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Biomedical subjects

A E Hardman

Publications and source records attributed to A E Hardman.

At least 37 records · Page 2Linked to original sources
PubMed1999

Interaction of physical activity and diet: implications for lipoprotein metabolism.

OBJECTIVE: To consider how physical activity interacts with diet to modify lipoprotein metabolism and comment on implications for human health. DESIGN: An overview of lipoprotein metabolism is followed by a summary of the main effects of physical activity on lipoprotein metabolism. Interactions with dietary practice and the disposition of dietary lipid are reviewed, with comment on links with body fatness. SETTING: Literature is reviewed in relation to the risk of atherosclerotic disease. SUBJECTS: Although some data are presented on athletic groups, evidence relating to individuals with normal physical activity habits is mainly discussed. RESULTS: Physical inactivity is a risk factor for cardiovascular disease and one mechanism may involve changes to lipoprotein metabolism. The consensus is that aerobic activity involving an expenditure of > or = 8 MJ week(-1) results in an increase in HDL cholesterol and probably decreases in fasting triacylglycerol. These changes Occur despite the spontaneous increase in the proportion of dietary energy from carbohydrate which accompanies increased exercise. For this reason, exercise may be a means of reducing the hypertriglyceridaemic and HDL-lowering effects of low fat (high carbohydrate) diets. Decreases in total and low density lipoprotein cholesterol are sometimes, but not always, reported in sedentary individuals beginning exercise. One mechanism linking all these changes may be alterations to the dynamics of triacylglycerol-rich particles, particularly in the fed state. CONCLUSION: The expenditure of considerable amounts of energy through regular, frequent physical activity increases the turnover of lipid substrates, with effects on their transport and disposition which may reduce the progression of atherosclerosis.

Cardiovascular Diseases↗
PubMed1999

Physical activity, obesity and blood lipids.

PURPOSE: To present the evidence concerning the influence of physical activity on the dyslipidaemia of obesity and overweight. METHODS: Review of a personal library of literature on the interactions of physical activity, lipoprotein metabolism and body fatness. SUMMARY OF FINDINGS: Obesity, in particular abdominal obesity, is associated with dyslipidaemia--specifically elevated plasma concentrations of triacylglycerol (TAG) in the fasted state, an exaggerated postprandial rise in plasma TAG, low concentrations of high density lipoprotein cholesterol (HDL) and possibly a preponderance of small dense low density lipoproteins. Regular physical activity contributes to the avoidance of overweight and hence to the development of dyslipidaemia. Although low levels of body fatness contribute to the high levels of HDL cholesterol and the low levels of TAG in trained people there are other important determinants of these characteristics. In particular, exercise (and probably training, that is regular, frequent exercise over months and years) enhances the metabolic capacity for TAG, possibly through mechanisms involving increased activity of lipoprotein lipase. This, in turn, has effects on other lipoprotein species such that the transport of TAG and cholesterol in the circulation is improved. There is evidence for a dose-response relationship, with for example, higher levels of HDL cholesterol in men and women who expend more energy in exercise. For the majority of healthy, sedentary adults frequent, moderate intensity exercise equivalent to a total gross energy expenditure of about 8.5 MJ per week is probably a sufficient to influence lipoprotein lipids.

Adipose Tissue↗
PubMed1999

The endurance shuttle walk: a new field test for the assessment of endurance capacity in chronic obstructive pulmonary disease.

