Prolonged sedentary time and physical fitness among Canadian men and women aged 60 to 69
by Shilpa Dogra, Janine M. Clarke and Jennifer L. Copeland
Cardiorespiratory fitness is a predictor of morbidity and all-cause mortality among middle-aged and older adults.Note 1Note 2 Musculoskeletal fitness, particularly grip strength, is also a predictor of cardiovascular mortality and all-cause mortality―an even stronger predictor than systolic blood pressureNote 3―and is critical to functional autonomy and quality of life.Note 4
Fitness is influenced by a combination of age, genetics and physical activity. Aging is associated with a decline in both cardiorespiratory and musculoskeletal fitness, but some of these changes can be attributed to decreased physical activity.Note 5 In fact, multicomponent exercise programs that include strengthening, balance and/or flexibility have been shown to significantly affect the physical and cognitive function of older adults.Note 6 However, objectively measured data reveal that only 4.5% of Canadians aged 60 to 79 accumulate 30 minutes per day of physical activity in the recommended 10-minute bouts.Note 7 More than 90% of men and women older than age 60 are sedentary for at least 8 hours a day.Note 8
Even when physical activity levels are taken into account, sedentary time may influence health.Note 9 Among older adults, the amount of time spent sitting is associated with impaired glucose tolerance, dyslipidemia, high-risk waist circumference, coronary heart disease and poor perceived health.Note 8Note 10 Less is known about associations with measures of fitness, especially cardiorespiratory fitness.
In addition to total sedentary time, patterns of sedentary time may influence health outcomes. Prolonged sitting with few interruptions is associated with greater metabolic health risks compared with more fragmented sedentary periods.Note 11 Frequent interruptions may also positively influence lower extremity function and body composition in older adults.Note 12Note 13 However, little evidence is available on associations between patterns of sedentary time and cardiorespiratory and musculoskeletal fitness among older men and women.
Examining relationships between sedentary time and cardiorespiratory and musculoskeletal fitness, while accounting for physical activity levels, is critical for understanding the consequences of prolonged sitting for the health and autonomy of the older population. These associations are particularly important for people in their sixties, as targeted interventions may be able to slow declines in fitness. Based on data for 2007 through 2011 from the Canadian Health Measures Survey, this study analyzes associations between total sedentary time (self-reported and objectively measured) and breaks in sedentary time (objectively measured) and cardiorespiratory and musculoskeletal fitness among men and women aged 60 to 69.
Data and methods
Data from cycles 1 and 2 of the Canadian Health Measures Survey (CHMS) were used for analysis. The CHMS covers the Canadian population aged 3 to 79 living in private dwellings. Approximately 96% of the population is represented; residents of reserves, institutions and certain remote regions, and full-time members of the Canadian Forces are excluded.
Data were collected from March 2007 through February 2009 (cycle 1) and from August 2009 through November 2011 (cycle 2). Data collection occurred in two phases: a questionnaire on socio-demographic characteristics and health behaviours administered at the respondent’s home, and a series of physical measurements, including fitness tests, during a subsequent visit to a mobile examination centre.
Of the households selected across both survey cycles, 72.7% provided the sex and date of birth of all household members. Within each responding household, one or two members were chosen to participate in the survey. Of these, 89.3% completed the household questionnaire, of whom 83.3% visited the mobile examination centre. The final response rate for the combined cycles, after adjusting for the sampling strategy, was 53.5% (53.2% for males and 53.8% for females).Note 14
Ethics approval for the CHMS was obtained from the Research Ethics Board for Health Canada and the Public Health Agency of Canada, and informed, written consent was obtained from adult participants.Note 15
After their mobile examination centre visit, ambulatory respondents received an Actical accelerometer to wear on an elasticized belt over their right hip during waking hours for seven days.Note 16Note 17 The Actical measures acceleration of movement in all directions. Movement is captured and recorded as a digitized value summed over one-minute intervals, resulting in a count per minute (cpm). Accelerometer data reduction followed published guidelines to identify and remove invalid data.Note 18 Total daily accelerometer wear time was determined by identifying non-wear time and subtracting it from 24 hours. Non-wear time was defined as periods of at least 60 consecutive minutes of zero counts, with allowance for 1 or 2 minutes of counts between 0 and 100 cpm.Note 18 A valid day was defined as at least 10 hours of wear time; only participants with at least four valid days were included in this analysis.
