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Biomedical subjects

H A Keizer

Publications and source records attributed to H A Keizer.

At least 55 records · Page 3Linked to original sources
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↗
PubMed1993

Modulation of glycogen metabolism of rat skeletal muscles by endurance training and testosterone treatment.

The effects of training and/or testosterone treatment on glycogen content and the activities of glycogen synthase, glycogen phosphorylase, and fructose-6-phosphate kinase were studied in extensor digitorum longus (EDL) and soleus muscles of intact adult female rats. One group of rats remained sedentary, whereas another group was trained for 7 weeks. Thereafter, both the sedentary and trained rats were subdivided into two control and four testosterone-treated subgroups. Testosterone was administered by a silastic implant. Training was continued for 2 weeks. On the final day of the experiment rats from one trained control and one trained testosterone-treated subgroup ran for 60 min submaximally. Upon testosterone treatment of sedentary rats the glycogen concentration was not changed. However, in the soleus, but not in the EDL, the glycogen content was increased by training (P < 0.05) which could, at least partly, be explained by a decrease in activity of active glycogen phosphorylase (P < 0.05). In the EDL of trained rats testosterone treatment increased glycogen content significantly by both an increase in activity of active glycogen synthase and a decrease in activity of active glycogen phosphorylase (P < 0.05). In the EDL and soleus of testosterone-treated animals from the exercised subgroup a significant sparing of glycogen was observed, which could be explained by an increase in activity of active glycogen synthase and, in the soleus, could also be explained by a concerted decrease in active glycogen phosphorylase (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Muscle ultrastructure after strength training with placebo or anabolic steroid.

The influence of strength training on muscle fiber area, capillary ultrastructure, and capillary supply was studied in experienced male bodybuilders taking either anabolic steroids or a placebo. During 8 weeks, 13 subjects received a weekly injection of either placebo or nandrolone decanoate (starting dose 200 mg, followed by 100 mg weekly), in a double-blind, counterbalanced design. Before and after 8 weeks a needle biopsy was taken from the vastus lateralis muscle for studying morphometric characteristics of fibers and ultrastructure and morphometric characteristics of capillaries. The fiber cross-sectional area increased significantly only after steroid treatment. Capillary ultrastructure and capillary supply were not changed after the training period. In none of the measured parameters was any difference found between placebo and steroid treatment.

Adult↗
PubMed1992

High energy phosphates and related compounds, glycogen levels and histology in the rat tibialis anterior muscle after forced lengthening and isometric exercise.

Eccentric exercise may elicit damage to the contractile elements. This primary damage is followed by secondary changes, consisting of histological changes and changes in glycogen and energy metabolism. The mechanism underlying changes in glycogen homeostasis and energy metabolism is not well established. The aim of this study was to investigate the possible relationship between changes in adenine and guanine nucleotides, inosine monophosphate (IMP), creatine phosphate, glycogen content and histology in the rat tibialis anterior (TA) muscle after forced lengthening or isometric exercise. The right muscles were either forcibly lengthened or isometrically exercised, while the contralateral muscles served as non-exercised controls. The exercised muscles were dissected 0, 6 and 24 h post-exercise and the contents of adenine and guanine nucleotides, IMP, creatine phosphate, and glycogen determined. In addition, histological changes were assessed. Immediately after both types of exercise increases in tissue IMP levels were found. Irrespective of the type of exercise, glycogen content was decreased immediately post-exercise, but restored 6 h post-exercise. Twenty-four hours later a second decline in glycogen content was found after both types of exercise. In forcibly lengthened muscles ATP content was decreased 24 h post-exercise. In isometrically exercised muscles ATP was not decreased at any time. Gross structural changes were found in all forcibly lengthened muscles (9-12% of TA muscle volume). In isometrically exercised muscles structural changes were minor (up to 0.1% of muscle volume), were found only immediately post-exercise and in only 4 out of 18 muscles. It is concluded that forced lengthening results in decreased ATP levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine Nucleotides↗
PubMed1992

Modulation of fatty-acid-binding protein content of rat heart and skeletal muscle by endurance training and testosterone treatment.

The effects of training and/or testosterone treatment and its aromatization to oestradiol on fatty-acid-binding protein (FABP) content and cytochrome c oxidase activity in heart, soleus and extensor digitorum longus (EDL) muscles were studied in intact adult female rats. One group of rats remained sedentary, whereas the others were trained for 7 weeks. Thereafter the trained rats were divided into control and testosterone-treated groups, with or without an aromatase inhibitor. Testosterone was administered by a silastic implant. Training was continued for 2 weeks. In untreated sedentary rats the immunochemically assayed FABP contents were 497 +/- 28, 255 +/- 49 and 58 +/- 17 micrograms/g wet weight for the heart, soleus, and EDL respectively. In the heart the FABP content was increased after training (29%), testosterone treatment (33%) or both manipulations (53%). In soleus muscle FABP increased only after testosterone treatment (16%), whereas in EDL no changes were found. Inhibiting the aromatase enzyme complex abolished the testosterone-induced effect on FABP content in soleus (suggesting an oestradiol effect) but not in heart muscle. Among the three muscles studied the FABP content was found to be related to the cytochrome c oxidase activity in a non-linear way. In conclusion, it is shown that the FABP contents and mitochondrial activities of heart and skeletal muscle are affected by training and sex hormones and that these effects are different for heart and skeletal muscles.