BACKGROUND: The purpose of this study was to develop an externally controlled, constant paced field walking test to assess endurance capacity in patients with chronic obstructive pulmonary disease (COPD). There were four objectives: (1) to develop a protocol; (2) to compare treadmill and shuttle walk tests of endurance capacity; (3) to examine the repeatability of the endurance shuttle walk test; and (4) to compare the sensitivity to pulmonary rehabilitation of endurance and incremental shuttle walk tests. METHODS: The test was designed to complement the incremental shuttle walk test (ISWT) using the same 10 m shuttle course and an audio signal to control pace. The intensity of the field endurance test was related to a percentage of each patient's maximum field exercise performance assessed by the ISWT. A number of cassette tapes were pre-recorded with a range of audio signal frequencies to dictate walking speeds between 1.80 and 6.00 km/h. In the first limb of the study 10 patients with COPD (mean (SD) forced expiratory volume in one second (FEV1) 1.0 (0.36) 1, 35% predicted) performed three endurance shuttle walk tests (ESWTs) and three treadmill endurance tests. The walking speeds were calculated to elicit 75%, 85%, and 95% of each patient's maximum ISWT performance for the field tests and measured peak oxygen consumption for the treadmill tests. In a separate group of patients the repeatability of the ESWT at an intensity of 85% of the ISWT performance was evaluated. Finally, the ESWT (at the 85% intensity) and the ISWT were performed at the start of a five week control period and at the start and end of a seven week pulmonary rehabilitation programme in 21 patients with COPD (mean FEV1 0.80 (0.18) 1). RESULTS: The mean (SE) times achieved during the ESWT were 13.1 (2.3), 10.2 (2.5), and 5.3 (1.7) min for the walks at 75%, 85%, and 95% intensities, respectively. Patients tended to walk for longer on the treadmill than during the field tests at all intensities, but there were no significant differences between the end of test heart rates or Borg ratings of breathlessness or perceived exertion. Following one practice ESWT at the 85% intensity, the mean difference and limits of agreement (2SD) between tests 2 and 3 was +15 (42) s (p > 0.05). There was no significant change in performance on either test following the five week control period prior to rehabilitation. Following rehabilitation the ESWT duration increased by 160 (24)% and the ISWT distance increased by 32 (11)% (effect sizes 2.90 and 0.41, respectively). CONCLUSIONS: The ESWT was simple to perform, acceptable to all patients, and exhibited good repeatability after one practice walk. The test showed major improvement following rehabilitation and was more sensitive to change than the field test of maximal capacity.

Exercise Test↗
PubMed1998

The influence of exercise on postprandial triacylglycerol metabolism.

Trained people exhibit low plasma concentrations of triacylglcyeride (TAG) in both fasted and postprandial states. This mainly reflects enhanced uptake of TAG into skeletal muscle, via enhanced activity of lipoprotein lipase, the rate-limiting step in TAG removal. Endurance athletes possess a large, well-vascularised muscle mass and this may contribute through the increased availability of endothelial binding sites for LPL. However, each session of exercise stimulates a delayed increase in LPL activity so that prior exercise enhances uptake into muscle. Intramuscular TAG is one source of energy for muscular contraction so this may serve to replenish muscle nutrient stores which have been diminished by exercise. Regular, frequent aerobic exercise may oppose the atherogenic disturbances to lipoprotein metabolism evident during the postprandial period. It may also, by favouring the disposition of dietary fatty acids in muscle, improve the matching of fat oxidation to fat intake and hence help with maintenance of a desirable level of body fatness.

Exercise↗
PubMed1998

The effect of 13 weeks of running training followed by 9 d of detraining on postprandial lipaemia.

The present study examined the influence of training, followed by a short period of detraining, on postprandial lipaemia. Fourteen normolipidaemic, recreationally active young adults aged 18-31 years participated, in two self-selected groups: three men and five women (BMI 21.7-27.6 kg/m2) completed 13 weeks of running training, after which they refrained from exercise for 9 d; three men and three women (BMI 21.5-25.6 kg/m2) maintained their usual lifestyle. Oral fat tolerance tests were conducted at baseline and again 15 h, 60 h and 9 d after the runners' last training session. Blood samples were drawn after an overnight fast and at intervals for 6 h after consumption of a high-fat meal (1.2 g fat, 1.4 g carbohydrate, 70.6 kJ energy/kg body mass). Heparin was then administered (100 IU/kg) and a further blood sample was drawn for measurement of plasma lipoprotein lipase (EC 3.1.1.34; LPL) activity. Endurance fitness improved in runners, relative to controls (maximal O2 uptake +3.2 (SE 1.1) ml/kg per min v. -1.3 (SE 1.2) ml/kg per min; P < 0.05). In the absence of the acute effect of exercise, i.e. 60 h after the last training session, there was no effect of training on either postprandial lipaemia or on post-heparin LPL activity. However, changes during 9 d of detraining in both these variables differed significantly between groups; after 2d without exercise (60 h test), the runners' lipaemic response was 37% higher than it was the morning after their last training session (15 h test; runners v. controls P < 0.05), with a reciprocal decrease in post-heparin LPL activity (P < 0.01). These findings suggest that improved fitness does not necessarily confer an effect on postprandial lipaemia above that attributable to a single session of exercise.

