Ever noticed when your asked to move something heavy, you don't really think about it, its not really that heavy then you pick it up and it suddenly feels a lot heavier than it should? This is because you probably have not warmed up, but you probably wouldn't need to for that sort of weight our moving, so its more likely down to concentration. When you don't think about lifting something it can seem heavier than it really is.
I believe this is a problem that people take with them to the gym and to when they are lifting. Have you ever done a warmup weight and thought it was quite heavy only to go up to a heavier weight and find it easier? This is more than likely because you where not concentrating enough on the warmups. If your warmups feel heavy it can lose you confidence for the heavier lifts, and it can take more out of you than it needn't to do. Make sure that even the light warmups you focus and concentrate on what your doing, do not treat the weight any different to what you would heavy weight, give it as much respect, and focus on doing whatever lift as quick as possible. Keep this mentality even when it gets heavy, never think can I lift this weight, rather think how fast can I lift this weight.
When you get to the gym, you should already have in your head or written down what you are going to do, what exercises, what weights including the warmup weights. This stops you from having to think to much about what you are actually going to do and focus instead on doing it!. Forget what you did on the weekend,yesterday, just before coming to the gym or what you will do after the gym, all you need to be thinking is what is the next weight I am putting on the bar. Then lifting it.
A good trick for mental concentration is to load up the bar, and before you go to lift it imagine in your head lifting the bar like you would do, easily and quickly, this gives positive reinforcement mentally to help you prepare for the lift. Even before getting to the gym I find myself doing this.
Never start a lift thinking anything more than how you are going to lift the weight, maybe a few technique queues in your head to keep good form. Try and avoid ever thinking "this feels heavy" even if maybe it does ignore it tell yourself it feels light, easy, "Light weight babbbbbbby!" Ronnie Coleman.
Most people underestimate how much mentally goes into lifting weights, sometimes you can go into the gym and your body feels awful to the point even getting down the stairs felt a struggle but unless you are actually injured then just ignore it, because your body lies to you, and more often than if your mentally ready you will surprise yourself and still hit pb's. If you are truly concentrating you should never hear anybody encouraging you because you are just so focused on the task, any music in the background will not be there, it will be you and the bar only and will feel like no matter what weight was put on the bar you would lift it.
