We see it all the time at the gym: You stand there staring at the machines trying to figure out which one will be the least boring and give you the biggest bang for your exercise efforts. Or you just climb on and maintain the same pace until you can’t stand it another minute. No wonder so many of us dread going to the gym! We all need to put the excitement— and results—back into our cardio sessions, so we asked top trainers for their most effective routines to blast calories, boost your metabolism, sculpt muscle, and free you from that “When will it end?” mind-set. The secret: Don’t just change things up every month, change them during every session.

Do five or six of the following workouts in the next seven days (while watching what you eat) and you can say so long to a pound of flab. And who knows, maybe we’ll even catch you smiling the next time you hit the treadmill!