A good article I've edited down....
Lets look at friction and how it can affect our training. Friction is defined as - (1) A rubbing of one object or substance against another. (2) The resistance to motion of moving surfaces that touch.
When working with machines friction can become a problem, you have the situation of weight on the machine plus friction making it feel much heavier than the weight stack says it is. This can wreck your progression, let's say you're going along on lat pulldowns, last workout you made over 10 reps, you add 5lbs and start to pull and nothing happens, a big yank gets the weight moving and you have to use excessive momentum to keep it moving, all this cheating still only gets you 4 reps. You wonder "what's wrong?", friction that's what. Each time you use a machine, you should inspect in for any loose nuts and bolts, frayed cables, stuck pulleys or any broken plates on the weight stack. Any of these can cause you problems with friction. Also you should regularly keep machines oiled and otherwise well maintained.
There is another kind of friction I'd like to talk about, and that is the friction within your own body, yes, of course your body has it's own friction, and this gives us 3 levels of strength:
1) Positive strength - contracting your muscles to lift or pull a weight, during this phase you are working against your own bodies friction.
2) Holding strength - contracting your muscles to Keep a weight in one position, you are aided by your bodies friction here and can thus hold 20% more then you can lift.
3) Negative strength - lengthening your muscles to lower a weight, you are also aided in phase by friction and it has been found that most trainees can lower 40% more then they can lift.
This would mean that if your max on the bench press was 200lbs, that you could hold 240lbs and lower 280lbs. Research done by Nautilus in the 1970's showed that any increase in positive or negative strength would result in an increase in the other, of course, skill is also a factor. Now all this is very interesting. But, can it help us to build larger and stronger muscles? Yes, it can, let's take a look at some of the techniques that can come from this.
If your lowering strength is 40% more then your lifting strength, but you use the same weight for both then you will not be really be taxing your negative strength. We must find a way to make the negative harder, there are many ways to do this. One way is to do some of your exercises on Life Circuit machines they automatically make the negative 40% heavier then the positive, while these machines are good I feel they can be improved on due to a perceived lack of resistance during the change from positive to negative and then back again. Another way would be for your training partner to grab the bar and push down what he approximates to be 40% of what your lifting, have him do this on each negative of the set. And for safety have him have a good hold on the bar while doing this and make sure he's ready to stop pushing and Start pulling, in case you for some reason lose control of the weight. You can also try it this way, (use only a universal type machine for this, because you couldn't balance a barbell for this technique.) take a weight that's about 50% of what you usually use lift it with both arms and then lower it with your right arm only, lift it again with both arms and now lower it with your left arm only, continue to alternate the lowering arm till you make you target reps or until you can no longer lift the weight with both arms.
Other techniques would involve training the holding and lowering phases totally separate from the lifting phase. When doing this you would need at least two very strong training partners to lift the weight for you while you try to hold it in place as long as you can (a good position would be the sticking point for that particular lift), or you have them lift in up and then you lower it slowly and under control and they lift it again and then you lower it again, repeat for you target reps or till you can keep the bar moving slowly and controlled. Again for safety, your training partners should keep their hands on the bar and be ready to take the weight if you should lose control. You would also want to work gradually up to the really heavy poundage's.
These techniques will raise the intensity of you workouts and if used properly can help you reach new levels of size and strength.