SM (n = 8), hiking performance correlated to maximal isometric-eccentric knee extensor strength (rs = 0.67-0.74, P < 0.05), whereas no correlations emerged for the non-hikers (n = 7). Few correlations were observed between hiking performance and maximal concentric trunk flexor strength (rs = 0.69-0.92, P < 0.05). Unexpectedly, in SM correlations also were observed between hiking performance and maximal strength of the trunk extensors (rs = 0.46-0.53, hiker subgroup: rs = 0.64-0.67, P < 0.05). In conclusion, notably high levels of maximal eccentric knee extensor strength were observed for the male and female elite sailors examined in the present study. Furthermore, the present results suggest that hiking performance depends in part on maximal isometric-eccentric knee extensor strength. The maximal strength of the trunk extensors, which potentially stabilizes the lower back and spine, also seems to have some importance for the hiking performance of top-level sailors.

Adult↗

PubMed1998

Mortality and survival in myasthenia gravis: a Danish population based study.

OBJECTIVES: To study mortality and survival of patients with myasthenia gravis. METHODS: 290 patients with myasthenia gravis were studied, including 212 incident cases identified during a comprehensive epidemiological study of myasthenia gravis in western Denmark 1975-89. Follow up was performed on 31 December 1994. Survival curves were constructed using the life table method. Patient data were compared with data from the public Danish population statistics. Death certificates were provided from the National Registry of Death. RESULTS: The annual average crude mortality rate was 1.8 per million (range 1.5-2.2). The myasthenia gravis related mortality rate (myasthenia gravis as underlying or contributory cause) was 1.4 per million (range 1.1-1.8). The age specific mortality rates were low below 50 years. After this age the mortality increased with age in both sexes; after 60 years more rapidly in men than in women. The overall survival rates three, five, 10, and 20 years from diagnosis were 85%, 81%, 69%, and 63% respectively. The survival of both sexes was shorter than that of the corresponding Danish population. Old age at diagnosis, a classification in Osserman-Genkins group IIB or III, and the presence of a thymoma were associated with a less favourable prognosis. The three, five, 10, and 20 year survival rates of thymectomised patients were 94%, 94%, 86%, and 79% respectively. The corresponding figures for the non-thymectomised patients were 78%, 71%, 56%, and 51%. A Cox regression analysis showed that this apparently significant effect of thymectomy was because the thymectomised patients were younger than the non-thymectomised patients. Furthermore, at the time of diagnosis of myasthenia gravis the non-thymectomised patients had a higher frequency of serious conditions associated with myasthenia gravis than the thymectomised patients. CONCLUSION: Patients with myasthenia gravis generally have a relative good prognosis although their survival is shorter than that of the corresponding population. Old age, a classification in Osserman-Genkins group III, and the presence of a thymoma are associated with a less favourable prognosis. In this study, the apparently significant effect of thymectomy was because the thymectomised patients were younger than non-thymectomised patients and because the non-thymctomised patients had a higher frequency of serious conditions associated with myasthenia gravis.

Age Distribution↗

PubMed1998

Caffeine ingestion and metabolic responses of tetraplegic humans during electrical cycling.

Normally, caffeine ingestion results in a wide spectrum of neural and hormonal responses, making it difficult to evaluate which are critical regulatory factors. We examined the responses to caffeine (6 mg/kg) ingestion in a group of spinal cord-injured subjects [7 tetraplegic (C5-7) and 2 paraplegic (T4) subjects] at rest and during functional electrical stimulation of their paralyzed limbs to the point of fatigue. Plasma insulin did not change, caffeine had no effect on plasma epinephrine, and there was a slight increase (P < 0. 05) in norepinephrine after 15 min of exercise. Nevertheless, serum free fatty acids were increased (P < 0.05) after caffeine ingestion after 60 min of rest and throughout the first 15 min of exercise, but the respiratory exchange ratio was not affected. The exercise time was increased (P < 0.05) by 6% or 1.26 +/- 0.57 min. These data suggest that caffeine had direct effects on both the adipose tissue and the active muscle. It is proposed that the ergogenic action of caffeine is occurring, at least in part, by a direct action of the drug on muscle.

Adult↗

PubMed1998

Hepatic glucose production during exercise.

Hepatic glucose production increases during exercise as a sum of liver glycogenolysis and gluconeogenesis. Whereas the former dominates during intense exercise, the latter contributes substantially with prolonged exercise and the concomitant decline in liver glycogen stores and with increased gluconeogenic precursor supply. Afferent neural feedback signals from contracting muscle and feedback signals mediated via the blood stream, can stimulate glucose production to maintain euglycemia. A rise in blood glucose directly inhibits hepatic glucose production, whereas a decline in blood glucose enhances liver glucose production via release of glucoregulatory hormones. In addition to this, central mechanisms coupled to the degree of motor center activity can be responsible for part of the increase in glucose mobilization, especially during intense exercise where hepatic glucose release exceeds peripheral glucose uptake and plasma glucose rises. A decline in plasma insulin is important for the rise in glucose production during exercise in a variety of species, whereas an increase in plasma glucagon is probably more important in other species than man, where glucagon plays a role only in prolonged exercise. Sympathetic nervous activity to the liver and circulating norepinephrine has been demonstrated to be without any role in glucose production, whereas epinephrine has a minor stimulating effect on hepatic glucose mobilization during intense exercise. Growth hormone and cortisol contribute only minimally to the exercise induced rise in liver glucose output.

Animals↗

PubMed1997

Postoperative radiotherapy in high-risk premenopausal women with breast cancer who receive adjuvant chemotherapy. Danish Breast Cancer Cooperative Group 82b Trial.

BACKGROUND: Irradiation after mastectomy can reduce locoregional recurrences in women with breast cancer, but whether it prolongs survival remains controversial. We conducted a randomized trial of radiotherapy after mastectomy in high-risk premenopausal women, all of whom also received adjuvant systemic chemotherapy with cyclophosphamide, methotrexate, and fluorouracil (CMF). METHODS: A total of 1708 women who had undergone mastectomy for pathological stage II or III breast cancer were randomly assigned to receive eight cycles of CMF plus irradiation of the chest wall and regional lymph nodes (852 women) or nine cycles of CMF alone (856 women). The median length of follow-up was 114 months. The end points were locoregional recurrence, distant metastases, disease-free survival, and overall survival. RESULTS: The frequency of locoregional recurrence alone or with distant metastases was 9 percent among the women who received radiotherapy plus CMF and 32 percent among those who received CMF alone (P<0.001). The probability of survival free of disease after 10 years was 48 percent among the women assigned to radiotherapy plus CMF and 34 percent among those treated only with CMF (P<0.001). Overall survival at 10 years was 54 percent among those given radiotherapy and CMF and 45 percent among those who received CMF alone (P<0.001). Multivariate analysis demonstrated that irradiation after mastectomy significantly improved disease-free survival and overall survival, irrespective of tumor size, the number of positive nodes, or the histopathological grade. CONCLUSIONS: The addition of postoperative irradiation to mastectomy and adjuvant chemotherapy reduces locoregional recurrences and prolongs survival in high-risk premenopausal women with breast cancer.

Adult↗