A common misconception about the word mobility is that it means someone is flexible. This is actually an inaccurate definition. To have mobility is not about flexibility, and it’s also not about strength - though both of those elements are components of mobility. It’s about range of motion. Mobility defined is the ability of a joint to move actively through a range of motion, and for the body to be stable while completing that motion.
Just because you are flexible or strong doesn’t mean you’re stable. Picture someone trying to reach for an item and being off balance. While they can stretch their limb without pain, if they don’t have mobility, they are not stable enough to do it without falling or becoming imbalanced.
A lot of injuries can occur due to a lack of mobility. If you overextend yourself while working out, or even just doing day to day activities, you can become injured. Your joints can be hyper-extended, your tissues and muscles can tear, your imbalance can cause you to fall, etc...
That’s why when you’re working out, you need to be focused on more than just getting stronger, and more than just being flexible. You need a combination of those two elements along with balance, to be able to have a good range of motion. With proper mobility training, you can strengthen your muscles and tissues, and even work out any knots that may be present in your tissues, while improving your flexibility so that you can move more freely with less chance of injury.
When you start working out, there is a reason that trainers will focus a lot on form first. It’s because they want your body to have improved mobility. Proper training is not about the number of repetitions you can do in any given exercise. You have to be doing them correctly for them to have the best effect on your body. Then, once your body gets used to doing an exercise correctly, you can start increasing the number of reps and work on strength and flexibility the right way.
You’ll find that once you shift your focus from quantity to quality, your workouts will improve. You may have to relearn some stuff in the beginning, but by taking the time to do things the right way, you will get more out of the time you’re spending working out. As a result, your body will enjoy more mobility, you’ll be less prone to injury, and you’ll feel better overall.