ISSN:0112-1642    

DOI:10.2165/00007256-198603010-00001

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

ISSN:0112-1642    

DOI:10.2165/00007256-198603010-00002

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryThe blood lactate response to exercise has interested physiologists for over fifty years, but has more recently become as routine a variable to measure in many exercise laboratories as is heart rate. This rising popularity is probably due to: a) the ease of sampling and improved accuracy afforded by recently developed micro-assay methods and/or automated lactate analysers; and b) the predictive and evaluative power associated with the lactate response to exercise. Several studies suggest that the strong relationship between exercise performance and lactate-related variables can be attributed to a reflection by lactate during exercise of not only the functional capacity of the central circulatory apparati to transport oxygen to exercising muscles, but also the peripheral capacity of the musculature to utilise this oxygen. For example, several studies contrast the relationship between V̇O2 maxand endurance running performance with that between a lactate variable and the same running performance. In every study, the lactate variable is more highly correlated with performance. Similarly, prescribing training intensity as a function of the lactate concentration elicited by the training may prove to be a means of obtaining a more homogeneous adaptation to training in a group of athletes or subjects than is obtained by setting intensity as a function of maximal heart rate or % V̇O2 max. A review of the recent literature shows that the lactate response to supramaximal exercise is a sensitive indicator of adaptation to ‘sprint training’ and is correlated with supramaximal exercise performance. This review also describes the possible applications of lactate measurements to enhance the rate of recovery from high intensity exercise. Although the lactate response to exercise is reproducible under standardised conditions it can be influenced by the site of blood sampling, ambient temperature, changes in the bodys’s acid-base balance prior to exercise, prior exercise, dietary manipulations, or pharmacological interpretation.

ISSN:0112-1642    

DOI:10.2165/00007256-198603010-00003

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryPopulation levels of habitual activity have probably contributed to both the recent epidemic of cardiovascular disease and its waning. Evidence supporting the exercise hypothesis can be drawn from comparisons of individuals with differing levels of occupational and leisure activity. Both suggest that regular, endurance-type activity may halve the incidence of cardiac morbidity and mortality. This is an important prophylactic benefit, although Bradford Hills’s criteria of a causal association have yet to be fully satisfied. Following the onset of clinical disease, both uncontrolled and randomised controlled trials suggest that progressive exercise rehabilitation improves prognosis by a useful 20 to 30%, but formal statistical proof is again difficult for technical reasons. Although over-enthusiastic vigorous physical activity can cause an immediate rise of cardiovascular events, this disadvantage is substantially outweighed by long term gains from regular physical activity.Classical epidemiology has proven its case by the experimental step of removing exposure to the causal agent. It is difficult to carry out such an analysis linking physical activity with the recent epidemic of ischaemic heart disease, although the recent waning of the disease may be attributed in part to an increase of habitual physical activity in many western nations.Evidence linking exercise to the prevention of clinical disease (‘secondary prevention’) is derived from large scale surveys of groups with supposed differences in occupational activity, athletic participation, active leisure pursuits or overall lifestyle.The majority of occupational comparisons have shown advantages to active workers in terms of deaths from cardiac disease, sudden death, cardiac morbidity, ECG abnormalities, and cardiac abnormalities at postmortem. However, concerns have been raised with regard to the accuracy of job classification, the intensity of occupational activity relative to active leisure, the adequacy of disease classification, and confounding influences due to differences of social class, stress and potential alienation.Studies comparing athletes and non-athletes have been faulted on grounds of initial selection for sport by body-build and uncertainties regarding continuing differences of endurance activity between recognised university athletes and their classmates. In general, no advantage of life expectancy has been seen in athletes, Karvonen and associates reported a 4 to 5 year advantage of longevity in Finnish cross-country skiing champions, although this might be attributable to other facets of their lifestyle.Community studies of leisure activity have sometimes obtained equivocal results because the majority of the community were inactive, or it was necessary to rely upon rather crude indices of habitual activity. In some cases, it has also been uncertain whether preexisting disease caused inactivity, or the converse was true. However, a substantial number of well-designed prospective trials have now established that new cardiac events are only about half as frequent in people who undertake regular, endurance type physical activity. This relationship holds after controlling for other major risk factors, apparently reaching maximum benefit with the deliberate expenditure of about 8000kJ (2000 calories) per week, although it is difficult to exclude all possibility that active people are also ‘health conscious’.There have been a number of reports suggesting a low incidence of cardiovascular disease in indigenous populations where a high level of energy expenditure is needed for survival. Even if statistics on cardiovascular disease were more certain, it would be extremely difficult to separate effects of exercise from other unusual facets of lifestyle.Direct experimental studies of the exercise hypothesis have been thwarted by lack of a good animal model, and the enormous estimated cost of prospective trials on human volunteers (due mainly to poor compliance rates). It is suggested that instead one might apply Bradford Hills’s criteria of a causal association (strength of association, consistence, temporality, specificity, biological gradient, plausibility, coherence, experimental verification, and analogy) to the available epidemiological evidence. Proof is less strong than for the association between lung cancer and cigarette smoking; the biological gradient is only about 2-fold from active to inactive, and there are exceptions to the criteria of specificity and coherence. Moreover, there is as yet no good experimental verification, nor do we have a simple analogue of the protective process. Nevertheless, the apparent twofold change of incidence has great practical importance, given the widespread prevalence of cardiovascular disease.There are also practical problems in demonstrating benefit from enhanced physical activity in ‘tertiary prevention’ after clinical disease has become apparent. Patients classified as developing ischaemic heart disease differ widely in the extent and type of disease. The timing of referral for exercise programme is very variable and those referred tend to be low risk patients. Studies have been plagued by inadequate sample size, effects of group therapy, poor compliance, contamination of controls, changes in other aspects of treatment, an inadequate total duration of study, and an inappropriate end-point (usually a search for a change in time to death or recurrence, tested over 1 to 3 years).Uncontrolled trials have been almost unanimous in showing a low recurrence rate among patients enrolled in exercise rehabilitation programmes, but much of this apparent benefit could reflect non-random selection of the subjects. Possible approaches to this difficulty include an adjustment of prognosis for known risk factors, and comparisons of prognosis within the referred patients as training develops.At least 10 randomised controlled trials have been conducted to date. Considered individually, all were too small to provide an adequate test of the exercise hypothesis. If minor differences of protocol are ignored, and results are combined, there is fairly strong evidence of a 20 to 30% advantage to exercised patients.The tentative reduction of morbidity and mortality in secondary and tertiary preventive programmes must be weighed against the risks of injury, environmental stress, and the chance that exercise may provoke myocardial infarction. Both in secondary and tertiary programmes, exercise increases the acute cardiac risk 5- to 10-fold. While it is difficult to identify the vulnerable patient, specific precautions can minimise this risk. Moreover, if the prognosis is considered on a 24-hour basis, the long term benefits of exercise substantially outweigh the short term risks.

