Short-sleeve season may still seem months away—but now's the time to get ready. Joe Dowdell, the founder of Peak Performance in New York City and the author of Ultimate You, developed this simple plan to quickly build muscle and add strength and definition. Click on photos or exercise names to launch our how-to videos.

Exercise: Chin Up (Video)
Guys often skip chin-ups—a key upper-body move that bulks up the biceps—because they think they can only do a few. Get a grip (palms facing you) and rise above! Try for three sets of eight to ten reps.
Exercise: The Dip (Video)
Grab dip bars and lower yourself until your biceps touch your forearms, then lift yourself up. Don't lean forward—or you'll work the chest more than the arms. Do three sets of eight to ten reps.
Exercise: Preacher Curl (Video)
Sit at the preacher stand and grip an EZ-curl bar, hands slightly narrower than shoulder width. Curl up, then lower the weight, fully extending your arms. Do three sets of ten to twelve reps.
Exercise: Hammer Curl (Video)
Stand, with a pair of dumbbells, palms facing each other, arms slightly behind your rib cage. Brace your core and curl up as high as possible without moving your elbows forward, then slowly lower.
Exercise: Decline Extension (Video)
Lie on a decline bench so your hips are higher than your head. Hold a pair of dumbbells with your palms facing each other, your arms extending straight up. Keeping your elbows pointed at the ceiling, curl the dumbbells down to your shoulders in a controlled motion. Bring back to start position to complete the rep.
Exercise: Towel Hang (Video)
Drape two towels over a pull-up bar. Grab each one and hang with your arms fully extended for 30 seconds. Do three sets.
Exercise: Farmer Walk (Video)
Because these drain you so fast, don't include in the circuit. Instead, add them at the end of the workout. Grab a set of very heavy dumbbells. With your chest tall, chin up, and shoulders back, walk forward for 30 seconds. If space is tight in your gym, march in a figure-eight pattern. Do three sets.

Check out more "30 Days" exercise workouts, including our guides to killer abs, a stronger back, and running a faster 5K.