REVIEW ARTICLE
Sports Med 2008; 38 (9): 751-758
0112-1642/08/0009-0751/$48.00/0
© 2008 Adis Data Information BV. All rights reserved.
Is Active Commuting the Answer to
Population Health?
Roy J. Shephard
Faculty of Physical Education & Health and Department of Public Health Sciences, Faculty of
Medicine, University of Toronto, Toronto, Ontario, Canada
Contents
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 751
1. Walking or Cycling? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 752
2. Historic Trends in Active Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 753
3. Potential to Modify Walking and Cycling Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 754
4. Impact of Active Commuting on Health Outcomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755
4.1 Theoretical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755
4.2 Empirical Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 756
5. Areas Needing Further Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 756
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 756
Abstract
This brief review examines whether active commuting is an effective method
of controlling the current obesity epidemic and enhancing the cardiovascular
health of the population. Of the many potential methods of active commuting,
walking and cycling are the usual choices. Children and adolescents prefer
cycling, but for adults issues of safety, cycle storage and company dress codes
make walking the preferred option, particularly in North American cities, where
urban design and weather conditions often do not favour cycling. Active transportation is more frequent in some European countries with dedicated cycle and
pedestrian paths, but in most developed societies, active transportation has
declined in recent years.
Attempts to increase walking behaviour in the sedentary population have had
only limited success to date. A weekly gross energy expenditure of at least 4 MJ is
recommended to reduce all-cause and cardiovascular mortality. This can be
achieved by walking 1.9 km in 22 minutes twice per day, 5 days per week, or by
cycling at 16 km/h for 11 minutes twice per day, 5 days per week. When engaged
in level walking, the intensity of effort may be adequate for cardiovascular benefit
in older adults, but in fit young workers, it is necessary to either increase the pace
or choose a hilly route in order to induce cardio-respiratory benefit; in contrast,
cycling is likely to provide an adequate cardiovascular stimulus even for young
adults.
Empirical data to date have yielded mixed results: a reduced all-cause and
cardiovascular mortality has been observed more frequently in cyclists than in
walkers, and more frequently in women and older men than in young active
752
Shephard
commuters. More information is needed concerning the typical weekly dose of
activity provided by active commuting, and the impact of such commuting on
overall attitudes towards physical activity. It is also necessary to find better
methods of involving the sedentary population, through both counselling and
changes in urban design.
Expert groups, focusing primarily on the outcome of all-cause mortality, have concluded that the
minimum physical activity recommendation for the
adult population is 30 minutes of moderately vigorous physical activity on most days of the week.[1]
However, some groups have argued that adults need
60 or even 90 minutes per day if the current epidemic of obesity is to be contained.[2-4] Minimum requirements for cardiovascular health are also much
greater in children and youths.[5,6] For those individuals who have appropriate motor skills and enjoy
competition, the necessary physical activity can be
obtained by participating in team or individual
sports. However, a few simple calculations show
that this is not an appropriate solution for an entire
national population,[7] whether one considers the
demands on limited reserves of land (e.g. for soccer
pitches) or the huge capital costs involved in providing multiple facilities such as skating rinks and
tennis courts. Governments have therefore shifted
their emphasis to the advocacy of ‘active living’, the
incorporation of the needed physical activity into
normal daily life (see, for example, the Canadian
Coalition for Active Living [www.activeliving.ca]
and the Leadership for Healthy Communities program of the Robert Wood Johnson Foundation [www.activelivingleadership.org/]).
One possible component of such an active living
initiative would be to encourage physically active
commuting to and from the place of work or schooling, either by bicycle or on foot. There are two
immediate advantages to such a suggestion: it is
difficult to ‘forget’ work or schooling (in contrast to
the ease of missing attendance at a scheduled exercise class), and the replacement of cars by bicycles
and pedestrians could be a big help in meeting the
reduction of carbon dioxide emissions mandated by
the Kyoto Accord.[8] There may be many other
economic dividends from a shift to active transpor© 2008 Adis Data Information BV. All rights reserved.
tation. One recent analysis estimated that in Canada,
the 7.8% of Canadian workers who currently engage
in active commuting save the national economy
some $Can2 billion per year by not using cars or
public transport for this purpose.[9]
This article makes a brief assessment of active
commuting as a means of maintaining and enhancing population health. It looks at the choice between
walking and cycling, examines secular trends in
both these modes of transportation, evaluates our
ability to increase the proportion of the population
who engage in active commuting, assesses the likely
impact of such commuting on population health, and
indicates some areas for further research.
