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Chapter 9: Excessive Appetite vs. Inadequate Physical Activity in the Pathology of Obesity: Evidence from Objective Monitoring

Chapter 9: Excessive Appetite vs. Inadequate Physical Activity in the Pathology of Obesity: Evidence from Objective Monitoring

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Roy J. Shephard

the adults and children concerned. However, the cause of this disruption is less

clear. Hypotheses that have been advanced include increased sales of dietary

products with a high content of refined carbohydrates, particularly soft drinks [5],

an ever-greater consumption of “fast food” [6], an increased portion size in many

restaurants [7], and the decrease of habitual physical activity associated with

automation of the workplace and personal transportation [8], prolonged television

watching [9] and the use of personal computing devices [10].

However, there has been difficulty in deciding among these possibilities, in part

because the process of weight gain is slow. Often obesity develops over many

months and even years. One recent review set the likely maximal accumulation of

fat at 6–10 % of body mass per year [11], or about 4–7 kg/year. Neither dietary nor

physical activity questionnaires have had the sensitivity to detect a 6 % discrepancy

between energy intake and expenditure, although some nutritionists (ignoring the

slow nature of the process) have argued that an increase of physical activity was

unlikely to correct an accumulation of body fat, because even a long bout of

exercise burnt a relatively small quantity of fat. Often, these negative opinions

were apparently supported by small changes in overall body mass after weeks of

exercising; many nutritionists ignored the fact that an increase of daily physical

activity could replace fat with lean tissue, with little net change in overall body

mass. A further issue in some trials was that the additional energy expenditure

developed in an out-patient exercise programme was countered, either by an

increased intake of food or a reduction in the volume of activities performed outside

of the rehabilitation centre. Twenty-four hour objective monitoring of study participants is important in ensuring that such compensatory reductions of physical

activity do not occur.

The widespread availability of inexpensive objective monitoring equipment in

recent years has offered the possibility of demonstrating both that the obese

undertake insufficient physical activity for good health, and that their condition

can be improved through an appropriately designed exercise programme. There

have been quite a few papers examining relationships between careful estimates of

habitual physical activity and body fat content. We will look first at a growing

volume of cross-sectional epidemiological evidence showing differences in patterns of habitual physical activity between those with a healthy body mass and those

who are overweight or obese. We will then comment on the potential motivational

value of the pedometer as a means of stimulating an increase of physical activity

among those who are initially obese, and we will note the uniform finding of a slow

but consistent decrease of body mass among those who succeed in increasing their

daily step count. After underlining additional advantages of an increase of physical

activity, including increases of aerobic power, muscle mass and bone strength, and

a reduction of cardiac and metabolic risk factors, we will finally point to some

limitations of pedometers and accelerometers in the management of obesity.

9 Excessive Appetite vs. Inadequate Physical Activity in the Pathology of. . .



Inadequate Habitual Physical Activity and Obesity

Many large-scale epidemiological studies have linked obesity with inadequate

habitual physical activity, as demonstrated by objective monitoring of both adults

and children.


Studies of Adults

Data for adults include the NHANES study in the U.S., and the Canadian Health

Measures Survey in Canada. We link the obesity-related differences of activity with

their likely impact upon the accumulation of body fat.


Actigraph data were collected on a large and representative sample of U.S. adults

aged >20 years during the 2005–2006 NHANES study [12]. The Actigraph readings were censored to eliminate individuals who did not provide at least one day of

realistic data; information was accepted on 3522 individuals.

The Actigraph is recognized to be more sensitive to low accelerations than many

commonly used pedometers; thus, to allow comparisons with other research, data

were further censored to eliminate periods of the day when the counting rate for any

participant dropped below 500 activity counts/minute (this reduced the overall

reported activity by about 3000 steps/day). The censored values (Table 9.1) averaged 7190 steps/day for individuals with a healthy body mass. Those who were

overweight took only slightly fewer steps (6879/day), but in those who were obese

the count was reduced by 1406, to 5784 steps/day. The accelerometer records also

showed that those with a normal body mass were meeting the minimal public health

recommendation for aerobic activity (30 minutes/day), whereas the obese were

falling some 10 minutes short of this target in terms of moderate and vigorous

physical activity.

