摘要:

The effect of sprint training and detraining on supramaximal performances was studied in relation to muscle enzyme adaptations in eight students trained four times a week for 9 weeks on a cycle ergometer. The subjects were tested for peak oxygen uptake (V˙O2 peak), maximal aerobic power (MAP) and maximal short‐term power output (W˙max) before and after training and after 7 weeks of detraining. During these periods, biopsies were taken from vastus lateralis muscle for the determination of creatine kinase (CK), adenylate kinase (AK), glycogen phosphorylase (PHOS), hexokinase (HK), phosphofructokinase (PFK), lactate dehydrogenase (LDH) and its isozymes, 3‐hydroxy‐acyl‐CoA dehydrogenase (HAD) and citrate synthase (CS) activities. Training induced large improvements in W˙max(28%) with slight increases (3%) in V˙O2 peak}(P < 0.10). This was associated with a greater glycolytic potential as shown by higher activities for PHOS (9%), PFK (17%) and LDH (31%) after training, without changes in CK and oxidative markers (CS and HAD). Detraining induced significant decreases in V˙O2 peak(4%), MAP (5%) and oxidative markers (10–16%), while W˙maxand the anaerobic potential were maintained at a high level. This suggests a high level in supramaximal power output as a result of a muscle glycogenolytic and glycolytic adaptation. A long interruption in training has negligible effects on short‐sprint ability and muscle anaerobic potential. On the other hand, a persistent training stimulus is required to maintain high aerobic capacity and muscle oxidative potential. This may contribute to a rapid return to competitive fitness for sprinte

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00244.x

出版商:Blackwell Science Ltd    

年代:1997

数据来源: WILEY

摘要:

The aim of this mixed cross‐sectional longitudinal study covering a total age range of 11–17 years, i.e. the entire pubertal growth period, was (1) to specify the changes in maximal breathing pattern during incremental exercise; (2) to determine what parts of the changes are due to anthropometric characteristics, physical fitness and inspiratory or expiratory muscle strength; and (3) to determine if the role of these variables is identical before, during and after pubertal growth spurt. This study was conducted in 44 untrained schoolboys separated into three groups, with an initial age of 11.2 ± 0.2 years for group A, 12.9 ± 0.25 years for group B, and 14.9 ± 0.26 years for group C. These children were subsequently followed for 3 years, during the same time period each year. The maximal inspiratory and expiratory pressures (PI maxandPE max) were used as an index of the respiratory muscle strength. During an incremental exercise test, maximal ventilation (V˙E max), tidal volume (VT max), breathing frequency (fmax), inspiratory and expiratory times (tI maxandtE max) and mean inspiratory flow (VT/tI max) were measured at maximal oxygen uptake (V˙O2max). Our study showed that there was a marked increase with age inV˙E max,VT max, andVT/tI max, and no significant changes infmax,tI maxandtE max.PI maxandPE maxshowed a general trend towards an increase between 11 and 17 years. The study of the linear correlations between maximal breathing pattern and the anthropometric characteristics, physical fitness and inspiratory or expiratory muscle strength showed that, in the three groups of children, (1) lean body mass was the major determinant ofV˙E max,VT maxandVT/tI maxand the relationships were significantly different before, during and after the pubertal growth spurt; (2) physical fitness was the main determinant oftI max,tE maxandfmaxbefore and after the pubertal growth spurt; and (3) maximal respiratory strength did not play a significant role. In conclusion, this mixed cross‐sectional longitudinal study showed, at maximal exercise, a significant increase inV˙E maxduring growth due only to a significant increase inVT maxandVT/tI max, and that the relationships of anthropometric characteristics and physica

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00245.x

出版商:Blackwell Science Ltd    

年代:1997

数据来源: WILEY

摘要:

Six healthy subjects performed endurance training of the same duration with legs and arms consecutively. Performance and muscle structure were measured before and after training in lower and upper limbs. Training induced similar increases in maximal oxygen consumption (6 ± 1 vs. 7 ± 2 mL min−1 kg−1: legs vs. arms,P > 0.05) and mitochondrial volume in leg and arm muscles (42 ± 12 vs. 31 ± 11%: legs vs. arms,P > 0.05). The gain in mitochondrial volume after training was achieved solely by increasing the fraction of mitochondria (+40 ± 11%,P  0.05) in the legs. In contrast, increased muscle volume (+14 ± 3%,P  0.05), occurred in the arms after training. Thus, similar improvements in muscle oxidative capacity in upper and lower limbs were brought about by different mechanisms. It is suggested that due to infrequent use and a lack of load‐bearing function, arm muscle volume is underdeveloped in untrained, sedentary or detrained/injured subjects and that the mode of endurance training used in this s

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00246.x

出版商:Blackwell Science Ltd    

年代:1997

数据来源: WILEY

摘要:

