If our jobs require us to do a lot of sitting, we will gradually stretch out our backs until sitting becomes more tolerable. If we run for 40 minutes a day, our hamstrings – muscles in back of our legs – will get stronger and shorter to adapt to the distance trained. This is a normal occurrence, but it has some practical implications.
Our overstretched sitting muscles and stronger running muscles create an imbalance of movement. If the desk worker who runs on the weekends has developed an overstretched back and short hamstrings, when the worker moves to bend over, the body will move in the path of least resistance. Most of the movement would then occur at the worker’s low back, and this is not optimal. Ideally, when someone bends forward, much of the movement happens at the hips and legs. However, when our desk worker bends forward, the low back moves excessively due to changes from posture and exercise. After multiple times of bending forward, a strained back is possible.
So, you may be wondering if this person stop exercising. The answer is absolutely not. I would simply recommend this person makes sure to undo any unintended effects of his or her lifestyle and exercise. In this case, spending time sitting with the leg stretched out while at the office and adding some back strengthening exercise could allow all the benefits of exercise without the possible problems. Our bodies will give us exactly what we train for.