Higher levels of physical activity are unquestionably important for maintaining good physical and cognitive health. Surprisingly, however, we know relatively little about the amount of energy United States (U.S.) adults expend in physically active behaviors each day.
One way to estimate the amount of energy expended in physical activity is to calculate one’s physical activity level (PAL) as the ratio of total energy expenditure to resting metabolic rate. Higher PALs have been associated with lower mortality risk in older adults, and they are often used to classify activity levels when calculating daily energy requirements.
A PAL of < 1.4 is consistent with engaging only in basic activities of daily living and is classified as “inactive.” A PAL of > 1.6 is classified as “physically active.” Extreme PALs have been measured for elite riders during multiday cycling races (PAL > 2.5) and for hunter-gatherers in Tanzania (PAL ~2.0).
Surprisingly, we were unaware of PAL estimates from representative samples of U.S. adults, or how much energy they expend in physically active behaviors on a given day.
Our study, published in the May 2023 issue of Medicine & Science in Sports & Exercise®, addressed this gap by conducting a nationwide survey of 2,640 U.S. adults (20-75 years of age). The study used a self-administered previous-day recall instrument, Activities Completed over Time in 24 Hours (ACT24), to estimate PALs, and the results are a snapshot of PALs in U.S. adults on a given day. (The ACT24 is accurate for estimating PAL values in comparison to the doubly labeled water technique at the population level and is a freely available tool for researchers and educators to use in their work.)
In our study, U.S. adults reported an average PAL of 1.63, and nearly 40% reported being “physically active” (PAL ≥ 1.6) on a given day. Men reported higher PALs (1.67) than women (1.59), and adults who were 65-74 years old reported lower PALs (1.58) than adults 20-34 years of age (1.66). Household and occupational activities were the behavioral drivers of higher PALs in the population, while exercise and recreational activities were instead minor contributors.
The balance of time spent sedentary and physically active was a clear driver of higher PALs. Adults who were “physically active” spent 50% of their waking day sitting (8.0 hours/day) and the remaining time engaged in light-, moderate- or vigorous-intensity physical activity, for a total of 8.3 hours/day in daily activity. In contrast, “inactive” adults spent 81% of their waking day sedentary (12.1 hours/day).
Our results provide the first estimates of physical activity energy expenditure in a representative sample of U.S. adults and describe the amount of sedentary time and types of physical activity that are associated with higher PALs.
So, get up and go find a good PAL to be active with whenever you can. Nearly 40% of U.S. adult appear to be physically active on a given day — find your PAL and join them!
We hope our findings spur further research in these areas.
Charles E. Matthews, PhD, is a physical activity epidemiologist and senior investigator in the Division of Cancer Epidemiology and Genetics within the Metabolic Epidemiology Branch at the National Cancer Institute. His research focuses on understanding the health benefits of physical activity, the adverse health effects of sedentary time, and works to develop new, “better” methods to measure these behaviors in large epidemiologic studies. Connect with Dr. Matthews: charles.matthews2@nih.gov.
Pedro Saint-Maurice, PhD, is a physical activity and sleep epidemiologist and research fellow in the Division of Cancer Epidemiology and Genetics within the Metabolic Epidemiology Branch at the National Cancer Institute. His research examines how profiles of sleep and ambulatory movement throughout the day are associated with cancer risk and mortality. Connect with Dr. Saint-Maurice: pedro.saintmaurice@nih.gov.
