From walking around holding them with your left arm when they were babies, or from something else?

Walking/carrying at all crazy hours once they were >30kg. Holding 40kg of sick kid around is fun. Ours all refused to sit in the stroller very early which is what made it so much worse (our oldest was two, the other two refused point blank the second they could walk).

not OP but - walking, carrying, holding, being pulled in random directions, catching kids when they jump at you from unexpected places, kids using your arms to practice tug-of-war/rock-climbing, pushing (empty) stroller with one hand, and carrying kid with other....