Table 9.1 Censored data from the 2005–2006 NHANES survey, showing Actigraph estimates of

habitual physical activitya patterns for adults aged >20 years, classified as having a normal body

mass, as overweight and as obese






Total activity





Moderate activity





Vigorous activity





Eliminating periods when the activity counting rate was <500/minute



Roy J. Shephard

Table 9.2 Associations of body mass index with patterns of physical activity and Actical

accelerometer step count readings

Body mass

index (kg/m2)

Normal (<25)



Obese (>30)





Light activity














Step count









Based on data from the Canadian Health Measures Survey (2007–2009) [13]

Canadian Health Measures Survey

In Canada, the Canadian Health Measures Survey [13] collected similar objective

information on habitual physical activity to that obtained during the NHANES

survey, although the Canadian investigators used the Actical monitor. Each of the

subjects included in the Canadian analysis had also yielded valid accelerometer

records on 4 or more days, rather than a single day.

Differences in body mass index (BMI) among the Canadian participants were

more closely associated with accelerometer step-count readings than with estimates

of the intensity of physical activity (Table 9.2). The time spent on sedentary or light

activities bore little relationship to BMI. However, as in the U.S. survey, there was a

small obesity-related gradient in the time allocated to moderate and vigorous

activity, so that those of normal BMI took 15 minutes more of such activity than

those who were obese. As in the U.S., those of normal weight slightly exceeded the

minimum recommended dose of activity, where the obese fell an average of

11 minutes short of this target. The BMI showed a closer relationship to the

individual’s daily step count, with those of normal body weight taking an average

of 2235 more steps/day more than those who were obese.

Likely Impact of Differences in Habitual Physical Activity upon

Body Fat

Taking the Canadian differential of daily step count (2235 steps/day higher in

individuals with a healthy body mass), and making the debatable assumption of

a consistent pace length of 0.7 m, this would equate to an additional walking

distance of 1.56 km, or 18.7 minutes if covered at a speed of 5 km/hour. The net

energy expenditure would be about 16 kJ/minute if a man of average body mass

was walking purposefully at this pace, and with 18.7 minutes of such activity,

energy usage would be increased by a total of 299 kJ/day or 2.09 MJ/week. Given

that the metabolism of 1 g of fat yields approximately 29 kJ of energy, this equates

to a fat consumption of about 72.2 g per week, or 3.75 kg/year. Assuming the

9 Excessive Appetite vs. Inadequate Physical Activity in the Pathology of. . .


sedentary individuals ate no less food than their more active peers, they would

thus accumulate 3.75 kg of fat per year. This calculation demonstrates that

although the difference in habitual physical activity is quite small, it could account

for the accumulation of a substantial quantity of body fat over 20–30 years of

adult life.

The minimum difference of body mass between a healthy individual (with a

BMI of 25 kg/m2 or less) and someone who is obese (BMI >30 kg/m2) is about

15 kg. If 15 kg of fat was accumulated over a 10 year life span, this would amount to

a weight gain of 1.5 kg per year. A grossly obese person (BMI 40 kg/m2) would

carry some 45 kg of additional body fat, corresponding to a gain of 4.5 kg/year for

each of 10 years. These figures are plainly compatible with data from the Canadian

Health Measures Survey.


Studies in Children and Adolescents

Associations between objective measurements of habitual activity and obesity have

been studied much more frequently in preschool and school age children and

adolescents than in adults. Leech and associates were able to review 18 studies

looking at the clustering of low levels of physical activity, sedentary behaviour and

obesity in children [14], and Parikh and Stratton collected 8 reports concerning the

objectively measured intensity of effort and obesity [15]. As in the two studies of

adults that we have discussed, the investigations in children present consistent

evidence that those with an excessive body mass index (BMI) are engaging in

less moderate and vigorous physical activity than those with a healthy BMI. The

studies of children have often also examined the length and patterns of physical

inactivity (Chap. 7), although relatively few reports have found associations

between obesity and sedentary activities.

