#1 Not isolating the biceps in a biceps curl
Have you ever done a regular standing biceps curl and felt super strong, but then when you do a crouching curl, or preacher curl you have no power? Then you might be a perpetrator of this! This one is actually a triple-whammy.
1a is that some people use too much back to lift with biceps. When in the curl position, make sure you keep a straight back and never lean back to jut the weight up into position during the move. Bending the knees will also help.
1b is that some people have way too tight of a grip on the weight. It's possible to overwork the forearms and not the biceps as much by doing this. Obviously, don't drop the weight (!) but keeping a looser grip will focus more on the muscle.
1c is that some people have the elbows to far back. Ideally, your elbows should start in the middle or slightly towards the front of the rib cage, and then stay there as you move up. Next time, try an experiment and push your elbows forward a little bit before doing the move and see how much more the burn is in the biceps! An additional tip, make sure your elbows are stationary, they should not be moving back and forth as you curl.
#2 Bad Plank
Plank is a home-base position for more than just the standard plank hold. Every time you do a push up, floor sprint, in-and-out ab, etc. you are in plank position. The key to plank is to be a board (hence the name)! But without a mirror, it's tough to see what you actually look like. I've found most people perceive they are straight as a board when in reality there are two things wrong. A) the shoulders are not over the wrists, and B) the butt is in the air a little bit. To fix this, get into what you think is plank and then roll forward ever so slightly. I should actually be a little uncomfortable by the way! Before I do any plank exercise I always push forward like this to make sure I'm aligned correctly.
#3 Not working the back during a back exercise
The back is one of the weirdest things to work. In some ways, it's like shoulders, chest, and arms where you isolate the muscle with a heavy weighted exercise, but the back is such a large combination of different muscles that it is also kind of like the abs on the flip side. We can crunch the abs, but obviously we don't bend backwards to crunch the back!
To make up for this, many of the back exercises are pulling motions, like pull ups, rows, lawn mowers, and flys. No matter what exercise you do for the back you MUST always start with one simple move: bring the shoulder blades together. I will say it again: before you start your back exercise, bring the shoulder blades together. It will change everything, and actually make it easier to lift heavier because your back is so strong! Without engaging the back by bringing the shoulder blades together, you are using shoulders and arms, which are not as strong as the back.
I was sad that I could only lawmower pull about 25 lbs. when I started P90X. But when I learned this shoulder blade trick, I realized I was pulling it with my arms and shoulders, not my back! I immediately got up to 40 lbs. by tweaking my form, and was working my back correctly, and now I max out my Selecttech weights at 52.5 pounds and could probably go heavier.
#4 Your jabs are too high
Didn't expect a simple punch to be #4 did you? This is a funny one. In any MMA type workout where this is punching, I see people punching way too high. There is a simple reason for this: our eyes are above our nose. You should imagine your jab hitting your opponent square in the nose, and you probably think you are doing so, but because you want to punch into the range of your vision, you are likely punching a little higher around your opponents forehead. Try it in the mirror sometime and you'll be surprised how "low" it feels to punch squarely in the face! This slight adjustment will make you faster and it will be better for the shoulders.