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Biomedical subjects

R J Shephard

Publications and source records attributed to R J Shephard.

At least 235 records · Page 13Linked to original sources
PubMed1988

Cardiorespiratory fitness in highly active versus inactive paraplegics.

Maximum and submaximum arm crank exercise performances were assessed in male paraplegics (PARA) with the purpose of comparing cardiovascular responses among individuals of highly active (A, N = 15) vs inactive (I, N = 15) lifestyles. The A PARAs (average VO2 peak during arm cranking 2.24 l.min-1) demonstrated a significantly higher maximal cardiorespiratory fitness compared to I subjects (average VO2 peak 1.56 l.min-1). During graded arm exertion, at exercise intensities approximating 45%, 57%, and 70% of VO2 peak, the active subjects developed cardiac outputs (assessed via CO2-rebreathing) ranging from 9.07 to 11.21 l.min-1; a 34-44% advantage relative to their inactive counterparts (6.30-8.36 l.min-1). Similarly, exercise stroke volumes for A (76-80 ml) were 38-45% higher than for I paraplegics (55-56 ml). Although both groups demonstrated a distinctive circulatory hypokinesis during arm cranking, the immediate pattern of cardiovascular response was dissimilar for the highly active versus inactive subjects. The former demonstrated a predominantly "central" adaptation to steady-state arm exercise (exhibiting normal stroke volumes and arteriovenous O2 extractions for spinal cord-injured subjects), while the latter displayed markedly reduced stroke volumes concomitant with abnormally large peripheral arteriovenous oxygen extractions for a given oxygen uptake.

Adolescent↗
PubMed1987

Sleep deprivation and cardiorespiratory function. Influence of intermittent submaximal exercise.

The effects of 64 h of sleep deprivation upon cardiorespiratory function was studied in 11 young men (VO2max = 55.5 ml kg-1 min-1, STPD). Six subjects engaged in normal sedentary activities, while the others walked on a treadmill at 28% VO2max for one hour in every three; eight weeks later, sleep deprivation was repeated with a crossover of subjects. Immediate post-deprivation measurement of VO2max showed a small but statistically significant decrease (-3.8 ml min-1 kg-1, STPD), with no difference between exercise and control trials. The final decrement in aerobic power was not due to a loss of motivation, as 88% (21 of 24) of post-deprivation tests still showed a plateau of VO2max; in addition, terminal heart rates (198 vs 195 beats min-1), respiratory exchange ratios (1.14 vs 1.15) and blood lactate levels (12.1 vs 11.8 mmol l-1) were not significantly different after sleep deprivation. The decrease in VO2max was associated with a lower VEmax (127 vs 142 l min-1, BTPS) and a substantial haemodilution (13%). Physiological responses to sub-maximal exercise showed persistence of the normal diurnal rhythm in heart rate and oxygen consumption, with no added effects due to sleep deprivation. However, ratings of perceived exertion (Borg scale) increased significantly throughout sleep deprivation. The findings are consistent with a mild respiratory acidosis, secondary to reduced cortical arousal and/or a progressive depletion of tissue glycogen stores which are not altered appreciably by moderate physical activity.

Adult↗
PubMed1987

Cardiac effects of short term arm crank training in paraplegics: echocardiographic evidence.

The cardiac responses of male paraplegics to upper-body endurance training have been studied by M-mode echocardiography and CO2-rebreathing determination of cardiac output. Data for nine exercised subjects are compared with 5 controls. After 16 weeks of arm ergometer exercise, heart rates of trained individuals were 9 bt X min-1 lower during isometric handgrip effort (30% of MVC for 3 min), with a substantial decrease of rate pressure product (20%; p less than 0.05). In contrast (possibly because of greater anticipation) the control subjects developed a larger rate-pressure product with repetition of the standard isometric effort. Despite a significant increase of VO2 peak (19% and 31% after 8 and 16 weeks, respectively; p less than 0.05), echocardiographic LV mass, dimensions and indices of LV performance were unchanged by training, either at rest or during the isometric handgrip. Stroke volumes were significantly increased by 12-16% after training, both in isometric and in rhythmic work; at the highest intensity of arm ergometry, there was also a suggestion of increased cardiac output. We conclude that a short period of arm training is insufficient to induce cardiac hypertrophy, an increase of stroke volume with a decreased rate-pressure product but no change in echocardiographic indices of LV performance implies an improved myocardial efficiency. Possible explanations are a greater strength of the trained arms, and some increase of pre-loading (due to an increase of venous tone and more effective operation of the muscle pump after training).

