Flexion Leg Sit Up (Bent Knee) 101 Video Tutorial
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Exercise Synopsis
Target Muscle Group
Abs
Secondary Targets
Execution
Isolation
Force Type
Core
Required Equipment
Bodyweight
Fitness Level
Intermediate
Variations
None
Alternatives
None
Timer
Hour
Minute
Second
Stopwatch
00:00:00:00
Overview
The Flexion Leg Sit Up (Straight Arm) is a bodyweight core exercise that primarily targets the abdominal muscles while also engaging the hip flexors to assist with trunk flexion. Performed lying on the back with the legs extended and arms held straight, the movement emphasizes controlled spinal flexion as the torso lifts off the mat, increasing lever length through the arms to raise core demand. This variation challenges abdominal strength, coordination, and endurance while reinforcing proper bracing and controlled movement through the full range of motion.
How to Perform
Position yourself flat on your back on a mat, keeping your legs fully extended and relaxed on the floor.
Extend your arms straight upward so they remain vertical and aligned above your shoulders.
Brace your core by tightening your abdominal muscles and pressing your lower back gently into the mat.
Using controlled spinal flexion, lift your head, shoulders, and torso off the floor while maintaining straight arms and steady alignment.
Reach an upright position with tension maintained through the abs, briefly holding the top without swinging or using momentum.
Slowly reverse the movement, lowering your torso back to the mat under control while keeping constant core engagement, then repeat for the prescribed repetitions.
★ Bonus: For exercises that involve external weights (such as dumbbells, barbells, or machines), the One Rep Max (1RM) calculator can help you estimate your maximum lifting capacity. Use it to track your strength progress and adjust your training for optimal results.
Tips
Maintain fully extended arms from start to finish to preserve continuous tension through the abdominal muscles.
Actively brace your core prior to lifting your torso to ensure proper activation and stability.
Perform each repetition with deliberate control, preventing any swinging or jerking to assist the movement.
How Not to Perform
Do not bend your arms or let them drift backward, as this reduces abdominal tension and shifts effort away from the core.
Don’t initiate the movement by jerking your upper body or swinging your arms to gain momentum.
Avoid lifting your torso without first bracing your abs, as this places unnecessary strain on the lower back.
Do not allow your lower back to arch excessively off the mat during the lift or the descent.
Don’t rush through the repetitions; moving too quickly decreases time under tension for the abdominal muscles.
Avoid pulling with the neck or leading with the chin, which can cause cervical strain.
Do not rely excessively on the hip flexors to raise the torso instead of maintaining abdominal control.
Variations
Variations of fitness exercises refer to different ways of performing a specific exercise or movement to target various muscle groups, intensities, or goals. These variations aim to challenge the body differently, prevent plateaus, and cater to individuals with varying fitness levels.
Alternatives
Alternative exercises in fitness refer to different movements or activities that target similar muscle groups or serve the same training purpose as the primary exercise. These alternative exercises can be used as substitutes when the original exercise is unavailable or challenging to perform due to various reasons such as equipment limitations, injuries, or personal preferences.