The amplitude of a surface electromyogram is dependent on the number of active motor units, their size and the relative position of the recording electrode. It is not possible to interpret the surface electromyogram quantitatively without disentangling these different aspects. In this study the decline of different components of the motor unit potential with increasing radial distance from the motor unit is quantified. Fifty‐two motor units in the biceps brachii muscle were studied using 36‐channel surface electromyography combined with intramuscular scanning electromyography. Scanning electromyography was used to locate precisely the motor unit. The dependence of the surface motor unit potential magnitude on the radial distance between the motor unit and the recording electrodes can be described fairly well by an inverse power function. The steepness of this function depends on the chosen motor unit potential parameter and the interelectrode distance, but also varies between motor units. The change of the negative peak amplitude of the motor unit potential over the skin surface can be used to give a fairly accurate estimate of the location of the motor unit under the skin surface. We found that for all practical purposes the depth of a motor unit in the biceps brachii muscle can be estimated as 20% of the distance over the skin surface where motor unit potentials can be recorded with higher amplitudes than 50% of the maximal amplitude recorded at the skin surface caused by activity of the same motor u

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00247.x

出版商:Blackwell Science Ltd    

年代:1997

数据来源: WILEY

摘要:

Mammalian skeletal muscle expresses at least two isoforms of the cytoskeletal protein titin (connectin; MW ≈ 3000 kDa). These isoforms are associated with different passive force curves, and thus may affect physical performance. To study the distribution of titin and its possible influence on performance in humans, muscle biopsies were obtained from 15 males (X± SE; age = 25.4 ± 2.9 years, height = 177.7 ± 1.8 cm, weight = 76.5 ± 2.2 kg). Two biopsies were obtained on separate occasions from both the right and left vastus lateralis, and one biopsy each from the lateral head of the right gastrocnemius and the right soleus, with all biopsies handled identically. Fibre type analyses were performed via mATPase histochemistry. Expression of titin and myosin heavy chain isoforms were determined by SDS‐PAGE. Titin bands in the resulting gels were highly repeatable and were verified by migration patterns, as well as Western blot analysis. Two groups of subjects were identified: group 1 (n=10) expressed only one titin isoform (titin‐1) in all biopsies, and group 2 (n=5) expressed two titin isoforms (titin‐1 and titin‐2) in all biopsies. No significant differences (P>0.05) between groups were observed for percentage fibre types, percentage fibre type areas, fibre type cross‐sectional areas, and percentage myosin heavy chain expression when comparing individual muscles, sampling times or bilateral comparisons. This is the first report of differential titin isoform expression in healthy, mature human skeletal muscle, but it is not clear why this occurs or what influence this ma

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00252.x

出版商:Blackwell Science Ltd    

年代:1997

数据来源: WILEY

摘要:

We have investigated the difference in lipolysis caused by a β‐adrenergic agent between visceral and abdominal subcutaneous adipose tissuesin vivo. Glycerol levels (lipolysis index) were continuously monitored in mesenteric and abdominal subcutaneous adipose tissues of anaesthetized Wistar rats using the microdialysis technique. During microdialysis, increasing concentrations of the lipolytic agent, isoproterenol (10−8, 10−7, 10−6, 10−5mol L−1), were added to the perfusion. Glycerol concentrations in dialysate at each isoproterenol concentration, blood glucose concentrations during the experiment, and plasma insulin concentrations before and immediately after the experiment were measured. The effect of isoproterenol on local blood flow was investigated using the ethanol technique. The clearance rate of ethanol from the perfusion medium was used as the index of local blood flow. There was no significant change in blood glucose or plasma insulin concentrations during the study. Glycerol levels in dialysate were significantly higher in mesenteric than in abdominal subcutaneous adipose tissues at all isoproterenol concentrations. The percentage change of baseline ethanol ratio was not altered by increasing isoproterenol concentrations in both mesenteric and subcutaneous adipose tissues. There was also no significant difference in percentage change of the baseline ethanol ratio between mesenteric and abdominal subcutaneous adipose tissues. These results suggest that mesenteric adipose tissue is characterized by an even higher β‐adrenergic agonist‐induced lipolysis than abdominal subcutan

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00234.x

出版商:Blackwell Science Ltd    

年代:1997

数据来源: WILEY

摘要:

The H2‐receptor antagonist cimetidine reduces appetite and weight in overweight healthy subjects and in overweight subjects with type II diabetes mellitus. The aim of this study was to characterize the mechanisms of this effect in rodents. Drugs were administered three times a day, 30 min before 1 h periods of free access to food. In one group of rats (n=9), cimetidine (8 mg) treatment resulted in significantly lower cumulative food intake than in a control group (n=9). The total intakes of food during the observation period of 22 days were 325.3 ± 29.1 g and 346.3 ± 16.7 g in the cimetidine and control groups, respectively. During the observation period, the weight gain in the cimetidine group was 63.3 ± 15.8 g, which was significantly lower than the weight gain of 74.8 ± 14.2 g in the control group, i.e. the cimetidine induced a 15.4% reduction in the weight gain during the observation period of 22 days. The weight gained per weight of food ingested was 0.20 ± 0.04 (g/g) and 0.22 ± 0.04 (g/g) in the cimetidine and control groups, respectively (NS). In other experiments, ranitidine (3 mg) and famotidine (0.4 mg), but not omeprazole (0.4 mg), taken three times a day for 8 days reduced the weight gain when compared with a control group (n=7 in each group). We therefore conclude that the effects of the H2‐receptor antagonists are not mediated b

