What are some activities that may reduce complications that may arise due to prolonged sitting?

Sitting for too long is not good and may lead to body aches especially the back. There are many activities one may practice even while at work to avoid such complications.
Use your lunch break, walk around on the street rather than having a snack at your desk. You can also walk over to a colleague and talk to him or her instead of emailing them.
Stand up and get water from a dispenser to refill your glass. And if you need to use the washroom, walk to the farthest one.
Walk to the printers, photocopiers and scanners around the office when you need their services. Take the stairs to another floor or walk across the street to seek services you might need.
If you commute, in the evening drop off a stage ahead and walk the rest of the distance.

 

A common effect of sedentary jobs is the back pain.

Of course, walking can help but in my opinion, it is not nearly enough. You have to choose an activity that stretches and strengthens your muscles. I swear on yoga, but for example a friend of mine goes swimming multiple times a week.

In addition, there are objects that can also help in preventing or reducing pain, like using a fitball or a kneeler-chair. You can put a seat-cushion onto your chair, too.

If none of the above works, you can always choose to visit a professional massage therapist, which I'd strongly recommend because it not only helps with the pain but it also makes you feel relaxed after a heavy day.