1. Walking or Cycling?
In theory, there are many forms of active transport, including canoes, rowing boats and skateboards, but in reality, the choice for most people lies
between walking and cycling. Their decision will be
based in part on the distance to be covered. The size
of many cities is such that walking to work would be
practicable only if one decided to walk one or two
subway stops, or a section of a bus route. Age is also
a factor. Children and adolescents commonly prefer
cycling rather than walking, but for many adults
who work in the business centre of a city, there are
issues of traffic safety and cycle storage. Furthermore, unless a company opts to provide showers and
changing facilities, the commuting cyclist may have
difficulty in meeting office dress codes. In cities
with continental climates, concerns also arise from
the icing of streets and cycle paths during the winter
months.
In the Netherlands, Denmark, Sweden, parts of
Finland, and many less developed countries, cycling
to work remains commonplace, but in most North
American cities, a major issue is the danger to the
Sports Med 2008; 38 (9)
Is Active Commuting the Answer to Population Health?
cyclist from fast-moving motor traffic. Substantial
changes in the ‘built environment’ are needed if
cycling is to become a widely accepted option;[10,11]
for example, the provision of cycle lanes on major
roads, the use of traffic calming devices, the introduction of specific traffic signals for cycles and the
construction of dedicated cycle paths.[12-14] Companies could also encourage cycling by allocating
some of the savings realized through a reduction in
employer-paid car parking[15] to the construction of
cycle storage and changing facilities for active commuters.
Walking is the most popular form of physical
activity cited by most North American adults.[16]
When the average patient is asked what they do for
exercise, the most common response is “walking”; it
has been argued that this offers a ‘near perfect’ form
of exercise.[17] In the US, encouragement of walking
was found to be the most effective tactic for the
promotion of physical activity in the sedentary population.[18] Walking certainly has many attractions
for the older worker. However, it also has disadvantages, the main danger being from fast-moving traffic. Injuries from vehicles have become less frequent in recent years, although part of this decline
could reflect a decrease in the number of walkers,
rather than a true improvement in vehicle safety.[17]
In addition to collisions with motor vehicles, concerns include local exposure to carbon monoxide[19]
and an increased inhalation of oxidant smog,[20]
although the exposure for walkers is likely to be less
than for cyclists because of smaller respiratory minute volumes and less immediate contact with vehicles. Incidents of tripping on kerbs and broken pavement, slipping on ice or wet leaves, and collisions
with roadside furniture such as lamp standards are
also not unknown.[21,22] Despite these hazards, walking to work can be commended as a very safe form
of physical activity throughout a person’s working
career. Moreover, the intensity of such effort can
readily be adapted to the individual’s immediate
physical condition by choosing an appropriate pace.
In young children, the issue of safety can be addressed by simple expedients such as an organized
neighbourhood walk or cycle trip to school.[23]
© 2008 Adis Data Information BV. All rights reserved.
753
There are many advantages to adopting active
transportation as a major source of daily physical
activity. Participants have little need to purchase
expensive equipment or clothing, and with a little
forethought, the walk or leisurely cycle trip to work
can be combined with other pleasant activities, such
as conversation with a friend or colleague, or reflection on issues that have arisen during the working
day. Nevertheless, there are sometimes practical
problems associated with active transportation that
may need imaginative solutions; for example, the
occasional need to transport heavy articles, or the
need to combine personal commuting with the transportation of children to school or childcare. From
the health standpoint, critical issues are historic decreases in walking and cycling, the extent to which
weekly walking can be augmented by a public
health promotional campaign, and the impact of any
resulting change in behaviour upon various indices
of population health.
