Runners, bikers, skiers, and swimmers can all benefit from doing exercises that target muscles on the backs of the thighs, since strong hamstrings increase speed and endurance. And that's not all: toned hamstrings also make for shapely legs. Here are five exercises that are dedicated to that area. Repeat all five moves for a total of three rounds for an effective hamstring workout.

Bridge

• Lie on your back with your knees bent and your feet flat on the ground.
• Plant your palms on the floor by your side.
• Lift your hips off the floor as you push through your heels.
• Continue to raise your body up until your lower and mid-back are off the floor and only your shoulder blades are touching the ground.
• Hold for a beat, then lower your body.
• Repeat 12 to 15 times.

Hamstring Curl With Ball

• Start by lying flat on your back with an exercise ball under your heels. Bridge your hips up and hold that position through the entire exercise.
• Flex your feet and dig your heels into the ball. Place your arms straight out to your sides for support — don't use them, though; they are just for support.
• Slowly roll the ball toward your body as you curl your heels. Keep your hips in the bridge position; don't thrust them toward the ceiling as you do the move.
• Then slowly return to the start position (straight legs, hips bridged) to complete one rep.
• Slowly bend your knees back to the starting position. Repeat 15 times.

Romanian Deadlift

• Holding a barbell (or two dumbbells at your side), keep your arms straight and knees slightly bent.
• Slowly bend at your hip joint, not your waist, and lower the weights as far as possible without rounding your back, which should remain straight. Make sure you keep your spine neutral with a natural low-back arch, with shoulders down. Looking forward, not at the ground, will help you avoid rounding your back.
• Keep the barbell close to your legs, almost touching them.
• Squeeze your glutes to pull yourself up at a quicker pace than it took to bend down (beginners should take four seconds to bend down and two seconds to pull up). Don't use your back and do not round your spine.
• You should be using a weight that allows you to do three sets of 12 to 15 reps before fatiguing your muscles — but remember that you should be able to still do the move correctly on your last rep.

Elbow Plank With Donkey Kick

• Begin in an elbow plank with your elbows directly under your shoulders, abs engaged toward the spine. Don't let the pelvis sag down or pop up.
• Lift your right leg off the ground, bending your knee so the sole of your foot is toward the ceiling. Keep your pelvis square to the floor. Don't let your pelvis twist.
• Press your right heel toward the ceiling as high as you can without moving your pelvis or low back. The motion will not be huge, but concentrated on the booty and hamstring.
• Lower the bent leg slightly and repeat for a total of eight to 10 repetitions. Then switch sides.

Single-Leg Deadlifts

• Hold a kettlebell (between 10 and 20 pounds) in your right hand or a dumbbell in both hands, and lift your left foot slightly off the ground.
• Keeping your back neutral, lean your entire torso forward while raising your left leg, which should stay in line with your body. The kettlebell will lower toward the ground. Keep your left shoulder blade pulled down your back.
• With your back straight, return upright, coming to your starting position. This completes one rep. Maximize this move by keeping your left foot off the ground as you go through your reps.
• Do 12 reps on each leg, for three sets.