摘要:

The main purpose of this study was to investigate metabolic changes after anterior cruciate ligament reconstruction and to find out whether the statements on training intensity in the literature can also be applied to patients in rehabilitation. Twenty-four male patients. 16 wk (range: 11-21 wk) postoperative, volunteered to participate in the study. A new four-stage test with constant time and load increments on the legpress in the closed kinetic chain (CKC) was performed. Evaluative variables were the aerobic and anaerobic threshold, force at exhaustion, and the maximum strength. Besides the four-stage test, the other parameters evaluated were functional tests(one-legged single hop, one-legged triple hop), rating scales (Lysholm, subjective feeling scale), thigh circumference, peak torque (PT), work and explosive force in the open kinetic chain (OKC), and muscle activity via electromyographic examination. Positive correlations were established for the maximum force in the CKC and PT (P< 0.01) and maximum force in the CKC and the thigh circumference (P< 0.05). The Lysholm score correlated with the anaerobic threshold (P< 0.05) and with the functional tests (P< 0.01). Further correlations were established between the PT and the work (P< 0.05) and between the single hop and the triple hop (P< 0.001). While the maximum force of the uninvolved leg was significantly higher than that of the involved leg (P< 0.01), the forces measured at termination and at the aerobic and anaerobic threshold (given as percent of maximum force) were significantly higher in the involved leg (P< 0.01). It seems that the oxidative potential increases or remains constant in this phase of rehabilitation and therefore the intensity of strength training must be adapted to the needs of the patient. Our easy-to-perform method makes it possible to establish an optimal intensity of training.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

