Epidemiological studies often measure all-cause mortality. A recent study found lower death rates in people taking 8,000 versus 4,000 steps/day. This is important, but there is more to the story.
It is also known that people who meet the 2018 Physical Activity Guidelines (150 to 300 minutes a week of moderate-intensity or 75 to
150 minutes a week of vigorous-intensity aerobic physical activity) can still be at elevated risk for disease and death if they are also sedentary for most of the day. Simply put, it appears that the good of physical activity can be overcome, to some extent, by the bad of prolonged sitting and inactivity.
In a study that was published in the February 2021 issue of Medicine & Science in Sports & Exercise®, the premise was that unhealthy and yet unknown phenomena occur when people are inactive. They scientists used step counts per day to evaluate inactivity seeking to determine what is too low.
The study had subjects take either approximately 2,500, 5,000 or 8,500 steps/day on the days prior to the bout of running. Following the two lowest step counts, the postprandial increase in plasma triglyceride was elevated an unhealthy 22% to 23%, compared to when taking 8,500 steps/day (p<0.05). Along the same lines, whole body fat oxidation was significantly lower and unhealthy (16% to 19%, p<0.05, respectively) when taking 2,500 and 5,000 steps/day compared to 8,500 steps/day. We have termed the inability of a one- hour bout of exercise to improve fat metabolism as exercise resistance due to inactivity.
In practical terms, reducing physical activity to approximately 5,000 step/day and below in young healthy individuals impairs the ability of an exercise bout to improve fat metabolism the next day. The same deleterious responses were seen with both 2,500 and 5,000 steps/day. Thus the dose response was not linear. Taking 8,500 steps/day appears to promote a healthy improvement in fat metabolism. However, we don’t know about the effectiveness of step counts in the range of 5,000 to 8,500 steps/day.