Using myself as an example. I did a lat (back) workout today. I started doing dumbbell rows for 8 controlled reps using a 35lb dumbbell. I usually use 50 lb dumbbells but this week I am doing higher reps with lower weight. During the reps I lifted and lowered the weights slowly, allowing for my muscles to be strained and weaken to fail over the 8 reps. An important part of this exercise is that you do not move your shoulder up and down, use only your biceps and lats to lift the weight. On the two benches next to me, I watched as two other guys did the same exact exercise. However, both were going noticeably faster than me, lifting much more weight, moved their shoulders up and down to help get their weights up, and completely dismissed the negative portion, lowering the wights just as fast as they were lifting them. Granted, one guy was definitely stronger than me, but there are two big things wrong with this. One is that they are risking injury to themselves. I'm definitely not a doctor, but lifting heavy weights and jerking your shoulders hard and fast to lift the weight cannot be safe to your shoulders. Secondly, they're not allowing themselves to get the full workout! They are not allowing time for their muscles to feel the strain of the dumbbells on their lats and biceps. I would be interested to see how much weight these two guys could have actually lifted if they used good slow form, but I am sure it will be less weight than they were using today.
A good point to remember is that lifting the weights is just one half of the workout. In a dumbbell row, lifting the weight up is half of the strain that your muscles will face. The other half is the lowering (negative) portion. Doing your exercises slowly up AND slowly down will ensure that your are getting an optimal workout without putting yourself in unnecessary danger of injury.
Take Care,
Jaime