Search PubMed⌕ Search

Biomedical subjects

R J Shephard

Publications and source records attributed to R J Shephard.

At least 199 records · Page 11Linked to original sources
PubMed1991

Some consequences of polar stress: data from a transpolar ski-trek.

Findings from the recent Canadian/Soviet transpolar skitrek are reviewed. Comparison of field heart rate measurements with laboratory data suggests a high rate of energy expenditure over the trek; the 13 participants covered some 20 km/day at a speed of about 3.5 km/h, while carrying 37-45 kg packs. Strength increased and body fat decreased over the journey, but aerobic power data showed an anomalous decline, possibly related in part to intensive pre-trip training and an increase of skiing efficiency during the trek. Two of the 13 participants suffered sufficient local cold exposure to develop significant frostbite, and all had sufficient cold exposure to show some general cold acclimatization. Eight of the 13 also suffered from excessive ultraviolet exposure. The main psychological problems were related to inter-personal conflicts and difficulties of communication between the two teams. Hormonal changes were extensive, but generally in line with expectations for a combination of vigorous exercise, cold exposure and psychological stress. Nutritional responses reflect a high rate of fat usage, with a significant increase of HDL-cholesterol levels. It is concluded that well-trained young and middle-aged adults from an urban environment can participate in a well-planned and prolonged arctic winter traverse without serious adverse effects on either physiological or psychological systems.

Arctic Regions↗
PubMed1990

Physical activity and cancer.

Evidence that physical activity may protect against various forms of cancer is examined in relation to occupational demands, leisure activities and participation in sport while at university. The variety of forms of neoplasm and equally varied physical activity histories militate against finding any simple relationship between the risk of malignancy and the individual's physical activity history. Nevertheless, five of seven major occupational studies suggest that a physically active occupation offers some protection against colon cancer, and an application of Bradford Hill's criteria generally supports the causal nature of the relationship between physical inactivity and an increased risk of intestinal neoplasia. However, existing reports are by no means conclusive; there thus remains a need for well-designed epidemiological studies of this issue. Data from one laboratory also suggest that in women a history of active leisure is associated with a reduced prevalence of breast and reproductive system cancers. Physical activity potentially encourages a healthy lifestyle, and it could have more direct effects on certain forms of carcinogenesis (for instance, by a speeding of gastro-intestinal transit, or a moderation of sex hormone levels). However, there are also potential negative effects from some types of exercise, particularly an excessive exposure to ultra-violet light in certain water sports. Since moderate exercise elevates mood and helps to conserve lean tissue, it may finally be a helpful component of treatment after a neoplasm has been diagnosed.

Animals↗
PubMed1990

On the generality of the "sit and reach" test: an analysis of flexibility data for an aging population.

Head rotation, shoulder extension and rotation, ankle plantar and dorsiflexion, hip flexion, and sit and reach (SR) scores were examined in 41 women and 39 men, aged 45-75 years. The SR gave more reproducible data than the other measurements (intraclass test/retest correlation over 8 months, r = .83). SR scores were independent of standing height (r2 = .068) but were greater in women (p less than .002). The flexibility at all joints was less than reported for young adults. There were age-related decreases of flexibility scores for the head and shoulder joints (p less than .01), with a parallel trend (p less than .05) for ankle plantar flexion and SR scores (the last only after inclusion of an age-gender interaction term). A principal components analysis identified three factors (tentatively identified as general trunk, ankle, and shoulder flexibility) accounting for 55.9% of total variance. SR scores had a moderate correlation with the first factor (r = .61) but only weak correlations with the second and third. Although the SR test is the most reliable simple instrument, it provides only limited information about the flexibility at other joints in an older population.

Adult↗
PubMed1990

Strength training for wheelchair users.