Total daily measured time (minutes) spent in sedentary and moderate-to-vigorous physical activity (MVPA) was determined based on values of 100 cpm or less and more than 1,535 cpm, respectively, on each valid day.Note 19Note 20 Daily average sedentary time and time spent in MVPA were calculated as the total number of minutes for all valid days, divided by the number of valid days. Daily average sedentary time spent in bouts of at least 20 minutes and the average number of bouts were determined. A bout was a continuous period of at least 20 minutes with 100 cpm or less (allowing for interruptions up to 2 minutes with cpm greater than 100).Note 21 The daily average number of breaks in sedentary time was determined. A break was any interruption (activity counts more than 100 cpm) of sedentary time lasting at least 1 minute. The percentage of total sedentary time spent in bouts of at least 20 minutes was calculated as average sedentary time in bouts divided by average sedentary time.Note 13
Self-reported sedentary time was based on the combined number of hours per week respondents said they typically spent watching TV, playing video games, using computers and reading. In cycle 1, respondents selected from a list of pre-determined durations (none, less than 1 hour, 1 to 2 hours, 3 to 5 hours, 6 to 10 hours, 11 to 14 hours, 15 to 20 hours, or more than 20 hours). The derived variable for the total number of self-reported sedentary hours per week was the sum of the mid-point of the answer category for each question, which was grouped into the following categories (in hours): less than 5, 5 to less than 10, 10 to less than 15, 15 to less than 20, 20 to less than 25, 25 to less than 30, 30 to less than 35, 35 to less than 40, 40 to less than 45, or more than 45. In cycle 2, respondents provided an exact duration (to the nearest half hour) for each question. The derived variable for the total number of self-reported sedentary hours per week was the sum of all four responses. To allow for comparability between cycles, the derived variable in cycle 2 was grouped into the cycle 1 categories. The mid-point of each category was used to calculate average self-reported sedentary minutes per day.
Detailed descriptions of the eligibility criteria and measurement procedures for each CHMS fitness test are available elsewhere.Note 16Note 17Note 22 Briefly, at the beginning of the mobile examination centre visit, respondents answered a series of screening questions (including completing the Physical Activity Readiness Questionnaire (PAR-Q))Note 22 and had their resting blood pressure and heart rate measured to assess their risk of engaging in the tests.
The modified Canadian Aerobic Fitness Test (mCAFT) is a multi-stage sub-maximal test used to assess aerobic fitness. Stepping stages were completed until the respondent’s heart rate reached 85% of maximum at the end of a stage (or until the respondent could no longer continue). Heart rate, the oxygen cost of the last stepping stage, and weight were used to calculate cardiorespiratory fitness.Note 22
Sit-and-reach was measured with a flexometer (Fit Systems Inc., Calgary, Canada). Each respondent completed two trials; the best score (centimetres) was used.Note 22
Grip strength was measured with a Smedley III dynamometer (Takei Scientific Instruments, Japan). Respondents completed two trials with each hand; the best scores from each hand were summed to calculate total grip strength (kilograms).
Covariates in the analysis were age, sex, education (postsecondary graduation, yes/no), body mass index, and smoking (smoker, yes/no).
The total sample consisted of 1,405 respondents aged 60 to 69. Of these, 14 were excluded from this analysis because they were screened out of the grip strength test (owing to an acute condition, a positive response to the PAR-Q or an unspecified reason). Another 234 were excluded because of incomplete grip strength or covariate data. The final study sample numbered 1,157, of whom 1,109 had complete sit-and-reach data, and 616 had complete mCAFT data. A total of 48 and 576 respondents were screened out of sit-and-reach and mCAFT, respectively, mainly because of medication use or a positive response to the PAR-Q.
Basic descriptive statistics were used to present the characteristics of the sample, fitness scores, sedentary time (measured and self-reported), and physical activity levels by sex. Linear regression models were used to evaluate associations between the fitness outcomes and self-reported and measured sedentary time. Beta estimates, 95% confidence intervals, and p-values were calculated. Linear regression was also used to evaluate adjusted associations between fitness and the percentage of sedentary time spent in intervals lasting at least 20 minutes and the daily number of breaks in sedentary time. All models were adjusted for age, sex, education, body mass index and smoking. To evaluate independent associations with fitness, models were further adjusted for total MVPA. Statistical significance was set at α < 0.05.