2. Historic Trends in
Active Transportation
What proportion of the population are currently
active commuters? Much depends on the national
culture. A study in Copenhagen found that about 10
years ago, 20–30% of adults cycled to work, spending 3 hours per week on their bicycles; the proportion of cyclists dropped from 28% in the least educated to 20% in the best educated.[24] In Denmark as
a whole, 46% of 25-year-old men and women used a
bicycle to travel to work every day throughout the
year, and the percentage rose to about 70% during
the summer months.[25] In the Netherlands, 19% of
workers walked and 27% cycled to work, and in
Sweden the corresponding figures were 39% and
10%.[9] However, in other developed countries, the
percentage of adults who are presently cycling is
very small. Two decades ago, only 7% of adult
Londoners cycled to work,[26] and more recently,
adult Canadians who had adopted active modes of
transportation accounted for only 7.8% of the working population, 6.6% of the total being walkers and
1.2% cyclists.[9] Weather conditions may be an important determinant of behaviour, particularly in
Sports Med 2008; 38 (9)
754
Shephard
central Canada, since in the more temperate climate
of Victoria (BC), one survey found 10.4% of walkers and 4.8% of cyclists.[9] A recent report from
small-town Japan showed that in those aged 65–74
years, the energy expended on active transportation
averaged 10.8 MET-hours (metabolic equivalent
task-hours) per week (about 3 hours of moderately
paced walking), although the figure was lower in
older age groups.[27]
Short walks were still quite popular among British adults in 1992–4, with 81% making journeys
under 1.6 km on foot. However, walking accounted
for only 24% of journeys over distances between 1.6
and 3.2 km. Moreover, tolerance of 1.6–3.2 km
walks dropped from 32% of the adult population in
1985–6 to 24% in 1992–4.[28] A more recent report
has confirmed these disturbing trends.[29]
As cars have become widely available, and the
perceived hazards of urban walking and cycling
have increased, most developed nations have seen a
progressive decrease in active commuting by school
children. One report from the UK estimated that
there had been a 20% decrease in the number of
children walking to school between 1970 and
1991.[30] A second report found a 28% reduction in
the total distance walked by children in 1975–6 and
1992–4.[28] By 1993, half of British primary school
children were being driven distances of less than 1.6
km (1 mile) to their place of schooling.[31] In the US,
likewise, personal chauffeuring led to a 37% decrease in children’s trips by bicycle or on foot between 1977 and 1995.[32,33]
3. Potential to Modify Walking and
Cycling Behaviour
Most studies of adults have examined responses
to the encouragement of walking rather than cycling. One recent meta-analysis focused on the ability of various interventions to augment walking behaviour.[34] An exhaustive search was made of 25
databases, 12 websites, prior systematic reviews and
the input of an international panel of experts; this
yielded a total of 53 491 papers. Despite this large
list, the literature search was limited to the period
1990–2006, and unfortunately a number of impor© 2008 Adis Data Information BV. All rights reserved.
tant studies of walking were conducted prior to that
date. Furthermore, as in so many meta-analyses,
after a quick scan, only 441 texts from an initial list
of 53 491 were studied in any detail. The primary
criterion for inclusion in the final analysis was selfreported or objective data on walking behaviour
before and after the intervention. Ultimately, the
study was restricted to 19 randomized controlled
trials and 29 non-randomized controlled trials. In the
most promising studies, the immediate response to
the intervention was a 30- to 60-minute increase per
week in the time allocated to walking. However,
studies provided no information on long-term adherence, possible compensating reductions in other forms of voluntary activity, or adverse consequences of
regular walking (such as injuries). Relatively few of
the interventions were in the context of active commuting, and in such studies the increases in walking
were generally smaller (15–30 minutes per week)
than in other types of walking programme. Investigations having a commuter focus were in general
targeted to those already considering such an initiative, and there was personal tailoring of the intervention (for example, in children, safe routes were
mapped for active commuting to school).[35] Increases in walking were seen when interventions
were addressed to individuals, households or
groups, but evidence of gains from workplace,
school or community-wide initiatives was less convincing.
The average impact on commuters (15–30 minutes’ increase in walking per week) is disappointing
relative to current recommendations that adults enhance their cardiovascular health by taking 30–60
minutes of moderate physical activity per day.
