SLDL's can be a good leg bicep exercise but not a great one for most people. If you keep the back straight, rather than rounded when trying for a full stretch, you should get more of a muscle action on the back of the legs. Doing the actual function of the leg biceps and curling up the heels to meet the butt should be first choice. Though SLDL's can be a part of the whole when include with leg curls. The Ham's are worked when squating and DL'ing mostly as supporting factors, though very importing to these lifts. A personal choice would be GM'ing over the SLDL's as a superior influence on the Ham's themselves. If you want a different feel/stretch to either of these exercises, than place the toes on a 2X4, BB plate, etc. Though go with caution at first and not used extra heavy weight on the bar.
Might consider working leg curls (in any form) one leg at a time for a better focus on the exercise. The one legged standing leg curl (machine) is excellent for most.
If you have a training Bud, have him/her apply resistance with a towel, strap, belt or even hands for leg curls. Lying on a bench or ground, while doing leg curls, can give both positive and negative resistance to the exercise. A lot of sprinters and other track& field athletics include this one during a training workout. Exceptional Ham's on most of them. And strong too, which is the major requirement of these people.
Taking the towel/strap resistance to another direction, this can be a excellent tricep mass developer also. With that positive/negative contraction & extension kept throughout most of the exercise. Good Luck.