Analyses were completed using SAS v9.2 and SUDAAN v10. Results were weighted using the activity monitor subsample weights. Standard errors, coefficients of variation and 95% CI were calculated with the bootstrap technique. The CHMS combined cycle 1 and 2 study design requires that 24 degrees of freedom be specified in the software.Note 14
Characteristics of sample
The average age of respondents was 64 (Table 1). Three-quarters (74%) were married/common-law, and 55% were postsecondary graduates. According to accelerometer data, they accumulated a daily average of 595 minutes (95% CI: 589 to 601) of sedentary time, most of which (83% or 501 minutes, 95% CI: 491 to 510) were in bouts lasting at least 20 minutes. An estimated 12% of respondents aged 60 to 69 met the Canadian Physical Activity Guidelines of 150 minutes per week of MVPA.
Sedentary time and fitness
In the fully adjusted models, no fitness measures were associated with the amount of self-reported TV/video game/computer/reading time among men or women (Table 2).
For measured total sedentary time, a significant and negative association was noted for cardiorespiratory fitness in the combined sample of men and women in the fully adjusted model (β:-0.1283, p < 0.01). The association between grip strength and measured sedentary time was also significant in the combined sample of men and women in the fully adjusted model (β: -0.017, p = 0.03) (Table 2).
In the combined sample of men and women, cardiorespiratory fitness was significantly and negatively associated with the percentage of sedentary time spent in bouts lasting at least 20 minutes (β:-0.581, p < 0.01) (Table 3). After adjustment for total MVPA, the relationship remained significant (β:-0.529, p = 0.01). No significant associations were evident between sedentary time in bouts of at least 20 minutes and grip strength or sit-and-reach.
The association between the number of breaks in sedentary time and cardiorespiratory fitness was positive and significant in the combined sample of men and women, even when adjusted for MVPA (β:0.468, p = 0.02) (Table 4). However, the association reflected the situation among women; the number of breaks in sedentary time was not significantly related to men’s cardiorespiratory fitness. The number of breaks in sedentary time was positively and significantly associated with sit-and-reach among men (β:0.145, p = 0.02). Breaks in sedentary time were not associated with the grip strength of either sex.
This study examined associations between sedentary time and fitness among Canadians in their sixties. The main findings were that, after adjusting for MVPA: 1) objectively measured sedentary time was inversely associated with cardiorespiratory fitness and grip strength; 2) the number of breaks in sedentary time was positively associated with cardiorespiratory fitness; 3) the percentage of sedentary time spent in bouts of at least 20 minutes was inversely associated with cardiorespiratory fitness; 4) associations between sedentary time in bouts of at least 20 minutes and breaks in sedentary time and cardiorespiratory fitness were not consistent between sexes, nor were associations between sedentary time and grip strength; and 5) self-reported sedentary time was not related to any fitness variable. The last conforms with previous work showing measured sedentary time to be more consistently related to health outcomes than are self-reported measures.Note 8 Together, these results indicate that prolonged sedentary time may affect age-related losses in cardiorespiratory and musculoskeletal fitness, and that breaking it up with light-intensity activity could positively influence fitness levels in older adults, regardless of moderate-to-vigorous physical activity levels.
Earlier research indicates that sedentary time and patterns of sedentary time are associated with older adults’ health and functional fitness.Note 8Note 10Note 23 In the present study, the percentage of total sedentary time spent in bouts of at least 20 minutes was inversely associated with cardiorespiratory fitness, and a greater number of breaks in sedentary time was associated with better cardiorespiratory fitness. These findings are important because cardiorespiratory fitness is a strong predictor of morbidity and all-cause mortality.Note 2 In 2015, Oudegeest-Sander et al. demonstrated that non-exercising older adults with higher cardiorespiratory fitness have better vascular function and lower cardiovascular risk.Note 24 They suggested that greater amounts of non-exercise activity, such as activities of daily living, may partly explain the fitness and vascular health of some older individuals who do not engage in purposeful physical actvity.Note 24 It is possible that adaptations in the vasculature, and likely other components such as muscle oxidative capacity, are stimulated by light intensity activities. While mechanistic studies are required, the present results support the potential importance of non-exercise activity by demonstrating that breaks in prolonged sitting may influence cardiorespiratory fitness in older adults. Frequent interruptions of sedentary periods may be particularly important for older adults, who tend to accumulate considerable daily sedentary time.Note 7Note 8 However, the CHMS data are cross-sectional, so it is possible that older adults with lower cardiorespiratory fitness find it more difficult to break up their sedentary time. Intervention research is needed to determine the impact that breaking up sedentary time has on cardiorespiratory fitness.