During exercise in highly-trained older master athletes (MA), the impairment of pulmonary gas exchanges has been shown to be associated with a concomitant increase in histamine release(2). To determine the role of the histamine released (% H) during exercise-induced hypoxemia, seven MA (age 63.2 yr ± 1.9), all of whom were known to develop exercise-induced hypoxemia, performed two maximal incremental exercise tests at a one-month interval after administration of nedocromil sodium (which inhibits histamine and other mediator release) or placebo in random double-blind order. During exercise testing, blood samples for arterial blood gas analysis and histamine assay were drawn at rest, exercise and recovery. Nedocromil sodium induced an inhibition in% H (0.57 ± 0.03 at maximal load (Pmax) with placebo vs 0.24 ± 0.02 with nedocromil sodium) linked with an improvement of pulmonary gas exchange (PaO2: 71.1± 1.4 at Pmaxwith placebo vs 83.4 ± 3 with nedocromil sodium: D(Ai-a)O2: 37.5 ± 1.4 at Pmaxvs 19.1 ± 3.1, respectively). These results confirm the link established between the increase in histamine and exercise-induced hypoxemia in master athletes.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Dietary fat may be associated with coronary heart disease (CHD). Studies suggest that restricting fat intake may compromise endurance performance and that increasing fat intake may improve endurance performance. We studied the effects of varying dietary fat intake on CHD risk factors in runners. Twelve male and 13 female runners increased fat from 16% to 30% of daily calories (4 wk each). Of this group, six males and six females increased fat to 42% of daily calories (4 wk). Physiological and lipoprotein risk factors were measured after each diet. Results were analyzed by repeated measures ANOVA. Increasing dietary fat from 16% to 42% of daily calories did not change adiposity, weight, heart rate, blood pressure, serum triglycerides, total cholesterol, LDL cholesterol. Apolipoprotein B, or the Apo Al/Apo B ratio. Compared with those eating higher fat, subjects eating 16% fat had lower HDL cholesterol (50 ± 3 vs 62 ± 3 mg·dl-1,P< 0.0001) and Apolipoprotein A1 (111 ± 6 v. 134 ± 6 mg/dl,P< 0.0005) and a higher TC/HDL-C ratio (4.05 ± 0.27 vs 3.42 ± 0.24,P< 0.0005). Runners who increased fat intake to 42% further raised HDL cholesterol (64 ± 6 to 69 ± 5 mg·dl-1,P< 0.04) without adversely affecting other lipoproteins. In conclusion, a 42% fat diet maintained favorable CHD risk factors in female and male runners whereas a 16% fat diet lowered Apo A1 and HDL-C and raised the TC/HDL-C ratio.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Although not common, injuries that result in death do occur in youth baseball. Specifically, in the 5- to 14-year old age group a total of 68 deaths between 1973 and 1995 have been directly attributed to impacts from baseballs to the head and chest. The purpose of this work was to determine the effect of lowering ball modulus and ball mass on the likelihood of reducing impact injury. A theoretical model, based upon the assumption of ideal elastic behavior, was used to calculate the impact response of the head. At a constant ball velocity, lowering both modulus and mass had the greatest influence in decreasing peak head acceleration. Gadd Severity Index, and Head Injury Criterion. Independently lowering the modulus or the mass decreased the impact variables and the estimates of injury, but the decreases varied with the specific impact variable and injury criterion. To study the impact response of the ball and chest, an existing viscoelastic lumped-element model of the chest was used. Lowering ball modulus and mass had various effects, e.g., lowering ball modulus did not affect peak sternal displacement, but it did decrease peak sternal velocity. These theoretical models aid in illustrating that impact response depends upon ball modulus and mass, the physical properties of the target, and the specific impact variable studied. This theoretical model suggests that a softer and lighter than traditional baseball would be the most likely ball model to minimize impact injuries because this ball consistently reduced all impact response variables studied. Since impact injury criteria for youths are presently not validated, the degree to which impact injuries may be reduced remains uncertain.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Although research on the relationship between exercise training and physiological stress reactivity is increasing, we know little about the involvement of brain neurochemistry. Moreover, the few studies that have been performed have concentrated on animals with normally functioning neurochemistry exposed to an acute stressor. Biomedical research is drawing an association between hypoactivation of the physiological stress response and certain medical conditions. As such, there is a need for an animal model that manifests a chronic hypoactivity of the stress system. In this report we describe the results from studies on norepinephrine changes with actual and simulated weightlessness in animals and humans. There is consistent evidence with rats that 14 d of simulated weightlessness produces reduced norepinephrine turnover in selected brainstem nuclei and peripheral tissue mediating the physiological stress response. Little is known about other brain regions, particularly the hypothlamus. These preliminary data suggest that simulated weightlessness is one method by which a chronic hypoactivity of norepinephrine biosynthesis or release might be induced to study exercise training as an intervention.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Fatigue of voluntary muscular effort is a complex phenomenon. To date, relatively little attention has been placed on the role of the central nervous system (CNS) in fatigue during exercise despite the fact that the unwillingness to generate and maintain adequate CNS drive to the working muscle is the most likely explanation of fatigue for most people during normal activities. Several biological mechanisms have been proposed to explain CNS fatigue. Hypotheses have been developed for several neurotransmitters including serotonin (5-HT; 5-hydroxytryptamine), dopamine, and acetylcholine. The most prominent one involves an increase in 5-HT activity in various brain regions. Good evidence suggests that increases and decreases in brain 5-HT activity during prolonged exercise hasten and delay fatigue, respectively, and nutritional manipulations designed to attenuate brain 5-HT synthesis during prolonged exercise improve endurance performance. Other neuromodulators that may influence fatigue during exercise include cytokines and ammonia. Increases in several cytokines have been associated with reduced exercise tolerance associated with acute viral or bacterial infection. Accumulation of ammonia in the blood and brain during exercise could also negatively effect the CNS function and fatigue. Clearly fatigue during prolonged exercise is influenced by multiple CNS and peripheral factors. Further elucidation of how CNS influences affect fatigue is relevant for achieving optimal muscular performance in athletics as well as everyday life.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

