Characteristics of physical activity and sedentary behavior in patients undergoing outpatient cardiac rehabilitation

In this study, we objectively measured the PA and sedentary time of home-based patients undergoing outpatient cardiac rehabilitation and analyzed their characteristics in detail. The study results suggest that patients undergoing outpatient cardiac rehabilitation tend to be sedentary at home, possibly owing to the self-regulation of PA. A previous study³⁰ also reported that older cardiac patients, regardless of their stage of recovery, remain seated for 70% of their waking hours, which is consistent with the results of this study. These findings highlight the need for safe and appropriate activity guidance in rehabilitation programs. Therefore, it is essential to comprehend patients’ daily activity patterns and offer personalized activity programs based on these patterns.

This study revealed differences in activity levels based on sex, which is consistent with previous research³¹. Sex differences in physical activity and sedentary behavior may be shaped not only by physiological factors but also by social and psychological influences, including daily routines and health awareness. In Japanese society, for instance, men often work in more sedentary occupations, while women tend to take on a larger share of household responsibilities. However, it is essential to recognize that these patterns are general trends and may not apply universally to all individuals. The observed sex-specific activity patterns, including men’s tendency towards more sedentary behavior and women’s higher engagement in household tasks, are thought to vary with age, necessitating age-specific investigations. Furthermore, understanding these sex-specific activity characteristics is crucial for designing effective rehabilitation programs. Based on our findings, it is proposed that men should focus on reducing sitting time and increasing interruptions, while promoting walking, which might be a more acceptable approach for increasing their activity levels. For women, reconsidering household tasks and adjusting their intensity may be a more acceptable way to ensure adequate activity levels.

The results of this study reveal that each unit increase in BMI corresponds to an approximate 3.8% decrease in walking activity time. For instance, when BMI rises from 25 to 26, the median walking time of 43.1 min/day is estimated to drop to about 41.5 min/day. Additionally, with each year of aging, moderate-to-vigorous physical activity (MVPA) decreases by approximately 3.4%, and activity above the anaerobic threshold (AT) diminishes by about 4.3%. For example, comparing a 70-year-old patient to an 80-year-old patient, the median MVPA of 25.6 min/day is projected to decrease to about 18.1 min/day, and the mean activity above AT of 36.8 min/day is expected to reduce to around 23.9 min/day. These findings highlight the significant impact of physical factors such as age and obesity on more strenuous physical activities.

The observed trend of reduced activity with higher obesity levels suggests that obesity acts as a limiting factor for physical activity. This relationship has been frequently reported in previous studies^32,33, highlighting the mutual reinforcement between decreased physical activity and obesity. Furthermore, the decline in activity with advancing age, as shown in prior research³⁴, underscores aging as a critical factor limiting physical activity. These factors are essential considerations for developing and evaluating rehabilitation programs.

Our study also found that for every 1 MET increase in AT, MVPA rises by approximately 44.3%. For example, if AT increases from 3 METs to 4 METs, the median MVPA of 25.6 min/day is expected to increase to about 36.9 min/day. Additionally, activity above the AT level decreases by about 87.2%, while activity below the AT level increases by 56.6 min/day. Specifically, an increase in AT from 3 METs to 4 METs is projected to reduce the mean activity above AT from 36.8 min/day to about 4.7 min/day and increase activity below AT from a mean of 997.2 min/day to 1053.8 min/day. Given that MVPA is crucial for preventing and managing cardiovascular disease³⁵ and has been linked to reduced mortality and adverse outcomes in patients with cardiovascular disease³⁶, these findings underscore the importance of improving aerobic capacity through cardiac rehabilitation to enhance physical activity.

In interpreting the results, it is important to consider the relatively advanced age of the participants, with a mean age of 74.3 ± 16.4 years. Older patients have unique needs, and their physical activity patterns may differ from those of younger individuals. Previous research has identified several notable characteristics of physical activity patterns in older adults. Age-related physiological changes, such as decreased muscle strength, reduced balance, and diminished endurance, can significantly impact both the quantity and quality of physical activity³⁷. Additionally, the prevalence of multiple chronic conditions among older adults often limits their physical activity³⁸. Social factors, including lifestyle changes post-retirement and shrinking social networks, can also influence activity levels³⁹. Lastly, safety concerns, particularly the increased risk of falls, may lead older adults to avoid high-intensity activities⁴⁰.

These factors suggest that the physical activity patterns observed in our study may differ from those of younger cardiac rehabilitation patients. The relatively brief duration of MVPA and the extended time spent in sedentary behavior observed in our study may reflect activity patterns specific to older adults. Given these considerations, caution should be exercised in generalizing the results of this study. Different approaches may be needed for younger and middle-aged patients undergoing cardiac rehabilitation. Future research should include age-stratified analyses and comparative studies with younger age groups to gain a deeper understanding of the differences in physical activity patterns across age groups.

Although this study focused on objectively measuring physical activity (PA) in outpatient cardiac rehabilitation programs, it is crucial to address the significant challenges related to the long-term efficacy and sustainability of these programs. As noted by Perk (2020), one of the main concerns regarding traditional cardiac rehabilitation interventions is long-term adherence and the associated dropout rate⁴¹. To address this issue, various approaches, primarily based on home-based or hybrid intervention strategies, have been developed. The meta-analysis by Dibben et al. (2023) indicates that exercise-based cardiac rehabilitation can reduce cardiovascular mortality and hospitalization rates in patients with coronary heart disease, although the effects may vary depending on the type of intervention (center-based, home-based, or hybrid)⁴². This finding underscores the need to tailor cardiac rehabilitation programs to patients’ needs and preferences. Moreover, the study by Mazzoni et al. (2022) highlights the importance of promoting and maintaining physically active lifestyles in older outpatients two years after acute coronary syndrome⁴³. Their research emphasizes the significance of individualized approaches and follow-ups, aligning with the findings of our study.

This study has several limitations. First, it only investigated patients from a single facility; thus, caution is required when generalizing the results. Second, this study included patients with multiple or coexisting diseases; however, the limited number of cases prevented us from conducting detailed stratified analyses. Additionally, due to the small sample size, we were unable to examine the associations between left ventricular ejection fraction, medication use, comorbidities, and the outcomes. Third, the details of PA were unclear because triaxial accelerometers were used in this study. While we determined the intensity of activities, the specific content of activities at each intensity level was not identified. Additionally, the lack of data regarding activities during non-wear time is a limitation of this study. Future research should incorporate questionnaires to address these gaps and provide a more comprehensive understanding of activity patterns. Fourth, the study did not include patients with dementia or those requiring assistance in daily living, potentially introducing a selection bias. Fifth, the duration since onset was unknown and its impact was not examined. The time since the onset of the condition could potentially influence physical activity levels, so future studies should incorporate this factor into their analysis. Additionally, a significant limitation was our inability to fully assess the cardiorespiratory fitness (CRF) of our participants. Due to safety concerns, many CPX were terminated shortly after reaching the AT, which prevented us from obtaining maximum oxygen uptake values. This limitation hindered our ability to calculate net and gross relative intensity averages for 3 METs, which could have offered a more precise physiological context for the MVPA threshold in our population. Given that the mean AT in our results was 3.2 METs, using the traditional absolute value of 3 METs as the MVPA threshold may not accurately represent the physiological demands for this patient group. Furthermore, we did not account for potential correlations between same-day data points, treating each independently. Future research should explore methods such as mixed-effects models to address these correlations, which could provide deeper insights into daily variations and their impact on our findings. Finally, this study could not investigate the relationship between the characteristics of PA and SB and outcomes such as readmission rates or mortality.

In conclusion, our findings suggest that physical activity and sedentary behavior among home-based patients undergoing outpatient cardiac rehabilitation are influenced by factors such as sex, BMI, age, and AT. Understanding these factors is crucial for designing effective, individualized rehabilitation programs tailored to each patient’s characteristics. These insights hold significant implications for future rehabilitation research and practice. Further research into the physical activity patterns and specific needs of older cardiac rehabilitation patients is recommended. Such research will be pivotal in developing more effective, age-appropriate rehabilitation strategies and improving outcomes for this growing population. Future studies should focus on developing more tailored interventions for patients by considering the specific characteristics of their PA and SB. Additionally, alternative methods should be explored to assess exercise tolerance and establish appropriate MVPA thresholds that account for the unique characteristics and safety requirements of this population.