I have been wondering what role the heel on top of the opposite toe plays in the heel to toe crunch. With several of my clients, it seems to activate the hip flexors. Obviously a flexibility routine has been implemented to reduce this issue, but still I wonder what role the heel on toe plays in this exercise.
Let's be honest. There are countless variations and progressions of "the crunch." Many of them, such as the version you're referring to, do load the lumbar flexors (i.e., rectus abdominis , int/ext oblique, etc.) as well as the hip flexors. Your concern here is very valid and raises an intelligent and rather common question(s): spinal flexion exercises are everywhere, but why? How practical/functional is it really? How much do we need to be doing? There's a common belief/myth that, "You can/should train your abs in this manner everyday." Why? For what? Says who? Science has well established that, other than plastic surgery, "spot reduction" of fat is a fallacy at best. So knowing that, what fitness, aesthetic, functional or performance-related goal could possibly be accomplished through hundreds of reps of the countless variations of "the crunch" day after day? Research has shown that over training these muscles within the context of this movement pattern can and will cause a host of problems with respiration and circulation as well as dysfunction in the visceral, immune and musculoskeletal systems. For a much more in depth discussion on these topics, please check the "related articles" at right.