Sport – only one element of daily physical activity

Participation in organised or volitional sport and exercise programmes can contribute to daily physical activity quotas. However, our recent population-based research measuring lifetime physical activity produced an unexpected finding – sporting activity formed a small fraction of overall physical activity compared with occupational and household activity (figure 1). This was true whether sport was measured as energy expenditure or as knee and hip joint force.2

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Figure 1

Lifetime energy expenditure for sport by gender (reported in metabolic equivalent (MET)–hours per week)

Historically, epidemiological studies primarily based physical activity estimates on occupation. These data were gender biased due to the male-dominated workforce. As physical activity has declined significantly in most occupations, there has been a greater emphasis in recent decades for physical activity inventories to capture sports and leisure-time activity. Despite this shift, we found that the occupation and household domains remain the most important. Using a rigorously developed and validated3 computer-guided lifetime physical activity questionnaire in a sample of 4269 Canadian adults aged 45–90 years, we found that women spent about 10 times more energy in household activity (70.5 vs 7.3 metabolic equivalent – hours/week) and 5.5 times more in occupational activity (40.5 vs 7.3 metabolic equivalent – hours/week) than in sport/recreational activity. Men spent four times more energy on occupational activity (64.9 vs 16.9 metabolic equivalent – hours/week) and 1.5 times more on household activity (28.4 vs 16.9 metabolic equivalent – hours/week) than on sport/recreation.

Women have greater total activity than men

The other unexpected finding was that women, whether measuring energy expenditure or joint force, had slightly higher total (all domains combined) activity than men, driven largely by the household and occupation domains (figure 2A,B). Over the past several decades, women have increased occupational and sport/recreational activity, while largely maintaining high levels of household activity.4

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Figure 2

(A) Lifetime energy expenditure for occupation and sport by gender. (B) Lifetime energy expenditure for household and sport by gender (both figures 1A and 1B, in metabolic equivalent (MET)-hours per week). Adapted from Ratzlaff CR, Doerfling P, Steininger G, Koehoorn M, Cibere J, Liang M, et al. Lifetime trajectory of physical activity according to energy expenditure and joint force. Arthritis Care Res (Hoboken) 2010;62:1452–9.

These findin gs provide bad news and good news. The bad news is that population levels of exercise fall below the recommendations of public health bodies and expert clinical groups. Despite concerted, consistent and rigorous efforts, sport and exercise is clearly not the panacea for public health. The good news is that occupational and household activity matter.

Most studies on the relationship between physical activity and health outcomes have focused on sport/recreation and have not investigated the combined effect of sport, occupation and household activity and have not completely classified physical activity. Biologically, it seems likely that different activities have a cumulative effect. Therefore, most previous studies, by measuring only one or two domains or not assessing frequency and duration of physical activity, are vulnerable to missing important exposure information.

A clear example is the evidence regarding physical activity in women. While women often spend 40+ hours a week at a full-time job and anywhere from 20 to 45 h a week working in the home, surveys used in many existing studies often fail to measure the frequency, duration and intensity of physical activities actually performed by women.4 In Ainsworth's 1999 study of minority women,5 less than 41% met Centers for Disease Control and Prevention/American College of Sports Medicine guidelines for 30 min of moderate activity on most days if measures were limited to sports/recreational and lawn/garden pursuits. However, using a broader definition that included household activities, 87% met the guidelines. In a Canadian study of more than 6600 women, non-leisure (household chores) energy expenditure represented on average 82% of women's total activity.6 When the definition of regular physical activity measured in surveys is expanded to include household and other non-leisure activities, physical activity levels increase and associations with health outcomes are more apparent – including protective relationships with cancer,7 cardiovascular disease and myocardial infarction,6 and an inverse relationship with all-cause mortality.6

Public health implications

Levine et al have addressed the huge potential of non-exercise-related activity to contribute to improved health through non-exercise activity thermogenesis – the energy expenditure of all physical activities other than volitional sport and recreational pursuits.8 Contemporary researchers argue for the need to develop strategies to promote standing and ambulating time9 ,10 and re-engineer our computer-driven work, school and home environments to render active living the option of choice. In doing so, obese individuals could potentially expend an additional 350 kcal per day, or up to 30 pounds per year, without formally participating in sport or exercise.11

Sport and exercise do not promote osteoarthritis – injuries do!

There is more good news. Our research into the relationship between lifetime physical activity (using a newly developed measure of lifetime mechanical joint force) and hip and knee osteoarthritis (OA) revealed that cumulative lifelong physical activity is by and large safe for healthy hip and knee joints.12 ,13 In particular, sport and exercise was not associated with risk of knee or hip OA. This finding was consistent with a large number of longitudinal and case-control studies. BJSM readers will know that studies relating sport with knee OA have generally been in athlete groups in specific sports with high knee forces where joint injury is common.14

This provides strong evidence that the guideline dose of 150 min per week of moderate to vigorous activities daily will not lead to a rise in hip and knee OA – the leading impediment to physical disability in older adults. Sport/recreational activities – without acute injury – are largely safe for the joints; this supports the public health promotion of exercise and sports injury prevention.15 ,16

In conclusion, there are many ways for individuals to reach the guideline goals of physical activity for health. These important new data suggest that for most people in the cohort studies used to obtain the data, ‘sport’, strictly defined, provided less activity than did other tasks. This speaks to the need for the broad socioecological environment to be conducive to physical activity – from schools and the workplace through to active transport and the built environment.17