Preschool Children

A study of 357 U.S. preschool children demonstrated an association between

obesity and accelerometer determinations of moderately vigorous physical activity

in boys, but not in girls [16]. A second study by members of the same research

group was based on a total of 418 preschool children. It found an association

between accelerometer measurements of moderate to vigorous physical activity

(MVPA) and BMI, but after allowing for effects of the MVPA, there was no

independent effect attributable to sedentary time [17].


Roy J. Shephard

School-Age Children

Wittmeier and colleagues evaluated the odds of being overweight (>20 and >25 %

body fat) in a sample of 251 Canadian children aged 8–10 years [18]. Regression

equations suggested that the biggest effect upon both body fat content and BMI was

exerted by vigorous physical activity, as indicated by triaxial accelerometer. Comparing children who undertook less than 5 minutes of vigorous activity with those

who took more than 15 minutes, the first group were 4 times as likely to have >20 %

body fat, and 5.2 times as likely to be classed as overweight. Comparing those who

took less than 15 minutes of moderately vigorous activity with those who took >45

minutes, the risk of having >20 % fat was 4.2 greater for the former. These figures

appear to support the current public health guidelines on the minimal physical

activity needs of schoolchildren (at least 60 minutes of vigorous and moderately

vigorous physical activity per day).

Steele and associates used 1-week Actigraph records to examine the relative

impact of active and sedentary time upon the risk of obesity in a sample of 1862

10-year-old British children [19]. They found that the objectively measured sedentary time was associated with measures of obesity such as BMI and waist circumference, but that this association was greatly attenuated after co-varying for the time

allocated to moderate to vigorous physical activity. They thus reasoned that the key

to prevention of obesity was the promotion of moderately vigorous physical

activity, rather than discouraging sedentary pursuits.

Ness, Leary and Riddoch (Fig. 9.1) recruited 5500 British children

[20]. Actigraph measurements of habitual physical activity were examined in

relation to dual photon x-ray estimates of body fat, with obesity arbitrarily defined

as the top 10 % of the fat distribution in their sample. The data showed a graded

negative relationship between fat mass and the daily volume of moderately vigorous physical activity that was undertaken, stronger in boys than in girls, and

unaltered by adjustment of the data for the total daily volume of physical activity.

Rowlands and colleagues [21] conducted a second study using dual photon x-rays

Fig. 9.1 Chris Riddoch has

studied obesity and habitual

physical activity in a large

sample of British children

9 Excessive Appetite vs. Inadequate Physical Activity in the Pathology of. . .


Fig. 9.2 Ian Janssen has

carried out extensive

research on the activity

patterns of young children

estimates of body fat on a small sample of 38 girls and 38 boys aged 8–11 years. Fat

levels were significantly correlated with accelerometer measurements of total

physical activity and with vigorous physical activity; moderately vigorous physical

activity was only related to body fat content in the girls.

In Dublin, Hussey and associates [22] evaluated physical activity in 224 children

aged 7–10 years, using a triaxial accelerometer for periods of 4 days. The boys

showed gradients of both body weight and waist circumference with the daily

duration of vigorous physical activity, but no significant relationships were seen

in the girls, perhaps because on average they performed only a half as much

vigorous activity as the boys.

Mark and Janssen (Fig. 9.2) focussed upon inter-individual differences in

patterns of physical activity. They obtained objective Actigraph data on 2498

youth aged 8–17 years from the U.S. NHANES studies of 2003–2004 and

2005–2006 [23]. After controlling for the total volume of moderately vigorous

physical activity, they noted that the risk of being overweight was 0.38 for those

who were in the top quartile in terms of the accumulated number of bouts of such

activity. After controlling also for the times accumulated in short bouts of moderately vigorous physical activity, the risk ratio for those with frequent bouts of

activity was still only 0.55. They thus concluded that multiple bouts of moderately

vigorous activity protected against obesity; possibly, this finding could find a

physiological explanation in terms of the persistent increase of oxygen consumption following a bout of vigorous activity.

