From birth until around 30 years old most of us are building or maintaining muscle. However muscle mass begins to decline and physically inactive people can lose as much as 3% to 5% of their muscle mass each decade after age 30. The cause is age-related sarcopenia or sarcopenia with aging
It's a fact that activity is built into our genetic makeup. Nowadays we find every opportunity to avoid extra movement. We park as close to entrances as we can get. We take escalators instead of stairs. We sit for prolonged periods at work but the idea of adding some extra movement at the end of a long days sitting horrifies most of us.