Moreover, it is possible the response would have
been even smaller if the intervention had been applied on a population-wide basis, rather than
targeted at interested individuals.
A cross-sectional study among primary school
children looked at active commuting in relation to
overall physical activity. In boys, the overall physical activity was greater in those either walking or
cycling to school, but in girls, only walking was
associated with a greater overall weekly physical
Sports Med 2008; 38 (9)
Is Active Commuting the Answer to Population Health?
activity.[36] One potential issue in this study was the
use of accelerometers to measure overall physical
activity; such devices would have detected little of
the energy expended in cycling.
4. Impact of Active Commuting on
Health Outcomes
The likely impact of active commuting upon
health can be examined both in theoretical terms
(based on the likely amount and intensity of physical
activity that will be achieved) and empirically (by
looking at selected markers of health status either in
cross-section, or preferably, before and after the
introduction of various walking programmes).
4.1 Theoretical Analysis
In theoretical terms, the likely health impact of
active commuting can be estimated from the extent
of any increase in the commuter’s overall energy
expenditure. A number of epidemiological studies
on sedentary middle class US adults have demonstrated a favourable association between a cumulative gross energy expenditure of 4 MJ per week and
health outcomes such as overall and cardiovascular
mortalities.[37,38] The walking pace of a commuter is
likely to be around 5 km/h, although in the inner
city, the impact of such walking may be reduced by
prolonged halts at busy intersections. Depending on
an individual’s body mass, the gross energy cost of
walking at 5 km/h over a smooth and level surface
would be about 18 kJ/min.[39] Thus, a total energy
expenditure of 4 MJ per week would require no
more than a 1.9 km walk for 22 minutes in each
direction, 5 days per week. In terms of both the
distance to be walked and the time taken, this seems
a reasonable expectation for a middle-aged commuter;[40] indeed, if a bus service is infrequent, this
amount of walking may take little longer than riding
the bus. In terms of cardiovascular health, the intensity of effort is a more important issue. Even without
enforced rests at traffic lights, the gross oxygen cost
of the commuter is some 12.5 mL/[kg • min]. In a
moderately fit young man, this amounts to only
30–35% of maximal oxygen intake, insufficient to
induce any aerobic training effect. However, this
© 2008 Adis Data Information BV. All rights reserved.
755
speed of walking may benefit a very unfit young
adult, and in a 65-year-old, where the maximal
oxygen intake has dropped to 25 mL/[kg • min], the
same speed of walking would demand around 50%
of aerobic power, at the bottom end of the aerobic
training zone. In older seniors, the impact would be
even greater.
If the commuter is relatively fit, several simple
tactics can be recommended to bring the intensity of
walking to a level where a wide spectrum of health
benefits are likely to accrue. The most obvious is to
increase the pace of walking; at a speed of 6.4 km/h,
the gross oxygen cost rises to about 16.2 mL/
[kg • min], with some saving of time and no decrease in the total energy cost over a fixed-distance
journey. Further increments of intensity can be introduced by the choice of a more hilly route. The
energy cost of climbing a 5% (1 in 20) incline is
about 50% higher than that of walking at the same
pace on the level.[39,41] Roughness of the terrain is
another important variable, and after a heavy snowfall there can be a 2- to 3-fold increase in the energy
cost of a given commute.[39] The individual’s perception of moderate effort or the ability to continue a
conversation provide subjective guides to an appropriate intensity of effort in the face of these several
variables.
Energy expenditures are more difficult to predict
for the cyclist. Much depends on the design of the
bicycle, the speed of riding, the terrain and any
head-winds that are encountered. On urban streets, a
speed of 16 km/h might be anticipated, with a cost of
about 7 METs (24.5 mL/[kg • min] or approaching
36 kJ/min).[42] A cumulative energy expenditure of
4 MJ per week would then be reached with a daily
journey of only 11 minutes in each direction. The
intensity of effort would also reach the cardiovascular training zone even for a younger worker,
and many older individuals would probably need to
slow their speed in order to remain within the comfort zone.
Theoretical considerations therefore suggest that
from the viewpoint of health impact, cycling is the
preferred option for younger commuters, whereas
Sports Med 2008; 38 (9)
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Shephard
for those who are older, the answer lies in walking
all or part of the way to work.
