Over the long term leading a sedentary lifestyle is about as harmful to health and longevity as smoking. Thus there should also be short term changes that can be observed and measured, as is shown to the be the case here:
Researchers found that reducing daily physical activity for even a few days leads to decreases in the function of the inner lining of blood vessels in the legs of young, healthy subjects causing vascular dysfunction that can have prolonged effects. The vascular dysfunction induced by five days of inactivity requires more than one day of returning to physical activity and taking at least 10,000 steps a day to improve. "We know the negative consequences from not engaging in physical activity can be reversed. There is much data to indicate that at any stage of a disease, and at any time in your life, you can get active and prolong your life."
The researchers studied the early effects on the body's blood vessels when someone transitions from high daily physical activity - 10,000 or more steps per day - to low daily physical activity, less than 5,000 steps per day. Counting steps and daily physical activity is different than defined exercise, such as working out at the gym. While there are significant benefits to defined exercise, [this] research is based on what amounts to 30 minutes of moderate activity per day. "The impairment we saw in just five days was quite striking. It shows just how susceptible the vascular system is to physical inactivity."
The researchers studied inactivity and glycemic control as well as how inactivity affects blood flow and vascular function through the body. A decrease in blood vessel function has been shown in previous studies to be linked to early cardiovascular death and hypertension. Now, this research shows that even an acute period of inactivity of five days changes the measure that is already known to be important for long-term cardiovascular health. Also, although blood flow responses to glucose ingestion were not affected by five days of inactivity, impairments in glycemic control and insulin sensitivity are also a consequence of reduced daily physical activity.