Warm up by stretching your muscles, particularly your lower back and legs, before doing Russian sit ups.
Lie on the floor on your back. Spread your legs in a V. Make sure to keep your legs straight.
Lift your legs a few inches off the floor as you sit up. Sit up until your upper body is perpendicular to the floor. Hold for a second or two, then lower your legs back to the floor.
Return to the starting supine position. Repeat this movement to complete as many Russian sit ups as you are able to do.