Generally speaking, quadriceps femoris is straight leg, anatomically, it is bent leg and straight thigh. Generally speaking, sitting leg flexion and extension or sitting leg toys are used to train quadriceps. But if you have joint injuries and no training experience, these two movements may be difficult to master. Suggest several actions:

1. Simply squat down. You don't have to squat all over, just squat half. If you don't feel tired, you can properly carry the load under the condition of full warm-up.

2. Lift your legs. To put it bluntly, the upper limbs and trunk are fixed, and the load simply acts on the lower limbs (supine, lifting weights with legs, I don't even understand).

The relative load of these two movements is relatively easy to control and it is not easy to get hurt. Pay attention to the bending angle and just control yourself. There are individual differences for reference.