If it feels like lately you're just going through the workout motions, try these tips from New York City personal trainer Christa Bache. You'll increase the challenge of your go-to moves—and see faster results. (Do 10 to 20 reps of each exercise.)

Instead of a crunch, try...
A weighted crunch with a yoga block
Hold a 1- to 3-pound dumbbell with both hands behind your head and place the block between your thighs, feet on floor. Keep the weight behind your head while you crunch up.
The boost "Adding the dumbbell amps up the resistance, making the move harder, and the block brings in your pelvic floor and inner thigh muscles."

Instead of a dumbbell shoulder press, try...
Adding a resistance band
Stand on the middle of the band and hold an end and a dumbbell in each hand at shoulders. Press weights overhead, hold for 2 counts, then return to the starting position and repeat.
The boost "When you use resistance bands with weights, you force your muscles to work even harder."

Instead of a squat, try...
A deep squat followed by a half squat
Stand with feet shoulder-width apart and squat as low as you can. Hold for 5 seconds, then stand up. Perform a half squat (go down half as deep) and hold for 5 seconds to complete 1 rep.
The boost "Changing your range of motion gives your muscles more of a challenge."

Instead of standing biceps curls, try...
Incline curls on an adjustable bench
Hold a 3- to 5-pound dumbbell in each hand and sit on an incline bench with arms extended toward the floor, palms facing forward. Curl weights to your shoulders, lower, and repeat.
The boost "From this position, it's difficult to cheat by swinging your hips forward or leaning back."