Muscle groups work harder during a set if you focus on them

[Bouncer]

In the gym there’s no exercise that trains only the muscle group you want to stimulate. Other groups are always involved. That’s why it’s not so easy to achieve directed growth of particular parts of the body. If you have strong shoulders and weak chest muscles, it’s pretty difficult to develop good pecs. Or is it not that difficult after all? Sports scientists at the University of South Carolina Upstate discovered a very simple method. Focus.

Researchers describe in their article, which was published recently in the Journal of Strength and Conditioning Research, how they attached electrodes to the teres major [a muscle in your upper back, that runs over your shoulder blade], the biceps and the latissimus dorsi to their subjects. They then got the 8 women, aged between 18 and 35, to do lat pull-downs.

The researchers then repeated the activity. First they got the women to perform one set. Then a trainer told the women that they should concentrate on getting the power for the movement out of their latissimus dorsi muscles. That was why they were doing lat pull-downs: to develop the broad upper back muscle.

The trainer explained to the women exactly where the lats are located, and touched the muscles in the women. Then the women performed another set.

Focussing your attention on a muscle group while performing a set increases the intensity with which your muscle takes part in the movement. Isolating muscles is a matter of good ol’ fashioned focus & concentration.

The researchers had the women train at 30 percent of their maximal strength. That’s too light. Bodybuilders train at 60-85 percent of their maximum. The researchers don’t know whether using focus to isolate a muscle group works as well at higher intensity.

Source:
J Strength Cond Res. 2009 Nov;23(8):2204-9.

[Mr I]

I agree 100%, its all about what the brain tells the body to do. I can bench using chest shoulders and arms or just chest if I really focus, but with less weight.

I tend to do full ROM and use all muscles involved in that compound movement but for example I can spot a quality bodybuilder from 50 yards away even if he's wearing two pullovers and a dustbin bag, by the way he trains, for example when you see guys dumbell pressing for shoulders and they're form is so straight when they're in the grove you can tell its all shoulders and less arms

[Bouncer]

yep. arnold was right all along. you almost get into the muscle with your mind and focus on it filling with blood etc..

[Konitz]

When I work out try to physically feel the muscle contracting and visualize it in my head. I find I do much lower weight with this type of concentration.

[ROCKETW19]

Not to sound like a know it all cuzz I dont. But that is so old news bro. I always touch the muscle of someone I am training so they can focus on it.
when I workout I picture the muscle in red and the rest in white that helps me focus better.