Listen to your body, not your ego.
I wish I could take credit for that statement, but I heard it in a yoga class a little over a year ago.
Yoga (when taught well, as with anything else), is one of the most valuable teaching systems for body awareness, movement scaling, and just plain being smart about your own fitness. A good yoga teacher will tell you outright that you may not be able to assume the same shape as the person next to you - and guess what? It doesn't matter. What matters is that you're getting to the root of the pose and what the pose is intended to accomplish.
There's a valuable lesson in that.
Fitness programs have evolved to incorporate certain movement standards and common practices, which is not a bad thing in itself, but this development has taken us away from our ability to consider our goals and evaluate our progress relative to those goals. A few of the statements we have all come to know as casual "fact" are:
In order to do a movement properly, you must meet ___ movement standards (think: get your hip crease below your knees in a squat. Lock out your arms overhead in a press)
You will not make progress without progressively overloading (think: increasing weight or reps regularly in your workouts)
Once you can do the more advanced variation of a movement, you should not return to the regression (think: "graduating" from dumbbells to a barbell)
If you're not hurting, you're not improving (think: how do you feel when you're NOT sore after a workout?)
These belief systems are detrimental to our health (I've seen them result in injury more times than I can count), and they often contribute to the general fear many people have about starting a fitness program.
Some of these statements are true for genuinely competitive athletes (people who do a sport for money or some other extrinsic incentive).
For busy professionals and the general population, I want you to remember that fitness and health are PROCESS-BASED. There is usually a goal, and the best way to meet that goal is going to change every day. Our bodies are different every day. Our bodies are different from our friends' and coaches' bodies. How, then, do we ensure that we keep ourselves safe and on a good, healthy track with our fitness?
You MUST ask yourself these questions:
1) WHAT IS THE GOAL OF THIS ____ (workout, movement, program, etc.)?
2) AM I MEETING THAT GOAL IF I PERFORM THIS _____ IN THIS FASHION?
3) IS THIS ____ RISKY FOR MY SAFETY OR HEALTH?
The simplest piece:
If the answer to 3 is "yes," you should stop doing that thing, change your goal, or regress back to a point where you are NOT at risk. Getting injured doing a movement completely negates any positive progress you might think you're making by doing that movement in the first place. Stop that! Be safe, first and foremost!
The other two require a bit more investigation.
Let's take a simple movement like a bicep curl as an example.
Usually, the goal of a biceps curl is to grow your biceps muscles (or strengthen your biceps). Let's say one day that your trainer tells you to grab a heavier pair of weights, or you decide to do so because your friend is out-lifting you. As you perform your curls you notice that you are needing to swing your hips in order to get the weights to your shoulders. You ask yourself, "is this going to accomplish my goal to strengthen my biceps?" ...maybe. But it'll happen a hell of a lot slower than if you weren't performing the movement that way.
What if, in the same scenario, you notice that performing those curls causes a stabbing and unrelenting pain in your elbow? Do you think you're going to engage the proper muscles and make decent progress in that instance?
And you may also wind up unable to bend your arm for a few weeks if you continue to push.
The above example applies to any movement in the gym, any pre-hab or rehab practices, and any program. If you find yourself compensating with other parts of your body during movements in the gym, pushing through "bad" pain in order to meet an arbitrary standard, or not seeing the results that you want to see, it is VERY possible that you are focusing on an unimportant end-state rather than on the best possible way to meet your goals that day.
Listen to your body. Think critically about your goals. Ask about the goal of a certain movement or program. Get a coach who knows how to modify and progress movements based on your needs. Take care of YOU.