We use kettlebells a lot during class workout, including my strength & balance class and I always tend to use the heaviest one I can lift, then depending on what we’re doing, I can always switch down a weight 
I never stick to one exercise routine for long for fear of becoming it stagnant and not progressing in my strength development. So I usually switch things up every 3 or 4 weeks, even the classes I attend do that. I think it helps keep your body active and on the alert to whatever is coming next…got to keep it on its toes 
These are all seated leg curl variations
This one uses a straight length of resistance band tide into a look and be hooked around the leg of a table at home.
This a standing leg curl that can be done at home, again with the use of resistance band.
This one uses a ready looped resistance band.
I like this variation of seat leg curl because the way he does it also gives the abdominal muscles a bit of a workout too 
And this is a leg curl machine you find in a gym.
Here’s a sample resistance level guide for the bands, although colour schemes for bands do vary amongst brands.
