Sculpting a lean set of perfect abs can be quite the challenge, a vast majority of people are convinced endless crunches are the solution, when in fact... they are NOT! , Abs are muscles just like your pecs and lats, so why not train them in a similar way? Endless abdominal crunches are never going to build impressive abs any more than bodyweight pushups will develop a Schwarzenegger-sized chest. Don't be afraid to perform weighted abdominal exercises that limit you to just 12-15 solid reps if you really want some deep cut abs in your midsection.
If there's any muscle group that should be exercised with slow, controlled reps, it’s your abs. Most guys simply perform hundreds if not thousands of crunches at speed with minimal control and insufficient movement . To achieve those perfectly sculpted abs you must pay careful attention to achieving a full range of motion from stretch to contraction, with a tight squeeze at the peak. Fast reps will do nothing to overload the abs and will more likely just result in injury.
Even advanced lifters at the gym have a habit of anchoring their feet under pads when doing crunches or various crunch machines. This not only shifts much of the emphasis off the abs and onto the hip flexors, but can also result in lower back pain over time. Noticing back pain at the end of a workout? This is why!