Doing FLOOR flies has the same effect as doing bench flies. The main thing is FORM. Don't use a weight that is so heavy the you have dificult time maintaining proper form. Any exercise designed for a bench can be done on the floor. This is not Weightlifting this is Weight Training.  Who started calling this Weightlifting?

You might not be getting the full range of motion-- which might mean only parts of the muscle are getting worked out. (I know this is true for not doing the full range of motion with bicep curls, but I'm not sure about flies) you might try propping your head and chest up a bit with a pillow to get a little extra range in there?

Hi!  I have been trying to set up a routine of some weightlifting from the Fitness Plan on this site.  Since I don't have access to machines I've been working on the excercises suggested for dumbell use, and have a question about one.  Looking at the dumbell chest flies, does anyone know if it matters the angle your arms are at in the starting position?  In the animation it shows the person on a bench, so thier arms are at more of a 100 degree angle to thier torso.  I have a floor to do this excercise on, so my arms don't go more than a 90 degree angle back.  Is this better, worse, or not an issue?