In a recent study published in European Heart Journal, researchers demonstrated the benefits of moderate amounts of vigorous physical activity (VPA) completed in short bouts in reducing the risk of heart diseases and cancers.
The physical activity guidelines for Americans (second edition) and the 2020 World Health Organization (WHO) guidelines recommend 150 to 300 minutes of moderate-to-vigorous physical activity (MVPA) as a time-efficient substitute for regular exercise or achieving recommended physical activity levels.
Although based on prospective observational evidence, several studies have evidenced the health benefits of VPA. For instance, a recent study showed that when VPA contributed 30 to 50% of total MVPA time, it lowered all-cause mortality (ACM) risk by ~10%. However, there is a lack of understanding about how much VPA (VPA volume) is required to improve health and reduce mortality and disease incidence, especially cardiovascular diseases (CVDs) and cancers. Notably, device-based measurements are ideal for examining the dose response of short and intermittent VPA bursts.
About the study
In the present study, researchers enrolled 502629 participants, in the age group of 40 to 69 years, from the UK Biobank study between 2006 and 2010 to examine the dose-response association of device-measured VPA with mortality and CVD and cancer incidence. They excluded participants with prevalent CVD or cancer or diagnosed with any such event within the first 12 months after the landmark.
The team mailed an Axivity AX3 accelerometer to 103,684 participants between 2013 and 2015. They initialized all devices to collect data at 100 hertz (Hz) sampling frequency and a dynamic range between ± 8 g. The team asked all the participants to wear the AX3 accelerometers on their dominant wrist for 24 hours per day for seven days for physical activity assessments. They considered the start of the landmark period, denoted by the time of the accelerometry measurements, as the onset of follow-up time.
When the participants returned the devices, the researchers calibrated their data and identified non-wear periods per standard protocol. Only that data was analyzed or considered valid when the participants wore the device for greater than 16 h. Also, each participant needed a minimum of four valid monitoring days, with at least one of those days being a weekend day, to be included in the study analysis.
The study's physical activity scheme used features in the raw acceleration signal to quantify the time spent in different physical activities and their respective intensities in a 10 seconds window. The team calculated the VPA volume for each participant by summing the time spent in each activity intensity band across all valid wear days. Notably, 96% of VPA volume occurred in bouts lasting up to two minutes.
The study outcomes included ACM, CVD mortality, and cancer mortality, plus cancer and CVD incidence by VPA volume groups (no VPA to less than zero, 10, 30, 60 minutes per week, and ≥60 minutes per week). The team followed up with all the participants till October 31, 2021, for all outcome ascertainments. They used Poisson regression to calculate the dose-response absolute risk between VPA volume and each outcome and Cox proportional hazard model to compute hazard ratios (HRs).
The authors noted a consistent non-linear inverse correlation between VPA and all-cause and cancer mortality; however, the correlation between VPA and CVD mortality was a linear dose-response type. Moreover, there were comparable results for the optimal and minimal dose-induced incident disease and mortality, with a steep gradient for five-year CVD incidence risk. The current recommended 75 minutes per week of VPA were associated with the lowest risk in dose-response curves for all three mortality outcomes.
While ∼15 minutes per week of VPA lowered all-cause and cancer mortality by 16 to 18%, 20 minutes per week reduced CVD mortality risk by 40%. However, ∼53 minutes per week of VPA was associated with 36% lower ACM, with modest additional beneficial associations for more VPA. People with poor fitness or cardiovascular and cancer risk factors (e.g., obesity) accumulating VPA in short bouts of up to two minutes (four times a day) lowered their mortality risk by 27%.
Intriguingly, potentially beneficial VPA volume doses identified in the study were consistent across age, sex, and health risk factors. Thus, clinicians and health practitioners could encourage participation in VPA of any length throughout the day for adults of all ages and ensure their long-term engagement and adherence.
Prior questionnaire-based studies suggested 60 to 70 minutes per week of VPA attenuate mortality risk by 30%. Based on the device-based findings of the current study, a minimum of 20 minutes per week of VPA provided similar levels of lower mortality risk. Despite differences in constructs, the authors noted a ∼3:1 equivalence of VPA time captured by questionnaires and accelerometers.
Previous device-based studies measured physical activity in one-minute intervals (lower resolution). It might have masked short VPA durations and led to an underestimation of VPA volume. The current study used a higher physical activity resolution (10 seconds) and found that 92% of VPA durations lasted one minute or less. Overall, the study findings are quite relevant from a clinical perspective because time constraint remains the most commonly cited barrier to regular physical activity across age groups, genders, ethnicities, and health statuses.