I don't know if it was in Arnold's book or not, but someone a while back told me that doing situps in between sets of lifts that put extra emphasis on the lower-back (squats/deads) was good practice.

After a heavy set of deadlifts my lower back tends to be considerably sore, rightfully so. I've noticed that immediately sitting down and doing a light set of situps almots instantly alleviates this soreness. Also today after 5-rep max on squats my lower back started to ache so I layed on a bench and did 25 leg lifts, bam, back feels great and I rest a minute or so and do another set.

My question is, is there any negative effect I'm overlooking. I know stretching in between big sets is not recommended, so are situps 'loosening' those crucial lower back muscles and effect the subsequent lift? I also know that situps and abs involve the lower back, so shouldn't that make it worse rather than make the soreness go away? I'm not real sure on the mechanics behind this but I'm just guessing that it's basically a form of stretching in between sets... which I guess I should avoid?