Biomedical subjects

M A Van Baak

Publications and source records attributed to M A Van Baak.

14 recordsLinked to original sources

PubMed2005

Netherlands research programme weight gain prevention (NHF-NRG): rationale, objectives and strategies.

OBJECTIVE: To outline the rationale, objectives and strategies used in a systematically designed research programmme to study specific weight gain-inducing behaviours, their social-psychological as well as environmental determinants, and the effects of interventions aimed at the prevention of weight gain. DESIGN: The evidence for potential behavioural determinants and strategies to prevent weight gain was reviewed, and the methods applied within the Netherlands Research programme weight gain prevention (NHF-NRG) project were described. The project is designed according to the Intervention Mapping protocol. SETTING: The Netherlands. SUBJECTS: The main target groups are (a) adolescents (12-16 y) in secondary school, (b) young adults (20-40 y) at the workplace and (c) recently retired people (55-65 y) at home. INTERVENTIONS: Each intervention includes an individual component, in which computer-tailored information is provided. Additionally, interventions are aimed at changing environmental components. RESULTS: The short-term results of this project can be expected by the beginning of 2005. Guidelines for nationwide weight gain prevention, based on this research programme, will become available in 2007. CONCLUSIONS: Based on the few interventions that were evaluated to date, no robust conclusions can be drawn regarding the effectiveness of obesity prevention. The systematic and multidisciplinary design of the NHF-NRG programme enables the identification of potentially effective methods and strategies for the prevention of weight gain.

Adolescent↗

PubMed2003

Effects of dietary restraint vs exercise during weight maintenance in obese men.

OBJECTIVE: To investigate the effect of dietary restraint with or without exercise during weight maintenance after energy restriction. SUBJECTS AND METHODS: In total, 40 obese male subjects (mean BMI 32.3 kg/m(2); mean age 39 y) were recruited and randomly divided into a diet (D; n=20) and a diet plus exercise (DE; n=20) group. Both groups participated in an energy restriction programme (ER), which was followed by a weight maintenance phase (WM). Subjects in the DE also participated in an exercise programme. Body mass (BM) and the scores on the three factor eating questionnaire (TFEQ) were measured before and after the ER and after WM. RESULTS: No significant differences between both groups were found. All data taken together showed that BM loss during ER was explained by initial BM (r(2)=0.3, P<0.0005) and inversely by initial cognitive restraint (F1) (r(2)=0.4, P<0.0005) in a stepwise regression. BM regain during WM was explained by BM loss (r(2)=0.5, P<0.001) and by increase in F1 during ER (r(2)=0.6, P<0.001), while the exercise intervention did not contribute further to the explained variation. Subjects with a relatively high diet frequency prior to the study had relatively significant higher initial F1 scores (P<0.05). During ER, increase in F1 was associated with decrease in general hunger (F3). CONCLUSION: Successful BM loss was associated with higher initial BM and lower initial F1. Successful WM was explained by BM loss and increase in F1 during ER, irrespective of possible exercise training effects. Successful WM was reduced when F1 scores reach their limit, due to diet-frequency.

Adult↗

PubMed2001

beta-Adrenoceptor-mediated thermogenesis and lipolysis in patients with chronic obstructive pulmonary disease.

The present study investigated whether development or maintenance of a relatively increased fat mass in normal-weight patients with chronic obstructive pulmonary disease (COPD), despite periods of weight loss, may be related to impaired beta-adrenoceptor-mediated responses in lipid utilization and thermogenesis. Nine COPD patients and nine healthy controls (body mass index: 23.0 +/- 1.3 vs. 23.8 +/- 0.6 kg/m2, not significant; fat mass: 19.0 +/- 2.1 vs. 11.9 +/- 1.5 kg, P < 0.01) received consecutive 30-min infusions of 6, 12, and 24 ng x kg fat free mass(-1) x min(-1) isoproterenol. During beta-adrenergic stimulation, nonesterified fatty acid levels increased significantly less in COPD patients (P < 0.001). Respiratory exchange ratio decreased similarly in both groups, indicating a similar change in the rate of lipid to carbohydrate oxidation. Energy expenditure increased similarly in both groups during beta-adrenergic stimulation. However, because plasma isoproterenol concentrations were significantly higher in COPD patients, thermogenesis related to isoproterenol concentration was significantly reduced in this group (P < 0.05). In conclusion, beta-adrenoceptor-mediated lipolysis and thermogenesis are impaired in COPD patients. This may play a role in the development or maintenance of their relatively increased fat mass.

