90/90 Crunches: Understanding, Benefits, How to Perform, and Variations

What are 90 90 crunches?

The 90/90 crunch is a core-strengthening exercise performed from a supine position where the hips and knees are bent at a 90-degree angle, effectively isolating the rectus abdominis and reducing compensatory movements from the lower body.

Understanding the 90/90 Position

The "90/90" in 90/90 crunches refers to the specific positioning of your lower body. When lying on your back (supine), your hips are flexed to approximately 90 degrees, and your knees are also bent to approximately 90 degrees. This position is typically achieved by lifting your feet off the floor, often resting your shins on a bench, chair, or simply holding them suspended in the air. This precise anatomical setup serves a crucial biomechanical purpose: it neutralizes the hip flexors, preventing them from dominating the movement and allowing for a more targeted activation of the abdominal muscles.

Muscles Engaged

The 90/90 crunch primarily targets the core musculature, with a focus on the anterior abdominal wall.

• Primary Movers:
  • Rectus Abdominis: This is the "six-pack" muscle, responsible for trunk flexion (bringing the rib cage closer to the pelvis).
• Synergists and Stabilizers:
  • Obliques (Internal and External): These muscles assist in trunk flexion and provide rotational stability.
  • Transverse Abdominis: The deepest abdominal muscle, crucial for core stability and intra-abdominal pressure. While not a primary mover for flexion, it is actively engaged for stabilization.
  • Hip Flexors (Psoas Major, Iliacus): While the 90/90 position aims to minimize their involvement in the crunching movement itself, they are still engaged isometrically to maintain the leg position if not supported.

How to Perform 90/90 Crunches: Step-by-Step

Proper execution is key to maximizing the effectiveness and minimizing the risk of injury.

1. Starting Position:
   • Lie flat on your back on a mat or comfortable surface.
   • Lift your legs so your hips are flexed to 90 degrees and your knees are bent to 90 degrees. Your shins should be parallel to the floor. You can rest your calves on a bench or chair, or simply hold them suspended.
   • Place your fingertips lightly behind your ears or cross your arms over your chest. Avoid pulling on your neck.
   • Engage your core slightly to press your lower back gently into the floor.
2. The Crunch:
   • Exhale slowly as you initiate the movement by contracting your rectus abdominis.
   • Lift your head, shoulders, and upper back off the floor, curling your torso towards your pelvis. Focus on bringing your rib cage closer to your hips, not just lifting your head.
   • Keep your neck in a neutral position, maintaining a small gap between your chin and chest (imagine holding an apple there).
   • Crucially, maintain the 90-degree angles at your hips and knees throughout the movement.
3. Lowering Phase:
   • Inhale as you slowly and with control lower your upper body back to the starting position.
   • Avoid letting your head or shoulders completely relax on the floor between repetitions to maintain tension in the abdominal muscles.
   • Ensure your lower back remains in contact with the floor, preventing arching.

Benefits of the 90/90 Crunch

This specific crunch variation offers several distinct advantages, making it a valuable addition to many fitness routines.

• Reduced Lumbar Spine Stress: By keeping the legs elevated and bent, the 90/90 position helps to flatten the lumbar curve, reducing the arch in the lower back. This minimizes the shearing forces on the spinal discs often associated with traditional crunches where the feet are flat on the floor and the hip flexors pull excessively.
• Enhanced Abdominal Isolation: The primary benefit is the effective disengagement of the hip flexors. When the hip flexors are less involved, the rectus abdominis is forced to work harder to initiate and complete the trunk flexion, leading to more targeted and efficient abdominal training.
• Improved Mind-Muscle Connection: The controlled nature and reduced momentum of the 90/90 crunch encourage a greater focus on the abdominal contraction, helping individuals to better feel and activate their core muscles.
• Suitable for Various Fitness Levels: While challenging, the controlled nature of the movement makes it accessible for beginners learning proper core engagement, and effective for advanced individuals seeking deep abdominal activation.
• Prevention of Compensation: It helps prevent common compensations like pulling with the neck or using momentum from the legs, fostering better movement patterns.

Common Mistakes to Avoid

To ensure safety and maximize effectiveness, be mindful of these common errors:

• Pulling on the Neck: Using your hands to yank your head upwards can strain the cervical spine. Your hands are there for support, not assistance.
• Arching the Lower Back: Losing contact between your lower back and the floor indicates that your hip flexors might be taking over or your core isn't fully engaged. This can lead to lower back discomfort.
• Rushing the Movement: Performing crunches too quickly relies on momentum rather than muscle contraction. Focus on a slow, controlled ascent and descent.
• Letting Legs Drop: Allowing your knees to drift towards your chest or your feet to drop towards the floor can re-engage the hip flexors or reduce abdominal tension. Maintain the 90/90 angles consistently.
• Shallow Range of Motion: Not lifting the shoulders and upper back sufficiently means you're not fully engaging the rectus abdominis. Aim to curl your torso until your shoulder blades are off the floor.

Variations and Progressions

The 90/90 crunch can be modified to suit different fitness levels and goals.

• Easier Variations:
  • Hands on Thighs: Place your hands on your thighs and slide them towards your knees as you crunch, providing a tactile cue and slight assistance.
  • Support Legs on Bench: Resting your calves on a bench or chair can make it easier to maintain the 90/90 position without isometric hip flexor engagement.
• More Challenging Variations:
  • Arms Extended Overhead: Extending your arms straight behind your head increases the lever arm and makes the crunch more difficult.
  • Holding a Weight: Hold a light dumbbell or weight plate across your chest or overhead to add resistance.
  • Bicycle Crunch (from 90/90): From the 90/90 position, perform alternating elbow-to-knee movements, engaging the obliques more intensely.
  • Reverse Crunch (from 90/90): Instead of lifting the upper body, focus on lifting the hips slightly off the floor, bringing the knees towards the chest while maintaining the 90/90 angle. This targets the lower rectus abdominis.

Who Can Benefit?

The 90/90 crunch is a versatile exercise beneficial for a wide range of individuals:

• Beginners: It teaches proper abdominal isolation and reduces the risk of lower back strain common with poorly executed traditional crunches.
• Individuals with Lower Back Pain: By minimizing hip flexor involvement and lumbar arching, it's often a safer alternative for those prone to lower back discomfort.
• Fitness Enthusiasts and Athletes: It serves as an excellent exercise for targeted rectus abdominis development and can be incorporated into comprehensive core conditioning programs.
• Personal Trainers: It's a valuable tool for teaching clients how to effectively engage their core without compensation.

When to Incorporate Them

90/90 crunches can be strategically placed within your workout routine:

• Warm-up: A few sets can activate the core muscles, preparing them for more complex movements.
• Main Core Workout: As a primary exercise in a dedicated core training session.
• Circuit Training: Incorporated into a full-body circuit for core engagement.
• Cool-down/Finisher: As a controlled, focused exercise to fatigue the core at the end of a workout.

Conclusion

The 90/90 crunch is a highly effective, evidence-based exercise for targeting the rectus abdominis while minimizing stress on the lower back and reducing hip flexor dominance. By understanding its biomechanics, mastering proper form, and being aware of common pitfalls, individuals can safely and efficiently strengthen their core, contributing to improved posture, athletic performance, and overall spinal health. Integrate this intelligent crunch variation into your routine for a stronger, more resilient core.