A study of 10–12 year old children in Hungary and the Netherlands [24] divided

the students into quartiles, based upon their sedentary time, both self-reported use

of a television and personal computer and total sedentary time as measured by

an accelerometer. In terms of BMI, the difference between subjects in the most

sedentary and the least sedentary quartiles was greater for objective monitoring

(21 vs. 19 kg/m2) than for self-reports of participation in sedentary activities (20 vs.

19 kg/m2); inter-group differences in waist circumferences supported this trend.


Roy J. Shephard

An extension of the study to 766 students in 5 European countries divided children

of both sexes into 4 clusters, based on their sedentary times (ST) and duration of

moderately vigorous physical activity (MVPA) [25]. In the girls, there was a

substantial contrast of BMI (19.1 vs. 17.7 kg/m2) and waist circumference (66.1

vs. 62.6 cm) between the sedentary (ST 571 minutes, MVPA 18 minutes) and the

active (ST 453 minutes, MVPA 55 minutes) groups. In the boys, there were similar

contrasts of BMI 20.5 vs. 17.6 kg/m2) and waist circumference (70.5 vs. 63.7 cm)

between the sedentary (ST 546 minutes, MVPA 26 minutes) and the active

(ST 419 minutes, MVPA 70 minutes) groups, although in the boys the minutes of

MVPA seemed more important than the time that they were sedentary.


Sanchez et al. [26] studied cross-sectional associations between self-reports, accelerometer measurements and BMI in 878 American youth aged 11–15 years. Failure

to meet public health guidelines of 60 minutes of moderate to vigorous physical

activity per week had a strong association with BMI values at or above the 85th

percentile for participants in this investigation. Another report, apparently based on

the same sample of 878 youth, classified subjects as falling above or below the 85th

percentile of BMI [27]. In girls, the obese group undertook 3.5 minutes/day less

moderate physical activity and 2.1 minutes/day less vigorous activity than those

whose BMI fell below the 85th percentile; the heavier girls also devoted an

additional 13.8 minutes/day to television watching, with a resulting decrease of

573 kJ in their daily energy expenditure. In boys, the corresponding differences

were 6.6 minutes/day, 4.4 minutes/day, 33.1 minutes/day, and 1283 kJ/day.

Butte et al. [28] examined 897 Texan children and adolescents of Hispanic

origin, ranging in age from 4 to 19 years. Objectively measured physical activity

as determined by an Actiwatch accelerometer decreased progressively with age,

and was consistently less in the girls than in the boys. Total activity counts were

lower, and sedentary times were higher in obese than in non-obese students.

Lohman and associates [29] examined 1553 sixth grade U.S. female adolescents,

noting an association between triceps skinfold estimates of body fat and Actigraph

measurements of moderate and vigorous physical activity. Fat-free mass was also

determined in this study, and it was positively correlated with habitual physical


The HELENA study recruited 365 Spanish adolescents aged 12.5–17.5 years.

Body fat was determined by several methods (the sum of six skinfolds, dual photon

spectrophotometry and a pneumatic determination of body volume, the BodPod)

[30]. After controlling for age, sex, and pubertal status, all measures of body fat

were negatively correlated with accelerometer assessments of moderate, and especially with vigorous physical activity. Body fat was also negatively correlated with

aerobic fitness and with the strength of the lower limbs [31]. The accelerometer data

showed that muscular strength depended on engaging in either vigorous physical

activity, or at least 60 minutes of moderate to vigorous physical activity [32].

9 Excessive Appetite vs. Inadequate Physical Activity in the Pathology of. . .


Mitchell and associates made a prospective study of 789 children, following

them from the age of 9–15 years [33]. Increases of BMI over the 6 years were

negatively associated with accelerometer measurements of habitual physical activity for this period, and there were additional adverse effects from sedentary time,

particularly in the heavier children.

