Exercise guide · Intermediate · Compound
Flexion Leg Sit Up (Bent Knee): How to Do It & Muscles Worked
The flexion leg sit up (bent knee) is an abdominal exercise performed with body weight. It involves curling the upper body and bringing the knees toward the chest simultaneously, targeting the abs and hip flexors.
How to do the flexion leg sit up (bent knee)
- Step 1: Lie flat on your back with your knees bent and feet flat on the ground.
- Step 2: Place your hands behind your head with your elbows pointing outwards.
- Step 3: Engaging your abs, slowly lift your upper body off the ground, curling forward until your torso is at a 45-degree angle.
- Step 4: At the same time, lift your legs off the ground, bending your knees and bringing them towards your chest.
- Step 5: Pause for a moment at the top, then slowly lower your upper body and legs back down to the starting position.
- Step 6: Repeat for the desired number of repetitions.
Sets, reps and programming
| Goal | Sets | Reps | Rest | Effort |
|---|---|---|---|---|
| Strength | 3–5 | 3–6 | 3–5 min | 1–3 reps in reserve |
| Muscle growth | 3–4 | 6–12 | 2–3 min | 1–2 reps in reserve |
| Muscular endurance | 2–3 | 12–20 | 1–2 min | 1–3 reps in reserve |
Ranges follow the ACSM position stand on progression in resistance training. Muscle grows across a wide range of loads when sets end close to failure (Schoenfeld et al., 2017), longer rests between heavy sets support strength and size (Schoenfeld et al., 2016), and stopping a rep or two short of failure works about as well as training to failure (Grgic et al., 2022). Estimate your working weights with the strength calculators.
Flexion Leg Sit Up (Bent Knee) alternatives
More exercises that train the abs as their main target:
-
Arm Slingers Hanging Bent Knee Legs
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Arms Overhead Full Sit-Up (Male)
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Assisted Lying Leg Raise with Lateral Throw Down
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Assisted Lying Leg Raise with Throw Down
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Band Alternating V-Up
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Band Assisted Wheel Rollerout
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Band Bicycle Crunch
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Band Jack Knife Sit-Up
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More abs exercises
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Dead Bug
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Hanging Leg Raise
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3/4 Sit-Up
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45° Side Bend
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Air Bike
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Alternate Heel Touchers
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Sources
- American College of Sports Medicine. Progression models in resistance training for healthy adults. Med Sci Sports Exerc. 2009;41(3):687-708.
- Schoenfeld BJ, Grgic J, Ogborn D, Krieger JW. Strength and hypertrophy adaptations between low- vs. high-load resistance training. J Strength Cond Res. 2017;31(12):3508-3523.
- Schoenfeld BJ, Pope ZK, Benik FM, et al. Longer interset rest periods enhance muscle strength and hypertrophy in resistance-trained men. J Strength Cond Res. 2016;30(7):1805-1812.
- Grgic J, Schoenfeld BJ, Orazem J, Sabol F. Effects of resistance training performed to repetition failure or non-failure on muscular strength and hypertrophy: a systematic review and meta-analysis. J Sport Health Sci. 2022;11(2):202-211.
Step-by-step instructions and demonstration media are from the ExerciseDB exercise dataset.
This guide is general fitness information, not medical advice. Stop if an exercise causes pain and speak to a doctor or physiotherapist about injuries or health conditions before starting a new programme.