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Biomedical subjects

H Kuipers

Publications and source records attributed to H Kuipers.

At least 55 records · Page 3Linked to original sources
PubMed1998

Acute and sustained effects of isometric and lengthening muscle contractions on high-energy phosphates and glycogen metabolism in rat tibialis anterior muscle.

Previous studies have shown that lengthening contractions, in contrast to isometric contractions, readily result in sustained malfunctioning of the exercised muscles. The present study was performed to investigate whether an exercise period with many (240) lengthening contractions (LC) results in alterations in muscle high-energy phosphates and inosine monophosphate (IMP) content, different from muscles performing a few (60) lengthening or a few (60) or many (240) isometric contractions (IC). Moreover, we sought for a possible cause(s) of the inability to replenish muscle glycogen stores following LC. Rat tibialis anterior muscles were subjected in vivo to either 60 or 240 LC or IC. Structural muscle damage occurred only after 240 LC. The fact that tissue glycogen levels declined to a similar extent during LC and IC suggests that the energy demand was comparable during both types of exercise. Nevertheless, the observation that on the one hand tissue stores of adenine nucleotides showed a greater decline, and on the other hand the tissue content of IMP increased to a significantly higher level after LC than after IC, clearly indicates that muscle energy metabolism is more disturbed during LC than during IC. The high tissue levels of IMP may contribute to impaired mechanical function as previously observed in muscles subjected to LC. In contrast to 240 IC, 24 hours after 240 LC, tissue glycogen stores and high-energy phosphate levels were not restored to control values. The present findings indicate that depressed glycogen synthase activity and impaired activity of the mitochondrial marker enzyme cytochrome C oxidase probably contribute to a continuous disturbance of energy metabolism in the exercised muscles during the 24 hours following 240 LC.

Adenosine Diphosphate↗
PubMed1998

Skeletal muscle metabolic characteristics before and after energy restriction in human obesity: fibre type, enzymatic beta-oxidative capacity and fatty acid-binding protein content.

BACKGROUND: Skeletal muscle has the ability to adapt as result of dietary, hormonal or pharmacological interventions affecting energy metabolism. The aim of the present study was to investigate the effects of energy restriction on skeletal muscle metabolic characteristics in obese women. METHODS: The effects of 8 weeks' energy restriction on body composition, energy expenditure and skeletal muscle characteristics were investigated in 28 healthy obese women. Subjects were aged 37.9 +/- 1.5 years and had a body mass index of 32.0 +/- 0.8 kg m-2. RESULTS: Energy restriction (2800 kJ day-1) resulted in a 10.8 +/- 0.5 kg weight loss consisting of 8. 6 +/- 0.5 kg of fat mass and 2.2 +/- 0.3 kg of fat-free mass. Basal respiratory exchange ratio, sleeping metabolic rate and exercise-induced thermogenesis significantly declined in response to the diet. These changes were accompanied by an increase (P = 0.038) in the skeletal muscle content of cytosolic fatty acid-binding protein (H-FABP), whereas no changes occurred in fibre type distribution or activities of enzymes reflecting beta-oxidation and mitochondrial density (3-hydroxyacyl-CoA dehydrogenase and citrate synthase respectively). CONCLUSION: The results suggest that increased capacity of intracellular fatty acid transport in skeletal muscle cells is involved in the physiological adaptations of fat metabolism to energy restriction in obese female subjects.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1998

Isokinetic aerobic power output testing of the quadriceps muscle.

A stepwise increasing exercise protocol to measure the maximal aerobic power output of the quadriceps muscle is proposed for use in rehabilitation medicine. Sixteen healthy volunteers performed isokinetic knee extension/flexion exercises at an angular velocity of 180 degrees x s(-1). The protocol consisted of stages of 200 knee movements from 100 flexion to full extension, starting at 10% peak torque (PT) and increasing by 10% PT each following stage until exhaustion. Quadriceps work, oxygen uptake, heart rate, plasma lactate concentration and surface electromyography were monitored. Quadriceps power output (Pext) was highly related (r = 0.95) to the extension torque at which the subjects were instructed to exercise. The test-retest (r = 0.82) and left to right (r = 0.94) correlations of maximum quadriceps power output (Pmax) were high. Both sexes (males 43+/-9W, females 36+/-8W) achieved their Pmax at 47% PT. At submaximal power output stages oxygen uptake (r = 0.85) and EMG-amplitude (r = 0.88) were linearly related to Pext. Mechanical efficiency (optimum at 60% Pmax) showed a large variation between power output stages and between subjects. The relationship between relative oxygen uptake and heart rate or plasma lactate concentration was similar to that of whole body exercise, e.g. running. We conclude that the proposed test is reliable for assessing the maximal aerobic power output of the quadriceps muscle. This parameter of the muscle function may add useful information for assessing the rehabilitation process after knee immobilization.

