Search PubMed⌕ Search

Biomedical subjects

H Kuipers

Publications and source records attributed to H Kuipers.

At least 91 records · Page 5Linked to original sources
PubMed1989

Plasma activity of muscle enzymes: quantification of skeletal muscle damage and relationship with metabolic variables.

One hundred fourteen sedentary volunteers (34 +/- 8 years) took part in an endurance training study to be completed after 18-20 months with a marathon. Ultimately, 60 males and 18 females achieved that goal. The training program, carefully supervised, was divided into three periods with a maximum of 45-, 70-, and 110-km week training volume and concluded with a performance race of 15, 25, and 42.2 km, respectively. Three days before and 3 and 5 days after each race, 35 subjects were selected to perform a progressive treadmill test and the remaining subjects participated in field tests of 400 and 1000 m. A significant decrease in half-life time of CK enzyme plasma activity after running long distances in the course of the study from 20 h to 13 h was observed. Based on plasma enzyme activity and supposing that the total enzyme content left the muscle fiber, the estimated amount of muscle damage was found to be small. A gender difference in plasma enzyme activity increase (females demonstrated a lower increase) occurred only after the marathon.

Adaptation, Physiological↗
PubMed1989

Exercise-induced focal skeletal muscle fiber degeneration and capillary morphology.

The relationship between exercise-induced focal muscle fiber degeneration and changes in capillary morphology was investigated in male Wistar rats. Untrained animals ran on a treadmill for 1 h at submaximal intensity and were killed 0, 6, or 24 h after running. Nonexercised rats served as controls. In situ perfused soleus muscles were prepared for electron microscopy. Micrographed cross sections were quantitatively analyzed for parameters indicative of capillary blood flow or transcapillary exchange. Capillary lumina were ovally rather than circularly shaped, and no indications for obstruction of blood flow at the capillary level were found. Endothelial cells and their organelles had a normal appearance in all groups. However, immediately after exercise, capillaries showed a decreased thickness of their endothelium and basal membrane, probably caused by dehydration. Six hours after exercise, muscle fibers were swollen (28% increase in cross-sectional area), resulting in a slightly increased diffusion distance. This fiber swelling was not associated with an increase in muscle water content, a finding for which no explanation could be found. Twenty-four hours after the animals ran, capillaries located near degenerated muscle fibers had an increased cross-sectional luminal area and an increased luminal circumference. This effect decreased gradually with increasing distance from the degenerated fiber area. The present morphometric results do not support the hypothesis that changes in capillary morphology primarily contribute to exercise-induced focal muscle fiber degeneration.

Animals↗
PubMed1988

Comparison of heart rate as a non-invasive determinant of anaerobic threshold with the lactate threshold when cycling.

In 9 trained athletes and 4 sedentary subjects the anaerobic threshold was assessed on a cycle ergometer, using the deflection point of heart rate in a protocol in which the workload increased by 10 W every 45 s. The workload at which plasma lactate concentration equalled 4 mmol.l-1 was assessed under steady state conditions on separate occasions. In addition, in 3 subjects the non-invasive anaerobic threshold and the 4 mmol.l-1 lactate level under steady state conditions were assessed on a treadmill. On the cycle ergometer 6 subjects demonstrated a deflection point in the heart rate record, whereas the others failed to do so. The workload at which heart rate departed from linearity in the progressive protocol did not coincide with the steady state 4 mmol.l-1 workload but occurred at a higher workload. On the treadmill no deflection in heart rate was observed. It is concluded that in cyclists a deflection in heart rate does not always occur, and when it does, it does not coincide with the anaerobic threshold determined under steady state conditions.

Adult↗
PubMed1988

Overtraining in elite athletes. Review and directions for the future.

Overtraining is an imbalance between training and recovery. Short term overtraining or 'over-reaching' is reversible within days to weeks. Fatigue accompanied by a number of physical and psychological symptoms in the athlete is an indication of 'staleness' or 'overtraining syndrome'. Staleness is a dysfunction of the neuroendocrine system, localised at hypothalamic level. Staleness may occur when physical and emotional stress exceeds the individual coping capacity. However, the precise mechanism has yet to be established. Clinically the syndrome can be divided into the sympathetic and parasympathetic types, based upon the predominance of sympathetic or parasympathetic activity, respectively. The syndrome and its clinical manifestation can be explained as a stress response. At present, no sensitive and specific tests are available to prevent or diagnose overtraining. The diagnosis is based on the medical history and the clinical presentation. Complete recovery may take weeks to months.