Animals↗
PubMed1992

A new approach for the determination of ventilatory and lactate thresholds.

In order to determine the ventilatory threshold (VT) and the lactate threshold (LT) in a reliable way, a new method is proposed and compared with conventional methods. The new method consists of calculating the point that yields the maximal distance from a curve representing ventilatory and metabolic variables as a function of oxygen uptake (VO2) to the line formed by the two end points of the curve (Dmax method). Male cyclists (n = 8) performed two incremental exercise tests a week apart. Ventilatory/metabolic variables were measured and blood was sampled for later lactate measurement during each workload and immediately after exercise. No statistical differences were observed in the threshold values (expressed as absolute oxygen uptake; VO2) determined by the Dmax method and the conventional linear regression method (according to O2 equivalent; EqO2) and venous blood at the onset of blood lactate (OBLA), while VT assessed with the conventional linear method (according to the slope of CO2 output; Vslope) yielded significantly lower threshold values. Similar results were obtained from the reproducibility test. Thus, the Dmax method appears to be an objective and reliable method for threshold determination, which can be applied to various ventilatory or metabolic variables yet yield similar results. The results also showed that breathing frequency can be used to determine VT.

Adolescent↗
PubMed1992

Physiological changes in male competitive cyclists after two weeks of intensified training.

To study the physiological response to heavy training, seven male competitive cyclists intensified their normal training program for two weeks (IIT) in order to achieve a state of short-term overtraining. The subjects underwent a graded cycle ergometer test to exhaustion, an outdoor 8.5 km time trial and a computerized test to study reaction time and visual perception, before, during and after the two weeks of intensified training and after two weeks of recovery. Furthermore subjects kept a daily log in the form of a questionnaire. After two weeks of IIT all subjects showed symptoms of overtraining: the general state of well being declined as indicated by the questionnaire while performances on time trial (mean +/- SEM: 830 +/- 14 sec-871 +/- 19 sec), contests and maximal power output (mean +/- SEM: 336 7 watt-310 +/- 5 watt) declined significantly. Maximal (mean +/- SEM 11.8 +/- 1.1 mmol.l-1-5.9 +/- 0.5 mmol.l-1) and submaximal lactate values were significantly lowered during ergometer test after the IIT, while the workload at the 4 mmol point increased significantly (mean +/- SEM 234 +/- 10 watt-267 +/- 13 watt). Sleeping heart rate increased significantly (mean +/- SEM 49.5 +/- 9.3 BPM-54.3 +/- 8.8 BPM). Maximal heart rate (mean +/- SEM 185 +/- 3 BPM-178 +/- 2 BPM, mean heart rate during the time trial (mean +/- SEM 178 +/- 2 BPM-169 +/- 2 BPM) and VO2max (mean +/- SEM 4801 +/- 121 ml.min-1-4409 +/- 101 ml.min-1) were all significantly lowered by the IIT.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Low vertebral bone density values in young non-elite female runners.

Thirty-five female runners (26.6 +/- 0.9 years, range 17-35) were scheduled for bone mineral density evaluation, using quantitative computed tomography of the lumbar spine. In 17 women with oligo-amenorrhea, vertebral bone mineral density was under the normal range (defined from a control group of 46 sedentary healthy females in the same age range), while it was within the normal range in all runners with regular menses (n = 18). When age classes were considered, all runners aged 17-21 (11/11) were found to have oligo-amenorrhea and low bone mineral density values, the difference in mineral density with the controls of the same age quartile being highly significant (p less than 0.001). Runners from the two youngest age classes (17-21 and 22-26) had started training early after menarche (0.9 +/- 0.6 and 2.5 +/- 1.6 years, respectively). These results show that very young female runners with oligo-amenorrhea may have impressively low bone mineral density values. The possibility that early onset of training, close to menarcheal age, might be a risk factor for low mineral density, deserves further investigation.

Adolescent↗
PubMed1990

Use of the intact mouse skeletal-muscle preparation for metabolic studies. Evaluation of the model.

1. We examined the isolated mouse skeletal-muscle model in vitro, commonly used by many investigators, for its suitability for metabolic studies. 2. Despite the fact that pH, O2 saturation, osmolality and the release of the enzyme creatine kinase remained stable, histochemical studies showed large cores devoid of glycogen, suggesting that the incubated muscle had lost its viability. 3. This study indicates that caution should be exercised when interpreting the results of studies with intact isolated mouse muscles.

