If your goal is basic conditioning and you are training with oblique exercises for the first time, it’s generally recommended that you start out with a lower intensity. To get the best results from your training, you want to achieve muscular failure by the last rep of your set. You can safely start out a new program in a repetition range of ten to fifteen. If that does not feel like too much for you, go ahead and do as many as twelve to seventeen reps to muscle failure.
What is muscle failure? Good question, this may be a new term for some. When your muscle “fails” it can no longer generate sufficient force to complete another repetition with good form. Good form relates to alignment, range of motion, speed of movement, and degree of control over the motion. Always discontinue an exercise before you get to muscle failure. Going to failure too often results in injury.