Fatigue↗
PubMed1987

Carbohydrate feeding and glycogen synthesis during exercise in man.

In 7 male cyclists glycogen synthesis during exercise and rest was studied. Each subject did two exercise trials (A and B), in random order. In both trials, after determining the maximal workload (Wmax), intermittent exercise was given to exhaustion. After the exhaustive exercise and taking a muscle biopsy the subjects either exercised at 40% Wmax for 3 h (trial A) or rested for 3 h (trial B), during which they consumed approximately 2 l of a 25% malto-dextrine drink in both trials. After 3 h rest (trial A) or 3 h of mild exercise (trial B) a second muscle biopsy was taken for total glycogen and histochemistry (ATPase and PAS). Blood glucose and insulin levels were elevated during the first 2 h of exercise (p less than 0.05). Glycogen depletion was most pronounced in type I and to a less extent in type IIA fibers. In trial A muscle glycogen increased from 136 +/- 66 to 199 +/- 71 mmol/kg DW, and in trial B from 145 +/- 56 to 257 +/- 79 mmol/kg DW. During exercise glycogen repletion was restricted to type IIA and IIB fibers, whereas during rest glycogen synthesis occurred both in type I and type II fibers. The present study demonstrates that oral carbohydrate administered during exercise may not only provide substrate for energy metabolism, but can also be utilized for glycogen synthesis in the non-active muscle fibers.

Adult↗
PubMed1987

Influence of liquid and solid meals on muscle glycogen resynthesis, plasma fuel hormone response, and maximal physical working capacity.

The effect of forced liquid (L) or solid (S) carbohydrate (CHO)-rich feedings on plasma glucose, insulin, and glycogenesis after glycogen depletion was investigated. The relationship between glycogen restoration and maximal physical working capacity (MPWC) was studied as well. Eight males performed two experiments, with 2 weeks interval, on a bicycle ergometer. In each experiment, MPWC was determined in a graded test, which was immediately followed by interval work until exhaustion. After exercise cessation (EC), the subjects started to consume a standardized amount of concentrated L or CHO-rich food. Insulin and glucose concentration in blood were determined. Muscle glycogen was determined before, immediately after, 5 h after, and 22 h after EC. MPWC was determined again 22 h after EC. Four subjects performed a third experiment, in which solid food consumption was left ad libitum (AL). A rapid glycogen repletion was found 5 h after EC, i.e., from 72 +/- 40 to 198 +/- 38 mmol/kg in the S, and from 69 +/- 39 to 192 +/- 40 mmol/kg in the L experiment. The higher plasma glucose and insulin levels (P less than 0.05) during the 5 h after EC in the S experiments did not elicit a difference in glycogen repletion. Glycogen synthesis rate in the AL experiment was lower (P less than 0.05) than in the L and S experiments. Glycogen restoration in the L and S experiments was complete 22 h after depletion. However, despite repletion of glycogen, MPWC was decreased (P less than 0.05) in both experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Multiple hormonal responses to physical exercise in eumenorrheic trained and untrained women.

The aim of the present investigation was to compare the changes in plasma estradiol (E2), progesterone (P), luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (T), androstenedione (delta 4-A), dehydroepiandrosterone sulfate (DHEA-S), adrenocorticotropic hormone (ACTH), and prolactin (PRL) in standardized tests (15-min consecutive work loads of 60%, 70%, 80% VO2 max to exhaustion) in 13 eumenorrheic untrained (UT) and 8 highly trained women (MR). Blood was obtained 15 and 2 min before exercise and at the end of each work load or each 15 min period. The results showed a significant increase (0.05 greater than P less than 0.001, two-way ANOVA) in plasma E2 P, T delta 4-A, PRL, and ACTH both in UT and MR irrespective of the phase of the menstrual cycle. DHEA S levels increased significantly in the MR, but not in the UT, PRL and ACTH increased linearly with exercise in MR and nonlinearly in UT. In the latter group, only the 80% VO2 max work load was able to elicit significant increments in the plasma levels of these hormones. In the MR plasma T and delta 4-A levels increased relatively more pronounced (P less than 0.05) at comparable work loads and exercise times than in the UT. LH levels decreased with exercise both in the UT and MR, whereas FSH levels remained unchanged (MR) or decreased (UT). These findings suggest that during exercise the ovarian hormones are increased by more unspecific mechanisms such as a decreased metabolic clearance rate, whereas in the MR, adrenal secretion of androgens is enhanced.

