Biomedical subjects

R J Shephard

Publications and source records attributed to R J Shephard.

At least 19 recordsLinked to original sources

PubMed1992

Return to work after spinal cord injury: the potential contribution of physical fitness.

The history, physical characteristics and fitness status of 60 persons who had sustained a spinal cord injury at least 3 years previously were considered in relation to current occupation. All subjects had completed their education, 39 being gainfully employed and 21 unemployed. The general characteristics of the sample, mainly beneficiaries of the Quebec Automobile Insurance Plan, were typical of spinal cord injured individuals in North America. The working group had a significantly higher current level of education than those who were unemployed (p less than .01). In terms of physical fitness, the workers were lighter, with a lower body mass index and a higher aerobic power (p less than .05). Isokinetic testing suggested a trend toward a higher peak torque in the workers. The total work performed (Nm.kg-1) during an isokinetic endurance test (25 biphasic contraction at 180 degrees.sec-1) was significantly higher in the workers, suggesting that such muscular endurance might be even more useful than greater peak isokinetic strength during vocational activities. However, the likelihood of employment was unrelated to habitual patterns of either aerobic exercise or overall physical activity. No significant differences of physical fitness or physical activity habits were found between workers holding sedentary versus physically demanding jobs. The results verified the positive relationship between physical fitness (body composition, aerobic power, muscular endurance) and the gainful employment of paraplegics, but failed to show any significant relationship between physical fitness and the acceptance of physically demanding work by such individuals.

Adolescent↗

PubMed1992

Acute exercise and immune function. Relationship between lymphocyte activity and changes in subset counts.

Twenty-one young male subjects exercised on a cycle ergometer for 60 min at 60% of VO2max. Blood samples collected every 30 min throughout exercise and continuing to 120 min recovery served for the immunological tests. Exercise induced biphasic changes in the various leucocyte subsets. There was a granulocytosis, lymphocytosis and monocytosis during exercise, and a further granulocytosis and a slight monocytosis, but a lymphocytopenia during recovery. All lymphocyte subsets (CD3+, CD19+, CD4+, CD8+, and CD16+ cells) increased in number during exercise, were decreased 30 min after exercise, and had not returned to baseline levels by 120 min of recovery. The apparent lymphocyte responsiveness to the mitogens phytohaemagglutinin (PHA) and pokeweed mitogen (PWM) declined significantly during exercise, returning to normal by 120 min of recovery. The natural killer (NK) activity rose markedly during exercise, but decreased to almost half the pre-exercise level at 30 and 60 min of recovery, returning to baseline levels after 120 min of recovery. Functional capability correlated well with the percentage of each major responder subset in the assay, suggesting that the in vitro lymphocyte PHA- and PWM-responsiveness and the NK activity did not change significantly on a per cell basis. The analysis of lymphocyte marker antigen density revealed that the CD3+, CD4+, CD8+ and CD19+ lymphocytes mobilized into the circulation during exercise did not express the respective CD3, CD4, CD8 and CD19 molecules as strongly as did the subsets circulating at rest, whereas the expression of the CD16 antigen on CD16+ lymphocytes remained unchanged.

Adult↗

PubMed1992

Cold, fitness and the exercise electrocardiogram. A 20 year longitudinal study of Canadian Inuit.

A 20 year longitudinal study has examined fitness, lung function and exercise electrocardiograms in the Inuit of Igloolik (NWT, 69 degrees 40' N). When first examined (1969/70), an energy expenditure of up to 16 MJ/day was estimated from Kofranyi-Michaelis respirometry. Step test predictions of maximal oxygen intake were also high initially, but values declined progressively with acculturation to a sedentary lifestyle. Throughout the 20 years, right-branch bundle block (RBBB) has been somewhat more prevalent than in southern Canada. The majority of those affected have shown no more than slight R-wave notching. In 1969/70, a few of the more marked cases of RBBB may have been attributable to chronic respiratory disease, but the majority of cases have shown high normal values for both lung function and maximal oxygen intake. We thus conclude that the major cause of RBBB in this community is a ventricular hypertrophy due to the vigorous physical demands of the traditional lifestyle.

Adolescent↗

PubMed1992

Does exercise reduce all-cancer death rates?

A reanalysis is made of earlier data relating to initial physical fitness and the likelihood of death from all forms of cancer. It is argued that the original analysis may have been biased by an association between initial fitness and other health habits, particularly cigarette smoking. The association with fitness status remains after reanalysis of the data on the assumption that current smoking leads to a uniform doubling of the risk of cancer death, but the effect is weaker than previously reported. There remains some potential bias, in that the quantity of current smoking may have been linked to fitness status. Some 55% of deaths were untraced, but it is argued that any socioeconomic or other bias from this cause is likely to account for the association between cancer risk and low fitness status. Any reduction of cancer risk is associated with the change from an extremely sedentary to a moderately sedentary lifestyle. It thus cannot be explained in terms of the mechanisms previously invoked to explain low risks of colonic and reproductive cancers in endurance athletes.