Adrenergic beta-Agonists↗

PubMed2000

The effect of caffeine on endurance performance after nonselective beta-adrenergic blockade.

PURPOSE: This study was designed to test the hypothesis that combined administration of propranolol and caffeine (Pr+C) would increase endurance performance compared with the administration of propranolol alone (Pr) if caffeine would be able to increase plasma free fatty acid (FFA) availability and/or lower plasma potassium concentration compared with propranolol administration alone. METHODS: Fifteen volunteers participated in the double-blind placebo-controlled randomized cross-over study. An endurance exercise test until exhaustion was performed after ingestion of placebo (Pl), 80-mg propranolol (Pr), and 80-mg propranolol plus 5 mg x kg(-1) caffeine (Pr+C). RESULTS: Endurance time (+/-SD) was 79.3 +/- 20.4 min in the Pl trial, 22.6 +/- 10.8 min in the Pr trial and 31.2 +/- 17.2 min in the Pr+C trial (P < 0.001). The difference between the Pr and Pr+C trials just failed to reach statistical significance (P = 0.056). Plasma FFA concentration and plasma potassium concentrations were similar in the Pr and Pr+C trials, but differed significantly from the Pl trial (P < 0.05). CONCLUSION: Although there was a clear tendency for an improved performance in the Pr+C trial compared to the Pr trial, this improvement was not associated with increased plasma FFA concentration and/or reduced plasma potassium concentration in the Pr+C compared to the Pr trial. These results do not support the hypothesis that caffeine improves endurance performance by stimulating lipolysis or lowering plasma potassium concentration.

Adolescent↗

PubMed1998

Physical training of school children with spastic cerebral palsy: effects on daily activity, fat mass and fitness.

Effects of two 9-month sports programmes (four or two sessions per week) on level of daily physical activity (PA), fat mass (FM), and physical fitness were assessed in children with spastic cerebral palsy (CP; n = 20, 9.2 +/- 1.4 yr), randomly assigned to an experimental and control group after matching. Four sessions per week tended to increase PA ratio (24-h energy expenditure/sleeping (resting) energy expenditure) after 9 months from 1.34 +/- 0.25 to 1.55 +/- 0.18 (P = 0.07; not different versus controls). FM increased continuously in the control group (after 9 months + 1.1 +/- 1.6 kg, P < 0.05), whereas the experimental groups showed no changes. Training (respectively four and two sessions) increased peak aerobic power 35% (P < 0.01; P < 0.05 versus controls) and 21% (P < 0.01; P = 0.17 versus controls). Results also suggest that training has a favourable effect on isokinetic muscle strength. No training-related effects were found on anaerobic power. It was concluded that although aerobic training has a limited effect on PA in children with CP, it may prevent deterioration in body composition and muscle strength. Furthermore, training has a favourable effect on peak aerobic power.

Activities of Daily Living↗

PubMed1998

Effect of aging on beta-adrenergically mediated thermogenesis in men.

The age-dependent alterations in beta-adrenergically mediated thermogenesis were investigated in 11 young (mean +/- SE age: 21.9 +/- 0.5 yr) and 9 older (52.9 +/- 2.1 yr) men during intravenous infusion of the nonselective beta-agonist isoprenaline (Iso). The older men had higher basal plasma norepinephrine (327.7 +/- 35.8 vs. 159.0 +/- 18.2 pg/ml, P < 0.001) and epinephrine (75.1 +/- 18.1 vs. 29.1 +/- 5.3 pg/ml, P < 0.05) concentrations than the young. The beta-adrenergically mediated thermogenesis was diminished in the older men, as reflected by the significantly higher plasma Iso concentration needed to increase resting energy expenditure by 15% (236.1 +/- 51.0 vs. 107.6 +/- 11.4 pg/ml, P < 0.05). Additionally, both dose (39.4 +/- 6.6 vs. 19.1 +/- 1.5 ng . kg fat-free mass-1 . min-1, P < 0.01) and plasma concentration (332.2 +/- 59.1 vs. 119.3 +/- 14.0 pg/ml, P < 0.01) of Iso needed to increase resting heart rate by 25 beats/min were higher in older than in younger subjects, suggesting that the age-related decline in beta-adrenergic sensitivity is a generalized defect not related to a specific tissue or response. In conclusion, aging is associated with a diminished beta-adrenergically mediated thermogenesis. This blunted thermogenic response may contribute to a positive energy balance and thus promote increased fat storage and obesity.

