of course some degree of contraction is required to empty the bowel. But if the stool is soft you don't have to push as hard. I recommend you consume a couple tablespoons of high quality oil every day, like coconut or olive oil. Make sure it's organic and extra virgin.
Take a look at this website: http://wildblessings.com/constipation-2/
It has one of the best articles I have ever read regarding constipation
Try to relax before going, take deep breaths. Give the squat position a try, when ready, put your feet up on a stool, the bend forward a bit so your armpits touch your knees. This really helps me empty.