Adolescent↗
PubMed1998

Training effects of short and long bouts of brisk walking in sedentary women.

This study compared the effects of short and long bouts of brisk walking in sedentary women. Forty seven women aged 44.4 +/- 6.2 yr (mean +/- SD) were randomly assigned to either three 10-min walks per day (short bouts), one 30-min walk per day (long bouts) or no training (control). Brisk walking was done on 5 d x wk(-1), at 70 to 80% of maximal heart rate, typically at speeds between 1.6 and 1.8 m x s(-1) (3.5 and 4.0 mph), for 10 wk. Subjects agreed not to make changes to their diet. Twelve short-bout walkers, 12 long-bout walkers, and 10 controls completed the study. Relative to controls, VO2max (short-bout, +2.3 +/- 0.1 mL x kg(-1) x min(-1); long-bout, +2.4 +/- 0.1 mL x kg(-1) x min(-1); controls, -0.5 +/- 0.1 mL x kg(-1) x min[-1]) and the VO2 at a blood lactate concentration of 2 mmol x L(-1) increased in walkers (both P < 0.05), with no difference in response between walking groups. Neither heart rate during standard, submaximal exercise nor resting systolic blood pressure changed in a different way in walkers and controls. The sum of four skinfold thicknesses decreased in both walking groups (P < 0.05) but body mass (short-bout, -1.7 +/- 1.7 kg; long-bout, -0.9 +/- 2.0 kg; controls, +0.6 +/- 0.7 kg) and waist circumference decreased significantly only in short-bout walkers. Changes in anthropometric variables did not differ between short- and long-bout walkers. Thus short bouts of brisk walking resulted in similar improvements in fitness and were at least as effective in decreasing body fatness as long bouts of the same total duration.

Adult↗
PubMed1998

Postprandial lipemia: effects of intermittent versus continuous exercise.

PURPOSE: The purpose of this study was to assess whether exercise performed in continuous and discontinuous formats reduced postprandial lipemia to a similar degree. METHODS: Fifteen normolipidemic and three borderline hyperlipidemic healthy males (ages 30.6 +/- 9.0 (mean +/- SD) yr, BMI 23.1 +/- 1.4 kg.m-2) participated in three trials, each conducted over 2 d. Subjects refrained from exercise for the 2 d preceding each trial. On day one, subjects rested (control trial), or ran at 60% of maximal oxygen uptake in either one 90-min session (continuous exercise trial), or three 30-min sessions (intermittent exercise trial). On day two, subjects ingested a high-fat test breakfast (1.2 g fat, 1.2 g carbohydrate, 70 kJ energy per kilogram body mass). Blood samples were obtained in the fasted state and at intervals for 6 h postprandially. RESULTS: Fasting plasma triacylglycerol (TAG) concentrations did not differ between trials. Areas under the TAG versus time curves were 18.1 +/- 6.7% (mean +/- SEM) and 17.7 +/- 7.6% (both P < 0.05) lower than control in the continuous exercise and intermittent exercise trials, respectively. Plasma glucose responses to the test meal did not differ between trials, but the serum insulin response was lower in the intermittent exercise trial compared with that in the control. CONCLUSION: The results suggest that both intermittent and continuous exercise can reduce postprandial lipemia.

Adult↗
PubMed1998

Postprandial lipemia in endurance-trained people during a short interruption to training.