Adipose Tissue↗

PubMed1994

Beta-adrenergic stimulation of energy expenditure and forearm skeletal muscle metabolism in lean and obese men.

The effect of beta-adrenergic stimulation on whole body energy expenditure and forearm skeletal muscle metabolism was investigated in lean and obese men. Whole body energy expenditure was determined during rest and during intravenous infusion of increasing doses of the nonselective beta-agonist isoprenaline (Iso). Forearm skeletal muscle metabolism was investigated with Iso infusion with and without simultaneous infusion of the beta 1-blocker atenolol (AT) by measuring skeletal muscle blood flow (SMBF) and arteriovenous concentration differences of various metabolites. The changes in SMBF were estimated from forearm total (venous occlusion plethysmography), skin (laser doppler), and fat tissue blood flow (133Xe washout). The increase in whole body energy expenditure with Iso was similar in lean and obese subjects. With Iso, the rise in arterial or arterialized glycerol and nonesterified fatty acids (NEFA) was lower in obese than lean subjects, which may reflect a lower beta-adrenergically mediated lipolysis in obesity. During infusion of increasing doses of Iso, the respiratory exchange ratio decreased significantly in lean subjects but not in the obese subjects, which indicates a more pronounced increase in fat oxidation in lean subjects. This is confirmed by the data on skeletal muscle metabolism, where NEFA uptake was increased in lean subjects, whereas the obese subjects showed a tendency toward an increased glucose uptake and a significantly increased lactate release. With Iso plus AT (mainly beta 2-adrenergic stimulation), both groups showed an increased skeletal muscle lactate release. In conclusion, although the thermogenic response to Iso was similar in lean and obese subjects, the utilization of fat seems to be impaired in obesity.

Adrenergic beta-Agonists↗

PubMed1994

beta-Adrenergic stimulation of skeletal muscle metabolism in relation to weight reduction in obese men.

In a companion study [Blaak, E.E., M.A. van Baak, G.J. Kemerink, M.T.W. Pakbiers, G.A.K. Heidendal, and W.H.M. Saris. Am. J. Physiol. 267 (Endocrinol. Metab. 30): E306-E315, 1994.], we found that during infusion of the nonselective beta-agonist isoprenaline (Iso), obese males had a lowered Iso-induced rise in arterial glycerol and nonesterified fatty acids (NEFA) and a lowered muscle NEFA oxidation. The present study was intended to investigate whether a period of weight reduction would alter this impaired fat utilization in obese males. Before and after a 5-wk diet intervention (very low calorie diet) whole body energy expenditure was determined during rest and during intravenous infusion of increasing doses of Iso. In addition, forearm muscle metabolism was investigated with Iso infusion with and without simultaneous infusion of the beta 1-blocker atenolol (AT) by measuring skeletal muscle blood flow and arteriovenous concentration differences of various metabolites across muscle. The Iso-induced whole body thermogenesis tended to increase as a result of weight loss when this response was related to the plasma Iso concentration (P = 0.09), whereas both before and after diet there were no changes in the respiratory exchange ratio during Iso infusion. The increases in arterial NEFA and glycerol concentrations as a result of Iso infusion were not significantly different before and after weight reduction. In addition, muscle NEFA uptake did not change as a result of Iso or Iso plus AT infusion both before and after diet, whereas muscle glucose uptake and lactate release tended to be more pronounced after weight reduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Agonists↗

PubMed1994

Effect of glucose infusion on endurance performance after beta-adrenoceptor blocker administration.

