I was messing around curling a 27lb bucket of cat litter the other day and found that I was getting a better arm workout than when I used my 35lb weights. After being confused for a couple of days when I wasn't able to recreate the effect in subsequent cat litter curling routines I realised what I'd done.
Since the cat litter was 8lbs lighter than my normal weights I did the reps very slowly. When I repeated the exercise and conciously counted a second pause at the point of maximal bicep contraction and followed the normal 12, 10, 8, 6, 12, 12 routine I found that I experienced a very effective curl workout, i.e. my bicep ached for a couple of days.
I've known about the benefits of slow reps, particularly for slow twitch muscle fibres, for years and thought that I was going slow enough. Now I realise that I have just been fooling myself all this time. From now on I'll be reciting "One one thousand, two one thousand, three one thousand etc." so that I get a proper rep rather than the slight pause cheating which I have been doing for so long.
Do you pause during maximal contration of exercise reps?