This paper reviews data concerning the effects of acute physical exercise(treadmil running) in trained rats. Works from the 1980's have established that acute running increases brain serotonin (5-hydroxytryptamine: 5-HT) synthesis in two ways. Lipolysis-elicited release of free fatty acids in the blood compartment displaces the binding of the essential amino acid tryptophan to albumin, thereby increasing the concentration of the so-called “free tryptophan” portion, and because exercise increases the ratio of circulating free tryptophan to the sum of the concentrations of the amino acids that compete with tryptophan for uptake at the blood-brain barrier level, tryptophan enters markedly in the brain compartment. However, this marked increase in central tryptophan levels increases only to a low extent brain 5-HT synthesis, as assessed by the analysis of 5-hydroxyindoleacetic acid levels, thereby suggesting that exercise promotes feedback regulatory mechanisms. Indirect indices of 5-HT functions open the possibility that acute exercise-induced increases in 5-HT biosynthesis are associated with (or lead to) increases in 5-HT release. Lastly, the hypothesis that training and/or acute exercise triggers changes in 5-HT receptors has been examined in several studies; actually, both positive and negative results have been reached. Taken together, all these data support the need for future studies on the functional effects of exercise on 5-HT, including those related to the hypothesis that the positive mood effects of exercise rely (partly or totally) on central serotonergic systems.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

This paper summarizes our studies examining whether changes in levels of brain monoamines after chronic exercise are associated with altered behavioral and endocrine responses to stressors other than exercise. The focus is on using animal models relevant for understanding reports by humans that regular physical activity reduces depression and anxiety. We studied the effects of chronic activity wheel running or treadmill exercise training on levels of norepinephrine (NE) measured in brain cell bodies and terminal regions at rest and after behavioral stress. We also measured brain levels of serotonin, i.e., 5-hydroxytryptamine (5-HT), dopamine (DA), and gamma aminobutyric acid (GABA), which function as both antagonists and synergists with NE. In general, we found that chronic activity wheel running increased NE levels in the pons medulla at rest and protected against NE depletion in locus coeruleus cell bodies after footshock: the concomitant reduction in escape-latency was consistent with an antidepressant effect. Wheel running also decreased the density of GABAAreceptors in the corpus striatum while increasing open-field locomotion, consistent with an anxiolytic effect, but had no effect on hypothalamic-pituitary-adrenal cortical response to footshock measured by plasma levels of adrenocorticotropic hormone (ACTH), corticosterone, and prolactin. In contrast, treadmill exercise training increased the metabolism of NE in brain ascending terminal areas for NE, increased the secretion of ACTH after footshock and immobilization stress and had no effect on GABAAreceptor density or open field locomotion. The validity of animal models for studying depression and anxiety after forced versus voluntary exercise is discussed. Recommendations are offered for improving the methods used in this area of research.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

To determine whether chronological age, independent of changes in aerobic capacity, alters cardiac output (˙Qc), the central hemodynamic responses to intermittent incremental cycle exercise were studied in two groups of men. ˙Qcwas measured at rest and during exercise at 35%, 60%, 75%, and 85% peak aerobic capacity (˙VO2peak) using a CO2rebreathing method in seven trained older (65 ± 2 yr) and eight normally active but untrained young men (26 ± 1 yr) matched for˙VO2peakand anthropometric measures. Subjects were tested in both a thermoneutral (22°C) and a warm (36°C) environment to investigate possible differential cardiovascular responses to exercise in the heat. Only subjects with no history of pulmonary, cardiac, neuromuscular, or endocrine disease and a normal electrocardiogram were studied. The older men had significantly lower (P< 0.05) ˙Qcrelative to the younger men at intensities greater than 60% ˙VO2peakin both environmental conditions. At these higher intensities, the older men had a significantly higher stroke volume (SV) and lower heart rate (HR) (P< 0.05). A higher arteriovenous oxygen difference ((a-[horizontal bar over]v)O2)) compared with their younger counterparts enabled the older men to exercise at the same absolute intensity, most likely because of training induced changes in left-ventricular performance and oxygen extraction. The addition of an exogenous heat source did not alter the˙Qcresponse in either group of men; however, a higher HR(P< 0.05) and smaller SV (P> 0.05) were observed in the young men during exercise in the heat. This may reflect previously reported differences in the skin blood flow response of˙VO2peak-matched young and older men during exercise. It is suggested that endurance trained older men can enhance left-ventricular performance to augment SV, but not sufficiently to maintain ˙Qcin light of an attenuated HR response during exercise at intensities above 60%˙VO2peak.

ISSN:0195-9131    

出版商:OVID    

年代:1997

数据来源: OVID