Sitting for long periods of time can have a detrimental effect on the muscles supporting your back. Sitting can cause a multiple amount of health issues. If you sit for more than six hours a day after two weeks, your muscles start to shrink. If you sit for more than 6 hours a day after a year you can start to experience weight gain and high cholesterol. After 10-20 years, the risk of dying from breast and heart cancer increase greatly. The health benefits of standing greatly outweigh the risks.