Without knowing your current workout schedule - Could you possibly be overtraining?
Sissy squats helped me a great deal.
i can’t do sissy…
basically my leg workout is:
4x8 leg extension
4x6 romanian DL
4x15 leg curl (or 4xMax natural GHR)
in a different day I train calves:
4x4 seated calf
4x10 standing calf
3xMax donkey rise
(max means that I do all the rep I can with a given weight…)
i train calves on Thursday and quads+hamstrings on Friday…
I have strenght and resistance improvement but I lack on “mass” on the vastus lateralis… :\
I would say that your volume is low IMO. Step ups is just as you thought, step up on a box or stairs, BB or DB (stairs). I would definitely have a narrower stance for the squats and I would not do the leg press to build the VL, it is primarily a hip flexor movement with secondary response on the quads and very little for the VL, in fact Leg Press can do some damage to the knees. IE My wife has knee issues as well and can not do sissy squats and leg press is iffy as she feels her knees hurt if she is not careful, by careful I mean keeping the knees from moving inward when the weight is heavy, usually a shoulder width is ideal for leg press and therefor better for the knees and thus eliminating full stimulation on the VL, IMO again. I would like to see more volume and this is coming from a guy that does a lot of HIT work so take this as you want, I’m just trying to help out.
Program sugestions for legs, I agree you cannot specifically train for VL development, it usually is a by product of total leg development.
20 rep squats (shoulder width max stance) Just break parallel, any lower may cause knee problems.
3x12-15 leg extensions (lean back on bench about 30 deg., do not stay upright if possible)
3x12 SLDL (knees have slight bend)
3x12 Leg curl (let the hips rise naturally)
3x20 Donkey raise
3x12 seated calf raise
3x12 One legged standing DB calf raise
3x12 Back squat
3x12 Front squat
2x12 Leg curl
3x15 Donkey raise (pause for 5 count at top)
3x20 seated calf raise
3x10 step ups
SLDL is important for knee strength and also for hamm development (as you know)
Both forms of hamm exercise is vital for knee strength and if the leg extensions does not bother you, then it will provide knee strength as well.
I’ve played football and never had knee injuries while maintaining this workout, my VL was/is pretty good. Sprints are also good finishers.