How to Do Prone Leg Curls on a Leg Extension Curl Machine

We all love the feeling of a heavy squat or a leg press. Those big movements make us feel strong and powerful. However, there is a massive muscle group on the back of your legs that often gets neglected. We are talking about the hamstrings. If you have invested in a space-saving home gym setup like the RitFit PLC01 Leg Extension Curl Machine, you have the perfect tool to correct this imbalance.

Many people skip leg curls because setting up a combination machine can feel complicated. It involves moving pins and adjusting pads and changing angles. It is easier to just skip it. Please do not make that mistake. The prone leg curl is one of the most important exercises for knee health and complete leg development. This guide will walk you through the entire process from machine setup to the perfect rep.

Why You Need to Train Your Posterior Chain

Before we jump into the mechanics, let us look at why this exercise matters. Your hamstrings are not just there for decoration. They are a vital part of your posterior chain, which is the powerhouse of your body.

The Anatomy of the Hamstring

When you perform a prone leg curl, you are primarily targeting three distinct muscles:

• Biceps Femoris
• Semitendinosus
• Semimembranosus

These muscles work together to perform knee flexion, which is the scientific term for bending your knee. You also recruit your gastrocnemius, or calf muscles, as synergists to help complete the movement.

Knee Health and Injury Prevention

Building a strong squat is great, but if your quadriceps are significantly stronger than your hamstrings, you create a muscle imbalance. Clinical studies demonstrate that a low Hamstring-to-Quadriceps (H:Q) strength ratio is a primary risk factor for non-contact ACL injuries^[1]. Strengthening the hamstrings helps balance this ratio. A strong hamstring acts like a natural brake for your knee joint and can help protect ligaments like the ACL during sports and daily activities.

Aesthetic Benefits

If you care about how your legs look, the prone leg curl is essential. It builds the "hamstring sweep" that is visible from the side and back. It gives the leg a three-dimensional look that squats alone cannot achieve.

Setting Up Your Leg Extension Curl Machine

This is the part where most home gym owners get confused. Since you are using a machine that combines two functions into one, you must convert it from extension mode to curl mode. Proper setup is critical. If the machine is not set up correctly, you will feel stress on your lower back or knees instead of your muscles.

Step 1: Adjust the Backrest

On a standard combination unit like the RitFit PLC01 the backrest is adjustable. For a lying leg curl, you need to be in a prone position, which means lying flat on your stomach.

• Locate the adjustment pin for the back pad.
• Lower the backrest all the way down until it is flat.
• Ensure it locks securely into place so it provides a stable platform for your torso.

Step 2: Align the Axis of Rotation

This is the most important technical detail. Every machine has a pivot point or a cam where the weight arm rotates. Look for the bolt or heavy-duty joint that the arm swings from.

• The Rule: This mechanical axis of rotation must align directly with your own knee joint.
• When you lie down, your knees should be right next to this pivot point.
• If your knees are too far forward or too far back, you will create shear force on the knee joint.
• Adjust your body position on the pad until the center of your knee lines up perfectly with the center of the machine cam.

Step 3: Set the Sundial and Starting Angle

The rotating plate, often called a sundial, determines where the movement begins. For leg extensions the arm starts down low. For leg curls you need the arm to start higher up.

• Pull the pop pin on the cam.
• Move the arm to a high position so that when you lie down your legs are almost fully straight.
• You want your legs to be extended but not hyperextended. There should be a very slight bend in the knee at the starting position to maintain tension.

Step 4: Adjust the Roller Pad

The final piece of the puzzle is the ankle pad.

• Situate the roller pad so it rests comfortably on the back of your leg.
• Correct Placement: It should sit right on the Achilles tendon area just above the heel but below the calf muscle belly.
• If the pad is too high on your calves, the lever arm is too short, and the movement will feel awkward.
• If the pad is on your heels, it might slip off during the movement.

Step-by-Step Execution Guide

Now that your machine is set up specifically for your body, let us perform the movement. The prone leg curl is an isolation exercise, meaning movement should only occur at one joint.

The Starting Position

Lie face down on the machine. Your chest should be flat against the pad. Reach forward or to the sides and grasp the handles firmly. These handles are there for stability. By gripping them tight, you can create tension in your upper body, which helps stabilize your torso.

• Crucial Alignment: Ensure your knees are just off the edge of the bench pad and aligned with the pivot point.

The Concentric Phase (The Curl)

This is the lifting portion of the exercise.

