Why is this study important?

Physical activity advice given to the general public tends to centre on moderate-to-vigorous physical activity (MVPA), the “brisk walking to running” end of the activity intensity spectrum. For example, the World Health Organization (WHO) currently recommends 150-300 minutes of MVPA per week. However, many people, such as older adults, those with chronic conditions, or simply exercise novices, may find it hard to initiate or sustain MVPA.

That’s where light-intensity physical activity (LPA) comes in. LPA refers to activities that use more energy than sitting but don’t leave you puffing, such as easy walking, household tasks, shopping, and gentle gardening. Growing evidence has linked LPA to health benefits, including lower mortality risk, yet LPA has only recently been incorporated into guidelines, and the language has been vague. For example, the Canadian 24-hour Movement Guidelines recommend “several hours” of LPA, leaving practitioners unsure how much LPA should be promoted.

Our study tackles a practical question: How does LPA benefit health in the context of existing MVPA recommendations, and who benefits most from adding more light movements?

How did the study go about this?

We used data from 71,715 UK Biobank participants who wore a wrist accelerometer for 7 consecutive days, giving objective estimates of daily minutes spent in LPA and MVPA. Participants were followed for a median of 8 years, during which 2,195 of them died.

Instead of assessing “correlation” or “associations”, which most existing studies examined, we used a causal inference approach to estimate the dose-response effect of LPA on mortality risk at low (5 mins/day), medium (25 mins/day) and high (67 mins/day) MVPA, and also at MVPA levels matching the WHO guideline thresholds (low threshold: around 22 mins/day, high threshold: around 44 mins/day). We also created an app (click here), to test “what-if” scenarios. For example: what would the 10-year risk of death look like if everyone did X minutes of MVPA and Y minutes of LPA? 

What did the study find? 

Our study revealed several main findings:

• LPA is the most beneficial when MVPA is low: The protective effects of LPA on all-cause mortality are the most prominent when individuals engage in minimal MVPA levels of around 5 min/day.

• The “extra benefit” of LPA shrinks as MVPA increases: The dose-response effects of LPA on all-cause mortality differ across low, medium and high levels of MVPA, and the added benefit of LPA on mortality appears to decrease as MVPA increases.

• LPA may be beneficial even when meeting the MVPA recommendations: Engaging in some LPA in addition to the WHO’s recommended MVPA levels still confers benefits, and the optimal LPA level is around 195–225 mins/day (about 3.25–3.75 hours/day).

What are the key take-home points?

Our study strengthens the evidence base for LPA as an important contributor to health, complementing existing MVPA guidelines and recommendations. It highlights the potential value of accumulating several hours of LPA each day, especially for people with low levels of MVPA. Health professionals need to prioritise LPA promotion among those least able to achieve MVPA, while continuing to promote MVPA where feasible.

Authors

Mengyun Luo (1,2), Philip J Clare (1,2,3), Ding Ding (1,2)

1. Prevention Research Collaboration, Sydney School of Public Health, Faculty of Medicine and Health, The University of Sydney, Camperdown, Australia.

2. Charles Perkins Centre, The University of Sydney, Camperdown, Australia. 

3. National Drug and Alcohol Research Centre, UNSW Sydney, Sydney, Australia.