Few studies have examined how different proportions of moderate and vigorous physical activity affect health outcomes.
To examine whether the proportion of total moderate to vigorous activity (MVPA) that is achieved through vigorous activity is associated with all-cause mortality independently of the total amount of MVPA.
Design, Setting, and Participants
We performed a prospective cohort study with activity data linked to all-cause mortality data from February 1, 2006, through June 15, 2014, in 204 542 adults aged 45 through 75 years from the 45 and Up population-based cohort study from New South Wales, Australia (mean [SD] follow-up, 6.52 [1.23] years). Associations between different contributions of vigorous activity to total MVPA and mortality were examined using Cox proportional hazards models, adjusted for total MVPA and sociodemographic and health covariates.
Different proportions of total MVPA as vigorous activity. Physical activity was measured with the Active Australia Survey.
Main Outcomes and Measures
All-cause mortality during the follow-up period.
During 1 444 927 person-years of follow-up, 7435 deaths were registered. Compared with those who reported no MVPA (crude death rate, 8.34%), the adjusted hazard ratios for all-cause mortality were 0.66 (95% CI, 0.61-0.71; crude death rate, 4.81%), 0.53 (95% CI, 0.48-0.57; crude death rate, 3.17%), and 0.46 (95% CI, 0.43-0.49; crude death rate, 2.64%) for reporting 10 through 149, 150 through 299, and 300 min/wk or more of activity, respectively. Among those who reported any MVPA, the proportion of vigorous activity revealed an inverse dose-response relationship with all-cause mortality: compared with those reporting no vigorous activity (crude death rate, 3.84%) the fully adjusted hazard ratio was 0.91 (95% CI, 0.84-0.98; crude death rate, 2.35%) in those who reported some vigorous activity (but <30% of total activity) and 0.87 (95% CI, 0.81-0.93; crude death rate, 2.08%) among those who reported 30% or more of activity as vigorous. These associations were consistent in men and women, across categories of body mass index and volume of MVPA, and in those with and without existing cardiovascular disease or diabetes mellitus.
Conclusions and Relevance
Among people reporting any activity, there was an inverse dose-response relationship between proportion of vigorous activity and mortality. Our findings suggest that vigorous activities should be endorsed in clinical and public health activity guidelines to maximize the population benefits of physical activity.
Numerous studies1,2 have found that physical activity decreases the risk of many chronic diseases and increases longevity. On the basis of epidemiologic and clinical studies,3 current US,4 UK,5 Australian,6 and World Health Organization7 guidelines suggest that significant health benefits can accrue through accumulation of at least 150 minutes of moderate activity (3-5.9 metabolic equivalent tasks [METs]) or 75 minutes of vigorous activity (≥6 METs) or an equivalent combination of moderate and vigorous activities where “2 minutes of moderate-intensity activity counts the same as 1 minute of vigorous-intensity activity.”4 Implicit in these guidelines is that these amounts of moderate and vigorous activity confer similar benefits, but this remains unclear.8-15
Independent of energy expenditure, vigorous physical activity is more efficient than moderate activity in inducing cardiorespiratory and metabolic fitness,16-21 which is a stronger predictor of morbidity and mortality than activity.3,9,22,23 Therefore, it could be hypothesized that there might be greater health benefits from vigorous activity than from moderate activities alone, even when the overall amount of activity is held constant.
There have been calls for more research to examine the role of activity intensity for health benefits.3,13,24-28 However, in doing this, it is important to account for the potential confounding of the total amount of activity because lower risk attributed to vigorous activities may simply reflect higher total energy expenditure.24 Systematic reviews and meta-analyses have concluded that self-reported activity intensity is a better predictor of mortality than total amount of activity26 and that vigorous activity provides more benefit in reducing mortality risk than moderate activity.8 However, Powell et al14 noted that several of these studies did not control for the overall amount of activity.
On the basis of a large Australian cohort, the aim of the present study was to examine whether the proportion of total moderate to vigorous physical activity (MVPA) that is achieved through vigorous activity is associated with all-cause mortality, independently of the total amount of MVPA. We hypothesized that, among those reporting any MVPA, higher proportions of vigorous activity would be associated with a lower risk of all-cause mortality.
