Adrianne E. Hardman

Walking to health.

SummaryWalking 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 1.6km 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. Trials across the age span are required in primary care and community programmes to evaluate such approaches, and the benefits and costs more generally of possible initiatives towards more walking.Walking, by quantity and pace, is under-researched, particularly in the middleaged and elderly. Randomised controlled trials are required of its physiological effects on blood pressure, thrombogenesis, immune function; and of walking in the prevention and/or treatment of non-insulin dependent (type II) diabetes mellitus, osteoporosis, anxiety and depression and back pain.Low levels of walking are a major factor in today’s widespread waste of the potential for health and well-being that is due to physical inactivity. This waste is manifest in impaired functional capacities, overweight, disease, disability, premature death and the concomitant human and economic costs. This review seeks to assemble evidence of the health gains of walking as a resource for the multifarious professionals and students, practitioners, investigators and policy makers.

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.

Exercise and postprandial lipid metabolism: an update on potential mechanisms and interactions with high-carbohydrate diets (review)

Endurance trained people exhibit low levels of postprandial lipemia. However, this favorable situation is rapidly reversed with de-training and it is likely that the triglyceride (TG) lowering effects of exercise are mainly the result of acute metabolic responses to recent exercise rather than long-term training adaptations. A large body of evidence suggests that postprandial lipemia can be attenuated following an individual exercise session, with the energy expended during exercise being an important determinant of the extent of TG lowering. Increased lipoprotein lipase-mediated TG clearance and reduced hepatic TG secretion are both likely to contribute to the exercise-induced TG reductions. These changes may occur in response to post-exercise substrate deficits in skeletal muscle and/or the liver. In addition, regular exercise can oppose the hypertriglyceridaemia sometimes seen with low-fat, high-carbohydrate diets. Levels of physical activity should therefore be taken into account when considering nutritional strategies for reducing the risk of cardiovascular disease.

Reduction in postprandial lipemia after walking: influence of exercise intensity.

This study compared the effects of low and moderate intensity walking on postprandial lipemia, holding energy expenditure constant. Nine healthy normolipidemic subjects (5 men, 4 women; age 27.7 +/- 0.9, fasting, plasma triacylglycerol 0.95 +/- 0.18 mmol.l-1, mean +/- SEM) who were physically active but not endurance-trained undertook three trials, each over 2 d, in a balanced design. On the afternoon of day 1 they either refrained from exercise (Control), walked for 3 h at low intensity (Walk low, 32 +/- 1% VO2max), or walked for 1.5 h at moderate intensity (Walk moderate, 63 +/- 1% VO2max). The following morning, after a 12-h fast, they consumed a high-fat meal (1.3 g fat, 1.2 g carbohydrate, 0.2 g protein, 76 kJ energy per kg body mass). Blood and expired air samples were obtained before the meal and for 6 h afterward. Postprandial lipemia (total area under triacylglycerol concentration vs time curve) was lower than control after low intensity walking as well as after moderate intensity walking (both P < 0.05) but did not differ between the two walking trials (Control, 8.09 +/- 1.09 mmol.l-1 h; Walk low, 5.46 +/- 0.63 mmol.l-1.h; Walk moderate, 5.53 +/- 0.58 mmol.l-1.h). The increase in energy production following the test meal did not differ between trials, but fat oxidation was increased in the fasting and postprandial states for both walking trials, compared with control (P < 0.05).

The effect of a single bout of brisk walking on postprandial lipemia in normolipidemic young adults

The purpose of this study was to examine the effect of one bout of low-intensity exercise on the lipemic response to a high-fat meal. Twelve (six women, six men) normolipidemic adults aged 25.8 +/- 1.2 years (mean +/- SEM) took part in two trials. In the exercise trial, subjects walked for 2 hours on a treadmill at 30.9% +/- 1.6% of maximal oxygen uptake (VO2 max) 15 hours before ingestion of the test meal. In the control trial, subjects rested the day before the test meal. After a 12-hour fast, blood samples were obtained by venous cannulation before ingestion and hourly after ingestion for 6 hours. Serum was analyzed for triacylglycerol (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and HDL2-C, apolipoproteins (apos) A-I and B, free fatty acids (FFA), free glycerol, glucose, and insulin. TG values were corrected for free glycerol. Fasting serum TG and peak TG concentrations were lower (Wilcoxon, P < .05) for the exercise trial than for the control trial (0.74 +/- 0.03 v 0.92 +/- 0.08 and 1.98 +/- 0.18 v 2.59 +/- 0.32 mmol.L-1, respectively). The total lipemic response (area under the TG/time curve, normalized to the 0-hour level) was 31% +/- 7% lower in the exercise trial (4.28 +/- 0.66 v 6.46 +/- 1.08 mmol.L-1.h, P < .01). No differences were found between trials in the other parameters. These results show that a single bout of low-intensity exercise reduces the extent of postprandial lipemia in normolipidemic young adults. One possible mechanism is enhanced lipoprotein lipase (LPL) activity in the exercised skeletal muscle.

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.