Adult↗
PubMed1998

Training and overtraining: an introduction.

Elite sport requires high training volumes. However, little is known about the relationship between training volume and performance development. This relationship appears to have an inverted U-shape. Short-term overtraining or overreaching is probably associated with insufficient metabolic recovery, resulting in a decline in ATP levels. Systemic overtraining or staleness is attributed to failure of the hypothalamus to cope with the total amount of stress. Clinically, a parasympathetic and sympathetic form has been distinguished. It is assumed that these two forms express different stages of staleness. No specific, simple, and reliable parameters are known to diagnose overreaching and overtraining in the earliest stage.

Athletic Injuries↗
PubMed1997

[The use of drugs to improve athletic performance].

In sports, medical drugs are applied for supposedly ergogenic effects. Forbidden drug use (doping) implies that the drug enhances performance, which is not always the case. Amphetamines are ergogenic particularly during short-term, explosive exercise. Amphetamines exert an ergolytic effect on high-intensity endurance exercise. Caffeine has an ergogenic effect on endurance performance in dosages of 3 to 6 mg/kg. Doping regulations allow a small amount of caffeine intake. Androgenic and anabolic steroids elicit an increase in muscle growth and strength. In females low doses appear to be ergogenic in all sport types. beta 2-adrenergic agonists appear to have a positive effect on strength and muscle growth. The effects on endurance performance are still unknown. Although growth hormone is used in sports, scientific studies show that compared with placebo no difference in strength and muscle volume is observed. Blood doping and administration of erythropoietin are effective in enhancing endurance performance.

Adrenergic beta-Agonists↗
PubMed1997

The Conconi test.

Explore the source record for details and available documents.

Anaerobic Threshold↗
PubMed1996

Structural muscle damage and muscle strength after incremental number of isometric and forced lengthening contractions.

Exercise-induced muscle damage is characterized by histological changes, like Z-line streaming, inflammatory response and decreased muscle function reflected in a prolonged decline in maximal isometric muscle strength after eccentric work. It is assumed that force decrement is mainly related to the amount of structural damage. However, the relationship between number of eccentric contractions, magnitude of structural damage and force decrement is not very well documented. Therefore we studied the effect of an increasing number of both isometric and eccentric (forced lengthening) contractions on histological parameters of muscle damage and maximal isometric force in an experimental in situ rat model. Tibialis anterior muscles of male Wistar rats were subjected to an increasing number of either isometric or eccentric contractions and were examined for histological markers of muscle damage. The present study shows that muscle damage increases progressively with the number of forced lengthening contractions. Maximal isometric torque was found to decline after both types of exercise. However, the decline after forced lengthening exercise was more pronounced. Only a weak relationship between percentage of histological muscle damage and isometric torque after forced lengthening contractions was found. The findings of the present study suggest that the decline in muscle force after eccentric exercise may partly be attributed to other factors than structural damage.

Analysis of Variance↗
PubMed1996

Impaired IgG-dependent anaphylaxis and Arthus reaction in Fc gamma RIII (CD16) deficient mice.

The family of receptors for IgG (Fc gamma R) plays an essential role in antibody-mediated effector functions of the immune system. However, the specific contribution of each of the Fc gamma R classes to in vivo immune reactions is still unclear. Here, we demonstrate that mice deficient for the ligand-binding alpha chain of Fc gamma RIII lack NK cell-mediated antibody-dependent cytotoxicity and phagocytosis of IgG1-coated particles by macrophages. Strikingly, these mice lack IgG-mediated mast cell degranulation, are resistant to IgG-dependent passive cutaneous anaphylaxis, and exhibit an impaired Arthus reaction. These results indicate a prominent role for Fc gamma RIII in inflammatory and anaphylactic responses, making this receptor a potential target in immunotherapy.

Animals↗
PubMed1996

Body composition, cardiovascular risk factors and liver function in long-term androgenic-anabolic steroids using bodybuilders three months after drug withdrawal.