The Sax Institute’s 45 and Up study is a large prospective cohort study of men and women from the general population of the state of New South Wales, Australia. The baseline data were collected in 2006-2009 (n = 267 153). Individuals 45 years and older were randomly sampled from the Medicare Australia database, through which national health care is administered and includes all citizens and permanent residents of Australia and some temporary residents and refugees. Eligible individuals received a mailed invitation to participate with an information leaflet, the study questionnaire, a consent form (including consent for long-term follow-up by linking their data to data from a variety of population databases), and a prepaid envelope. The overall participation rate to the mailed invitations to join the 45 and Up study was estimated to be 18%, similar to other cohort studies of this kind.29,30 However, it is difficult to specify the exact participation rate because some people may not have received the invitations if their address details were incorrect in the Medicare Australia database.31 Approximately 10% of the whole population of New South Wales 45 years and older were included in the final sample.32 A more detailed description of the 45 and Up study has been provided elsewhere.31 Participants older than 75 years (n = 45 211) were excluded from this analysis because the main outcome of interest was preventable deaths at an earlier age. Those with missing values for physical activity (n = 2850) were excluded from the analysis examining the association between total MVPA volume and mortality (n = 217 755). For investigating the association between the proportion of total MVPA by vigorous activity, we further excluded those who did not report any activity (n = 13 213), resulting in a final analytical sample size of 204 542 participants. Those with no MVPA were excluded from the latter analysis because we could not calculate a percentage of MVPA that was vigorous because the denominator would have been zero. The present project was approved by the New South Wales Population and Health Services Research Ethics Committee.
Self-reported data were used from the baseline questionnaire (http://www.45andUp.org.au). Moderate to vigorous physical activity was measured with items from the Active Australia Survey,33 which asks participants about sessions (bouts of at least 10 minutes) and duration of walking, moderate, and vigorous activity in the past week. In the questionnaire, vigorous activity is defined as activity “that made you breathe harder or puff and pant, like jogging, cycling, aerobics, competitive tennis, but not household chores or gardening.” For moderate activity examples “like gentle swimming, social tennis, vigorous gardening or work around the house” are provided. This instrument has acceptable reliability (coefficients for walking, moderate and vigorous activity frequency, and time ranging from 0.56 to 0.64) and validity (correlation of duration of self-reported activity with accelerometer data was 0.52).34,35 As well, a previous study36 found that in the Australian adult population the Active Australia survey had higher reliability and validity than the International Physical Activity Questionnaire and the Centers for Disease Control and Prevention Behavioral Risk Factor Surveillance System survey. Minutes per week of walking and MVPA (vigorous activity weighted by 2)33 were summed to create a total weighted amount of MVPA. The proportion of MVPA that was attributable to vigorous activity was calculated (vigorous activity × 2/weighted MVPA × 100%). Covariates included age, sex, educational level, marital status, urban or rural residence, body mass index (BMI; calculated as the weight in kilograms divided by height in meters squared), physical function, smoking status, alcohol consumption, fruit and vegetable consumption, and MVPA. The BMI was derived from self-reported measures of weight and height, which had excellent agreement with objectively measured BMI categories in a subsample of 45 and Up.37 Physical function was measured with the 10-item Medical Outcomes Study Physical Functioning scale, which has good reliability and validity.38,39 All-cause mortality was based on data from the New South Wales Registry of Births, Deaths, and Marriages from February 1, 2006, through June 15, 2014. The mortality data were linked to the baseline data from 45 and Up by the Centre for Health Record Linkage using probabilistic record linkage methods and commercially available software (ChoiceMaker, ChoiceMaker Technologies Inc). Manual clerical review was performed to check indeterminate matches. Evaluation of the accuracy of the overall linkage was determined by clerical review of samples of matched records.
