When Lex was very little (the whole first three months), she was pretty cranky. Not too much so, but she let me know–clearly–when she was uncomfortable. I quickly learned that motion was usually the thing that would calm baby, and even lull her to sleep. In the first few weeks I spent hours pacing the apartment with a burrito-wrapped bundle bouncing around. This turned into many sets of standing lunges, in all planes of motion; walking lunges, with and without twists; and squats-with twists, with kicks, with bounces.
Just like in the gym, I paid careful attention to my form: Feet parallel, knees stacked above feet; hips square, back straight; chest open, baby ‘weight’ secure and centered. This is great for cardio as well. After about five minutes of this I’m sucking wind.