What do astronauts in space and the seated worker have in common?
Astronauts lose muscle strength and bone density due to loss of gravity. Sitting for extended periods basically does the same. Muscle and bone strength require muscle contraction (movement) and resistance (gravity). When in next to zero gravity, like in space, or sitting we are not stressing the muscles or putting much weight against our skeleton. Our skeleton actually craves movement and resistance in order to stay healthy and strong.
Luckily, gravity here on Earth naturally puts stress on our bodies while we are moving about. Our muscles and bones thrive on this. Our bones are living structures mainly made of collagen and calcium providing bone flexibility and strength.
They also depend on several other things besides movement for their health: minerals, vitamins, especially the pro hormone vitamin D, hormones, and even the bodies pH environment. An acidic body pH will naturally draw on calcium and other alkalizing minerals within bone to maintain blood pH. You can't do much to change the blood's pH so the body will adjust as needed drawing from bone and muscle. So, resistance type exercising and eating a healthy diet, especially pH elevating greens, play a huge part in strong bone and muscle. Healthiest Certified Organic Super Food Greens 
If we're a seated worker, or just seem to sit a lot, there are things we can do to guard against muscle and bone loss. I've always suggested to my office working personal training clients that they exercise within the work day. One of the best office strength exercises is simply stand and sit 10 or more repetitions in a row 5 or more times each day, or even use office fitness software.
Here are some hip and thigh strengthening exercises done with a simple easy to carry resistance band
Georjia Motta-
ACE Certified Medical Exercise Specialist, Pilates Instructor and yoga teacher.