• Take a deep breath and brace your core.
• Exhale as you drive your heels up toward your glutes.
• Visualize pulling with the back of your thighs.
• Continue curling until the roller pad comes close to touching your buttocks or as far as your range of motion allows.
• Peak Contraction: At the very top of the movement, hold the weight for one full second. Squeeze your hamstrings hard.

The Eccentric Phase (The Lowering)

Do not let gravity take over here. The lowering phase is where a lot of muscle tissue breakdown and growth potential occurs.

• Inhale as you slowly lower the weight back to the starting position.
• Control the tempo. Aim for a count of two or three seconds on the way down.
• Stop just before the weight stack touches down to keep constant tension on the muscle.
• Repeat for your desired number of repetitions.

Common Mistakes and Risk Management

Even with a great machine, it is possible to do this exercise with poor form. Watch out for these common errors to keep your lower back safe and your knees healthy.

Hip Hiking

This is the most common error. When the weight gets heavy, many people instinctively lift their hips off the pad as they curl the weight up.

• The Risk: This shortens the range of motion and shifts the tension from your hamstrings to your lower back. This can lead to lower back pain.
• The Fix: Think about driving your hips and pelvis down into the pad throughout the entire movement. Your hips should be glued to the bench. If they rise up, the weight is likely too heavy.

Using Momentum

If you are swinging your legs to get the weight moving, you are cheating yourself.

• The Risk: Swinging creates inertial forces that can strain the hamstring tendon or the knee joint. It also takes the work away from the muscle belly.
• The Fix: Initiate the movement smoothly from a dead stop. Do not jerk the weight.

Incorrect Foot Position

Your foot position changes how the muscle works.

• Dorsiflexion: Pulling your toes toward your shins stretches the calf muscles, making them help more in the movement. This is the standard way to do the exercise.
• Plantarflexion: Pointing your toes like a ballerina disengages the calves. This forces the hamstrings to work much harder. This is a great variation if you really want to isolate the hamstrings, but you will likely need to use less weight.

Hyperextending the Neck

Many people try to look up or watch themselves in a mirror while lying face down.

• The Risk: This puts unnecessary strain on the cervical spine, or neck.
• The Fix: Keep your neck neutral. Look straight down at the floor or the machine frame.

Programming and Variations

To get the most out of your training, you need to know when and how to include this exercise in your routine.

Repetition Ranges

Because the prone leg curl is a single-joint isolation exercise, it is generally safer and more effective to use moderate to higher repetitions.

• Hypertrophy: Aim for 3 to 4 sets of 10 to 15 repetitions.
• Endurance: You can go as high as 15 to 20 repetitions to really burn out the muscle.
• Avoid extremely heavy weights for low reps (like 1 to 5), as this puts high shear force on the knee in this specific open kinetic chain position.

Unilateral Training

One of the best features of using a machine is the ability to train one leg at a time. If you notice one leg is smaller or weaker than the other, try doing single-leg curls.

• Perform all reps on your weaker leg first.
• Match that number of reps with your stronger leg.
• This ensures you do not worsen the asymmetry.

Workout Placement

You can place this exercise at different points in your workout depending on your goals.

• As a Warm-Up: Light leg curls are a great way to warm up before heavy squats because they get blood flowing to the knee joint.
• As a Finisher: After your heavy compound movements, do these at the end of your leg workout to really tire out your hamstrings.
• Pre-Exhaustion: Do these right before squats to wear out your hamstrings so your quads have to work harder during the squat.

Conclusion

The prone leg curl is a fundamental movement for anyone looking to build a complete and resilient lower body. While the setup on a dual-function machine like the RitFit PLC01 Leg Extension Curl Machine might seem tricky at first, it becomes second nature very quickly.

Remember the key cues. Align your knee with the pivot point. Keep your hips pressed firmly into the pad. Control the weight on the way down. By focusing on these technical details, you ensure that every repetition contributes to stronger knees and better muscular development.

Do not let that posterior chain go untrained. Take the time to set up your machine correctly and start reaping the benefits of strong and healthy hamstrings today. You have the knowledge and the equipment, so now it is time to put in the work. Enjoy your training!

References

1. Taketomi S, Kawaguchi K, Mizutani Y, Takei S, Yamagami R, Kono K, Murakami R, Kage T, Arakawa T, Fujiwara S, Tanaka S, Ogata T. Lower hamstring to quadriceps muscle strength ratio and lower body weight as factors associated with noncontact anterior cruciate ligament injury in male American football players: A prospective cohort study. Asia Pac J Sports Med Arthrosc Rehabil Technol. 2023 Dec 15;35:43-47. doi: 10.1016/j.asmart.2023.11.006. PMID: 38187929; PMCID: PMC10770439.