Exercise↗

PubMed1992

Potential markers of heavy training in highly trained distance runners.

Markers of a heavy increase in training were examined in ten highly trained distance runners (mean(s.d.) age 29.8(1.7) years, maximal oxygen intake 65.3 ml kg-1 min-1, personal best 10-km time 31 min 4 s) who undertook a deliberate 38% increment of training over a 3-week period. Their running performance did not improve, and six of the ten subjects developed sustained fatigue, suggesting that training was excessive, although the full clinical picture of overtraining did not develop. The Profile of Mood States was the best single marker of disturbed function, indicating increased fatigue and decreased vigour. There were no useful changes of resting heart rate or perceived exertion during submaximal running, sleep was undisturbed, and there were no orthopaedic injuries. Two subjects developed rhinoviral infections following the heavy training, and a third complained of symptoms that were diagnosed 2 weeks later as exercise-induced asthma. The increase of serum cortisol normally induced by 30 min of submaximal exercise was no longer seen when the same acute exercise was performed after heavy training. Resting lymphocyte proliferation tended to increase in response to phytohaematoglutinin (PHA) and concanavalin A (Con A), the ratio of helper to suppressor cells (H/S) decreased, and pokeweed mitogen induced smaller increases in IgG and IgM synthesis. Whereas before heavy training, PHA-stimulated lymphocyte proliferation was unchanged by 30 min of acute submaximal exercise, after 3 weeks of heavy training the same bout of exercise caused an 18% suppression of proliferation. Likewise, heavy training brought about a decrease of T-lymphocytes in response to acute submaximal exercise, but an abolition of the acute exercise-induced decrease in the H/S ratio. The previously observed exercise-induced decrease of IgG synthesis did not occur when the same acute bout of exercise was performed after heavy training. We conclude that such minor and transient changes of immune function may possibly be a warning that training is becoming excessive, but they have only a limited significance for overall immune function.

Adult↗

PubMed1992

Immune responses and increased training of the elite athlete.

Ten elite male runners (age, 29.8 +/- 1.7 yr; maximum oxygen consumption, 65.3 +/- 4.9 ml.kg-1.min-1; 10-km times, 31 min 43 s +/- 1 min 46 s) deliberately increased training schedules by an average of 38% for 3 wk. Resting heart rate and maximal oxygen intake were unchanged, but the heart rate response to acute exercise was decreased. Following heavy training, blood samples taken at rest showed trends to a decreased helper/suppressor cell ratio, an increased phytohemagglutinin (PHA)- and concanavalin (ConA)-stimulated lymphocyte proliferation, and a decreased production of immunoglobulins IgG and IgM. Whereas PHA-stimulated lymphocyte proliferation was initially unchanged by acute exercise, after 3 wk of heavy training the same acute exercise caused an 18% suppression of proliferation. Acute exercise following heavy training did not alter pokeweed-stimulated IgG or IgM synthesis. There was no correlation between changes in lymphocyte subpopulations, helper/suppressor ratios, and mitogen-induced cellular proliferation. The immune system of endurance-trained athletes at rest seemed to tolerate the stress of heavy training, but superimposition of a bout of acute exercise on the chronic stress of heavy training resulted in immunosuppression, which was transient and most likely not of clinical significance.

Adult↗

PubMed1992

Effectiveness of training programmes for prepubescent children.

Early investigators suggested that endurance training had little influence upon the aerobic function of the prepubescent child. It is shown that the twin explanations of this supposed phenomenon (a high intrinsic level of physical activity and an immaturity of biochemical systems) have little foundation. Moreover, critical examination of the original experiments shows a number of problems of experimental design, often including an inadequate sample size, a lack of control group, an inappropriate pattern of training relative to the initial fitness of the child, and too short a period of observation. Recent, well-designed studies all show a response in prepubescent children. Comparison with adults is hampered by difficulties in matching training intensity, but there is no immediate evidence that the training response of the prepubescent child is less than in an older person. The main basis for the increase of oxygen transport seems an increase of cardiac stroke volume. Plainly, the development of athletic performance and the attack upon cardiac risk factors can be begun before puberty, although in the average prepubescent it may be more important for the school programmes to develop positive, lifelong attitudes, than to maximise aerobic function.

Age Factors↗

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