Adult↗
PubMed1987

Prediction of leisure-time exercise behavior: a path analysis (LISREL V) model.

In an attempt to understand the inherent process underlying the regular practice of physical activity, the relationships among subjective norm, attitude, habit, intention, and future behaviors have been investigated in a random sample of 136 University of Toronto employees. For this purpose, leisure-time exercise behavior was measured on two occasions after a statement of intentions had been obtained: 3 weeks later (proximal behavior) and 2 months later (distal behavior). The results of a path analysis (LISREL) suggest that intention is directly influenced by habit and attitude, proximal behavior is the result of habit only, and distal behavior can be explained by a combination of intention and proximal behavior. Subjective norm was not a significant predictor of intention, proximal behavior, or distal behavior. This modeling approach offers a clearer understanding of the dynamics of exercise intention and behavior, strongly supporting the role of habit as a determinant of exercise behavior.

Adult↗
PubMed1987

The economics of prevention: a critique.

A recent claim that "few preventive programmes, if any, reduce medical expenditures" is critically reviewed with specific reference to the health value of regular exercise. It is argued that a focus upon medical expenditures biases the argument in favour of acute care by neglecting much of the investment in research, training and construction, and ignoring differences in the quality of life between fit and marginally healthy individuals. By focussing on a specific clinical condition, the widespread benefits of exercise are also overlooked, and by equating costs with the consumer price index, errors from differential inflation are ignored. Discounting of benefits weighs heavily against prevention, but is an inappropriate tactic in a steady-state situation. Likewise, the levying of incidental medical charges for an extended lifespan is inappropriate when the individual concerned is also contributing to society. Limited recruitment and poor adherence are the main current weaknesses of preventive medicine, but their impact should be reduced when a preventive philosophy becomes the norm for both the patient and his or her medical adviser. The collection of appropriate and unbiased estimates of costs and benefits is an important first step towards this objective.

Coronary Disease↗
PubMed1987

Specific muscular development in under-18 soccer players.

A comparison of the under-18 (U-18) and under-16 (U-16) squads of the Canadian national soccer team with a representative sample of Canadians (Canada Fitness Survey, 1983) showed a tendency for the development or selection of the older players in teams of stature (U-18, 175.8 cm; U-16, 171.1 cm; CFS, 170.9 cm) and lean body mass (U-18, 63.4; U-16, 57.9; CFS, 54.2 kg). The larger lean mass of the older players could not be explained simply by size. The U-18s also showed greater isokinetic leg extension force (particularly for rapid movements) and explosive strength (vertical jump) relative to the younger players, although the knee extension force was less than in some classes of athlete. Part of the gain in mass seems due to local training of the hip and leg muscles and part to a more general muscular development. Contrary to some reports, the hip flexibility of the Canadian players (sit and reach test) was greater than for a national sample; this may be important in avoiding soft tissue injuries to the legs. However, aerobic power (58.3 +/- 5.3 ml kg-1 min-1) and body fat (8.0 +/- 1.1%) were unremarkable.

Adolescent↗
PubMed1987

Grouping of runners during marathon competition.

Marathon runners tend to form clusters during competition, possibly as a means of improving their performance. Studies of international competitors in Fukuoka and Tokyo races have shown a density of 0.44 to 0.80 runners.m2 among those maintaining a pace of 4.8-5.6 m.s-1, clustering being most marked among elite performers. Some 95% of clustered runners maintained a minimum distance of 0.5-1.5 m from other competitors; moreover, such competitors avoided occupying an angle of +/- 15 degrees either before or behind other runners. The phenomenon merits closer study by those interested in the bettering of marathon performance.

Competitive Behavior↗
PubMed1987

Human rights and the older worker: changes in work capacity with age.

The aging of physical working capacity affects the employability of older individuals in heavy work through such factors as a decline in aerobic power, muscular strength, and tolerance of thermal load. Difficulties in setting an appropriate criterion for enforced retirement include, on the one hand, a tremendous inter-individual variation in the rate of aging, and on the other, the problem that a standard appropriate for older men cannot be met by even the youngest women. Vigorous training can reduce some components of biological age by as much as 20 yr, and it is manifestly unfair to require the retirement of those employees who have chosen a lifestyle that has conserved their physical condition. However, the development of reliable, valid, and convincing tests that will distinguish such individuals remains a fascinating medico-legal challenge.

Acclimatization↗