Sedentary adult males with spinal lesions, all habitual wheelchair users, were allocated to exercise (n = 11) and control (n = 4) groups. A Cybex II dynamometer was used to assess peak power, average power, total work and muscular endurance for elbow flexion/extension, shoulder flexion/extension and shoulder abduction/adduction at five angular velocities, on recruitment and after eight and 16 weeks of forearm ergometer training (three days/week). Small sub-groups of the exercised subjects were assigned to high or low intensity endurance effort (70 or 40 per cent of maximal oxygen intake) and long or short training sessions (40 or 20 minutes per session). Despite the aerobic nature of the activity, gains of average power were registered by the two muscle groups most involved in the ergometer task (shoulder extension and elbow flexion). In keeping with current theories of training, gains were largest with prolonged, high intensity activity at angular velocities approximating those adopted during training.

Adolescent↗
PubMed1990

The biology and medicine of sailing.

The physiological demands of sailing are highly specific, varying with wind conditions, type of craft, and crew position. In a light wind, the only physiological variable yet shown to influence performance is the resting blood sugar. Under high wind conditions, the skipper should be light (less than 60 kg), but crew members should be heavy (greater than 80 kg). Height does not seem a great advantage to crew, possibly because they then lack the muscular strength to exploit the added leverage. Muscle strength, endurance and a tolerance of anaerobic metabolism are all desirable attributes of crew, and competitive performance can be improved by a winter training programme that develops these aspects of muscle performance in the abdominal and thigh regions. The skipper must meet intense and prolonged cerebral demands in the face of periodic isometric work; performance may thus be helped by ingestion of carbohydrate over the course of a race. The ability to sustain isometric contractions in the 'hiking' position may also be improved if the muscles are preloaded with glycogen. The combination of a heavy body build, above average age for an athlete and sustained isometric contraction probably makes the yachting enthusiast vulnerable to ischaemic heart disease. Advisors to a sailing team must further take account of the risks presented by immersion in cold water, loss of sleep, circadian variations of performance over an event, and problems of motion sickness in rough weather.

Circadian Rhythm↗
PubMed1990

Use of attitude-behaviour models in exercise promotion.

Many studies have adopted a theoretical attitude-behaviour framework for the analysis of exercise behaviour. The most popular models include the Health Belief Model, the Protection Motivation Theory, the Social Cognitive Theory, the Theory of Reasoned Action, the Theory of Interpersonal Behaviour, and the Theory of Planned Behaviour. Aspects other than a preoccupation with health often have a strong influence upon an individual's decision whether or not to engage in exercise. Expectations of self-efficacy, attitudes towards exercising (the affective dimension), perceived barriers to exercise, and past behaviour exert strong influences upon behavioural intention, which in turn influences overt behaviour. In some instances, the variables explaining intention also exert a direct influence upon behaviour in parallel with their influence upon intention. Those promoting exercise behaviour should focus initial attention upon the habit of exercising rather than upon the development of traditional 'endurance fitness'.

Attitude to Health↗
PubMed1990

Meeting carbohydrate and fluid needs in soccer.

If a hard game of soccer is played under warm conditions, there are conflicting demands for carbohydrate and for fluid replenishment, with both variables having a potential influence upon competitive performance. The present review examines evidence concerning the extent of carbohydrate depletion during soccer play, its potential impact upon play, and the optimum choice of beverage for minimizing physiological problems. Players should be prepared for competition by eating a good mixed diet; this should assure a daily intake of at least 8 g of carbohydrate per kilogram of body mass. Although theoretical arguments favour the use of glucose/polymer drinks, in practice, these do not offer any great advantage relative to water or a dilute glucose solution. Some 500 mL of water or a low-concentration carbohydrate preparation can usefully be drunk in the thirty minutes immediately prior to a game, with a further 500 mL drink of the same fluid being taken at half time. During the recovery period following a soccer match, it is useful to increase the salt content of meals, and again to provide a good mixed diet with an emphasis upon carbohydrates.

Dietary Carbohydrates↗
PubMed1990

Moderate exercise and hemodilution during sleep deprivation.

The effect of 52 h of sleep deprivation (SD) upon blood constituents was studied in 12 young women aged 21.5 +/- 0.4 years. Subjects were individually isolated without time cues, performing a sequence of cognitive tasks. Significant decreases in hematocrit (p less than 0.002) and red cell count (p less than 0.04) developed, mainly over the first 28 h of SD, reaching a subsequent plateau or partial recovery. The calculated plasma volume also increased by 10.7 +/- 3.1% at 52 h, with recovery to a 6.9 +/- 3.2% increase the following day. About 1 L of water was retained over the first 30 h of SD, with a subsequent partial elimination of this excess. Plasma albumin and total protein concentrations were largely sustained in the face of the plasma expansion. The plasma pH showed a progressive fall from a baseline value of 7.381 +/- 0.014 to 7.332 +/- 0.006 at 52 h, while plasma bicarbonate decreased from a baseline figure of 31.2 +/- 0.7 to 26-27 mM/L (p less than 0.05). After 8 weeks, all subjects repeated the experiment, with the introduction of 30 min of exercise in the 40th h of wakefulness. Hematocrit and plasma volume changes were similar to those of the first experiment up to the time of exercise, but hematocrit decreased and plasma volume increased after the exercise bout, rather than reaching a plateau. Plasma pH increased with exercise, but returned to the previous low level at 52 h. Any arousing effect of the exercise bout was transient. The plasma expansion reflects metabolic and/or respiratory acidosis, plus possible effects of a prolonged period without recumbency.

Adult↗
PubMed1990

Assessment of occupational fitness in the context of human rights legislation.

The potential applications of occupational fitness assessment are briefly reviewed in the general context of recent human rights legislation. Limiting tasks in an industrial process must be examined, and bona fide occupational requirements must be defined in terms of psychomotor ability and physiological capacity. Heavy work may demand a high level of aerobic power, muscular strength, or tolerance of adverse environments. Such criteria can define an action limit, above which the task must be redesigned, or workers must be specially selected and trained. The courts may accept the results of field performance tests more readily than laboratory measurements of aerobic power or muscular strength. However, neither type of test currently has the reliability and validity needed to characterize the individual, or to distinguish a good worker from a poor worker. If the concern is public safety, employment must thus be based upon average data for a given population, while if the concern is employment equity, the only recourse seems a probationary period of employment.

Adult↗
PubMed1989

Anaerobic threshold, muscle volume and hypoxia.

Ventilatory threshold, apparent mechanical efficiency, oxygen debt repayment, heart rate and perceptions of exertion at the ventilatory threshold have been examined in 8 men and 8 women during the performance of four types of exercise (2-leg, 1-leg, arm plus shoulder, and arm ergometry) under normoxic and hypoxic (12% oxygen) conditions. The ventilatory threshold (percentage of task-specific VO2peak at which a disproportionate increase of ventilation begins) was not significantly affected by the sex of the subject, by hypoxia, or by the volume of active muscle involved in the activity, but showed poor reproducibility in small muscle tasks. The apparent mechanical efficiency in 2-leg ergometry was increased from 25.7 to 28.1% under hypoxic conditions, presumably reflecting an increased contribution of anaerobic effort to sub-maximal work. However, oxygen debt repayment following exhausting exercise was much smaller for arm than for leg ergometry. The heart rate corresponding to the ventilatory threshold decreased as the volume of active muscle was reduced. General and respiratory perceptions of effort were rather light for self regulation of an exercise prescription to the ventilatory threshold, and particularly with tasks involving the arm muscles, prescription may best be regulated by the intensity of local muscular sensations.

Adult↗
PubMed1989

Maximal aerobic exercise following prolonged sleep deprivation.

