Relative flexibility is a very important phenomenon that most people do not even begin to understand.  Shirley Sahrmann details this concept beautifully.  In her book "Diagnosis and Treatment of Movement Impairment Syndromes," she sums up the concept like this: "Because of the intersegmental variations in the springlike behavior of muscles, a reasonable hypothesis is that increased stiffness of one muscle group can cause compensatory movement at an adjoining joint that is controlled by muscles or joints with less stiffness."  Basically what this  means is that a particular muscle may not actually truly be stiff; it is just stiffer than a neighboring muscle or muscles. Here's a couple of good examples that I see all of the time and that Sahrmann discusses.

Lats are stiffer than the lumbar spine
I see this all of the time when I take new clients through assessments.  Someone flexes their shoulder (raises their arm overhead) and their low back extends (most likely hyperextends) rather than their shoulder reaching through to its end range. Since their lumbar spine is more flexible than their lat, this compensation occurs.  Chances are, if we can get their trunk muscles to stabilize their lumbar spine and get the stiffness in the low back up to par with the stiffness in the lats, the range of motion in shoulder flexion will improve.  It could also be a situation where you may need to decrease some of the stiffness in the lats AND increase the stiffness in the lumbar spine.  This is a great example of why assessments are so important.

Rectus Femoris is stiffer than the abdominals and supporting structures of the lumbar spine
In this situation, the rectus femoris (big quad muscle that crosses the hip and knee) is stiffer than the supporting trunk muscles.  When the knee is flexed, there will be excessive anterior tilt of the pelvis and the low back will extend.  At the same time, the knee will not flex to its ideal range.  In this situation, if we increase the ability of the trunk muscles to stabilize and stiffen, we might get better range of motion in knee flexion and less pelvic tilt and lumbar extension. In another light, it could be a situation that rectus is so stiff, that the body has to compensate by extending the low back and tilting the pelvis when the knee is flexed.  There are various implications that could be present and Sahrmann gets into great detail on them all.  But hopefully, this gives you a decent idea of what I am talking about.  In my experience, it is most often a combination of stiffness in the talked about muscle and lack of stiffness/weakness in the supporting muscles.  Both would be addressed to make the situation better.  Again, everyone has specific things going on so not every condition will be taken care of in the same way. 

A good real time example would be with the squat.  Someone with an overly stiff rectus femoris in comparison to their low back will generally stand with their pelvis tilted forward and their low back extended past neutral.  With this stiffness imbalance, there will be compensations within their squat pattern.  As they descend into a squat, they will get to a certain depth and when their hips run out of room to move, they will move where their relative flexibility allows them to, which in this case is their low back.  With someone like this, in most cases, the rectus will need some lengthening and their abdominals (usually the external obliques) will need some strengthening.  The glutes and hamstrings usually will need some work as well.  When you increase the ability of the muscles that posteriorly tilt the pelvis (abdominals, glutes, hamstrings, etc.) and improve the length in the muscles that anteriorly tilt the pelvis (in this case rectus femoris), the relative flexibility will be better and the squat will be a lot prettier with a stable trunk and mobile, nice moving hips. 

As I said earlier, it could be a condition where all you need to do is stretch rectus and your fine.  Could also be a condition where all you need to do is stiffen up the lumbar spine and your good.  From my experience, it is often some form of combination.  Whichever way it is, taking care of problems with relative flexibility can relieve a multitude of back, knee and shoulder pain and problems.

Hamstrings stiffer than the low back
Here is one more good example.  If you lay on your back and raise your leg straight up, how high can you go without your low back flattening into the ground?  If your hamstring is stiffer than your low back, your back will try to compensate by flattening in order to gain more movement.  A little trick to get your leg higher is to brace your abdominals as if someone is going to punch you in your stomach.  The added stability for your lumbar spine will allow your leg to raise farther without loss of a neutral spine.  This example is tricky though because if it is truly hip flexor muscles that are stiff, the pelvis may be anteriorly tilted to start; thus, giving the illusion of the hamstrings being the issue when in reality it is the hip flexors that are the issue.  See my past write up on misconceptions about hamstring stiffness to read more on this.  Either way, bracing the abdominals will help your cause with the leg raise. Being sure that the pelvis is in a neutral position to start can clear things up.

Notice how all of these examples feature an issue with the lumbar spine being unstable and too mobile?  Stability and the ability to stiffen when needed needs to be developed around the abdominal wall and lumbar spine.  The inability to do this is one of the biggest and most repeated causes of back issues, knee issues and performance detriments that you will find.  Yet, tons of people continue to promote more movement here with blind stretches and exercises.  I've touched on this multiple times as have some of the best strength coaches, therapists and specialists in the world.  Rationalize what you do.  If you really do need more movement here, than by all means you better work on it.  In my experience, this is a rare case. 

