It all starts with poor posture. Whether you are at work hunched over your keyboard, out and about with your nose in your cell phone or even working out with improper form, the problem is poor posture. Why should you care you may ask? That’s an excellent question! The answer is that poor posture will result in muscle developing around your bones – but not in the way it was intended to be – altering joint motions and eventually causing pain and discomfort. Since muscle tissues are very adaptive it’s imperative that we maintain good posture to insure muscle develops in proper balance to maintain optimal joint motion.
Imagine for a moment that you’ve been hunching for many years and now you have muscle that developed around your new posture. Then all of a sudden you develop what you might think is an unrelated problem (e.g. you can’t lift your arm above your head without experiencing shoulder pain). So now your poor posture resulted in weak trapezius(traps), tight latissimus dorsi (lats) and pectoralis(pecs) and have permanently altered your range of motion at the shoulder joint. If this is you, don’t fret, you can still change it but you need to address it with physical therapists and fitness professionals. Do not attempt to do this yourself. You will need physical therapists to massage and stretch your tight muscles while you work with fitness professionals to strengthen your weak ones. Without this process you will end up with more stiffness, aches and even numbness.
Muscle imbalance is one of the main reasons we experience knee pain when running. Most people don’t realize just how much our knees rely on proper muscle proportions to support them. 
Look at some of the leg muscles that get recruited when we run. They all need to be in proper balance with each other. The knee provides the stability function when we run and therefore if any of those muscles are not in proper balance it will throw the stabilization off and place pressure on the unintended part of the knee causing trauma. As a workout solution to this particular problem I would advise that instead of using machines, perform lunges and squats with free weights to insure proper muscle distribution. Also, include stabilizing exercises to trigger those specific muscles to develop and get stronger. Running doesn’t cause “runner’s knees” but rather it fleshes out lack of stabilization or improper muscle balance. Address this issue before you give up on running altogether.
Poor posture at the gym is not a new thing. It’s something we all observe on a regular basis. At first you might think it’s not really a big deal but again, long term effects will change your mind on that. When performing certain exercises some people like to look at themselves in the mirror but many times this will result in a neck strain which can lead to tight traps and neck injuries. Just because you know how to perform certain exercises doesn’t mean you have the proper form, so please be careful and watch your neck position especially when handling very heavy weights.
So to summarize, watch your posture whether at work, during your leisure time or while working out. It’s important if you want to avoid long term effects of muscle imbalance. But if you find yourself in an unfortunate position where you already have bad posture, work actively to improve it by addressing it with professionals in the area and continue being mindful of any joint motion pain. It could be your body sending you a message that you need to correct something.