Bodywork is best applied to working with the body rather than against it. The body is in constant renewal of tissue (muscle, bone, skin, etc.) it will build it self correctly given the right encouragement. The body wants to do everything in the easiest most efficient manner possible; every endeavor to that end provides greater self efficacy.
For example, should you break a bone in your arm. A doctor will set it in the proper position and cast it to protect it. That isn't fixed. It isn't healed. It will take months for your body to go through the process of rebuilding bone across the break and all the other tissues traumatized in the event. What the doctor has done is provide the best possible condition in which the repair process will proceed. If you did not have the bone set the body would still attempt to bridge the gap of the bone break. The result however will be weaker, less structurally sound. (The Smithsonian Institute Anthropology Wing in Washington D.C. has exquisite displays of American Colonists who survived bone breaks and healing but the skeletons clearly show the breaks were not set in the proper location for healing.)
In the same manner of setting bone for healing, massage therapy sets the stage for better repair. The repair doesn't have to be from dramatic injury. The body only builds a stronger muscle if it was challenged and torn itself in the process. This occurs on a microscopic level. Sometimes you don't even realize you tore a little bit of muscle. Other times you know, "I'll regret this in the morning." Or, "I used to be able to this, I guess I'm finally getting old."
Your muscles were much weaker when you were a child and have since grown bigger and stronger. Even if you didn't know it was happening, your body was tearing down itself and rebuilding it stronger your entire childhood and into adulthood. One of the indicators of inefficient rebuilding is loss of flexibility. Or in more broad terms, a reduction in Range of Motion (ROM). Muscle strength and flexibility are not mutually exclusive.