Timing of Activity Bouts

Use of objective monitors with time-stamp devices allows the observer to identify

those specific times of the day when physical activity is lower in the obese than in

those who have a healthy weight; such information may be helpful in planning

corrective tactics. An analysis of Canadian children aged 6–19 years demonstrated

that boys (but not girls) who were obese took more sedentary time after 3 p.m. on

weekdays (282 vs. 259 minutes). Each 60 additional minutes of sedentary time was

associated with a gain in BMI of 1.4 kg/m2 [34]. Further, the obese boys engaged in

more prolonged bouts of sedentary activity.

An extension of this research demonstrated that frequent breaks in sedentary

periods were associated with a favourable cardiometabolic risk profile [35], including lower values for BMI and waist circumference.

Conclusions Regarding Obesity in Children and Adolescents

General conclusions from the studies of children and adolescents are that associations between habitual physical activity and body fat are stronger for boys than for

girls, that prevention of obesity is associated with the practice of moderate to

vigorous and vigorous physical activity, and that any relationships with sedentary

time are weaker than for those with vigorous physical activity.


Motivational Value of Pedometer

Given that there is sometimes a substantial reactive response to the wearing of a

pedometer or an accelerometer (Chap. 1), one would anticipate that the use of such

instrumentation would be helpful, at least initially, in motivating a person to an

increase of habitual physical activity. However, given the rapid waning of any

reactive response, it is less clear how long the boosting of motivation might persist,

particularly in sedentary individuals without immediate manifestations of

disease [36].

Much probably depends on how the pedometer is presented to the client, and

details of the motivational plan. In some studies, participants have simply been told

to aim for a daily count of 10,000 steps/minute, whereas in other investigations the

physical activity target has been individually prescribed, and adjusted upwards as


Roy J. Shephard

the physical condition of the client improved. There is some evidence that the

provision of objective monitors is most effective in stimulating the physical activity

of those who are initially overweight or obese [37].


Characteristics of Effective Pedometer-Based Walking


Several studies have suggested that over the first few months, the provision of a

pedometer and a daily walking distance target can increase the step counts of

initially sedentary individuals by 2500–3000 steps/day [38, 39]. Tudor-Jones and

Lutes [40] have reflected upon the circumstances in which pedometers and accelerometers are successful in motivating greater physical activity. One striking

weakness is that only about a third of studies introducing pedometers as motivational tools have to date given even token consideration to theories of behavioural

change [41]. However, such a theoretical framework would probably have a

substantial influence upon the response of the client.

We will comment briefly upon appropriate characteristics for the monitoring

instrument, the setting of activity targets, and the continuing need for long-term

studies of the motivational response.


Appropriate Instrument Characteristics

If the purpose of wearing a pedometer or accelerometer is to stimulate greater

physical activity rather than to collect research data, then the instrument will be

worn for a long period, and it needs to be unobtrusive. It must also be reasonably

accurate but inexpensive, presenting a summary of the daily activity that has been

performed in a manner that is easily understood by the average client. Rather than

accumulating data to be down-loaded at the end of the day, week or month, the

requirement is for an instantaneous feedback of the day’s activity to date, allowing

the wearer to plan further periods of physical activity if the prescribed activity

target for the day has not been met.


Optimal Use of the Pedometer as a Motivational Tool

Motivation to an increase of physical activity is helped by the setting of clear goals.

In some experimental studies, clients have simply been told to aim for a count of

10,000 steps/day. In other trials, the pedometer/accelerometer has been used as a

part of a well-designed and regular, guided feedback process, with a focus upon the

9 Excessive Appetite vs. Inadequate Physical Activity in the Pathology of. . .


Fig. 9.3 Mark Adams has

investigated the impact of

pedometer use upon the

activity motivation of obese


establishment of moderate and progressive goals of increased walking distance and

the building of a sense of self-efficacy. Important variables influencing the effectiveness of activity monitors are (1) whether the daily activity target was set by the

observer or the study participant, and (2) whether feedback was provided by a

professional, a member of a peer group, or simply by a computer programme based

on the recorded step count.