Adrenal Cortex Hormones↗
PubMed1987

Exercise-induced changes in the percentage of free testosterone and estradiol in trained and untrained women.

We have studied the effect of exercise on the percentage of free plasma estradiol 17-beta (E2) and testosterone (T) in 13 untrained (UT) and 8 trained (marathon runners, MR) eumenorrheic women. All women performed a standardized bicycle ergometer (UT) or treadmill (MR) test in the follicular and luteal phases of their menstrual cycles (15-min consecutive work loads of 60%, 70%, and 80% VO2 max to exhaustion). Blood was drawn through an indwelling venous catheter at 15 and 2 min before and immediately after exercise. Free E2 and T was assayed by centrifugal ultrafiltration using undiluted plasma at 37 degrees C (basal samples) and 39 degrees C (exercise samples). Statistical analysis was performed by a two-tailed paired t test. In the UT, the basal percentage of free E2 was measured to be 1.55% +/- 0.24% (mean +/- SD) in the follicular phase and 1.62% +/- 0.32% in the luteal phase (differences NS). In the MR, these values were 1.22% +/- 0.25% and 1.25% +/- 0.12% for the follicular and luteal phases, respectively. The differences between the groups were not significant. Exercise did not provoke significant changes in free E2 in either of the groups. Constrastingly, exercise induced a significant (P less than 0.02) increase in the percentage of free T from 1.56% +/- 0.27% to 2.1% +/- 0.36% and from 1.6% +/- 0.27% to 2.12% +/- 0.33% in the UT in the follicular and luteal phases, respectively. In the MR, the free percentage of T increased from 1.04% +/- 0.39% to 1.6% +/-0.16% (follicular phase) and from 1.24% +/- 0.22% to 1.67% +/- 0.18% (P less than 0.02).

Adult↗
PubMed1987

Effect of a 3-month endurance training program on metabolic and multiple hormonal responses to exercise.

We have investigated the effect of a 3-month endurance training program (running and cycling) on plasma hormone responses during standardized bicycle ergometer work (15-min consecutive work loads of 60%, 70%, 80%, and eventually 90% VO2 max) in eight previously untrained eumenorrheic women. The subjects were investigated before and after training both in the follicular and luteal phases of the menstrual cycle (between the 7th-10th and 20th-25th days of their menstrual cycle, respectively). Blood was obtained 15 and 2 min before the onset of exercise and at the end of each work load from an indwelling catheter. In each sample, the plasma concentrations of estradiol 17 beta (E2), progesterone (P), testosterone (T), androstenedione (delta 4-A), dehydroepiandrosterone sulfate (DHEA-S), prolactin (PRL), and adrenocorticotropic hormone (ACTH) were assayed in duplicate by RIA; lactate was assayed as well. The hormone concentrations were expressed in absolute as well as in relative values. After training basal DHEA-S and ACTH levels were significantly (P less than 0.05) lower in both phases of the menstrual cycle, whereas basal luteal phase E2 and T levels were significantly (0.05 greater than P greater than 0.01) lower after training. Exercise induced significant increments in the relative values of all hormones in both phases (0.05 greater than P greater than 0.001). After training, T and DHEA-S increased relatively more pronounced (0.05 greater than P greater than 0.02) in the follicular and luteal phase, respectively.

Adrenal Cortex Hormones↗
PubMed1987

Substrate utilization in leg muscle of men after heat acclimation.