4.2 Empirical Data
Controlled studies examining the health impact
of walking have shown little agreement, in part
because few observers have considered the critical
influence of age on the relative intensity of the
activity. A recent meta-analysis concluded that there
were no significant differences in health outcomes
between those who were persuaded to increase their
walking by 30–60 minutes per week and appropriate
control groups.[34] However, other investigators
have questioned whether the criteria of this particular meta-analysis excluded studies where a significant response had been shown.[43,44] Trials showing
benefit have generally involved older individuals
who were walking substantial daily distances without compensatory reductions in their other activities,
and who were exercising at a substantial fraction of
their heart rate reserve.[45-47] A recent study from
China found that among active commuters, all-cause
mortality was less strongly associated with walking
than with cycling.[48] A report from Finland[40] noted
that spending ≥15 minutes per day in walking or
cycling to work was associated with reduced allcause and cardiovascular mortality in women, but
not in men. All of these observations seem in keeping with theoretical concerns about the relative intensity of walking in younger and fitter individuals,
as noted above.
A number of cross-sectional studies of both children and adults have found that cardiovascular
health was substantially better in those who cycled
to school or to work. In Odense, Denmark, children
and adolescents who cycled to school were substantially more fit than those who walked or were driven
to school.[49] Likewise, a prospective study of adults
followed more than 30 000 men and women living
in Copenhagen for an average of 14.5 years. Over
this period, all-cause mortality was 40% lower in the
cyclists than in other commuters, even after adjustment of the data for reported leisure-time activities.[12] In the UK, the incidence of myocardial infarction among those cycling to work was said to be
© 2008 Adis Data Information BV. All rights reserved.
only half of that in the general population,[26] and in
Shanghai, all-cause mortality was inversely correlated with cycling to work after adjustment of data for
other forms of physical activity.[48] Such observations cannot establish cause and effect; there is
always the possibility that those who choose to cycle
to work have a better initial health or a better lifestyle than the comparison group. Nevertheless, the
apparent benefits of cycling are in line with the
theoretical calculations of energy expenditures, noted in section 4.1 of this article.
5. Areas Needing Further Research
Much more information is needed before we can
make a categorical assessment of the impact of
active commuting on population health. We need a
more detailed picture of the typical dose of exercise
arising from such activity (the typical duration and
intensity of bouts, and number of times performed
per week), together with a clearer assessment as to
how far active commuting may discourage an individual from engaging in other forms of physical
activity. In the case of young people, there is also a
need for attitudinal studies; does active commuting
instil a love of walking or cycling that will persist
into adulthood, or will it push adolescents into use of
a car once a driving licence has been obtained? How
far is the likelihood of active commuting persisting
into adult life influenced by the prevailing culture
(for example, how large are differences between
North America and some bicycle-friendly European
countries)? More objective information is also
needed on how to persuade the general population to
engage in active commuting; this should involve
studies not only of counselling, but also of the built
environment; how could simple and more complex
modifications of the urban landscape encourage active transportation?[10-14]
6. Conclusions
Active commuting has the potential to generate
the 4 MJ weekly volume of physical activity commonly associated with enhanced health. In the case
of cycling, the intensity also appears to fall into the
cardio-respiratory training zone. The usual intensity
Sports Med 2008; 38 (9)
Is Active Commuting the Answer to Population Health?
of walking may be insufficient to benefit the cardiovascular health of fit young adults, although some
adjustments are possible by adoption of a rapid pace.
Currently, relatively few people in the developed
world use walking as a regular means of transport,
and there are even fewer cyclists. The challenge thus
remains to find an appropriate combination of counselling and changes in urban design that will attract a
substantial fraction of the general population to engage in this form of healthy activity.
Acknowledgements
The author served as a consultant to TRL Consulting
(UK) on a project entitled “Physical Activity, Absenteeism
and Productivity: An Evidence-Based Review” during 2007.
No funding was received for the preparation of this review.
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Correspondence: Prof. Roy J. Shephard, PO Box 521, Brackendale, BC V0N 1H0, Canada.
E-mail: [email protected]
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