Not a bad exercise. Just make sure you keep tension in your abs and really squeeze your muscles tightly each time for max effect. Also don't use your lower back too much, you should feel your butt, hams, triceps, lats and abs
How To Tell If You're Working Out Hard Enough, And How To Fix It If Not
5 signs you're not working out hard enough: you're not sore the next day. you're not noticing any changes. you can talk normally throughout the workout. You do the same workout every day. you don't reach the right heart rate (moderate: hard: of your max).