Physical activity and cancer risk

Population-based studies of human pregnancies show that periconceptional folate supplementation has a significant protective effect for embryos during early development, resulting in a significant reduction in developmental defects of the face, the neural tube, and the cono-truncal region of the heart. These results have been supported by experiments with animal models. An obvious quality held in common by these three anatomical regions is that the normal development of each region depends on a set of multi-potent cells that originate in the mid-dorsal region of the neural epithelium. However, the reason for the sensitive dependence of these particular cells on folic acid for normal development has not been obvious, and there is no consensus about the biological basis of the dramatic rescue with periconceptional folate supplementation. There are two principal hypotheses for the impact of folate insufficiency on development; each of these hypotheses has a micronutrient component and a genetic component. In the first hypothesis the effect of low folate is direct, limiting the availability of folic acid to cells within the embryo itself; thus compromising normal function and limiting proliferation. The second hypothetical effect is indirect; low folate disrupts methionine metabolism; homocysteine increases in the maternal serum; homocysteine induces abnormal development by inhibiting the function of N-methyl-D-aspartate (NMDA) receptors in the neural epithelium. There are three general families of genes whose level of expression may need to be considered in the context of these two related hypotheses: folate-receptor genes; genes that regulate methionine-homocysteine metabolism; NMDA-receptor genes.

Moderate exercise, postprandial lipaemia and triacylglycerol clearance.

Moderate intensity exercise reduces postprandial triacylglycerol (TG) concentrations. We tested whether this reflects increased TG clearance.

Different patterns of brisk walking are equally effective in decreasing postprandial lipaemia

OBJECTIVE: To compare the effects of different patterns of brisk walking on day-long plasma triacylglycerol concentrations in sedentary adults.DESIGN: A three-trial, repeated measures design in which subjects were studied in the fasted state and throughout a day during which they consumed three standardized, mixed meals. On different occasions, subjects undertook no exercise (control), walked briskly for 10 min before each meal (short walks) or walked briskly for 30 min before breakfast (long walk).SUBJECTS: Seven postmenopausal sedentary women and three sedentary men aged between 34 and 66 y, with body mass index between 24 and 35 kg/m2.MEASUREMENTS: Plasma concentrations of triacylglycerol, non-esterified fatty acids, glucose and insulin, metabolic rate and whole-body substrate oxidation in the fasted state and at hourly intervals for 3 h after each meal.RESULTS: Postprandial plasma triacylglycerol concentrations were lower (P=0.009) during the walking trials than during the control trial (average values: control 2.08±0.28 mmol/l; short walks 1.83±0.22 mmol/l; long walk 1.84±0.22 mmol/l (mean±s.e.) but did not differ between the two patterns of walking. The difference between control and walking trials increased as successive meals were consumed (interaction of trial×meal P=0.03). Plasma triacylglycerol concentration increased during the 3 h after breakfast, changed little after lunch and decreased after the evening meal (interaction of meal×time P=0.001). When both walking trials were treated as one condition, walking increased postprandial fat oxidation (average values: control, 0.066±0.009 g/min; walking 0.074± 0.008 g/min; P<0.01).CONCLUSIONS: Thirty minutes of brisk walking, undertaken in one session or accumulated throughout a day, reduces postprandial plasma triacylglycerol concentrations and increases fat oxidation.

Influence of 12 weeks of training by brisk walking on postprandial lipemia and insulinemia in sedentary middle-aged women.

The purpose of this study was to examine the influence of brisk walking on postprandial lipemia in 26 sedentary women aged 41 to 55 years. The lipemic response to a high-fat meal (mean +/- SEM: 73.8 +/- 1.3 g fat, 66% energy; 81.8 +/- 1.4 g carbohydrate) was determined pretraining and posttraining. Blood samples were obtained in the fasted state and hourly for 6 hours after the meal. Serum was analyzed for triacylglycerol (TAG), total cholesterol, high-density lipoprotein (HDL) and HDL2 cholesterol, apolipoproteins (apos) A-I and B, nonesterified fatty acids (NEFA), glucose, and insulin. Subjects were randomly assigned to one of two groups: walkers (n = 13) followed a program of brisk walking (average of 21 +/- 1 [range, 17 to 27] min.d-1 at 1.76 +/- 0.02 m.s-1), whereas controls (n = 13) maintained their habitual life-style. Procedures were repeated 12 weeks later, with 48 hours between the last training session and determination of postprandial lipemia. Eleven walkers and 13 controls completed the study. Responses over time were compared between groups (Mann-Whitney U, P < .05). Brisk walking improved endurance fitness and decreased body fatness, but had no influence on peak TAG concentration (walkers, 1.6 +/- 0.2 v 1.6 +/- 0.2 mmol.L-1; controls, 1.9 +/- 0.3 v 2.1 +/- 0.3) or the area under the TAG/time curve after the test meal. The area under the insulin/time curve decreased in walkers relative to controls. These results suggest that in sedentary women aged 41 to 55, brisk walking attenuates the serum insulin response, but not the lipemic response, to consumption of a high-fat mixed meal when these responses are determined 48 hours after the last exercise bout.