Animals↗
PubMed1990

Physical exercise and menstrual cycle alterations. What are the mechanisms?

The prevalence of menstrual cycle alterations in athletes is considerably higher than in sedentary controls. There appears to be a multicausal aetiology, which makes it extremely difficult to dissociate the effects of physical exercise on the menstrual cycle from the other predisposing factors. From cross-sectional studies it appeared that physical training eventually might lead to shortening of the luteal phase and secondary amenorrhoea. Prospective studies in both trained and previously untrained women have shown that the amount and/or the intensity of exercise has to exceed a certain limit in order to elicit this phenomenon. We hypothesise, therefore, that apart from a certain predisposition, athletes with a training-induced altered menstrual cycle are overreached (short term overtraining, which is reversible in days to weeks after training reduction). Menstrual cycle alterations are most likely caused by subtle changes in the episodic secretion pattern of luteinising hormone (LH) as have been found in sedentary women with hypothalamic amenorrhoea as well as in athletes after very demanding training. The altered LH secretion then, might be caused by an increased corticotrophin-releasing hormone (CRH) secretion which inhibits the gonadotrophin-releasing hormone (GnRH) release. In addition, increased CRH tone will lead to increased beta-endorphin levels which will also inhibit the GnRH signaller. Finally, the continuous activation of the adrenals will result in a higher catecholamine production, which may be converted to catecholestrogens. These compounds are known to be potent inhibitors of GnRH secretion. In conclusion, menstrual cycle alterations are likely to occur after very demanding training, which causes an increase secretion of antireproductive hormones. These hormones can inhibit the normal pulsatile secretion pattern of the gonadotrophins.

Amenorrhea↗
PubMed1989

Metabolic changes induced by sustained exhaustive cycling and diet manipulation.

Thirteen highly trained subjects were studied concerning the effect of consuming a normal carbohydrate-rich diet (N) on energy exchange, substrate metabolism, and performance. Six of these subjects performed the same protocol receiving N supplemented with a high-maltodextrin, low-fructose beverage (Mf). The studies were performed in random order. The subjects performed 2 days of sustained exhausting cycling, preceded and followed by a standardized resting day, in a respiration chamber, allowing continuous gas analysis, weighed food and fluid intake procedures, collection of excretes, and drawing of blood samples at 7:00 AM, 12:00 AM (halfway exercise) and 3:00 PM at exhaustion. Muscle biopsies were taken prior to, 45 min after, and 24 h after exercise (energy expenditure 25.2-26.6 MJ.day-1). The results showed that while consuming a normal diet, the cyclists developed a negative energy balance (-9 MJ.day-1) and regulated their hormone levels in such a way that fat oxidation and protein breakdown were increased and CHO oxidation became depressed. When supplemented with Mf, the subjects showed increased blood glucose, insulin and decreased glucagon levels. Fat metabolism was significantly depressed as indicated by the levels of blood fatty acids, glycerol, and ketones. A significant glycogen sparing, as well as supercompensation within 24 h of recovery, was observed after Mf supplementation. The normal CHO-rich diet, available ad libitum, was insufficient to fully restore glycogen within 24 h. The changes in substrate availability and glycogen depletion were accompanied by a significant performance improvement, 126% when cycling a final 90% Wmax bout, when supplemented with Mf compared with N.

Adult↗
PubMed1989

Glycogen synthesis during exercise and rest with carbohydrate feeding in males and females.

Since it has been demonstrated that endurance-trained cyclists are able to synthesize glycogen during mild exercise, glycogen synthesis was investigated in non-endurance-trained males and females as well. Seven males and nine females exercised on a cycle ergometer to deplete muscle glycogen. After the exhaustive exercise and taking a muscle biopsy, the males either exercised 2.5 h at 40% of maximal work load (trial A) or rested for 2.5 h (trial B). In both trials the subjects drank a 25% maltodextrin-fructose solution. After 2.5 h of exercise or rest, a second muscle biopsy was taken for determination of glycogen and for histochemistry (ATPase and PAS). In the females glycogen synthesis was only studied during 2.5 h rest, after prior glycogen depletion. In the male subjects, during mild exercise with carbohydrate feeding muscle glycogen did not increase. During rest muscle glycogen increased in the males from 123 +/- 49 mmol/kg DW at exhaustion to 229 +/- 70 mmol/kg DW (P less than 0.001), resulting in a net increase of 42 mmol/kg DW/h. Glycogen synthesis during rest occurred both in type I and type II fibers. In the females, during 2.5 h of rest, muscle glycogen increased from 130 +/- 56 mmol/kg DW at exhaustion to 224 +/- 51 mmol/kg DW, resulting in a net increase of 37 mmol/kg DW/h. The results demonstrate that glycogen synthesis during mild exercise does not occur in non-endurance-trained athletes, whereas in the resting state glycogen synthesis in non-endurance-trained males is not different from endurance-trained cyclists. In addition, glycogen synthesis during rest is similar in males and females.

Adult↗
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↗