90 Degrees Single Knee Crunch
90 Degrees Single Knee Crunch Exercise Description
The 90 Degrees Single Knee Crunch is a bodyweight abdominal exercise that emphasizes spinal flexion to train the rectus abdominis, with support from the internal and external obliques. Holding one hip and knee at 90 degrees (“tabletop”) increases the lever arm on the trunk and encourages a slight posterior pelvic tilt, helping you keep the lumbar spine in contact with the floor during the curl. The single‑leg position also adds a small anti‑rotation demand, cueing the obliques to stabilize the pelvis so the movement stays in the torso rather than the hips. Range of motion is modest: lift the head and shoulder blades just enough to bring the ribcage toward the pelvis without yanking on the neck or losing lumbopelvic control. This variation is useful for practicing precise trunk flexion mechanics, consistent breathing, and bracing—key elements for safe, effective core training with minimal equipment.
- Muscle Groups: Abs, Core, Waist
- Target Muscles: Rectus Abdominis
- Assisting Muscles: External Obliques, Internal Obliques
- Stabilizing Muscles: Iliacus, Multifidus, Psoas Major, Quadratus Lumborum, Transversus Abdominis
- Body Area: Upper Body
- Body Parts: Core, Torso
- Body Surface: Front
- Body Symmetry: Unilateral
- Equipment: Bodyweight
- Exercise Patterns: Other
- Exercise Type: Strength
- Functional Grouping: Trunk Flexors
- Joint Involvement: Single-joint
- Muscle Location: Stomach
- Movement Direction: Vertical
- Muscle Position: Anterior
- Gender: Female
How To Do The 90 Degrees Single Knee Crunch Exercise
‘- Lie supine on a mat. Plant one foot, knee bent. Raise the other leg so the hip and knee are both at 90°, shin parallel to the floor.
– Place arms across chest or fingertips lightly behind ears. Keep elbows wide; do not pull on the head.
– Before moving, exhale gently, brace the abdominal wall, and posteriorly tilt the pelvis to lightly flatten the low back to the mat.
– Keep the raised leg fixed at 90° and the pelvis level—no swinging or shifting.
– Curl the torso: think “ribs to pelvis.” Lift head and shoulder blades until the lower scapulae clear the mat. Eyes look up, not forward.
– Maintain a smooth exhale through the effort; keep the chin slightly tucked to preserve a neutral cervical spine.
– Pause briefly at the top with controlled tension; avoid thrusting the ribcage.
– Inhale and lower the torso slowly until the shoulder blades touch down, keeping the low back lightly grounded.
– Repeat for the desired amount, then switch legs to train both sides evenly.
90 Degrees Single Knee Crunch Tips
‘- Set up with one foot planted and the other hip and knee at 90°, shin parallel to the floor.
– Lightly flatten your low back to the mat with a small posterior pelvic tilt before you start curling.
– Keep the raised leg fixed at 90° and the pelvis level—avoid swinging the leg or shifting the hips.
– Place fingertips lightly behind your ears or cross your arms on your chest, and keep the elbows wide so you don’t pull on your head.
– Initiate the movement by curling your torso, thinking “ribs to pelvis,” rather than leading with your neck.
– Lift only until your lower shoulder blades clear the mat to keep the range of motion modest and controlled.
– Maintain a smooth exhale during the effort phase of the curl, keeping the abdominal wall braced.
– Keep your eyes looking up and your chin slightly tucked to maintain a neutral cervical spine.
– Pause briefly at the top with controlled tension, avoiding any thrusting of the ribcage.
– Inhale as you lower the torso slowly until the shoulder blades touch down, keeping the low back lightly grounded, then switch legs to train both sides.
90 Degrees Single Knee Crunch Beginner Introduction
The 90 Degrees Single Knee Crunch is a bodyweight move for the abs that centers on a controlled curl of the upper spine. One leg stays planted while the other hovers in a bent, “tabletop‑style” position, which lengthens the lever from the hips to the trunk. This arrangement places extra demand on the mid‑section, while the side abs assist by resisting any twisting or tipping of the pelvis so the motion stays mostly through the torso.
Only a small lift of the head, neck, and shoulder blades from the floor is involved, bringing the front of the ribcage closer to the hips in a compact, deliberate arc. The exercise highlights careful trunk mechanics, steady breathing, and a firm brace through the core rather than large, sweeping movements. Because the setup relies on just bodyweight and a mat, it often serves as a practical way to build awareness of how the abs and side abs coordinate during precise curling work with minimal equipment.