I remain convinced that, if you’re just looking to tone and maintain, you can blitz any given muscle group in 15 minutes tops. Here’s the circuit I like to use for my back:
Pull-ups–Lots and lots of pull-ups! I find these to be the best exercises for carving out a defined back. Positioning your hands a little wider than shoulder width to keep the emphasis on the back and off the biceps as much as possible, come all the way down. Try not to hang there! Bring it right back up. It’s also okay to use a pull-up machine if you need a little assistance. If you don’t have access to a pull-up machine, you can put a chair or bench under the pull-up bar. This will enable you to complete more reps and maintain form. Check it out here: