I agree with Arnold jr, who makes good points. Remembering that with the DL, the bar is being held stable, while the blunt of the lift (motion) is being done by the hips/glutes/quads & hams. Weither starting from the floor or around knee height, the affect on the total back/traps/lats remains about the same. And more weight can be used from a higher starting position.
If concerned about the lower back, and lifting from the floor, than SLDL's might be used in a DL rack pull workout. Or you may try just doing the SLDL by it's self. A great exercise when done right. Using SLDL's for a month or so, as the only pulling movement from the floor , and than returning to the regular DL workout, should greatly increase that regular floor DL. GoodMornings are another power and muscle building exercise for building lower back & hams strength. This also has a wonderful affect of low back strength. SLDL's & GM'ing can improve the squating quite well also.
If doing the SLDL with heavy weigh (4-7 reps), just go as low as the 45's allow. On occasion try standing on a 4" platform, block, etc for a extra stretch., with lighter weight.... 12-15 reps. But never more that this.
As Overload suggested, might try alternating the rack DL with SLDL's every momth or so. In any event the lower back and the regular (floor) DL should gain improvement and power. Good Luck.
