A very effective supplementary exercise!
A while ago, I watched an elderly strength training broadcast on NHK.
It looked like a single-leg squat or lunge, but since I don't know Japanese, I only understood the video.
Holding the back of a chair with both hands, I put one leg back in a lunge position and do a squat with just one leg.
I do it slowly when lowering and quickly when raising, 10 repetitions on each side.
I tried 3 sets, and the results were good, so I tried 3 sets of 10 repetitions on each side with a Smith machine at the gym using the basic bar at 25kg (?), and it's really great.
The most important thing is that the back foot should not touch the ground here. And you do it with your main foot in the center.
The other day I did 3 sets of 12 repetitions on each side, and I feel much more stimulation in both erector spinae muscles than in my legs. It's probably because they're weaker than my thighs and glutes!
I'm confident that if you do it 2-3 times a week, or whenever you grab a chair at home or at the office, it will be very effective.
It doesn't take much time and seems to have good exercise results.
In the field, it seems to increase power too!