Eight men were heat acclimated (39.6 degrees C and 29.2% rh) for 8 days to examine changes in substrate utilization. A heat exercise test (HET), (cycling for 60 min; 50% maximal O2 consumption) was performed before (UN-HET) and after (ACC-HET) the acclimation period. Muscle glycogen utilization (67.0 vs. 37.6 mmol/kg wet wt), respiratory exchange ratio (0.85 +/- 0.002 vs. 0.83 +/- 0.001), and calculated rate of carbohydrate oxidation (75.15 +/- 1.38 vs. 64.80 +/- 1.52 g/h) were significantly reduced (P less than 0.05) during the ACC-HET. Significantly lower (P less than 0.05) femoral venous glucose (15, 30, and 45 min) and lactate (15 min) levels were observed during the ACC-HET. No differences were observed in plasma free fatty acid (FFA) and glycerol concentrations or glucose, lactate and glycerol arteriovenous uptake/release between tests. A small but significant increase (P less than 0.05) above resting levels in FFA uptake was observed during the ACC-HET. Leg blood flow was slightly greater (P greater than 0.05) during the ACC-HET (4.64 +/- 0.13 vs. 4.80 +/- 0.13 l/min). These findings indicate a reduced use of muscle glycogen following heat acclimation. However, the decrease is not completely explained by a shift toward greater lipid oxidation or increased blood flow.

Acclimatization↗
PubMed1986

Regulation and structure of an Escherichia coli gene coding for an outer membrane protein involved in export of K88ab fimbrial subunits.

The nucleotide sequence of the faeD gene of Escherichia coli and the amino acid sequence of its product is presented. The faeD product is an outer membrane protein required for transport of K88ab fimbrial subunits across the outer membrane. The protein is synthesized as a precursor containing a signal peptide, and the tentative mature protein comprises 777 amino acid residues. The distribution of amino acids in the faeD protein is similar to that of other outer membrane proteins; showing a fairly even distribution of charged residues and the absence of extensive hydrophobic stretches. Secondary structure predictions revealed a region of 250 amino acid residues which might be embedded in the outer membrane. The 5'-end of faeD is located within a region showing dyad symmetry. This region serves to couple translation of faeD to the translation of the gene preceding it (faeC). The 3'-end of faeD shows an overlap of 5 bases with the next gene (faeE).

Amino Acid Sequence↗
PubMed1986

Glucose feeding and exercise in trained rats: mechanisms for glycogen sparing.

This investigation studied the effect of an oral glucose feeding on glycogen sparing during exercise in non-glycogen-depleted and glycogen-depleted endurance-trained rats. The non-glycogen-depleted rats received via a stomach tube 2 ml of a 20% glucose solution labeled with [U-14C]glucose just prior to exercise (1 h at 25 m/min). Another group of rats ran for 40 min at higher intensity to deplete glycogen stores, after which they received the same glucose feeding and continued running for 1 h at 25 m/min. The initial 40-min run depleted glycogen in heart, skeletal muscle, and liver. In the non-glycogen-depleted rats the glucose feeding spared glycogen in the liver, primarily from the oxidation of blood-borne glucose in muscle. In the glycogen-depleted rats, muscle glycogen was repleted after the feeding, but sources other than the administered glucose also contributed to glycogen synthesis. The results suggest that glycogen depletion rather than the glucose feeding per se stimulates glycogen resynthesis in muscle during exercise in endurance-trained rats.

Animals↗
PubMed1985

Variability of aerobic performance in the laboratory and its physiologic correlates.

To study the physiologic basis of variability of physical performance in the laboratory, ten male subjects were studied once a week, during a 9-12 month period. Previously, the reference maximal work load attained (Wref) was determined in each subject. The test protocol of the actual study was based on the individual Wref and started at 70% Wref for 5 min whereupon the work load was increased by 5% Wref every 2.5 min to exhaustion. The maximal work load attained (Wmax) was considered as the test performance. Heart rate, respiratory variables, oxygen uptake (VO2), and blood lactate concentration were determined at each work load. The rate of perceived exertion during submaximal and maximal work was also scored. In all subjects, Wmax and VO2max varied randomly, while the coefficient of variation in VO2max (4.20% - 11.35%) exceeded that in Wmax (2.95%-6.83%). No seasonal influences on VO2 max and Wmax were observed. In all subjects the physiologic variables, when plotted as a function of external work load, were shifted to the right with higher Wmax values and to the left with lower Wmax values. With lower Wmax values, the rate of perceived exertion during submaximal work tended to increase. The results suggest that the magnitude of physiologic responses to exercise is related to relative work load and that variability of physical performance is related to changes in gross mechanical efficiency.

Adult↗