How to Perform the Lying Leg Curl
Here at Tiger Fitness, we embrace leg days - feathered quads and bulging hamstrings are a telltale sign of a hard-working athlete. Most leg days start with a heavy squat variation or heavy hip hinge variation like deadlift or good morning.
After these heavy compound movements for low to moderate reps most lifters move on to the isolation exercises. Isolation exercises targeting the quadriceps and hamstrings are a critical component of a well-rounded leg day.
The lying leg curl is an incredible isolation movement for pumping up, stretching, and packing mass on to the hamstrings. Contrary to popular belief it doesn't have to be performed after compound exercises to be effective.
The lying leg curl is an excellent warm-up and pre-exhaust exercise prior to performing heavy compound movements. The hamstrings are contracted and worked during the knee flexion/pulling portion of this exercise. This machine-based exercise can be plate, cable, or lever-loaded.
The lying leg curl targets the hamstrings, a muscle group comprised of three muscles (biceps femoris long head & short head, semitendinosus, and semimembranosus).  This exercise engages the gastrocnemius (calf), sartorius & gracilis (inner thigh), and popliteus (knee flexor) to assist in completing the movement. The tibialis anterior (shin) and rectus femoris (quadricep) act as stabilizers during the exercise. 
Compared to seated leg curls the hamstring is facing up towards the ceiling and your hamstring won't be squished under a thigh pad as it becomes engorged with blood.
MTS Nutrition CEO Marc Lobliner explains how to perform the lying leg curl.
How to Perform the Lying Leg CurlApproach the lying leg curl machine and select the appropriate working weight. If this is your first time performing the exercise then pick a conservative weight that you can safely lift for 8 to 12 repetitions. The machine may allow you to load each leg separately.
If this is the case add an even amount of weight to both sides to ensure even development of the hamstrings. As you become more advanced and/or experience a significant imbalance in size or strength between hamstrings you can experiment with uneven loading protocols.
Once you've selected the appropriate working weight approach the angled bench apparatus and stand in between the bench and padded lever. Lie down so that your face is pointing towards the ground, your entire torso above the hips is on the flat part of the bench, and your upper thighs are resting on the angled part of the bench.
Adjust your body so that your knees are not resting on the angled bench. Adjust the lever pad so that when your legs are fully stretched your lower calf/upper ankle is the point of contact when the lever is in the bottom resting position.
If available, lightly grasp the supporting handles on either side of the flat bench portion. Decide whether you're going to point your toes at a right angle to your shin, pointed up towards your shin, or pointed away from your shin.
Take a deep breath prior to initiating the lift and then begin flexing your knee and pulling your ankle towards your glutes. As you pull your ankle and the lever pad closer to you glutes focus on the contraction of your hamstring. During this pull, you can either breathe out in a slow and controlled manner or hold your breath until you reach the top of the rep.
Pull your ankle as close to your glutes as close as the lever pad and your flexibility allows. At the top of the rep, your hamstrings should be contracted and your quadriceps will be elongated. it's crucial to keep tension on the hamstrings at the top of rep; don't bounce the lever pad off of your upper thigh and glutes.
Once you've held the lever pad at the top of the rep for the desired duration, slowly lower your ankle until the knees and legs are straight but not hyperextended. You can inhale during the lowering portion or choose to hold your breath for the entire duration of the rep. Regardless of which breathing style you prefer, keep it consistent throughout each rep.
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During both the pulling and lowering portions of the lift ensure your torso and upper thighs remains on the bench at all times. This cue will encourage strict form, high-quality reps, and a decreased likelihood of hyperextending the lower back.
This exercise can be performed using straight sets, pre-exhaust sets, drop sets, rest-pause sets, supersets, trisets, giant sets, paused reps, partial reps, forced reps, or slow negatives. As with any exercise, the two most important components are high-quality form and progression. Progression can take a variety of forms (e.g. more weight, sets, or reps, decreased rest period, improved rep quality, etc...) but strive to improve every time you walk into the gym.
Lying Leg Curl Form Tips
Avoid Momentum - The lying leg curl is an isolation exercise that should be performed with strict form. You should be in control of the weight at all times. Avoid swinging and jerking any part of your body to complete the rep; this dramatically increases the risk of lower back and hamstring injuries.
Stay Tight - Brace your abs and ensure all parts of your body above the knee remain in contact with the bench throughout the entire movement. it's common to see lifters squeezing the supporting handles with a death grip so that they pull their bodies closer to the pad.
Not only will this death-grip unnecessarily tighten up the shoulders and upper back, but it could also take tension off the hamstrings. Most folks holding on to the handles for dear life are also probably swinging or jerking the weight.
Vary the Rep Speed - Slow negatives (lowering), slow contractions (pulling), and pausing at the top of the rep increase the intensity and time under tension of the exercise. Use this variations to blast through a progression plateau and trigger new muscle growth.
Use One Leg - If you're having trouble getting a good hamstring contraction or if one hamstring is lagging in size or strength compared to the other, perform the lying leg curl with one leg at a time. This will help improve the mind muscle connection during the exercise as well as even out any imbalance that may have developed between hamstrings. To perform a one-legged variation simply flex one knee and keep the other leg straight; perform the desired number of reps and then switch legs.
Vary the Toe Position - as you become more proficient in the exercise experiment with different toe positions. Common toe position variations include pulling them towards your shins, keeping them perpendicular with your shins, and pointed them as far away from your shins as possible.
Many lifters find each toe position to engage the hamstring slightly differently. Some lifters also blend the toe positions by point them towards their shins during the pulling portion and pointing them away during the lower position. Speaking from experience that variation provides the best burn in the hamstrings.
References1) Hamstrings. (n.d.).
2) "Lever Lying Leg Curl." ExRx (Exercise Prescription) on the Internet. N.p., n.d. Web. 2 Nov. 2015.