In developed countries, the life expectancy of adults has increased dramatically over the past century. This is largely due to decreases in smoking and reductions in infectious disease and cardiovascular disease brought about by modern medicine. However, due to a rise in labor-saving devices and electronic entertainment, many have suggested that we have engineered much of the physical activity (PA) out of our lives. In fact, reductions in PA are believed to have led to deteriorations in both cardiorespiratory and muscular fitness and contributed to high rates of diabetes and obesity in recent decades. PA is an important human behavior that has a tremendous influence on health and well-being.
With traditional instruments for assessing PA, such as questionnaires and time-use diaries, it has been difficult to track time trends in habitual PA. However, the advent of small, wearable activity monitors has greatly improved our ability to track time trends in PA. Our study, published in the February 2022 issue of Medicine & Science in Sports & Exercise®, investigated these trends. Using a systematic review and meta-analytic approach, we analyzed time trends of PA in research studies that used wearable devices. We identified 16 studies from participant populations from eight different European, Asian and North American countries. All studies reported a snapshot of PA during at least two different time points, separated by at least one year, between 1995 and 2017.
Overall, these studies reported a significant decline in PA that equated to a decrease of around 1,100 steps per day over the entire duration of the studies. While the decrease in PA was apparent in all age groups, the decrease in children and adults were considerably smaller than the decrease of about 2,300 steps per day observed in adolescents (11-19 years). When expressed as a rate of decline over time, studies of adolescents demonstrated a dramatic rate of decline: nearly 1,500 steps per day per decade. Rates of decline were similar among both adolescent boys and girls.
While we anticipated that we would find a decrease in PA across the duration of the studies, the large decrease in PA among adolescents was unexpected. We should not interpret the small decrease in adults as “a job well done.” The decrease in PA in adults has probably been occurring for more than a century, with the largest decreases occurring prior to 1995. However, the decrease in PA in adolescents appears to be a more recent development. There are many factors that have contributed to the decrease in PA among adolescents, including reductions in physical education and active commuting to school. However, the decrease in adolescent PA also occurred at around the same time as the increase in smartphone technology, social media use, and electronic entertainment. It is likely that these factors have played a role in the decreases in PA among all age groups, but especially among adolescents.
The results of this study suggest that we still have some work to do in the promotion of PA across all age groups. In particular, more focus should be placed on increasing PA in adolescent boys and girls.
Scott A. Conger, PhD, FACSM, is an exercise physiologist and an associate professor in the Department of Kinesiology at Boise State University. His research focuses primarily on the monitoring and assessment of physical activity. He has been an active member of ACSM for more than 20 years.
David R. Bassett Jr., PhD, FACSM, is a professor and head of the Department of Kinesiology, Recreation, and Sport Studies at the University of Tennessee, Knoxville. His current research focuses on physical activity measurement and the importance of ambulatory activity in preventing chronic diseases.
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