This study examined changes in postprandial lipemia in endurance-trained people during a short interruption to training. Nine men and one woman (ages 18-55 yr) undertook fat tolerance tests after 15 h, 60 h, and 6.5 days without exercise. The test meal (1.2 g fat, 1.1 g carbohydrate, 66 kJ/kg body mass) was consumed after a 12-h fast. Postprandial lipemia increased rapidly with detraining (area under plasma triacylglycerol vs. time curve: 8.42 +/- 1.40, 11. 35 +/- 1.38, and 11.97 mM x 6 h at 15 h, 60 h and 6.5 days, respectively). In the fasted state, plasma triacylglycerol concentration (0.85 +/- 0.15, 1.09 +/- 0.12, and 1.10 +/- 0.11 mM at 15 h, 60 h and 6.5 days, respectively) and the ratio of total cholesterol to high-density-lipoprotein cholesterol increased with detraining. Values were significantly higher at 60 h and 6.5 days than values at 15 h ( P < 0.05) for each of these three variables. The serum insulin response was higher ( P < 0.05) at 6.5 days than at 15 h (81.6 +/- 11.3, 87.6 +/- 11.4, and 94.5 +/- 9.4 microIU/ml x 6 h at 15 h, 60 h, and 6.5 days, respectively). Frequent exercise is needed to maintain a low level of postprandial lipemia and insulinemia in trained people.

Adolescent↗
PubMed1998

Does vitamin D receptor polymorphism influence the response of bone to brisk walking in postmenopausal women?

Vitamin D receptor (VDR) polymorphism may be a genetic factor affecting bone mineral density (BMD). This study examined the interaction of VDR genotype with the effect of an exercise intervention on bone measurements in UK postmenopausal women. 33 walkers, who completed 20.4 +/- 3.9 (mean +/- SD) min day-1 of brisk walking over 1 year, and 36 controls agreed to give DNA samples. BMD was measured at the lumbar spine, femoral neck and calcaneus by dual energy X-ray absorptiometry and broadband ultrasonic attenuation (BUA) was measured at the calcaneus. VDR genotype was determined by BsmI restriction fragment length polymorphisms and the presence, or absence, of the restriction site was signified by 'b' or 'B', respectively. At baseline there was no significant difference in BMD between VDR genotypes, but BUA was significantly higher in the BB genotype than in the Bb or bb genotype. Although there was no significant difference in 1-year change (%) in BMD and BUA between the three genotypes, the 1-year changes in spinal BMD and BUA in the bb walkers (0.75 and 2.35%, respectively) were significantly different from those in the bb controls (-1.25 and -6.10%, respectively). These results suggest that in the bb genotype of VDR, bone may be more responsive to exercise than in other VDR genotypes in British postmenopausal women.

Absorptiometry, Photon↗
PubMed1997

Brisk walking reduces calcaneal bone loss in post-menopausal women.

1. This study examined the influence of brisk walking on skeletal status in post-menopausal women. 2. Subjects were 84 healthy women aged 60-70 years. Who were previously sedentary and at least 5 years post-menopausal. Subjects were randomly assigned to walking (n = 43) and control (n = 41) groups. Walkers followed a 12-month, largely unsupervised programme of brisk walking. The bone mineral density of the lumbar spine, femoral neck and calcaneus and broadband ultrasonic attention of the calcaneus were measured at baseline and after 12 months. 3. Forty control subjects and 38 walkers completed the study. Walkers built up to 20.4 +/- 3.8 min/day (mean +/- SD) of brisk walking. Body mass increased in control subjects relative to walkers [mean change (SE) +0.9 (0.3) and -0.1 (0.3) kg respectively; P = 0.04]. Predicted maximum oxygen uptake increased in walkers by 2.1 (0.9) ml min-1 kg-1 (P = 0.02). Bone mineral density in the lumbar spine and calcaneus fell in control subjects [-0.005 (0.004) and -0.010 (0.004) g/cm2, respectively] but not in walkers [+0.006 (0.004) and +0.001 (0.004) g/cm2]. The difference in response between groups was significant in the calcaneus (P = 0.04) but not in the lumbar spine (P = 0.08). Mean femoral neck bone mineral density did not change significantly in either group, although changes in walkers were related to the amount of walking completed (r = 0.51, P = 0.001). The change in broadband ultrasonic attenuation of the calcaneus differed between groups [control subjects, -3.7 (0.8); walkers, -0.7 (0.8) dB/MHz; P = 0.01]. 4. Walking decreased bone loss in the calcaneus and possibly in the lumbar spine. It also improved functional capacity and enabled walkers to avoid the increase in body mass seen in control subjects.

