When we regularly use and contract our muscles, they're like a moist sponge, soaking up the sugar from the bloodstream. But when we don't regularly use and contract our muscle, like a dry and shriveled up sponge, not really good at soaking up anything. Now here's the key. When we exercise, it rewets the sponge. But eventually, that sponge dries out if you get little to no movement the rest of your day.