The purpose of this study was to investigate in a cross-sectional design body composition, muscle fiber characteristics, cardiovascular risk factors and liver enzymes in long-term androgenic-anabolic steroids (AAS) using bodybuilders three months after drug withdrawal (AAS group; n = 16) and in non-users (CO group; n = 12). Training and dietary data were collected in all subjects. Anthropometry included weight, height, 8 skinfolds and 11 circumferences. Percentage fat (%FAT), fat mass (FM) and lean body mass (LBM) were calculated. In a muscle biopsy from the vastus lateralis muscle water content, fiber type distribution and diameters of fiber type I and type II were determined. Age, height, training characteristics, nutrition, skinfolds, %FAT and FM did not differ between the groups. The AAS group had greater BW and LBM, and larger circumferences of thorax, waist, upper arm and thigh than the CO group. Muscle biopsy data were comparable, except for muscle fiber diameter of type I which was larger in the AAS group. No differences in serum values of total cholesterol, HDL-cholesterol and triglycerides, nor in systolic and diastolic blood pressure were observed. In both groups serum alkaline phosphatase and gamma GT were within the normal range. This study suggests that in long term AAS using body-builders, after a three months AAS free period, BW is greater than in non drug users. This is reflected in larger LBM, circumferences and diameter of muscle fiber type I. In addition, no differences in fat mass, blood pressure, lipoprotein profiles and liver enzymes exist between AAS users three months after interrupted drug use and their non drug using counterparts.

Adult↗
PubMed1995

Glucose and insulin responses after commonly used sport feedings before and after a 1-hr training session.

This investigation examined the plasma glucose and insulin response in 6 trained athletes after consumption of four commercially available sport feedings 2 hr before as well as immediately after 1 hr of running under common training conditions. Four feedings were compared: Feeding 1, 160 g CHO/400 ml; Feeding 2, 69 g CHO/400 ml; Feeding 3, 69 g CHO + 6 g protein/400 ml; and Feeding 4, solid 69 g CHO + 5 g protein + 4 g fat. Before the training session, there were no differences between the four sport feedings in the area under the glucose and insulin curves and the insulin/glucose ratio. However, after exercise, Feeding 2 resulted in a significantly greater area under the glucose curve compared with Feedings 1, 3, and 4 (respectively, 352 vs. 241, 251, and 182) and a significantly lower insulin/glucose ratio compared with Feeding 1 (respectively, 6.2 vs. 15.8). Therefore, it is concluded that the kind of sport feeding may influence postexercise glucose and insulin responses.

Adult↗
PubMed1995

Beta-adrenoceptor blockade and skeletal muscle energy metabolism during endurance exercise.

Twelve healthy male volunteers cycled to exhaustion at a workload corresponding to 70% of maximal aerobic power after administration of 80 mg of the beta 1+2-adrenoceptor antagonist propranolol and after administration of placebo by mouth. Exercise times until exhaustion were 39 +/- 7 and 86 +/- 7 min in the propranolol and placebo groups, respectively. Muscle inosine 5'-monophosphate content was significantly increased above resting levels at exhaustion after placebo. At exhaustion after propranolol, inosine 5'-monophosphate was not increased significantly and was lower than at exhaustion after placebo. No changes in ATP and the total adenine nucleotide content during exercise were found in the two tests. Muscle glycogen content was significantly reduced at exhaustion after placebo as well as after propranolol, but the levels were still significantly higher at exhaustion after propranolol than after placebo. No evidence for a shift in glycogen utilization among types I, IIa, and IIb fibers after propranolol was found. The results show that neither an imbalance between ATP utilization and ATP regeneration nor premature glycogen depletion, either in the whole muscle or in specific muscle fiber types, provides a satisfactory explanation for the premature fatigue during endurance exercise after propranolol.

Adenine Nucleotides↗
PubMed1995

Overtraining following intensified training with normal muscle glycogen.

The purpose of this study was to determine if consumption of appropriate amounts of carbohydrate during a period of increased exercise training would protect the athletes from becoming overtrained. Eight male competitive cyclists were monitored and tested during three training periods: a) normal training (moderate intensity, long duration, 7 d, NORM); b) overtraining (high intensity training, 15 d, OVER); and c) recovery (minimal training, 6 d, REC). Throughout the training 160 g of liquid carbohydrate were consumed within the first 2 h after the daily exercise bout. Mean dietary intake (NORM = 13.7 +/- 1.6, OVER = 14.1 +/- 1.0 MJ.d-1) and carbohydrate percent (NORM = 64.0 +/- 2.1, OVER = 67.4 +/- 2.5%) were not different during the different training periods. Similarly, resting muscle glycogen levels were not different (NORM = 530.9 +/- 42.5, OVER = 571.2 +/- 27.5 mumol.g-1 dry weight). Five criteria were used to determine if overtraining occurred in a subject (decreased maximal workload, maximal heart rate, ratio of maximal lactate to rating of perceived exertion (HLa:RPE), and resting plasma cortisol levels, increased affirmative response to a daily questionnaire). All subjects met at least three of the five criteria and thus were classified as overtrained. Therefore, short-term overtraining may occur even when resting muscle glycogen levels are maintained.