Absorptiometry, Photon↗
PubMed1997

Acute effects of exercise on postprandial lipemia: a comparative study in trained and untrained middle-aged women.

Repeated episodes of exaggerated postprandial lipemia may hasten the progression of atherosclerosis. The purpose of this study was to compare the lipemic response to a high-fat meal in trained and untrained women in the presence and absence of the acute effects of exercise. Nine endurance-trained and thirteen untrained women aged 40.4 +/- 3.3 and 43.8 +/- 4.3 y (mean +/- SD), with maximal oxygen uptake of 50.3 +/- 5.9 and 31.7 +/- 3.6 mL.kg-1.min-1, and a body mass index (kg/m2) of 22.2 +/- 0.9 and 22.9 +/- 2.3, respectively, underwent two trials, each over 2 d. Subjects did not exercise during the 2 d leading up to a trial. On day 1 they either walked for 90 min at 60% of maximal oxygen uptake (exercise), or refrained from exercise (control). On day 2 venous blood and expired air samples were obtained in the fasted state and for 6 h after consumption of a high-fat meal (1.70 g fat, 1.65 g carbohydrate, and 0.25 g protein/kg fat-free mass). Exercise decreased lipemia as determined by the mean (+/-SEM) area under the plasma triacylglycerol concentration versus time curve: trained, 6.96 +/- 0.48 compared with 4.87 +/- 0.33 mmol.h/L; untrained, 8.36 +/- 0.83 compared with 7.01 +/- 0.79 mmol.h/L (control and exercise trials, respectively, both P < 0.05). Lipemia differed significantly between groups in the presence of this acute effect of exercise but not in its absence. Exercise decreased insulinemia in trained women (543 +/- 25 compared with 433 +/- 24 pmol.h/L, P < 0.01) but had no effect in untrained women (592 +/- 34 compared with 585 +/- 47 pmol.h/L). Total oxidation of fat over the 6-h postprandial period was enhanced by exercise, and to a similar degree in each group of women.

Adult↗
PubMed1997

Walking to health.

Walking is a rhythmic, dynamic, aerobic activity of large skeletal muscles that confers the multifarious benefits of this with minimal adverse effects. Walking, faster than customary, and regularly in sufficient quantity into the 'training zone' of over 70% of maximal heart rate, develops and sustains physical fitness: the cardiovascular capacity and endurance (stamina) for bodily work and movement in everyday life that also provides reserves for meeting exceptional demands. Muscles of the legs, limb girdle and lower trunk are strengthened and the flexibility of their cardinal joints preserved; posture and carriage may improve. Any amount of walking, and at any pace, expends energy. Hence the potential, long term, of walking for weight control. Dynamic aerobic exercise, as in walking, enhances a multitude of bodily processes that are inherent in skeletal muscle activity, including the metabolism of high density lipoproteins and insulin/glucose dynamics. Walking is also the most common weight-bearing activity, and there are indications at all ages of an increase in related bone strength. The pleasurable and therapeutic, psychological and social dimensions of walking, whilst evident, have been surprisingly little studied. Nor has an economic assessment of the benefits and costs of walking been attempted. Walking is beneficial through engendering improved fitness and/or greater physiological activity and energy turnover. Two main modes of such action are distinguished as: (i) acute, short term effects of the exercise; and (ii) chronic, cumulative adaptations depending on habitual activity over weeks and months. Walking is often included in studies of exercise in relation to disease but it has seldom been specifically tested. There is, nevertheless, growing evidence of gains in the prevention of heart attack and reduction of total death rates, in the treatment of hypertension, intermittent claudication and musculoskeletal disorders, and in rehabilitation after heart attack and in chronic respiratory disease. Walking is the most natural activity and the only sustained dynamic aerobic exercise that is common to everyone except for the seriously disabled or very frail. No special skills or equipment are required. Walking is convenient and may be accommodated in occupational and domestic routines. It is self-regulated in intensity, duration and frequency, and, having a low ground impact, is inherently safe. Unlike so much physical activity, there is little, if any, decline in middle age. It is a year-round, readily repeatable, self-reinforcing, habit-forming activity and the main option for increasing physical activity in sedentary populations. Present levels of walking are often low. Familiar social inequalities may be evident. There are indications of a serious decline of walking in children, though further surveys of their activity, fitness and health are required. The downside relates to the incidence of fatal and non-fatal road casualties, especially among children and old people, and the deteriorating air quality due to traffic fumes which mounting evidence implicates in the several stages of respiratory disease. Walking is ideal as a gentle start-up for the sedentary, including the inactive, immobile elderly, bringing a bonus of independence and social well-being. As general policy, a gradual progression is indicated from slow, to regular pace and on to 30 minutes or more of brisk (i.e. 6.4 km/h) walking on most days. These levels should achieve the major gains of activity and health-related fitness without adverse effects. Alternatively, such targets as this can be suggested for personal motivation, clinical practice, and public health. The average middle-aged person should be able to walk 1.6 km comfortably on the level at 6.4 km/h and on a slope of 1 in 20 at 4.8 km/h, however, many cannot do so because of inactivity-induced unfitness. The physiological threshold of 'comfort' represents 70% of maximum heart rate. (ABSTRACT TRUNCATED)