To investigate the effect of glucose (Glc) infusion on endurance performance after beta-adrenoceptor blockade, eight healthy male volunteers performed four endurance cycle ergometer tests at 67% of maximal work load after 80 mg of propranolol (Pr) or placebo (Pl) were administered orally in combination with a continuous infusion of Glc (0.5 g/min) or saline (Sal). The order of the tests was randomized. Endurance times were 53 +/- 6 (SE), 64 +/- 7, 26 +/- 5, and 31 +/- 6 min after Pl+Sal, Pl+Glc, Pr+Sal, and Pr+Glc, respectively (P < 0.001). Glc infusion increased endurance after Pl (P < 0.05) but not after Pr. Glc infusion resulted in significantly higher plasma Glc concentrations during exercise compared with Sal infusion (P < 0.001). Glc infusion had no effect on cardiorespiratory or other metabolic variables. Plasma ammonia concentration was increased during the Pr tests (P < 0.001) but reached similar values at exhaustion in all tests and was not affected by Glc infusion. The maintenance of plasma Glc concentration during endurance exercise at or above preexercise levels did not improve the reduction of endurance performance after Pr, indicating that the availability of blood Glc is not a limiting factor in this process.

Adrenergic beta-Antagonists↗

PubMed1993

Physical activity, fitness, and selected risk factors for CHD in active men and women.

The association of physical activity and cardiovascular fitness with risk factors such as blood pressure, body composition, and smoking habits was evaluated in middle-aged men and women active in sports. Data were available for 2009 men and 898 women, all volunteers over 40 yr of age who were active in sports, were available. Physical activity was recorded as sport activity (number and type of sport, frequency, and duration), occupational activity, and the use of the bicycle for transport. Cardiovascular fitness was expressed as maximal power output (Wmax.kg-1) achieved during a progressive maximal cycle ergometer test. Pearson's product moment correlations between cardiovascular fitness and risk factors indicated significantly lower risks among more fit individuals. Except for smoking habits all risk factors showed better associations with fitness in women than in men. The association of physical activity indicators and risk factors was less strong than the fitness-risk factor association in both genders. In both genders, joggers had the most favorable risk profile compared with subjects who were active in one of the other four most popular sports. We conclude that in this relatively active and healthy population comparable associations of physical activity and cardiovascular fitness with risk factors for cardiovascular disease were found as in studies on less active populations.

Adult↗

PubMed1992

An interactive computer program for randomization analysis of response curves with facilities for multiple comparisons.

An interactive Fortran program, MUCRA, is presented. The program can perform randomization analysis of a completely randomized or randomized-blocks design extended to growth and response curves. A single-step Scheffé-type procedure as well as the Peritz's closed step-down procedure have been implemented which control the familywise type I error-rate. In general, MUCRA is suitable as a computer tool for a distribution-free analysis of variance with repeated measures. The use of MUCRA is demonstrated by analyzing the effects oxprenolol and atenolol have on exercise heart rate. Oxprenolol is a non-selective beta-blocker with moderate intrinsic sympathomimetic activity (ISA), given by the Oros delivery system. Atenolol is a beta 1-selective blocker without ISA. A randomized placebo-controlled crossover design was used to compare the effects of the beta 1-blockers on heart rate during a progressive maximal exercise test on a bicycle ergometer. Application of the Scheffé-type procedure showed that the two drugs significantly (alpha = .05) reduce the heart rate during the exercise test at the three prechosen times (2, 5, and 24 hr) after intake. The reduction from atenolol is more pronounced than from oxprenolol Oros at 2 and 5 hr.

Adult↗

PubMed1992

Effect of hand heating by a warm air box on O2 consumption of the contralateral arm.

Arterialization of venous blood is often used in studying forearm metabolism. Astrup et al. [Am. J. Physiol. 255 (Endocrinol. Metab. 18): E572-E578, 1988] showed that heating of the hand by a warming blanket caused a redistribution of blood flow in the contralateral arm and thus introduced errors in forearm skeletal muscle flux calculations. The present study was undertaken to investigate how hand heating by a warm air box (60 degrees C) would affect metabolism and blood flow in the contralateral arm before and during 3 h after a glucose load. Eleven healthy volunteers (5 males, 6 females) underwent an oral glucose tolerance test (70 g) on two different occasions, one test with and one without heating of the contralateral hand, in random order. Heating the hand for 30 min before glucose intake did not affect skin temperature, rectal temperature, deep venous oxygen saturation, forearm blood flow, or oxygen consumption of forearm skeletal muscle. Although, after the glucose load, heating significantly increased forearm blood flow (P less than 0.05), the integrated response after glucose was not significantly different between control and heating experiments [67 +/- 43 and 117 +/- 41 (SE) ml/100 ml tissue]. With both conditions, there was an increase in skin temperature (P less than 0.001, integrated response control: 369 +/- 79 and heating: 416 +/- 203 degrees C) and oxygen consumption of forearm muscle (control: 290 +/- 73, P less than 0.05 and heating: 390 +/- 130 mumol/100 ml, P less than 0.05) after glucose intake. These responses did not significantly differ between the conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Exercise performance during captopril and atenolol treatment in hypertensive patients.

