Killer abs and legs without moving - isometric exercise

Isometric exercises put the muscles under pressure without requiring movement. Iso = equal, and metric = length.

While your whole routine would not be based on isometric exercises, they are a great way to isolate and also to pre-fatigue muscles before you go into your usual routine.
For example, squatting against a wall and setting the timer for 1 minute before you go and do your barbell squats will ensure your glutes are already on fire! It also recruits your deep abdominal muscles to maintain the hold.
Here are your moves. How Long Do I Hold? As Long As You Can.

Glutes. Quadriceps. Abdominals. Slide down the wall into a squat - your knees and ankles should be in a straight line and your shoulders pressed back towards the wall (no hunching!) Keep your chin parallel to the ground and eyes ahead. Challenge yourself - set the stopwatch and try to beat your best time in a few days.

Glutes. Quadriceps. Adductors (inner thighs).What about my inner thighs, I hear you screaming. I know. Grab a lightweight ball or a yoga block that allows you to keep your knees roughly hip width and perform your squat-hold while pressing the ball between your knees. Hello hot pants!

Abdominals. Quadriceps. Hip flexors. This is a tough one. "Boat Pose" in yoga. If you want to start a little easier, bend at the knees and keep your shins parallel to the ground. You MUST keep your shoulders back and chest open. Hunching over is cheating. Check out your form in a side mirror or ask a trainer to assess your technique.