We often take the the simple act of walking for granted. Have you ever taken a moment to actually consider what is happening in your legs with each step you take. Wrapping ourselves about the workings of our bones and skeleton it's the muscles that do all of the work to get and keep us moving. A series of perfectly timed contractions triggered by nerve impulses via the fuel we use to energize our bodies. Keep in mind there are as many as 840 muscles in the human body with about half of them being of concern only to Doctors and specialists in certain anatomical fields of study. That leaves roughly four hundred attached to our skeleton's 200+ bones always pulling in opposite directions to stabilize and move us through our daily lives. Here's what our leg muscles are up to when we walk!
The point I'm trying to make is that there are an infinite amount of minuscule variations of where these muscles attach, the capacity of work they can endure and the maximum force they can exert in each movement. When someone tells you that they get enough exercise at work that just isn't the case. Exercise takes your muscles to their limits in a controlled and safe manner while obtaining a high degree of nerve activity which stimulates the muscles to grow. Walking from your desk to the printer or copier does not do that!
Video courtesy of The CARDAN Learning Portal