1. Maximal aerobic exercise capacity, submaximal endurance exercise performance, and exercise haemodynamics have been studied in sixteen patients with mild to moderate essential hypertension during treatment with captopril and atenolol. 2. Administration of atenolol (1 x 100 mg day-1) or captopril (1 x 100 mg day-1) for 6 weeks resulted in similar supine and erect systolic and diastolic blood pressures. Heart rate was significantly lower during atenolol treatment. 3. Exercise heart rate and systolic blood pressure were significantly lower during atenolol than during captopril treatment, exercise diastolic blood pressure (at 100W) did not differ significantly. With atenolol exercise cardiac output was significantly lower and exercise stroke volume significantly higher than with captopril. 4. Maximal work rate, maximal oxygen consumption and maximal heart rate were significantly lower during atenolol than during captopril treatment (respectively 6%, 8% and 25%). Maximal respiratory exchange ratio and lactate concentration did not differ. 5. No statistically significant difference in submaximal endurance time between atenolol and captopril was found. Endurance time was reduced by 19% during atenolol and by 13% during captopril as compared with placebo. No difference in rating of perceived exertion between atenolol and captopril was present. 6. The results indicate that atenolol will reduce blood pressure during exercise more effectively than captopril in patients with hypertension. The limitation of submaximal endurance exercise performance by both agents is of similar magnitude. This may be regarded as an unwanted side effect in certain physically active patients with hypertension.

Atenolol↗

PubMed1988

Beta-adrenoceptor blockade and exercise. An update.

Blockade of beta-adrenoceptors interferes with haemodynamic and metabolic adaptations and ion balance during dynamic exercise. After administration of a beta-blocker exercise heart rate is reduced. Exercise cardiac output and blood pressure are reduced also, but to a lesser extent than heart rate. At submaximal exercise intensities blood flow to the active skeletal muscle is also reduced. The availability of non-esterified fatty acids for energy production is decreased, due to inhibition of beta-adrenoceptor-mediated adipose tissue lipolysis, and possibly also of intramuscular triglyceride breakdown. During submaximal exercise muscle glycogenolysis is unaffected, but there are indications that the maximal glycogenolytic rate at high exercise intensities is decreased. In normally fed subjects plasma glucose concentration is maintained at a normal level during submaximal endurance exercise after beta-blocker administration, although lower glucose concentrations are found in fasting subjects and during high intensity exercise after beta-blocker administration. Plasma lactate concentrations tend to be somewhat lower after beta-blocker administration while plasma potassium concentration during exercise is increased. beta-Blocker administration may also interfere with thermoregulation during prolonged exercise. Maximal aerobic exercise capacity is reduced in normotensive and probably also in hypertensive subjects after beta-blocker administration. Submaximal endurance performance is impaired to a much more important extent in both groups of subjects. In patients with coronary artery disease, on the other hand, symptom-limited exercise capacity is improved during beta-blocker treatment. Studies on trainability during beta-blocker treatment show inconsistent results in healthy subjects, although the majority of studies suggest a similar training-induced increase in VO2max during placebo and beta-blocker treatment. In patients with coronary artery disease the training effects are also similar in patients treated with beta-blockers and those without. The negative effects of beta-blockers on maximal and especially submaximal exercise capacity should be considered when prescribing beta-blockers to physically active hypertensive patients. The negative influence is shared by all types of beta-blockers, although the impairment of submaximal exercise capacity is more pronounced with non-selective than with beta 1-selective beta-blockers. beta-Blockers with intrinsic sympathomimetic activity have similar effects during exercise to those without intrinsic sympathomimetic activity.

Adrenergic beta-Antagonists↗