Exercise without moving as muscle? Yes, of course. A tried and tested system perhaps not to turn yourself into a man or woman of steel, but nevertheless an accepted and documented way of reviving much of your younger days tuning.
There are many and varied training methods. When I worked in the London hospitals (so many years ago!) I was actively involved in Exercise Study. A passionate student of BRIME Brief Repetitive Isometric Exercise, that was the In Thing!
Isometric means staying the same length when contracted. The joint which the aimed-at muscle moves does not move. In the case of the quadriceps, which control the knee, nothing moves. The joint stays straight and firm.
Of particular value for aiding quadriceps recovery, the schedule ran thus:
In the case of re-tuning the quadriceps, that big set of four muscles of the thigh, the front of the upper leg, start by lying down on your back. Put a largish weight say several bags of sugar? on your instep, where your shoe laces tie up.
You want to find that weight which you can JUST straight-leg lift up three or four inches for exactly ten seconds before you simply HAVE to drop the leg...