It is well established that a lack of exercise can raise the risk of chronic disease, including type 2 diabetes and heart disease. New research, however, finds that the risk of such conditions could increase with as little as 2 weeks of inactivity.
In a study of young, healthy adults, researchers found that switching from moderate-to-vigorous activity to near-sedentary behavior for just 14 days led to metabolic changes that could raise the risk of chronic disease, and even premature death.
Current guidelines recommend that adults aged between 18 and 64 years engage in at least 150 minutes of moderate-intensity activity or 75 minutes of vigorous-intensity activity every week.
However, the Centers for Disease Control and Prevention (CDC) report that fewer than 50 percent of adults meet the exercise recommendations.
Lack of regular physical activity is a key contributor to obesity. In turn, this can raise the risk of type 2 diabetes, heart disease, heart failure, and even some types of cancer. Insufficient exercise can also hinder bone and muscle health.
Testing the effects of a step-reduction protocol
For their study, Dr. Cuthbertson and colleagues set out to investigate how just 2 weeks of physical inactivity affects the body.
The researchers enrolled 28 healthy adults with a mean age of 25 years. The adults had a mean body mass index (BMI) of 25, and they were all physically active, clocking up an average of 10,000 steps every day.
For 14 days, subjects were required to participate in a step-reduction protocol, whereby they reduced their daily steps by 80 percent, to around 1,500. All participants underwent extensive health checks before and after the study, and activity trackers were worn throughout.
In order to ensure that any health effects could be attributed to changes in physical activity rather than diet, participants were required to keep a dietary journal.
The 14-day step-reduction protocol led to a 125-minute reduction in daily physical activity, from 161 minutes per day to just 36 minutes. Concurrently, participants' sedentary time increased by an average of 129 minutes per day.
Reduced activity led to loss of muscle mass, increased body fat
The researchers found that reducing physical activity for just 14 days led to a loss of skeletal muscle mass in the participants; total lean mass reduced by an average of 0.36 kilograms, while an average 0.21-kilogram loss was observed for leg lean mass.
Additionally, the 14-day step-reduction protocol led to an increase in total body fat. Notably, body fat was most likely to accumulate centrally, which the team notes is a significant risk factor for chronic disease.
The researchers also identified a reduction in cardiorespiratory fitness and the function of mitochondria, which are the cells' powerhouses. The latter finding, however, was not statistically significant.
Overall, the researchers believe that their findings highlight the importance of engaging in regular physical activity and avoiding prolonged periods of sedentary behavior.
"In a group of physically active, healthy young individuals that met the recommended physical activity guidelines, just 14 days of increased sedentary behavior resulted in small but significant reductions in fitness that were accompanied by reductions in muscle mass and increases in body fat.
Such changes can lead to chronic metabolic disease and premature mortality. The results emphasize the importance of remaining physically active, and highlight the dangerous consequences of continuous sedentary behavior."
Dr. Dan Cuthbertson