Cox proportional hazards regression models were used to examine the association of the proportion of total MVPA reported as vigorous activity with all-cause mortality. Survival time was measured as the time from the baseline survey to death or the censor point (June 15, 2014). Total MVPA was calculated using the guidelines provided for Active Australia questions33 and then categorized as 0, 10 to 149, 150 to 299, and 300 min/wk or more. Among those reporting any physical activity, 3 categories were used for the percentage of total MVPA that was vigorous: no vigorous activity (0%), some vigorous activity (>0% to <30%), and 30% or more of total MVPA as vigorous activity. The 30% cutoff point was based on careful inspection of the data distribution and on plotting the association between the percentage of vigorous activity and mortality using a segmented regression model, where the magnitude of association changed substantially when vigorous activity reached approximately 30%.
All Cox proportional hazards models were adjusted for baseline age, sex, educational level, marital status, urban or rural residence, BMI, smoking status, physical function, alcohol consumption, fruit and vegetable consumption, and total MVPA. Regression models were repeated stratified by sex, weight status (obese vs nonobese), volume of MVPA, and cardiometabolic diseases (based on reported diagnosis by a physician of heart disease, stroke, thrombosis, and diabetes mellitus). We examined effect modification by age, sex, weight status (obese vs nonobese), amount of MVPA, and chronic disease, using likelihood ratio tests to compare models with and without an interaction term. Further stratified analyses were conducted to compare the models of each subsample. To maximize statistical power, participants with missing values for any covariate were assigned to a separate category for that variable. To account for potential confounding through occult disease at baseline, the analyses were repeated excluding those who died in the first year of follow-up. All analyses were conducted using SAS statistical software, version 9.3 (SAS Institute Inc).
Descriptive statistics of the sample are presented in Table 1. Of the 217 755 participants 55.2% were women, 63.8% were overweight or obese, 25.5% had completed a university degree, 78.3% met minimal activity recommendations, and 62.1% met the new Australian high active recommendation40 of 300 min/wk or more of activity. Of those who reported some MVPA, more than half (55.3%) did not report any vigorous activity, 16.3% reported more than 0% to less than 30%, and 28.4% reported 30% or more of their total MVPA as vigorous activity. Younger, better educated, and male participants were more likely to report 30% or more of their MVPA as vigorous activity, and those with underweight or obese BMI and with poor physical function scores were less likely to report this.
In Table 2, death rates among those who reported any MVPA are given by levels of activity and by the proportion of MVPA as vigorous activity. There was an inverse association between total MVPA and crude death rates, and within each volume category (10-149 [not meeting guidelines], 150-299, and ≥300 min/wk), there was an inverse association between the percentage of vigorous activity and crude death rates. For those who did not meet guidelines and for the most active participants, 30% or more of MVPA as vigorous activity conferred the most benefit.
Proportion of Total Activity as Vigorous Activity and All-Cause Mortality
During 1 444 927 person-years of follow-up (mean [SD] follow-up, 6.52 [1.23] years), 7435 deaths were registered. Compared with those who reported no MVPA, the adjusted hazard ratios for all-cause mortality were 0.66 (95% CI, 0.61-0.71), 0.53 (95% CI, 0.48-0.57), and 0.46 (95% CI, 0.43-0.49) for reporting 10 through 149, 150 through 299, and for 300 min/wk or more of activity, respectively. Among those who reported any MVPA, compared with those who did not report any vigorous activity, the adjusted hazard ratios for all-cause mortality were 0.91 (95% CI, 0.84-0.98) and 0.87 (95% CI, 0.81-0.93) for more than 0% to less than 30% and for 30% or more of total MVPA time achieved by vigorous activity, respectively. The association between the proportion of MVPA as vigorous activity and all-cause mortality was consistent across age groups, sexes, activity levels, obese and nonobese participants, and participants with and without existing cardiometabolic disease (there were no statistically significant interactions at P < .05) (Table 3).
