Sometimes, Jiu-jitsu seems to require us to move in exactly the opposite way than what seems logical. We have to work against what many of our instincts tell us and train our bodies to move in more effective ways.
One example of an instinctive habit that has to be broken in order to do bjj well is stiff-arming. A good example of what I mean when I say stiff-arming is what most people instinctively do when someone gets into mount and puts all their weight on you. For most people just starting out, their reaction to all that weight is to push the person off of them and try to keep them off with stiffened arms. Another time when I really notice it is when a person's guard has being passed and they are trying to keep the person from getting into side control by pushing them away with their arms, using all their strength.
There are a number of reasons why this is not the best method to get out from under someone. I'll outline the ones I can think of. If you have any to add, feel free to post them:
1. When your arms are completely outstretched, they are vulnerable to attack. This is especially true when you are under someone mounted on you, but it is also true if you are under someone's side control. Stretching out your arms to try to push someone off is like handing them an armbar on a silver platter.
2. The stiff-arm will wear you out. If you are pushing someone off of you, or holding them at bay with all your strength, you are losing energy that you could be using much more effectively. You can tell if this is happening by the feeling of having "jello arms" or "heavy arms" after you just spent thirty seconds trying to push some heavy dude--or dudette--off of you. Those feelings of muscle exhaustion happen after you've put them through a sustained contraction. Simply put, you deplete your muscles of their energy.
3. Stiff-arming is ineffective. After all that energy exertion, most of the time you will find that you either were not able to push that heavier person off of you or that you ended up having your guard passed and are caught in side control. The reason why is that your arms vs someone's entrie body weight is not really a fair match up.
Another common instinct that has to be overcome is holding. Holding happens usually when a person doesn't know what to do and is worried about either losing control of the other person or are scared of what the other person might be trying to do to them. So, for example, when starting out, you might be worried about what the other person has planned, so you grab onto their wrists and hold on for dear life, using your strength to keep the other person from moving their arms. Or, if you happen to get into a bad position, like bottom mount, you might respond by latching onto the persons arms or neck, using muscle to hold them so they can't try to submit you. It can even happen when you get into a dominant position, like side control. You hold onto them as tight as you can because you don't want them to escape.
The same general downfalls that apply to stiff arming, also apply to holding.
1. Whenever you are holding onto someone with all of your strength, you have committed to that position and other people can use it against you. While you are expending all your energy trying to hold him, he is working underneath you--getting underhooks, slipping a knee in, setting up a sweep.
2. Again, you are depleting your muscles and tiring yourself out.
3. Holding only works if you are stronger than the other person. If a person--bigger or smaller than you--knows more technique, they will be able to use your holding against you, like in the video I posted. So you will have wasted your energy.
Stiff arming and holding are both examples of what people who pracitce jiu-jitsu call "muscling". If you are wondering whether something you are doing falls under that category, here are some tell tale signs you can check to see:
1. If you are doing something with so much force that you are using all your strength and you can't breathe easily, then chances are whatever technique you are trying to do has gone awry somewhere and you are now trying to make it work out of sheer strength and will power. That might get you somewhere with smaller people. But people your size or people who out rank you will overcome that.
2. If you don't know what to do and so you are using all of your strength to try to keep a person off of you, that's using your muscle instead of technique.
3. If someone is trying to submit you and your only way to escape is to try to rip your arm out of their grasp like the hulk, that is muscling. Again, you might be able to pull your arm out if the person is smaller, but if it is someone your size or someone who ranks higher, chances are that your arm will end up barred.
If you are a stiff armer or a holder, don't worry. Everyone who does bjj starts out doing these things. We don't know what else to do. As you start to learn more and the number of techniques and concepts you understand increases, the less muscling you will do. You will replace your instincts with new, more effective ways to move out from under heavy people. You will learn how to do escapes that don't rely on brute strength and how to do submissions that don't drain every ounce of life out of you while you're applying them.
Like so many things, it just takes time. As a beginner, the best thing you can do is to try to not rely on your strength. Focus on figuring out what the problem is (ex: that you are under mount) and ask your instructor what techniques you need to learn to get out from under mount (ex: hip out or an upa roll).
At first, you will feel like you are getting squashed and submitted all the time. You might think the techniques aren't working and be tempted to fall back on strength. But keep working on the little details, and through trial and error find out how to make those techniques work for you. As you add more and more tools to your toolbox, you will start to find out that you know what to do when someone gets into mount and you won't have to rely on the instinctive urge to try to push them off of you. You will re-train your brain until your instincts line up with the techniques you are learning in class.