Get a Bikini Body in 4 Weeks: The Workout Plan

Part 1: Cardio Slim-Down

Pick three days each week to get in 30 minutes of cardio: Run, bike, swim, hit the elliptical, hike, play tennis, or try Lyons's walk-to-jog Twist 'n' Sweat session, below. "It's my go-to on the treadmill, but you can do it wherever you walk," she says. "The intervals are digestible bits that make time fly by" -- and the pounds peel off.

Twist 'n' Sweat
Start out at an easy walking pace for 5 minutes. Next, do this 5-minute series a total of 4 times.

Minutes 0-3
Go at just under the pace that you would break into a jog at. (If you're on a treadmill, increase the incline to 2 or 3 percent and keep it there until it's time to cool down.)

Minutes 3-4
Do side-to-side twists as you stride: Hold a light medicine ball in front of your chest if you're on a treadmill (place it in cup holder or on floor after interval) or clasp hands together, centered just below chest, if you're outside. Keeping hips steady, rotate upper body to left (as you step forward with left foot) and then to right (as you step with right foot) to complete 1 rep. Do 50 reps.

Minutes 4-5
Jog at a brisk pace.

Cool down with an easy 5-minute walk.

Calories burned: 152*
*Approximate calories burned are based on a 140-pound woman.

Download the playlist for this workout