"Added strain" refers to an increase in pressure or stress. It implies that an extra burden or demand has been placed on someone or something, making the situation more difficult or challenging. Full definition
Today's world puts added strain on the liver, which means we need to be extra kind to it and give it nutrients it needs to perform. (detoxdiy.com)
Just 5 extra pounds puts added strain on your dog's joints and muscles. (twohandsfourpaws.com)
Also, is it possible to add some kefir grains to your yogurt, along with the yogurt starter, in order to add those strains of probiotics to the yogurt as well? (kefir.net)