ISSN:0112-1642    

DOI:10.2165/00007256-198603010-00004

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummarySoccer is characterised as a high intensity, intermittent non-continuous exercise. Players cover approximately 10km of ground per game, of which 8 to 18% is at the highest individual speed. In higher levels of competition there is a greater number of tackles and headings plus a greater percentage of the game is performed at maximum speed. The average aerobic energy yield during a national level game is around 80% of the individual maximum. Blood lactate concentration during a game averages 7 to 8 mmol/L. Because of a high energy yield most players have empty muscle glycogen stores at the end of the game, were hypohydrated and also have an increased body temperature.Soccer players of national and international standard have a maximal aerobic power of around 60 to 65 ml/kg/min, an above average anaerobic alactacid power, and a greater buffer capacity and muscle strength compared with untrained controls, yet seem to be less flexible.

ISSN:0112-1642    

DOI:10.2165/00007256-198603010-00005

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryMany competitive and recreational athletes perform resistance training as a part of their conditioning programmes. Resistance training in addition to increasing muscular strength and hypertrophy may also aid in the prevention of injuries. Research indicates that resistance training promotes growth and/or increases in the strength of ligaments, tendons, tendon to bone and ligament to bone junction strength, joint cartilage and the connective tissue sheaths within muscle. Studies involving humans and animal models also demonstrate resistance training can cause increased bone mineral content and therefore may aid in prevention of skeletal injuries.Investigations to date suggest resistance training can aid in injury prevention. The incidence of various types of overuse injuries, such as swimmers shoulder and tennis elbow, may be reduced by the performance of sport and/or motion specific resistance training activities. Screening of athletes for agonist and antagonist muscle strength imbalances can be utilised to identify athletes possessing a predisposition for injury. Resistance training may then be performed to correct the imbalance and therefore reduce the incidence of injury.

ISSN:0112-1642    

DOI:10.2165/00007256-198603010-00006

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryThe analysis of 6153 accidents reported to the insurance company of the French Rhône-Alpes Soccer Association, for the 1980–81 season was undertaken, providing a survey of acute pathology in French soccer accidents and an estimation of the cost of this pathology to French society. Findings from this study include: (a) injuries — ankle sprain is the most common; fractures prevail in the young players pathology; (b) exposure — the average risk is one accident for 20 matches; the highest risk is for the senior category; collisions with opponents is the main cause of accidents; the first 5 minutes of the second half have a peak of accidents; the players exposure is roughly the same whatever their position on the ground; (c) risk — winter should not increase the risk if the matches are played under good conditions; the risk is unevenly distributed according to the level of practice; (d) cost — the cost for France over 1 year was estimated at US$20,000,000 and the total number of sick leave days at 2000 years; games with several accidents are very common in January and for the adult category. Consequently, tightening up the safety measures would be a very good investment.

ISSN:0112-1642    

DOI:10.2165/00007256-198603010-00007

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS