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Biomedical subjects

R J Shephard

Publications and source records attributed to R J Shephard.

At least 163 records · Page 9Linked to original sources
PubMed1992

Aging and muscle function.

Most of the available data on the aging of muscle function are cross-sectional in type. Static and dynamic muscle strength seem well preserved to about 45 years of age, but performance deteriorates by about 5% per decade thereafter. There is a parallel loss of lean tissue. Because muscle biopsy specimens are not always representative of an entire muscle, it is unclear whether there is a general hypotrophy or atrophy of the muscle fibres or a selective hypoplasia and degeneration of type II fibres associated with a loss of terminal sprouting. Other influences may include a deterioration of end-plate structures with impaired excitation-contraction coupling and impaired fibre recruitment. Both contraction time and half-relaxation time are prolonged with aging, and there is a decrease of maximal contraction velocity, more marked in the legs than in the arms. On the other hand, endurance at a fixed fraction of maximal force is increased. Potential factors leading to the enhanced endurance include a poorer maximal effort and an increased proportion of type I fibres; however, there is little evidence that muscle capillarity is altered. The loss of function is generally less in the arms than in the legs, but it remains unclear whether this is an inherent biological difference, or merely a reflection of differential changes in activity patterns between the upper and the lower limbs. The male/female strength ratio does not seem to change with age, but substantial slowing or reversal of the aging process is possible through appropriate activity programmes. The preservation of muscle function has important implications for the quality of life in the frail elderly, counteracting dyspnoea, stabilising joints and extending the period of independent living by up to 20 years.

Aging↗
PubMed1992

Fat metabolism, exercise, and the cold.

Whereas short-term cold exposure depletes glycogen reserves, repeated and prolonged moderate exercise in a cold environment creates an energy deficit that is satisfied by an increased metabolism of depot fat. Factors contributing to the fat loss include an exercise-induced hypertrophy of lean tissue, a loss of energy through a cold-induced ketonuria, a stimulation of resting metabolism, increases in the energy cost of movement, and a lower yield of energy per litre of oxygen consumed. Biochemical explanations of the enhanced lipolysis include increased catecholamine secretion, altered sensitivity of catecholamine receptors, and decreases of circulating insulin. The enhanced fat loss with combinations of cold and exercise may be helpful in the therapy of obesity, although the response seems less well developed in women than in men. Moreover, there may be other objections to cold exposure in an older obese population. Short-term glycogen depletion has negative implications for the endurance competitor. Cold acclimation, by favoring an insulative response to cold, reduces glycogen depletion; endurance training may supplement this effect by enhancing the activity of fat-metabolizing enzymes.

Acclimatization↗
PubMed1992

Design of a calf muscle ergometer for the study of local muscle blood flow.

A simple ergometer is described that allows highly reproducible plethysmographic measurements of blood flow to be made within 10 seconds of ceasing rhythmic quantitated exercise of the calf muscle. A power output of some 25 Watts is developed with a mechanical efficiency of some 20%. The device seems applicable to a variety of clinical assessments.

Ergometry↗
PubMed1992

Evaluating the influence of sleep deprivation upon circadian rhythms of exercise metabolism.

Cardiorespiratory and gas exchange responses to a moderate, standardized treadmill walking task showed a weak circadian rhythm, with larger superimposed peaks attributable to feeding. However, both rhythms became progressively attenuated during a period of sleep deprivation. A method of exploring this phenomenon is illustrated by an analysis of data on walking heart rate, respiratory minute volume, oxygen intake, and rating of perceived exertion, collected on 11 young men at 3-hr intervals during 60 hours of sleep deprivation.

Adult↗
PubMed1992

Revision of the Physical Activity Readiness Questionnaire (PAR-Q).

The original Physical Activity Readiness Questionnaire (PAR-Q) offers a safe preliminary screening of candidates for exercise testing and prescription, but it screens out what seems an excessive proportion of apparently healthy older adults. To reduce unnecessary exclusions, an expert committee established by Fitness Canada has now revised the questionnaire wording. The present study compares responses to the original and the revised PAR-Q questionnaire in 399 men and women attending 40 accredited fitness testing centres across Canada. The number of subjects screened out by the revised test decreased significantly (p < .05), from 68 to 48 of the 399 subjects. The change reflects in part the inclusion of individuals who had made an erroneous positive response to the original question regarding high blood pressure. There is no simple gold standard to provide an objective evaluation of the sensitivity and specificity of either questionnaire format, but the revised wording has apparently had the intended effect of reducing positive responses, particularly to the question regarding an elevation of blood pressure.

Adult↗
PubMed1992

A comparison of the perceived and the ECG measured heart rate during cycle ergometer, treadmill and stairmill exercise before and after perceived heart rate training.

The ability to perceive exercise heart rate before and after training was tested in six young male university students, perceptions of heart rate being compared with ECG monitored heart rates during cycle ergometry, treadmill running and stairmill climbing. Between initial and final tests, subjects undertook 13 weeks of running training (2 h/day, 3-4 days/week), and during this period they compared their perceptions of heart rate with values observed on watch-type wrist-mounted pulse monitors. Individual initial perceptions showed only a moderate correlation with ECG values. This correspondence was improved as perceptions were compared with measured heart rates over the course of training, significantly so for the mode of exercise most similar to that adopted in the training sessions (treadmill running at a heart rate of 140 beats/min). The final accuracy of perceptions at a heart rate of 140 beats/min (error 8-9 beats/min during treadmill running) compared favourably with the accuracy of either pulse counting or the traditional rating of perceived exertion as commonly observed in the exercising public. This suggests that there may be an application for perceived heart rates in regulating the intensity of prescribed exercise.

Adult↗
PubMed1992

Vehicle injuries to joggers. Case report and review.

A medico-legal case is presented where a jogger was struck by a car while crossing an intersection and later sought major damages in a civil court. This incident is reviewed in the context of overall information on injury to joggers by vehicles, and the possibility (raised by the defendant's counsel) that the euphoria generated by prolonged exercise may have created a sense of "invincibility" that predisposed the jogger to reckless actions. The defendants argued that the young man concerned was taking an amount of exercise that could have led to a jogging addiction and alteration of consciousness in a susceptible individual, and a history of alcohol, drug and video addiction was advanced as evidence that he may indeed have been a susceptible person. During the actual incident, the jogger recognised that the driver of the vehicle had not seen him, but nevertheless he proceeded to enter a crosswalk that had already been 75% traversed by the car, leaving himself only 0.6 metres of space, a half of the lane width normally required by a runner. A calculation of the relative velocities of the car and the jogger suggests that the latter must have veered 1-2 metres onto the main highway in order to pass in front of the care and be hit from the side. The behaviour of the jogger was plainly reckless, but more information is needed on the relative incidence of traffic injuries in joggers and walkers, on the prevalence of jogging addiction, and on diagnostic criteria for this condition before the accident could be categorically attributed to a jogging-related euphoria.

Accidents, Traffic↗
PubMed1992

A critical analysis of work-site fitness programs and their postulated economic benefits.

Many early work-site exercise programs had a unique fitness focus. More recently, modular programs have addressed many facets of lifestyle. Their stated objective has often been to boost corporate morale or employee health rather than to have direct economic benefits, and evaluation has frequently been in terms of process rather than a cost-benefit or a cost-effectiveness analysis. Nevertheless, a growing number of authors have claimed fiscal dividends from such programs. A full economic evaluation must consider such issues as the transfer of benefits between various sectors of the economy, opportunity costs to participants, marginal costs and benefits, inflation, discounting, and the choice between cost-benefit and cost-effectiveness analyses. Suggested benefits include an improvement of corporate image, a decrease of employee turnover, gains of productivity, reduced absenteeism and medical costs, an improved employee lifestyle, and a decrease of industrial injuries. In practice, the corporate impact of a program is greatly attenuated, depending on prevalence of need, participation rate, program response of recruits, and continued employment of such individuals within a company. Costs to the corporation include promotion, facilities, equipment, and professional leadership. However, such items are often small relative to the opportunity costs incurred by the participant. For this reason, activities that can be built into the normal day of the employee (for example, walking or cycling to and from work) may prove more acceptable and more cost-effective than formal work-site classes.

Absenteeism↗
PubMed1992

Respiratory, muscular, and overall perceptions of effort: the influence of hypoxia and muscle mass.

Overall, respiratory and peripheral muscular perceptions of exercise have been examined in 16 subjects (eight men and eight women), each performing four types of exercise (two-leg, one-leg, arm + shoulder, and arm ergometry) under both normoxic and hypoxic (12% oxygen) conditions. Subjects could distinguish ratings for the three types of sensation. Both overall and peripheral muscular perceptions associated with a given oxygen intake or power output increased more than respiratory perceptions as the volume of active muscle was decreased. Hypoxia tended to increase both overall and respiratory perceptions for a given absolute oxygen consumption. Cross-modal comparisons suggested an average overall RPE of close to 13 units at 70% of a task and environment-specific peak oxygen intake, irrespective of exercise conditions, but the SD of individual responses varied by at least +/- 2 units about this average. Peripheral muscular sensations dominated small muscle tasks, but the peripheral muscular RPE became relatively consistent when related to external work rate per liter of active muscle. Respiratory perceptions provided some guide to the intensity of physical activity with a given mode of exercise and fixed environmental conditions. However, if respiratory RPE is used to "fine-tune" cross-modal exercise prescriptions, account must be taken of the distorting influence of active muscle volume and of hypoxia.

Adult↗
PubMed1992

Economic benefits of secondary and tertiary cardiac rehabilitation: a critical study.

At least seven criticisms have been advanced to those suggesting economic benefit from secondary and tertiary rehabilitation: (i) many existing data sets are weak, (ii) many analyses have been limited to self-selected exercise participants, (iii) the distribution of benefits between different sectors of the economy has been ignored, (iv) programme participation is not necessarily synonymous with economic benefit, (v) the discount rate has been neglected, (vi) opportunity costs have not been considered, and (viii) possible increases in pension costs could outweigh supposed benefits. Although there are limitations in the original calculations of economic benefit, there are also weaknesses in their critique. Cost-effectiveness analysis has some attractions over cost-benefit analysis, because areas of fiscal and ethical uncertainty are avoided. Given that patients who develop chronic diseases will require some form of treatment, exercise offers an attractive option for both secondary and tertiary prevention, particularly if programmes have low facility and opportunity costs, and attention is directed to high-risk segments of the population. The challenge to incorporate the lessons from such analyses into governmental and corporate-decision making.

Cardiac Rehabilitation↗
PubMed1992

Long term impact of a fitness programme--the Canada Life Study.

Information gathered over twelve years operation of the Canada Life Assurance fitness programme is reviewed. Motives leading to programme initiation included sale of a health-related product, managerial interest, and government and university support. Participation is now a little under capacity, at about 13% of eligible staff. Except in a small minority of members, the impact upon physical condition and lipid profile has been marginal. The reported community exercise participation of employees has increased since initiation of the programme. An early reduction of employee turnover has been sustained in programme participants. A reduction of absenteeism is limited to enthusiastic participants, with a 0.13% payroll saving for the company as a whole. An early analysis suggested a substantial Hawthorne effect, but a 2.7% gain of productivity relative to a matched control company. Medical insurance claims were also lowered in the first year after introduction of the programme, probably because of gains in perceived health. The Canadian Health Hazard Appraisal instrument showed a two-year reduction of appraised age in male participants. The gymnasium area was developed at a cost of about $175,000, or $700/m2 1990 Canadian dollars, and the current operating budget is about $110,000/year. The 400 members each pay $55/year, and the company provides an operating subsidy of about $200/member. Overall findings suggest the programme remains cost-effective and cost-beneficial.

Absenteeism↗
PubMed1992

Responses of the cardiac transplant patient to exercise and training.

Total denervation persists in the human heart following cardiac transplantation. At rest, there is some increase of heart rate and blood pressure. with a low normal cardiac output. The donor heart remains capable of a satisfactory acute response to exercise, based upon an increase of venous return (acting through the Frank-Starling mechanism) and slower chronotropic and inotropic responses to circulating catecholamines. During submaximal exercise, the stroke volume is greater than normal, but the cardiac output is somewhat reduced, leading to a widening of arteriovenous oxygen difference. Peak heart rate, peak stroke volume, and peak cardiac output are all less than in age-matched normals. Peak power output and peak oxygen intake are also subnormal immediately following cardiac transplantation. The poor ventricular performance reflects, in part, the condition of the transplanted myocardium and, in part, the increased afterloading associated with a loss of lean tissue mass. Although there have, as yet, been no controlled experiments, there is suggestive evidence that an appropriately graded training regimen facilitates restoration of lean tissue and, thus, functional recovery (including the correction of postoperative psychological disturbances). A suitably adapted exercise prescription is thus recommended as a useful component of treatment following cardiac transplantation. There is good evidence that a well-designed training program improves the quality of life for the recipient, although further study is needed to determine the impact of such therapy upon morbidity and mortality.

Exercise↗
PubMed1991

A short history of occupational fitness and health promotion.

The suggestion of a linkage between adequate exercise and occupational health dates back to Ramazzini's classical observations on cobblers and tailors. However, excessive hours of work at too high an intensity were of greater concern than increase of fitness or health promotion in the early phases of the industrial revolution. Loss of physical condition is a more recent phenomenon, and it can be traced to automation in industry and the home, progressive urbanization, and widespread use of the automobile. The Canadian government has seen worksite fitness and health promotion programs as convenient tactics to reverse this trend. Exercise programs apparently yield a healthier and more effective labor force, and major corporations have thus followed the government's lead in developing fitness and health promotional facilities as a part of personnel or occupational health departments. Some health economists have suggested a substantial return upon such investment, but most corporations still regard the promotion of fitness and a healthy lifestyle as an expression of good citizenship. Currently, unifocal fitness programs are being replaced by modular health programs that address a wide range of lifestyle issues, including nutrition, stress relaxation, cigarette addiction, and drug abuse. The purpose of the present brief review is to trace from a personal perspective the development of an interest in employee fitness as an important component of occupational health programs over the past 300 years. The linkage of this phenomenon to the changing human demands of the worksite will also be explored.

Canada↗