Which would you prefer- to stand or walk in a way that hurts or doesn't hurt? How about doing an exercise where you're clumsy or weak, or one you can do really well? Finally, would you rather do a tedious chore while you think about something else, or one that requires constant mental focus?
For most of us the answers are avoid pain, do what we do best, and ignore tedium. When it comes to improving our bodies though, more work and deliberate action are needed.
Injury and Pain
Avoiding pain is called antalgia. Specifically this means adopting a gait(walk) or posture(how we stand or sit) that reduces or eliminates a particular pain. For example, if the bottom of a foot hurts we take very short steps with that leg and put as little weight on it as possible.
The pain is an important signal from our body that something is wrong, and may mean that you should consult with a doctor(and remember, massage therapists and personal trainers usually aren't MDs.) When there is trauma to the body, such as closing a garage door on your foot or dropping a kettlebell on your knee, as this therapist has done, it is important to let the injury heal and to consider medical attention.
While the injury is healing, antalgia will discourage you from stressing the damaged tissue. It is hardly necessary to mention how powerful the reflex to avoid pain can be. Here's the problem: Avoiding pain can be so reflexive and constant that an entire new method of moving(ie antalgic gait) or standing(ie antalgic posture) becomes habitual and unconscious. The body's urge to avoid pain can be so strong that even after the injury has healed the new dysfunctional habit remains. Most insidiously, the new habit can actually feel "normal."
To the Gym
If you're really good at the bench press, you haven't been paying attention to this blog! (Sorry, that was humor.) OK, so if you're really good at the bench press, but lousy at deadlifts, that indicates that the deadlift and other posterior chain exercises are where you should focus. Instead of continuing to develop what is already strong, for fitness and health everyone should be focusing on where they're weak. Even for sports where particular actions are dominant, balanced strength is important. Sure, we have more fun doing our favorite exercises, but it's the difficult ones that bring improvement. Do both!
Next, when we lift a weight, do we use exactly the same amount of force with both hands or legs? Not likely, although doing so is an important goal. Either the load is lifted a bit off center if it is a bilateral exercise, or one side lifts less or with worse form if it is a unilateral exercise. Perhaps the handle on one side of the chest press machine is pushed harder, or your body tilts more while doing dumbbell curls with one hand than the other. This is where I mention the importance of awareness when exercising, and scold again not to use most machines because they conceal imbalances(some machines don't though, and rehabbing an injury is where they may be valuable.)
Exercises that are done often, maybe for years, become grooved into our neuromuscular system so they feel natural, and we enjoy the feeling of competence from performing an act we think we do well. And if we can pick up 50 pounds our usual way, but only 40 pounds in similar but "abnormal" feeling way, there is a strong tendency prefer the way where more weight gets lifted
Back to antalgia for a moment. When there is an injury, what do you suppose happens to the muscles that would normally act on the injured site? They do less work to avoid causing it to hurt, and for a muscle, doing less work means getting weaker. To paraphrase, "The weak get weaker and the strong get stronger." Some movements and exercises get easier, some get harder.
Two Plus Two Equals Three
Putting these tendencies together, we get "compensation." An injury leads to pain, which leads to faulty movement, which leads to weakness, which leads to compensating with another part of the body. Sometimes by favoring a different limb, sometimes by using synergists(muscles which would normally assist the movement) instead of agonists(the stronger primary muscle for the movement.)
The sequence works the other direction too- An area of weakness, a reliance on synergists, or loading a joint in a dysfunctional way can lead to further injury, and the cycle continues.
What to Do
First, to repeat myself, consider consulting with a doctor. Next, rehabilitating injuries is the realm of physical therapists, so treatment from a PT may be needed depending on the severity of the problem and your commitment to overcoming it.
If there isn't an acute problem or very apparent dysfunction with your body, working with a personal trainer, yoga instructor, or other movement and posture specialist will be helpful in finding and correcting these problems. A massage therapist or other bodyworker skilled in orthopedics can be very valuable in finding and loosening tight areas, and promoting proper healing after the acute stage of injury.
Finally, exercise and move fully aware of your body. Look, with the eyes and with internal senses, for asymmetry in movement and strength. Think about your workout and notice if you are doing the same old exercises or challenging yourself with new ones. Make sure that you work your body equally front and back, pulling and pushing, left side and right side. (Note that to overcome existing imbalances, more work in one area may be needed.) Choose exercises that reveal and require good form, skip those that conceal bad form, and don't cheat.
The result will be more and functional strength, better mobility, and less chance of further injury. Best of all, a better appreciation and enjoyment of using our bodies.