If you just want to get back in shape in 2017 and you're a crazy-busy dude, here's how to go from zero to hero in only 90 minutes a week, according to Brad Schoenfeld, Ph.D., the author of The M.A.X. Muscle Plan

How to do it: Perform each exercise for 8 to 15 repetitions, depending on whether your goal is muscle endurance (lower weights, higher reps) or strength (higher weights, lower reps), and go from one move to the next taking as little rest as possible. Do the circuit three times in 45 minutes.