Most leg strengthening exercises stress more than legs alone, but we call them "Legs" anyway because they mostly engage lower body. Many guys neglect lower body strength in favor of chests and arms.
Cardio doesn't do it at all - runners, for example, tend not to have much leg strength. Also, distance running isn't really a cardio stress anyway - pure endurance. I used to run for miles and hike hills all day, but my legs became neither strong or powerful. Especially for women, lower body bone strength can only be maintained with resistance exercise.
For strength, (not talking about cardio or endurance here) I try to keep it simple. For functional fitness and to postpone muscle deterioration, I think all an ordinary person needs to do are five sets (with increasing reps and/or weights over time) of most or many of these basics, weekly. Some are more Calisthenics, some plain Resistance - R or C:
Barbell squats - R
Squat with overhead press - R
Plain squats or jumping squats - C
Deadlift - R
Lunges with and/or without weights in hand - C+R
Step ups +/- step up and press - C
Kettlebell swings - C
Box jumps - C
Stair machine intervals - C + cardio
Calf lifts - C, Leg press - R, and leg extensions and curls - R, are optional approaches to building up strength for the big leg efforts, but not substitutes
When you think about it, most of these exercises stress not only lower body but core too and sometimes arms and shoulders. Furthermore, they all are cardio exercises to some degree: A barbell squat routine of 5 sets will leave you gasping for a few minutes, as will just one set 15 of kettlebell swings.
I would not advise doing Deads and Barbell Squats, or any leg "R" - on the same day or more than weekly. Recovery time is needed for the big muscles. "C" lower body exertions can be done as much as you want. I tend to do calis as circuits, and Rs as dedicated efforts.
