An often overlooked tenet of fitness by many athletes and gym goers is flexibility. An it's often done too the detriment of ones overall health. Here's why joints, tendons, and ligaments all have a limit as to the amount of stretching and or force that can be applied to the area before tearing/failure. And unfortunately the stronger and faster you are the more force you're applying to area of exertion. Analogy time. Your muscles are a car, your speed are the tires and lastly your flexibility is the airbag. More muscles = more mass and the faster you are moving in relation to this mass is putting you in a potentially dangerous situation. Once an obstacle or roadblock appears and you respond by one or more actions like a sudden stop or change in direction you're putting tremendous stress on the entire car. If there is a crash the airbag will soften the blow to the body. More flexibility = bigger airbag. Give yourself more cushion and you decrease the chances of injury. (Cartilage is the bodies natural cushion between bones and thus joints but it's finite. As you get older it erodes away so focus on what you can change to help you on your road to health)