In this large sample of middle-aged and older adults, we found that among those who reported any physical activity, engaging in vigorous activity was associated with risk reductions for mortality of 9% to 13%, even after adjusting for the total amount of activity. This finding is in line with other studies41-43 that have reported significant benefits of vigorous activity in reducing mortality. In this middle to older adult population, these findings suggest that even small amounts of vigorous activity may supplement the benefits of moderate activity alone. Our findings are in line with those from US cohort studies that found that independent of activity volume, activity intensity was associated with reduced risk of coronary heart disease44 and all-cause mortality in men.45 Moreover, a meta-analysis46 concluded that walking pace, rather than time spent walking, is associated with longevity.
A literature review27 concluded that, although moderate activity reduces cardiovascular risk, higher-intensity activities provide even more cardioprotection. Other clinical and epidemiologic studies have also found that, adjusted for activity amount, higher proportions of vigorous activity are beneficial for cardioprotection,17,44 metabolic health,17,21 and maintenance of physical function.47
In the present study, the protective effect of vigorous activity against mortality applied across age groups, sexes, activity levels, BMI categories, and participants with and without existing cardiometabolic disease. Meta-analyses have found that reductions in mortality through physical activity were significantly higher in women8,26,48 and older people.26 However, these reviews examined the effect of the total amount of activity rather than that of activity intensity.
Large meta-analyses8,48 of cohort studies have reported a 29% reduction in mortality when comparing groups with the lowest and highest amount of activity. Our effect sizes for the protective effect of activity volume against mortality were larger because we used 0 minutes of MVPA as the reference category.
A potential explanation for the positive effect of engaging in some vigorous activity on longevity might be that high-intensity activities lead to more physiologic adaptations, which improve function and capacity. For example, regular aerobic activities increase cardiac stroke volume and capillary density, improve endothelial function, and reduce peripheral resistance, all of which improve the delivery of oxygen and glucose to tissues.49 Some clinical trials with equal amounts of physical activity have found that participants exposed to higher- rather than lower-intensity activity had more improvements in maximum oxygen consumption, blood pressure, or lipid profiles.14 Similarly, a clinical trial50 found that, independent of energy expenditure, high-intensity training was more efficient in achieving anti-inflammatory effects in patients with type 2 diabetes and metabolic syndrome.
Implications for Physical Activity Guidelines
In the 1970s, physical activity recommendations focused only on vigorous exercise for health benefits.51 However, in the ensuing years, emerging evidence revealed that moderate activities were associated with significant health benefits,52 which led to a paradigm shift, highlighting the benefits of moderate activity.53,54 Current physical activity guidelines in the United States,4 United Kingdom,5 and Australia6 promote the benefits of both moderate and vigorous activities, leaving individuals to choose their activity patterns according to their preferences and abilities. However, emerging evidence, including findings from this study, indicates that independent of the volume of activity, engaging in some vigorous activity may be beneficial to health and that 2 minutes of moderate activity may not be equivalent to 1 minute of vigorous activity.9,21,44,47 Wen et al55 commented that running beats walking by a factor of 2:1 to 4:1 in mortality reduction at iso-volume. Lack of time is a major barrier to physical activity.56 Because vigorous activity is more time-efficient in achieving health benefits than moderate activity, promoting vigorous activity might be particularly fruitful for those for whom insufficient time is a major barrier.
Previous research indicates that it is possible to encourage overweight middle-aged men and women with a range of chronic health problems to safely participate in vigorous activity in the form of high-intensity interval training.19 Although vigorous exercise is associated with an increased risk of cardiovascular events and sudden death, the absolute risk of death is extremely low (1 sudden death per 1.5 million episodes of vigorous exertion).57 Therefore, in future activity guidelines, it may be reasonable to encourage wider consideration of vigorous activities for those who are capable of doing so by including statements such as “If you can, enjoy some regular vigorous-intensity activity for extra health and fitness benefits” as seen in the New Zealand58 and World Health Organization Western Pacific Regional guidelines.59
Strengths and Limitations
This prospective study is based on a large sample, with linkage to death records, and is adjusted for a range of covariates, particularly total amount of MVPA. One limitation is that we cannot exclude the possibility that the observed associations are artifacts of vigorous activity being a marker for good health. However, when we reran the analyses and excluded those who died in the first year of follow-up, the results were broadly the same as in the whole sample with only a slight attenuation of the hazard ratio for those who reported some vigorous physical activity.
We acknowledge that this is an epidemiologic cohort study and that these findings are observational. However, given that it is extremely difficult (because of compliance, adherence, and attrition issues) to conduct large long-term randomized clinical trials of different exercise prescriptions and follow-up for mortality outcomes, this level of evidence is informative and widely accepted. This type of study has been widely included in evidence reviews and is of interest to clinical and exercise professionals.3 Another limitation is that, typical for large cohort studies, all variables were ascertained by self-report and that there was no distinction between different kinds of vigorous activity or adjustment for age-related perceptions of what constituted vigorous activities.60 On the other hand, vigorous activities were the main focus of this study, and these tend to be better reported than activities of lesser intensity.61 It is possible that some of the moderate activity minutes reported by older participants may in fact have been performed at light intensity, and the reporting of vigorous activity time is a better self-report proxy of actually reaching health-enhancing energy-expending thresholds. A further limitation is the lack of follow-up data on physical activity. It is, of course, possible that activity levels may have changed during this 6-year period, and if this was the case, then our results would have likely underestimated the strength of the association between activity and mortality. The study sample tended to oversample those who are healthier and engaged in healthier lifestyles (eg, high level of activity). However, this is of no concern to our study aims because a comparison with a New South Wales population representative sample indicated that although the prevalence of risk factors differed, estimates of exposure-outcome associations were almost identical.62 This finding confirms the general epidemiologic axiom that relative risks based on internal comparisons are not dependent on the representativeness of the cohort.
Future Research Directions
Objective measures of physical activity would be desirable but are difficult to apply in very large cohort studies.8 More studies are needed that examine the association between different combinations of moderate and vigorous activity with multiple health outcomes, while controlling for the overall amount of activity.
Independent of the total amount of physical activity, engaging in some vigorous activity was protective against all-cause mortality. This finding applied to both sexes, all age categories, people with different weight status, and people with or without cardiometabolic disease. Doing some vigorous activity might be important for increasing longevity among middle-aged and older adults. If vigorous activities are consistently independently associated with health benefits, such activities should be more strongly encouraged in activity guidelines to maximize the population benefits of physical activity.
Accepted for Publication: January 28, 2015.
Corresponding Author: Klaus Gebel, PhD, Centre for Chronic Disease Prevention, College of Public Health, Medical, and Veterinary Sciences, James Cook University, PO Box 6811, Cairns QLD 4870, Australia (email@example.com).
Published Online: April 6, 2015. doi:10.1001/jamainternmed.2015.0541.
Author Contributions: Dr Ding and Ms Chey had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Gebel, Ding, Brown, Bauman.
Acquisition, analysis, or interpretation of data: All authors.
Drafting of the manuscript: Gebel, Ding, Stamatakis, Brown, Bauman.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Ding, Chey.
Obtained funding: Bauman.
Administrative, technical, or material support: Gebel, Bauman.
Study supervision: Stamatakis, Brown, Bauman.
Conflict of Interest Disclosures: None reported.
Funding/Support: This study was supported by project grant G170286 (Improving Outcomes for People With Cardiovascular Disease in the NSW Community) from the Heart Foundation of Australia.
Role of the Funder/Sponsor: The funding source had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and the decision to submit the manuscript for publication.
Additional Contributions: Kris Rogers, PhD, from the University of Sydney provided statistical advice. This research was completed using data collected through the Sax Institute’s 45 and Up Study (www.saxinstitute.org.au). The 45 and Up Study is managed by the Sax Institute in collaboration with major partner Cancer Council NSW and partners: the National Heart Foundation of Australia (NSW Division); NSW Ministry of Health; beyondblue; Ageing, Disability, and Home Care; Department of Family and Community Services; the Australian Red Cross Blood Service; and UnitingCare Ageing. We thank the many thousands of people participating in the 45 and Up Study.
Correction: This article was corrected on June 2, 2015, to fix an error in the text.
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