The effect of 60 h without sleep upon maximal oxygen intake was examined in 12 young women, using a cycle ergometer protocol. The arousal of the subjects was maintained by requiring the performance of a sequence of cognitive tasks throughout the experimental period. Well-defined oxygen intake plateaus were obtained both before and after sleep deprivation, and no change of maximal oxygen intake was observed immediately following sleep deprivation. The endurance time for exhausting exercise also remained unchanged, as did such markers of aerobic performance as peak exercise ventilation, peak heart rate, peak respiratory gas exchange ratio, and peak blood lactate. However, as in an earlier study of sleep deprivation with male subjects (in which a decrease of treadmill maximal oxygen intake was observed), the formula of Dill and Costill (4) indicated the development of a substantial (11.6%) increase of estimated plasma volume percentage with corresponding decreases in hematocrit and red cell count. Possible factors sustaining maximal oxygen intake under the conditions of the present experiment include (1) maintained arousal of the subjects with no decrease in peak exercise ventilation or the related respiratory work and (2) use of a cycle ergometer rather than a treadmill test with possible concurrent differences in the impact of hematocrit levels and plasma volume expansion upon peak cardiac output and thus oxygen delivery to the working muscles.

Adult↗
PubMed1989

Adolphe Abrahams memorial lecture, 1988. Exercise and lifestyle change.

While the evidence for a clustering of health habits is not particularly strong, there are both pedagogic and economic arguments in favour of a multifaceted approach to health education. The present review thus examines the impact of regular physical exercise upon other forms of health behaviour, testing the extent to which an activity programme can be a catalyst of improved lifestyle in both primary and secondary preventive therapy. The conceptual framework of health promotion is examined with particular reference to the models of Skinner, Becker, Fishbein, Triandis and Rokeach. Certain differences are noted between the decision to exercise and the marketing decisions for which Fishbein's model was originally designed. Nevertheless, in its later modifications, it provides a basic framework for understanding how human lifestyle is shaped. Theoretical mechanisms are suggested whereby exercise could influence such behaviours as cigarette smoking, alcohol consumption and drug usage, seat-belt usage, hypertension, body mass, lipid profile, promiscuous sexual behaviour, the carrying of lethal weapons, and acceptance of regular preventive medical examinations. The empirical evidence from both cross-sectional and longitudinal experiments shows a relatively weak association between exercise habits and other desirable forms of health behaviour. Moreover, it is arguable that other forms of health intervention such as smoking withdrawal or dieting might be equally effective as a primary change agent, and much of the observed association between exercise and other health habits could be attributable to a common dependence on demographic and socio-economic factors. On the other hand, the apparent weakness of associations may arise in part from difficulties in measuring both habitual physical activity and other forms of health behaviour, with a resultant attenuation of correlations. Possibly, a stronger association between exercise participation and other favourable health habits would be uncovered if attention were focused upon those forms of endurance exercise currently thought to enhance cardiac health. Given that moderate endurance exercise is also positive and pleasant advice, further examination of the potential of multifaceted but exercise-centered health promotion programmes appears warranted.

Exercise↗
PubMed1989

Current perspectives on the economics of fitness and sport with particular reference to worksite programmes.

Much of the research on the economic impact of fitness and sport programmes has been initiated with a view to cost containment, or the justification of specific exercise initiatives. Care must be taken when evaluating such reports to consider any resultant biasing of conclusions. Analyses should conform to sound scientific and economic principles, with cost-effectiveness measures generally being more appropriate than cost-benefit analyses. Critical issues of measurement include opportunity costs, marginal and intangible costs, discount and inflation rates, and programme participation rates. At the worksite, costs vary greatly with the scale of facilities and the level of programme supervision that are offered. Beyond a certain ceiling, further expenditures do not seem to enhance programme effectiveness. Likely benefits to a company include an improvement of corporate image, a recruitment of premium employees, gains in the quality and the quantity of production, a decrease of absenteeism and turnover, lower medical costs, an improvement of personal lifestyle (with a potential for future health savings), and a reduced incidence of industrial injuries. Community exercise programmes have the advantage of reaching certain target groups not serviced at the worksite, for instance the unemployed, women with young children and the elderly. Possible benefits of exercise participation arising in such groups included a reduced demand for medical services, an extended lifespan, and a reduction of disability in the final years of life. While current evidence has many limitations, it does suggest that exercise (particularly in the context of more general health promotion) is both cost-effective and cost-beneficial; the immediate return may be as much as $2 to $5 per dollar invested.

Cost-Benefit Analysis↗