Crunches isolate your upper abdominals and are a highly effective way to target and tone your abs, says lapaix. “all movements start at your. Webcrunches can be a valuable tool in your core training toolbox — as long as you're doing them right. Here's how (and how not to) do crunches. Webtraining your core is central to any strength training routine, and crunches are a classic exercise to improve your balance and stability, and as an added bonus, get.