ISSN:0112-1642    

DOI:10.2165/00007256-198603030-00001

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryScientific research in swimming over the past 10 to 15 years has been oriented toward multiple aspects that relate to applied and basic physiology, metabolism, biochemistry, and endocrinology. This review considers recent findings on: 1) specific physical characteristics of swimmers; 2) the energetics of swimming; 3) the evaluation of aerobic fitness in swimming; and 4) some metabolic and hormonal aspects related to swimmers.Firstly, the age of finalists in Olympic swimming is not much different from that of the participants from other sports. They are taller and heavier than a reference population of the same age. The height bias in swimming may be the reason for lack of success from some Asian and African countries. Experimental data point toward greater leanness, particularly in female swimmers, than was seen 10 years ago. Overall, female swimmers present a range of 14 to 19% body fat whereas males are much lower (5 to 10%).Secondly, the relationship between O2uptake and crawl swimming velocity (at training and competitive speeds) is thought to be linear. The energy cost varies between strokes with a dichotomy between the 2 symmetrical and the 2 asymmetrical strokes. Energy expenditure in swimming is represented by the sum of the cost of translational motion (drag) and maintenance of horizontal motion (gravity). The cost of the latter decreases as speed increases. Examination of the question of size-associated effects on the cost of swimming using Huxley’s allometric equation (Ŷ = axb) shows an almost direct relationship with passive drag. Expressing energy cost in litres of O2/m/kg is proposed as a better index of technical swimming ability than the traditional expression of V̇O2/distance in L/km.Thirdly, maximal direct conventional techniques used to evaluate maximal oxygen consumption (V̇V̇O2 max) in swimming include free swimming, tethered swimming, and flume swimming. Despite the individual pecularities of each method, with similar experimental conditions similar results for V̇O2 maxwill be found. Free swimming (unimpeded) using the backward extrapolation method will, however, lead to reliable and valid results obtained in a condition that is closer to the competitive situation than with a direct test. A maximal indirect field-test has been recently made available. This test can predict V̇O2 maxwith an acceptable accuracy (r = 0.877), and provides a mean to evaluate the functional maximal aerobic power in swimming which corresponds to the maximal aerobic swimming velocity.Finally, although general principles of metabolic and endocrine aspects of exercise also apply to swimming, researchers have given a new but growing attention to specific aspects of metabolic and hormonal responses in swimmers. Metabolic studies in swimming point to a certain degree of disparity between swim training and the competitive events as far as substrate utilisation is concerned. Lactate response during swimming has also been used extensively to estimate the kinetics of energy production at submaximal and maximal exercise levels. Reports on endocrine responses specifically related to swimmers have mainly been directed toward the study of the menstrual cycle. Contrary to female gymnasts, the age ofmenarche of girl swimmers has been shown to be somewhat delayed or not delayed at all, although a later age at menarche has been recently observed for the more competitive swimmers. The incidence of athletic amenorrhoea also appears to be higher in runners and ballet dancers than in swimmers.

ISSN:0112-1642    

DOI:10.2165/00007256-198603030-00002

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryPostnatal skeletal muscle growth in humans is generally ascribed to enlargement of existing muscle fibres rather than to cellular proliferation. Some evidence of muscle fibre division or splitting was provided in the nineteenth century. This evidence has more recently been supported by fibres obtained from regenerating muscle, and from muscle which has undergone stress-induced growth.Numerous investigators have reported indirect evidence for exercise-induced hypertrophy and hyperplasia. These findings are largely founded on secondary observations of fibre size or number differences expressed relative to muscle cross-sectional area. Since these observations in humans are open to methodological criticism, researchers have developed 3 animal models to represent exercise-induced human muscle growth. These include compensatory hypertrophy, stretch-induced hypertrophy, and weight lifting in trained animals. The results and criticisms of the experiments which have used these models are discussed in this review.In studies of muscle cross-sectional area, errors are created by fibres terminating intrafascicularly. Longitudinal growth of such fibres result in an overestimation of fibre number, and with the use of penniform muscles where fibres do not run parallel to the longitudinal axis of the muscle, the error is compounded. It was concluded that hyperplasia is not yet substantiated, and that new fibres, if present, may be the result of the development of satellite cells. Further experiments are required before a definitive answer can be provided. It is suggested that rigidly controlled exercise studies using contralateral control, fusiform muscles with analysis of individually teased muscle fibres be performed.