Adult↗
PubMed1994

Effect of exercise training on ambulatory blood pressure.

A possible hypotensive action of regular endurance exercise in normotensive sedentary subjects still remains a matter of debate. This is partly caused by the fact that the anticipated fall in resting blood pressure is rather small and fluctuations in blood pressure during the day can be large. The benefits of ambulatory blood pressure monitoring (ABP) originate to a great deal from the fact that the repeatability on different occasions of the ambulatory blood pressure average is improved by the greater number of readings. In this context we evaluated the effect of moderate exercise training in 19 sedentary male subjects, aged 22 to 44 years, with normal or slightly elevated blood pressure. They entered a randomized cross-over study. Measurements were performed before the study, after 6 weeks of sedentary life style (S) and after 6 weeks of training (T) on a cycle ergometer 3 times a week for 45 min at 75% VO2max. ABP was measured with a Spacelabs 90207 monitor and cardiac output at rest with echo-Doppler. Training increased VO2max from 3.13 +/- 0.09 to 3.40 +/- 0.08 l/min (p < 0.01). Resting heart rate decreased from 60 +/- 2 to 57 +/- 2 bpm (p < 0.05). Resting blood pressure was unchanged after training. Resting stroke volume increased from 82 +/- 3 to 89 +/- 3 ml (p < 0.02). Systemic vascular resistance index was significantly decreased due to conditioning (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Exercise-induced muscle damage.

Muscular overuse is associated with structural damage of the contractile elements and reflected in delayed onset muscle soreness (DOMS). Mechanical stress is supposed to be the major contributing factor for inducing muscle damage. The initial damage is followed by an inflammatory response and eventually by regeneration. Calcium is assumed to play an important role in triggering the inflammatory changes. Biopsy data in man indicate that the inflammatory changes in humans do not parallel the soreness ratings, leaving the delayed onset of muscle soreness unexplained. It is a well known phenomenon that one bout of eccentric exercise has a long lasting protective effect against damage induced by a second bout of exercise. Experimental evidence suggests that this adaptation can partly be attributed to an increase in connective tissue. Plasma CK activity has widely been used as a marker for the amount of muscle damage. It has been shown that gender differences in exercise-induced CK release are caused by sex hormones dependent differences in sarcolemmal permeability. Plasma CK activity does not necessarily reflect the amount of structural damage.

Creatine Kinase↗
PubMed1994

The relation between power output, oxygen uptake and heart rate in male athletes.

As the exercise intensity is often expressed as percentage of either maximal workload (%Wmax), percentage of maximal heart rate (%HRmax), or as percentage of maximal oxygen uptake, the relationship between %Wmax, %VO2max, and %HRmax was determined in 53 male cyclists. All subjects performed an incremental maximal cycle ergometer test. In all athletes examined, a linear relation between power output, oxygen uptake and heart rate was observed. The relationships between %Wmax and %VO2max as well as between %Wmax and %HRmax were linear (r = 0.98 and r = 0.97; p < 0.001). It is concluded that studies which are different in expression of exercise intensity (%Wmax or %VO2max) can be compared and that the relation between %Wmax and %HRmax needs to be determined individually when an appropriate individualized training intensity based on heart rate is required.

Adult↗
PubMed1994

Adaptation and overtraining in horses subjected to increasing training loads.

To evaluate markers for overtraining, seven male race horses were subjected to 272 days of training consisting of daily exercise bouts of either endurance running (heart rate 140/min) or interval training (maximal heart rate), both increasing in duration and intensity. An incremental exercise test was held every 4 wk, and from day 187 it was held every 2 wk. Muscle glycogen, muscle lactate, energy-rich phosphates, adrenal response to adrenocorticotropic hormone, plasma and red blood cell volumes, and a number of blood chemical variables were measured. The horses showed symptoms of weight loss, irritability, and an inability to complete the training after the intensity of the endurance exercise was increased. Test performance was not decreased. The adrenal response to adrenocorticotropic hormone was not changed during overtraining. The decline in muscle ATP concentration during maximal exercise was less during the period of staleness, whereas plasma volume, red blood cell volume, and blood chemical variables were unchanged. It was concluded that as long as exhaustive training is alternated by light exercise, overtraining is unlikely to occur. Furthermore, no single parameter can be used to detect early overtraining.

Adaptation, Physiological↗