Rage against the machines.
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You love the machines: You step up, find the right weight, and you push it up and down. But why not try something new? Do all the seated machines, but do them with your legs straight out in front of you and your core engaged. Force yourself to engage your core when you're on any machine; if it's a standing-type machine, go to one leg right away. Anything you do standing up, you can do standing up on one leg.