ISSN:0112-1642    

DOI:10.2165/00007256-198603030-00003

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryAppropriate tests can be used to accurately estimate: (a) an individual’s potential for success in long distance running; (b) his current level of conditioning; (c) his appropriate training and racing paces; and (d) his ideal bodyweight. The proposed tests include the study of V̇O2max, running efficiency, maximal steady-state, and body composition. Based on a review of the literature it was determined that V̇O2max, running efficiency, and body composition provide the information about long distance running potential, including specific paces for various events. Maximal steady-state running pace (pace that elicits 2 mmol/ L lactate) identifies appropriate running paces for various events. Relative maximal steady-state oxygen consumption (% V̇O2max) identifies the current level of conditioning. A comparison of maximal steady-state, running efficiency, and body composition by assessing current status with optimums, provide guidelines for appropriate changes.

ISSN:0112-1642    

DOI:10.2165/00007256-198603030-00004

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryThe ability of the cardiovascular system to meet the competing demands of skin and muscle for blood flow without compromising regulation of blood pressure is a critical factor influencing the capacity for prolonged work in hot environments. Unfortunately, this competition is exacerbated by the progressive reduction in blood volume (haemoconcentration) which can occur during exercise in the heat. Thermal stress alone induces haemoconcentration only above the upper limit of the prescriptive zone. Exercise performed in a supine or seated position is associated with an initial rapid haemoconcentration, which, if the environmental temperature is high, is followed by a slower, secondary haemoconcentration. Exercise performed in a standing position is associated with variable changes in blood volume, and effects of a superimposed thermal stress are small unless dehydration supervenes. The magnitude of exercise-induced primary haemoconcentration is limited, probably by oedema-preventing mechanisms, and is inversely related to the magnitude of any preceding postural haemoconcentration. Dehydration reduces absolute blood volume (induces hypovolemia), and accentuates exercise haemoconcentration. Heat acclimatisation attenutates dehydration by inducing hypervolemia, but still appears to accentuate exercise haemoconcentration. During exercise in the heat haemoconcentration represents an undesirable response, the effects of which can be mitigated by heat acclimatisation, endurance training, and preventing dehydration.

ISSN:0112-1642    

DOI:10.2165/00007256-198603030-00005

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryAnterior shoulder dislocations, primary and recurrent, are among the most disabling injuries to the shoulder that can plague the athlete. The diagnosis is easily made by the following: (a) the physical appearance of the shoulder; (b) loss of capability by the athlete to internally and externally rotate the shoulder with the elbow at his side; (c) by evaluating the mechanism of injury; and (d) x-rays. Anterior shoulder dislocations should be reduced as soon as possible after diagnosis, to minimise the stretching effect on the neurovascular structures while the humeral head is dislocated. The reduction isnotdone to allow the athlete to return immediately to sport. Use of a simple traction method in the first 10 to 15 minutes following the injury will result in a successful reduction in the vast majority of dislocations. Reduction of the humeral head can be confirmed by the athlete regaining the capability to internally and externally rotate his shoulder with his elbow at his side.Following reduction, the athlete should begin a treatment regimen which includes a restrengthening programme emphasising the muscles of internal rotation and adduction plus rigid restrictions of activities until the goals of the rehabilitation programme are satisfied. The author’s experience with this treatment regimen with athletes at the United States Naval Academy, has shown a decrease of the recurrence rate of primary anterior shoulder dislocations to 25% versus the 80% recurrence rate we have become familiar with from studies done which did not stress specific rehabilitation programmes. The athlete should also be instructed in a self-performed traction method for reduction should a re-dislocation occur, to minimise the stretching effect on the neurovascular structures and allow relief from discomfort.Surgery for primary and recurrent anterior dislocations should only be considered when the athlete fails to achieve the desired goals after participating in a specific, progressive, adequate rehabilitation programme.

ISSN:0112-1642    

DOI:10.2165/00007256-198603030-00006

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS