"Sitting has an extremely low demand for energy expenditure, because as this paper explains, there is virtually no muscle contraction of any major trunk or lower extremity muscles. With this reduction in energy demand for approximately 70-80% of our waking day, muscle fibers do no use their stored glycogen and resist the inflow of additional glucose which can be toxic to cells in excess amounts. Thus, insulin resistance develops along with elevated blood sugar (hyperglycemia) which is then converted to fat, raising serum trigylceride levels and increased size and number of fat cells.
"The insulin resistance, hyperglycemia, hyperlipidemia, and hypertension (known as the Metabolic Syndrome) contribute to the diseases associated with the corresponding increase in obesity. These metabolic derangements along with increasing waist girth leaves individuals at dramatically increased risk of cardiovascular disease, cardiac death, type II diabetes, and all-cause mortality."
Moral of the story? Get up!
*Wittink H, et al. The Dangers of Inactivity; Exercise and Inactivity Physiology for the manual therapist. Manual Therapy 2011; 16:209-216.