Try this 4-minute rowing circuit: Begin with 20 seconds of rowing followed by 10 seconds of rest. Look at how many meters you traveled in that time. (Don't get off the rowing machine or even let go of the handle when you rest, says Penfold.) Repeat this eight times, trying to beat your distance each time. When you're finished with this four-minute circuit, row a fast 500 meters and note how long it takes you. "That's the number you'll want to match or beat during your next rowing session," says Penfold.

There’s a reason everyone harps on about protein: Not only does it help keep you full, but it’s also responsible for repairing the tiny tears caused by strength training in your muscles. This helps them grow bigger and stronger, nudging out body fat in the process. As a general rule of thumb, aim to get at least 70 grams of protein throughout the day, says Dr. Cheskin.

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