Why Seated Leg Curls Hurt and What to Do About It

The differences you are experiencing between the lying and seated leg curl exercises are due to variations in biomechanics, muscle activation, and machine setup. Here’s a detailed explanation:

Why the Weight Increases for Lying Leg Curls

1. Positioning and Range of Motion: In lying leg curls, your hips are in a neutral or slightly extended position, which shortens the hamstrings compared to the seated version. This allows for a stronger contraction but less stretch, making it easier to lift heavier weights.
2. Muscle Length: The hamstrings are not as stretched in lying leg curls, so the exercise feels less demanding in terms of muscle length tension compared to seated leg curls.

Why Seated Leg Curls Cause Discomfort

1. Pad Pressure on Quads: In seated leg curls, your thighs press against the pad due to the positioning of your body. This can cause discomfort, especially if the pad is poorly adjusted or if your quads are tight or pumped from prior exercises.
2. Hamstring Stretch: Seated leg curls place your hamstrings in a more stretched position due to hip flexion (knees bent at 90 degrees), which increases muscle activation and hypertrophy potential but may also make the exercise feel more intense.
3. Machine Setup: If the pad is too tight or positioned incorrectly (too high on your thighs), it can exacerbate discomfort. Additionally, tight quads or improper seat adjustments can increase pressure on your thighs.

What You Should Do

To address these issues:

1. Adjust the Machine Properly:
   • Ensure the thigh pad is snug but not overly tight. It should stabilize your legs without excessive pressure.
   • Adjust the seat so that your knees align with the machine’s pivot point.
2. Stretch and Warm Up:
   • Perform dynamic stretches for your quads and hamstrings before using the seated leg curl machine.
   • Foam roll tight areas to reduce discomfort during exercise.
3. Modify Your Routine:
   • Alternate between seated and lying leg curls to balance muscle activation and avoid overloading one position.
   • Consider starting with lying leg curls if you find them more comfortable, then transition to seated curls as your flexibility improves.
4. Reduce Weight Temporarily:
   • Lower the weight on seated leg curls to minimize discomfort while focusing on proper form and gradual progression.
5. Experiment with Alternatives:
   • Try other hamstring exercises such as Romanian deadlifts, standing leg curls, or stability ball hamstring curls if discomfort persists.

By addressing machine setup and incorporating flexibility work, you can reduce discomfort while maximizing the benefits of both exercises for hamstring development.