Total sedentary time was inversely related to grip strength in men and women, even after adjusting for MVPA. As well, the association between breaks in sedentary time and sit-and-reach scores was positive among men. Therefore, sedentary time may also influence musculoskeletal fitness, which is crucial for independent living and autonomy.
A study by Santos et al. found that sedentary time was significantly related to functional fitness in older adults.Note 23 Similarly, Davis et al. reported that more breaks in sedentary time were associated with better physical function.Note 12 Both of these studies used functional performance tests to measure fitness in contrast to the more traditional fitness tests employed in the CHMS. It is possible that, similar to cardiorespiratory fitness, breaking up sedentary time with light-intensity weight-bearing activities provides a stimulus for adaptations in the working muscle. However, the CHMS does not include a lower body measure of muscular strength or endurance. Research is needed to assess associations between breaks in sedentary time and measures of lower body strength at older ages.
The two studies mentioned aboveNote 12Note 23 examined participants who were significantly older and had lower fitness than the CHMS sample. This makes the present findings noteworthy, as even among the sample, who were younger and healthier, an inverse association was apparent between both cardiorespiratory fitness and musculoskeletal fitness and sedentary time.
Relationships between the sedentary variables and cardiorespiratory fitness and musculoskeletal fitness were not consistent for men and women. Among women, the percentage of sedentary time spent in bouts of at least 20 minutes and breaks in sedentary time were associated with cardiorespiratory fitness; no significant associations were found among men. By contrast, for men, associations were noted between measured sedentary time and grip strength, and between breaks in sedentary time and sit-and-reach; similar associations were not observed for women.
At any given age, men’s cardiorespiratory fitness exceeds that of women. For example, in this sample, according to the mCAFT score, which was used to estimate cardiorespiratory fitness in ml/kg/min, the cardiorespiratory fitness for men was 27.1, compared with 24.1 for women (Table 1). Moreover, at ages 60 to 70, women fall in a critical range (15 to 20 ml/kg/min), where functional autonomy may become compromised.Note 25 It is possible that sedentary time influences cardiorespiratory fitness once it falls below a certain level. Due to screening restrictions placed on performing the aerobic test, the CHMS sample was also fitter and healthier than the general population. Thus, the association between patterns of sedentary time and cardiorespiratory fitness may be stronger in less fit women. Similarly, with regard to the differences in associations with sit-and-reach, it is possible that because women tend to have better flexibility than men,Note 26Note 27 men are more susceptible to the effects of sedentary time on flexibility, as prolonged sitting is associated with muscle stiffness.Note 28
The results for patterns of sedentary time are of particular interest as they suggest that breaking up sedentary time may positively influence cardiorespiratory fitness among women but not men, while such breaks affect flexibility in men but not in women. This may indicate that in household, leisure, transportation and occupation domains, men and women interrupt their sedentary time with different types of activity. It is clear that sex needs to be considered when assessing associations between sedentary time and fitness among older adults, as they point to a possible need for differences in intervention strategies.
Strengths and limitations
The strengths of the current analysis are the use of a large, nationally representative sample, and standardized, objective measurements of sedentary time, cardiorespiratory fitness and musculoskeletal fitness. However, the results should be interpreted in the context of several limitations. First, as a result of rigorous screening for CHMS fitness testing, the final sample was fitter and healthier than the population overall. Consequently, the findings may not be generalizable to all people in their sixties. In fact, associations between sedentary time and fitness might be even stronger among those with functional restrictions or chronic conditions. Second, the cross-sectional study design precludes drawing conclusions about the direction of observed relationships. Less-fit people may spend more time in sedentary activities, a possibility that could be explored in future studies.
These data demonstrate a significant relationship between directly measured sedentary time, breaks in sedentary time, and fitness among Canadians in their sixties. Given long-established associations between fitness and both health and functional autonomy for older adults, this study underscores the importance of minimizing total sedentary time and breaking up sedentary time, in addition to increasing physical activity. Differences in the results for men and women suggest that sex is a factor to consider when developing and evaluating intervention studies of older adults.