Cardiovascular Diseases↗
PubMed1996

Effects of low and moderate intensity treadmill walking on postprandial lipaemia in healthy young adults.

We have previously shown that the lipaemic response to a fatty meal was reduced when prolonged (2 h) low intensity exercise was taken some hours before eating. The purpose of this study was to test the hypothesis that the effect is quantitatively greater after exercise of moderate intensity than after exercise at low intensity. Six men and six women, mean age 26.9 (SEM 1.5) years, took part in three trials, each conducted over 2 days; on the afternoon of day 1 of each of two exercise trials the subjects walked on a treadmill for 90 min at either 31 (SEM 1) % or 61 (SEM 1) % of maximal oxygen uptake, i.e. low and moderate intensity, respectively; on the control trial the subjects refrained from exercise on day 1. On the morning of day 2 of each trial they ingested a test meal (1.28 g fat, 1.44 g carbohydrate, 76 kJ energy.kg-1 body mass); blood samples were obtained in the fasted state and for 6 h after the meal. Fasting serum triacylglycerol concentration and the area under the postprandial triacylglycerol-time curve were lower than in the control trial (P < 0.05) after moderate intensity walking but not after low intensity walking. The results suggest that the mitigation of the lipaemic response to a meal high in fat and carbohydrate is related to the intensity and/or the energy expenditure of the preceding exercise.

Adult↗
PubMed1996

Exercise in the prevention of atherosclerotic, metabolic and hypertensive diseases: a review.

Evidence that physical inactivity and low fitness confer an increased risk of coronary heart disease (CHD) is convincing. There is a graded relationship with the amount of physical activity (or physical fitness), with some evidence that an asymptote is reached in the mid-range. Epidemiological studies have also shown that physically inactive individuals are at greater risk of developing hypertension or non-insulin-dependent diabetes or of experiencing a stroke, but less is known about the nature of these relationships. The effects of exercise on blood pressure, glucose/insulin dynamics and lipoprotein metabolism may contribute to the lower risk of these diseases in people who exercise regularly. Long-term adaptations to regular exercise may result in improved insulin sensitivity and in higher serum concentrations of high-density lipoprotein cholesterol-mediated in part by improved weight regulation. However, the residual effects of individual exercise bouts may, cumulatively, also be important; these "acute' effects may be enhanced when functional capacity is increased through training. More intensive exercise may carry greater benefits in some respects, but it also carries higher risks, for example of orthopaedic injury or triggering of heart attack. Consequently, public health policies should aim to foster a long-lasting commitment to increased levels of frequent, moderate-intensity activity in as many people as possible.

Arteriosclerosis↗