Engel and Lindner [42] compared the amount of walking undertaken by a group

that received counselling with that observed in those who were also supplied with a

pedometer. Somewhat to their surprise, the wearing of the pedometer did not

increase the amount of walking relative to that of a group who received only

thorough counselling. In contrast, Mark Adams (Fig. 9.3) and colleagues [43]

compared responses between two small groups of women; both were issued with

pedometers. One group was set a static goal of 10,000 steps/day, and the other was

given a frequently adjusted daily step-count target. The latter group achieved a

much larger increase in their daily step-count.

A further practical question is whether the wearing of a pedometer provides a

unique stimulus to attaining the target volume of daily walking. Potentially, a

similar target could be set by measuring a walking distance carefully with a car

or a bicycle odometer, and then covering this distance on a regular daily basis. One

obvious advantage of using a pedometer is that it allows flexibility in the choice of

walking route, which should immediately encourage adherence.


Need for Long-Term Studies

In most motivational investigations, the pedometer or accelerometer has been used

for only a short period, although the need is for a long-term change of lifestyle.

Although the wearing of the monitor may stimulate an initial increase of physical

activity, it is less clear how far such monitoring contributes to long-term

programme adherence. Is there an optimal period of wear for the client to establish

lifelong exercise habits?



Roy J. Shephard

Objective Monitoring in the Treatment of Obesity

Richardson and associates [39] made a meta-analysis of the response to pedometercontrolled walking programmes where no specific diet was imposed upon individuals who were initially obese. They found 9 trials involving at least 5 subjects; the

investigations had continued for at least 4 weeks, with a total sample size of

307 participants. In general, the pedometer/accelerometer had been used as a

motivational device, typically setting individual goals for an increase in the daily

step count. However, the objective monitoring also served to ensure that study

participants had adhered to the prescribed programme. Bravata et al. [38] listed a

total of 8 controlled trials and 18 observational studies, only 4 of which were

included in the review of Richardson et al. [39]. These various investigations are

summarized in Table 9.3.

In many of the trials discussed by Richardson et al. [39] and Bravata et al. [38],

the immediate increase in pedometer count averaged 3000 steps/day or more. This

implies an increase in the daily walking distance of more than 2 km, perhaps

24 minutes of walking at a pace of 5 km/hour. The net increase of energy expenditure in a man of average body mass would be 384 kJ/day, and if we equate the

metabolism of 1 g of fat with 29 kJ of energy, the fat loss would amount to 0.093 kg

per week. The average length of the trial was 16 weeks, and the average decrease of

body mass was 1.27 kg, or a loss of about 0.05 kg per week, of the same general

order as the theoretical figure if there had been no change in the individual’s food

intake or resting metabolism.

One study evaluated possible changes of diet when healthy young adults

increased their daily step count by 2667 steps/day [49]. No changes of energy

intake were detected, although the authors admitted that a larger sample would be

needed to be certain of this finding.

In the analysis of Bravata et al. [38], 18 of 26 reports noted changes of body mass

and/or BMI. The BMI was decreased by an average of 0.38 kg/m2 over a period

averaging 18 weeks; assuming a height of 1.7 m, this would equate to a total fat loss

of 1.1 kg, or 0.061 kg/week. Bravata et al. [38] commented that the response was

larger in older individuals, was enhanced by goal setting, and was accompanied by

an average 3.8 mmHg decrease in systolic blood pressure. However, these investigators observed no significant changes of blood lipids or glucose tolerance.

Table 9.3 shows that the loss of body mass was very slow, but also remarkably

consistent from one trial to another; only one trial observed a very small gain of

body mass.


Associated Health Benefits

There are important secondary dividends if an obese individual increases their

physical activity, and for the most part these gains are not realized if fat loss is

attempted simply by a reduced intake of food. A modest exercise programme is

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Chapter 9: Excessive Appetite vs. Inadequate Physical Activity in the Pathology of Obesity: Evidence from Objective Monitoring

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