Randomly and blindly training for flexibility does many people more harm than good.  If you took the person from either of the last two example and stretched his low back and trunk muscles, his problem would become worse.  Both strength training and flexibility training need to be individualized and specific.  Relative flexibility is a great and proven concept. Contrary to conventional wisdom, sometimes stretching might not even be needed to improve flexibility at a certain joint.  Simply balancing out the relative flexibility by increasing the stiffness at a supporting or neighboring joint will take care of the movement at the area in question.  Think about how this could revolutionize what you do in the gym or in your sport.  Pretty powerful stuff!

Where do you think his flexibility/stiffness imbalance is?

Franco surely had better relative flexibility for the deadlift than the guy in the last picture

Don't think this guy understands the importance of proper movement and his back isn't going to like him for it

Proper movement is the base point of exercise and performance.  I don't care how great of shape you think you are in or how many times a week you go and workout; if you are not moving the right way, you are wasting a large amount of your time. 

"Oh my knee hurts!"  Well, if you had any idea how to squat and use your hips and glutes the correct way, your knee probably wouldn't hurt so much.  When you squat with your weight on your toes, heels off the ground and your knees are coming forward so far it hurts to watch, you're probably giving yourself knee pain. If you do this throughout the day with work activities, etc.  you can only imagine the issues you are creating.   "Oh but I went to physical therapy and they said I shouldn't squat."  Well sorry to tell you, but if you ever want to get better, you're going to have to learn how to use your hips and guess what, squatting is pretty much the best way to do that.  If your therapist was any good, they would have shown you how to move the right way and fix this problem but since they probably have no idea how to  move correctly themselves, they screwed you.  Sorry.  "Oh well I've worked with another trainer before and they gave me a workout plan."  Really!?  Well that workout plan and that trainer must've really sucked because they sure didn't teach you the most important aspect of any exercise program:  HOW TO MOVE!!!

"My back hurts" Well, lets see you pick this ball up.  Well since you just picked that up with a flexed lumbar spine, and you do repetitive motion like that at work all day, five days a week, you are probably causing problems.  Let me show you how to deadlift properly and that should begin to help you.  "Well, my friend works out like all the time and he said that deadlifts can hurt my back."  Well, your friend just proved that he has no right to an opinion on the matter.  Picking feathers up off of the ground with the form you just showed me is bad for your back.  Deadlifting respectable weights with proper form will help you like you wouldn't believe. 

(These were just generalizations, not directed towards any individual)

If you are trying to exercise and you are not performing free motion, multi joint movements either because you are scared to or don't think you need to, you have two options.  A- Just stay home and eat chips because you are wasting your time and probably creating future problems for yourself  B-Get help from an expert who can actually teach you proper movement patterns with effective exercises for yourself.

If you are performing multi joint, free motion movements but have terrible neuromuscular coordination and movement patterns then props to you for at least trying to do something worthwhile.  However, you still should refer to option B from above.  Get help from an expert who can actually teach you proper movement patterns and effective exercises for yourself. 

Movement is so important guys.  You need to learn to move through your hips with a stable trunk.  You need to learn how to squat both bilaterally and unilaterally while utilizing proper hip, knee and trunk position.  You need to learn how to pull and push with proper thoracic mechanics.  You need to learn how to rotate correctly.  You need to learn how to perform locomotion effectively.  You need to understand how to fire the correct muscles at the right times to do all of these things our bodies are meant to do the right way.  Its not as simple as going to the gym and guessing your way through random useless things.  A home video can't teach you if you have no idea how to feel things.  A magazine is even worse.  A lot of health professionals that deal with the body can't even help you (also a lot who can). I know this because I constantly see people who have been to other health professionals and still have absolutely atrocious movement skills.  It blows my mind. 

It all comes down to movement.  There are many great exercises that can do a lot for you, regardless of what your goals may be; however, the fact of the matter is that no matter how great the potential of an exercise, if your movement pattern is less than optimal, the exercise is not going to do what it should for you. 

You owe it to yourself.  If you are going to invest your time in exercise and bettering your body and life, you owe it to yourself to invest some time in learning how to do things the right way. I have talked about and could get into all of the trillion other things that go into proper and effective training and programming but no matter what topic or aspect I talk about, it still comes back to proper movement.  It is the essential base point for everything else and has to be mastered first.  So give yourself a great gift this holiday season and learn how to move!!