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00249.x

出版商:Blackwell Science Ltd    

年代:1997

数据来源: WILEY

摘要:

The effect of systemic or intracerebroventricular (ICV) infusion of the angiotensin AT1receptor antagonist losartan on blood pressure during hypotensive haemorrhage was investigated in five conscious sheep. Mean arterial pressure (MAP) was measured during haemorrhage (15 mL kg−1body wt). Losartan (1 or 0.33 mg h−1) was given to sheep by ICV, intravenous or intracarotid administration, beginning 60 min before and continuing during the haemorrhage. During control infusion of ICV artificial cerebrospinal fluid, MAP was maintained until 13.16 ± 0.84 mL kg−1blood loss, when a rapid reduction of at least 15 mmHg in arterial pressure occurred (the decompensation phase). ICV infusion of losartan at 1 mg h−1caused an early onset of the decompensation phase after only 9.8 ± 0.8 mL kg− 1of blood loss compared with control. Intravenous infusion of losartan (1 mg h−1) also caused an early onset (P < 0.05) of the decompensation phase at 10.2 ± 1.0 mL kg−1blood loss. This dose of losartan inhibited the pressor response to ICV angiotensin II, but not to intravenously administered angiotensin II, indicating that only central AT1receptors were blocked. Bilateral carotid arterial administration of losartan at 0.33 mg h−1caused an early onset of the decompensation phase during haemorrhage at 11.06 ± 0.91 mL kg−1blood loss (P < 0.05), which did not occur when infused by intravenous or ICV routes. The results indicate that an angiotensin AT1‐receptor‐mediated mechanism is involved in the maintena

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00266.x

出版商:Blackwell Science Ltd    

年代:1997

数据来源: WILEY

摘要:

The cardiovascular regulation in humans depends to a major extent on sympathetic reflexes originating from volume receptors in the arterial as well as the cardiopulmonary region. With experimental approaches, such as lower body negative pressure (LBNP) and tilting, signs of reduced efficiency with ageing have been shown. However, a confounding factor may be an age‐related decline in venous capacitance response of the lower limbs, reducing the decrease in central blood volume and thus the deactivation of baro/cardiopulmonary receptors. This potential error was addressed in the present study. Central hypovolaemic stress was produced by LBNP 60 cmH2O in 10 young (mean age 23, range 20–25 years) and 10 old males (mean age 65, range 61–70 years). Changes in tissue volume of the calf were studied by strain gauge volumetric technique. Transmission of negative pressure to the calf muscle was studied in two young and two old volunteers. The haemodynamic response to hypovolaemic circulatory stress was attenuated in the old as compared with the young subjects, with a less marked increase in heart rate and peripheral resistance. Further, in the old subjects, the decrease in systolic blood pressure, pulse pressure and forearm blood flow was attenuated. Transmission of negative pressure to the calf was equal in both groups. The capacitance response was reduced with age from 2.27 ± 0.14 to 1.64 ± 0.13 mL 100 mL−1(P < 0.005). However, the net capillary fluid filtration was unchanged. The reduced capacitance function might partly explain the declining reflex responses with age in humans, and thus seems to be of considerable importance when studying cardiovascular sympathet

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00243.x

出版商:Blackwell Science Ltd    

年代:1997

数据来源: WILEY

摘要:

We have used a partial sciatic nerve ligation model to examine the time course for changes in the expression of mRNA for three peptides related to pain transmission at spinal sites (dynorphin, enkephalin and substance P), during the development of allodynia. Enhanced expression of mRNA for dynorphin and substance P was observed in the dorsal horn on the same side as the partial nerve ligation. Increased expression of dynorphin mRNA was biphasic. The initial increases in expression of dynorphin mRNA occurred at 3 h, and a secondary peak was observed 1–3 days after surgery. The secondary increases coincided roughly with increased substance P mRNA expression. However, both dynorphin and substance P mRNA returned to control values after 1 week despite continuing allodynia. No significant changes in expression of mRNA for enkephalin were observed. The elevation of substance P mRNA in intrinsic spinal cord neurons may be secondary to changes in immediate early genesc‐fosandjun‐B, whereas the expression of dynorphin and enkephalin mRNA is differently regulated. The results also suggest that changes in the expression of the three neuropeptides are not critically involved in the development and maintenance of chronic pain or al

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00259.x

出版商:Blackwell Science Ltd    

年代:1997

数据来源: WILEY